Scholarly article on topic 'Environmental impact of estrogens on human, animal and plant life: A critical review'

Environmental impact of estrogens on human, animal and plant life: A critical review Academic research paper on "Environmental engineering"

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Abstract of research paper on Environmental engineering, author of scientific article — Muhammad Adeel, Xiaoming Song, Yuanyuan Wang, Dennis Francis, Yuesuo Yang

Abstract Background Since the inception of global industrialization, steroidal estrogens have become an emerging and serious concern. Worldwide, steroid estrogens including estrone, estradiol and estriol, pose serious threats to soil, plants, water resources and humans. Indeed, estrogens have gained notable attention in recent years, due to their rapidly increasing concentrations in soil and water all over the world. Concern has been expressed regarding the entry of estrogens into the human food chain which in turn relates to how plants take up and metabolism estrogens. Objectives In this review we explore the environmental fate of estrogens highlighting their release through effluent sources, their uptake, partitioning and physiological effects in the ecological system. We draw attention to the potential risk of intensive modern agriculture and waste disposal systems on estrogen release and their effects on human health. We also highlight their uptake and metabolism in plants. Methods We use MEDLINE and other search data bases for estrogens in the environment from 2005 to the present, with the majority of our sources spanning the past five years. Published acceptable daily intake of estrogens (μg/L) and predicted no effect concentrations (μg/L) are listed from published sources and used as thresholds to discuss reported levels of estrogens in the aquatic and terrestrial environments. Global levels of estrogens from river sources and from Waste Water Treatment Facilities have been mapped, together with transport pathways of estrogens in plants. Results Estrogens at polluting levels have been detected at sites close to waste water treatment facilities and in groundwater at various sites globally. Estrogens at pollutant levels have been linked with breast cancer in women and prostate cancer in men. Estrogens also perturb fish physiology and can affect reproductive development in both domestic and wild animals. Treatment of plants with steroid estrogen hormones or their precursors can affect root and shoot development, flowering and germination. However, estrogens can ameliorate the effects of other environmental stresses on the plant. Conclusions There is published evidence to establish a causal relationship between estrogens in the environment and breast cancer. However, there are serious gaps in our knowledge about estrogen levels in the environment and a call is required for a world wide effort to provide more data on many more samples sites. Of the data available, the synthetic estrogen, ethinyl estradiol, is more persistent in the environment than natural estrogens and may be a greater cause for environmental concern. Finally, we believe that there is an urgent requirement for inter-disciplinary studies of estrogens in order to better understand their ecological and environmental impact.

Academic research paper on topic "Environmental impact of estrogens on human, animal and plant life: A critical review"

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EI-03537; No of Pages 13

Environment International xxx (2016) xxx-xxx

Contents lists available at ScienceDirect

Environment International

journal homepage: www.elsevier.com/locate/envint

Review article

Environmental impact of estrogens on human, animal and plant life: A critical review

Muhammad Adeela, Xiaoming Song a, Yuanyuan Wang a, Dennis Francis a, Yuesuo Yang a,b'*

a Key Lab ofEco-restoration of Regional Contaminated Environment (Shenyang University), Ministry of Education, Shenyang 11044, PR China b Key Lab of Groundwater Resources & Environment (Jilin University), Ministry of Education, Changchun 130021, PR China

ARTICLE INFO

Article history:

Received 20 September 2016

Received in revised form 10 December 2016

Accepted 12 December 2016

Available online xxxx

Keywords:

Estrogens

Environmental fate

Endocrine disrupting chemical (EDC)

Plant uptake

Bioavailability

Aquatic ecology

Water and soil

ABSTRACT

Background: Since the inception of global industrialization, steroidal estrogens have become an emerging and serious concern. Worldwide, steroid estrogens including estrone, estradiol and estriol, pose serious threats to soil, plants, water resources and humans. Indeed, estrogens have gained notable attention in recent years, due to their rapidly increasing concentrations in soil and water all over the world. Concern has been expressed regarding the entry of estrogens into the human food chain which in turn relates to how plants take up and metabolism estrogens.

Objectives: In this review we explore the environmental fate of estrogens highlighting their release through effluent sources, their uptake, partitioning and physiological effects in the ecological system. We draw attention to the potential risk of intensive modern agriculture and waste disposal systems on estrogen release and their effects on human health. We also highlight their uptake and metabolism in plants. Methods: We use MEDLINE and other search data bases for estrogens in the environment from 2005 to the present, with the majority of our sources spanning the past five years. Published acceptable daily intake of estrogens (ng/L) and predicted no effect concentrations (ng/L) are listed from published sources and used as thresholds to discuss reported levels of estrogens in the aquatic and terrestrial environments. Global levels of estrogens from river sources and from Waste Water Treatment Facilities have been mapped, together with transport pathways of estrogens in plants.

Results: Estrogens at polluting levels have been detected at sites close to waste water treatment facilities and in groundwater at various sites globally. Estrogens at pollutant levels have been linked with breast cancer in women and prostate cancer in men. Estrogens also perturb fish physiology and can affect reproductive development in both domestic and wild animals. Treatment of plants with steroid estrogen hormones or their precursors can affect root and shoot development, flowering and germination. However, estrogens can ameliorate the effects of other environmental stresses on the plant.

Conclusions: There is published evidence to establish a causal relationship between estrogens in the environment and breast cancer. However, there are serious gaps in our knowledge about estrogen levels in the environment and a call is required for a world wide effort to provide more data on many more samples sites. Of the data available, the synthetic estrogen, ethinyl estradiol, is more persistent in the environment than natural estrogens and may be a greater cause for environmental concern. Finally, we believe that there is an urgent requirement for inter-disciplinary studies of estrogens in order to better understand their ecological and environmental impact.

© 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/).

Contents

1. Introduction............................................................... 0

2. Source of steroidal estrogens........................................................ 0

Abbreviations: E1, estrone; E2, estradiol; 17(i-E2,17p-estradiol; 17a-E2,17a-estradiol; E3, estriol; EE2, ethinyl estradiol; CAFOs, concentrated animal feeding operations; WWTPs, waste water treatment plants; MSH, mammalian sex hormones; CAT, catalase; POX, peroxidase; MSTPs, municipal sewage treatment plants; GLU, glucuronide; SUL, sulfate; STPs, sewage treatment plants; BW, body weight; PNEC, predicted-no-effect concentration; NOEL, no-observed-adverse-effect; JECFA, Joint Expert Committee on Food Additives; ADI, average daily intake; ROS, reactive oxygen species; SOD, superoxide dismutase; CAT, catalase; GPX, guaiacol peroxidase; AsA-GSH, ascorbate glutathione; APX, ascorbate peroxidase; MDHAR, mono dehydro ascorbate reductase; DHAR, dehydroascorbate reductase; GR, glutathione reductase; AsA, ascorbate; GSH, glutathione; VTG, vitellogenin; IOP, intraocular eye pressure; HRT, hormone replacement therapy.

* Corresponding author at: Key Lab of Eco-restoration of Regional Contaminated Environment (Shenyang University), Ministry of Education, Shenyang 11044, PR China.

E-mail address: yangyuesuo@jlu.edu.cn (M. Adeel).

http://dx.doi.org/10.1016/j.envint.2016.12.010

0160-4120/© 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

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3. Occurrence of steroidal estrogens in the environment..........................................................................................0

3.1. Human intake of estrogens..........................................................................................................0

3.2. Estrogens on a global scale..........................................................................................................0

4. Estrogen degradation and half-life..........................................................................................................0

5. Estrogen transformation cycle..............................................................................................................0

6. Effects of steroidal estrogens on fish, domestic animals and human health......................................................................0

6.1. Aquatic wildlife....................................................................................................................0

6.2. Domestic animals....................................................................................................................0

6.3. Humans............................................................................................................................0

7. Uptake and transport mechanisms in plant systems..........................................................................................0

7.1. Transport from the root to other plant parts............................................................................................0

8. Accumulation of estrogen in plants..........................................................................................................0

8.1. Effects of estrogens on plant growth..................................................................................................0

8.2. Effects of estrogen on plant antioxidant activity........................................................................................0

9. Conclusions................................................................................................................................0

Role of the funding source......................................................................................................................0

Appendix A. Supplementary data..............................................................................................................0

References......................................................................................................................................0

1. Introduction

Estrogens are biologically active hormones that are derived from cholesterol and released by the adrenal cortex, testes, ovary and placenta in humans and animals. Estrogenic compounds have also been found in plants (Hamid and Eskicioglu, 2012; Ying et al., 2002). Steroid estrogens can be classified as natural or synthetic hormones (Fig. 1) and can act as endocrine disrupting chemicals (EDCs).

Natural steroidal estrogens (also known as the C18 steroidal group) share the same tetracyclic molecular framework comprising four rings, one phenolic group, two cyclohexane and one cyclo-pentane ring (Fig. 1). Structural differences within the C18 group lie in the configuration of the D-ring at positions C16 and C17. For example, estrone (E1) has a carbonyl group on C17,17(3-estradiol (E2) has a hydroxyl group on C17, whilst estriol (E3) has two alcohol groups on C16 and C17 (Fig. 1). The C17 hydroxyl group of the E2 can either point downward or upward on the molecular plane, forming either the a- or (3-compound. Conjugated estrogens, which are also potential environmental hazards, are formed by esterification of free estrogens by glucuronide and sulfate groups at the position(s) of C3 and/ or C17 (Hamid and Eskicioglu, 2012; Khanal et al., 2006).

Understanding the physiochemical properties of steroidal estrogens compounds is crucial in order to resolve their fate in soil and water systems. The distribution of organic pollutants between water and other natural solids are often considered as a partitioning process between the aqueous and organic phase. The water partition coefficient (Kow), is the ratio of the concentration of a compound in n-octanol and water under equilibrium conditions at a particular temperature. Compounds with a high molecular weight and a high log Kow of > 5 are easily adsorbed to sediments and can be primarily removed by coagulation. Estrogens are expected to be absorbed onto the solid phases due to their significant log Kow (Pal et al., 2010). Accordingly, among the estrogens E2 has the highest hydrophobicity but all ste-roidal estrogens are moderately hydrophobic (log Kow = 2.4-4.0), nonvolatile (vapor pressure 9 x 10-13-3 x 10-8 Pa), weak acids

(pKa = 10.3-10.8) (see Table 1). These coefficients including Kd can be used to evaluate the fate of the organic compounds during experiments, thus avoiding an expensive and time-consuming analysis. Furthermore, they provide a calculation method to estimate the percentage of a substance being absorbed onto solid phase, which is finally discharged to the environment, and that which is dissolved in the liquid phase (Carballa et al., 2008).

Generally, unconjugated estrogens or free estrogens are not very soluble in water; EE2 is the least soluble. At pH 7, the order of aqueous solubility was E1 (one OH group) to E2 (two OH groups) and then EE2 with the added ethinyl groups at 17a-position on the D ring; solubility appeared to be the same at pH 4 and 7. However, solubility can be pH-dependent because, for example, at pH 10, relative solubility of estrogens are higher (Shareef et al., 2006).

The world's human population of about 7 billion discharges approximately 30,000 kg/yr. of natural steroidal estrogens (E1, E2, and E3) and an additional 700 kg/yr. of synthetic estrogens (EE2) solely from birth control pill practices. However, the possible release of estrogens to the environment from livestock is much higher. For example, in the United States and European Union, the annual estrogen discharge by livestock, at 83,000 kg/yr., is more than twice the rate of human discharge. Indeed, possible causal relationships have been established between concentrated animal feeding operations (CAFOs) and the detection of estrogens in the aquatic environment (Shrestha et al., 2012). Clearly, natural estrogens in animal and human waste pose a serious risk to the environment. This risk is heightened by the application of animal manure or sludge bio-solids to agriculture lands, being an alternative nutrient source for organic farming, a widely adopted practice in modern agriculture (Xuan et al., 2008). Indeed, application of animal manure to agricultural land has been identified as a main source of estrogens in the environment (Arnon et al., 2008).

Given the serious threat posed by estrogens as pollutants, our aim, here, is to provide a comprehensive account of their environmental impact for human and eco-environmental health perspectives. We have carried out an exhaustive search of the published literature and paid

Fig. 1. Chemical structure of natural and synthetic estrogenic compounds. Key: E1, estrone; 17p-E2,17(i-estradiol; 17a-estradiol; E3, estriol; 17a-EE2, ethinyl estradiol.

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Table 1

Physicochemical properties of steroidal estrogens.

Hormone

MP °C

LogKow

vp(Kpa)

Solubility

(mg/L)

Natural Estrone 17a-estradiol 17ß-estradiol

Synthetic Ethinylestradiol

C18H22O2 C18H24O2 C18H24O2

C20H22O2

258-260 178-179 178-179

182-183

270.4 272.4 270.4

3.43 4.01 3.94

10.3 NDA 10.6

3 x 10-8 3 x 10-8 3 x 10-8

6 x 10-9

2.44-2.7

2.65-2.86

MF: molecular formula; MP: melting point; MW: molecular weight; VP: vapor pressure; NDA: no data available.

particular attention to both the source and degradation of estrogens (i.e., transformation cycle, alteration of chemical structure) in different environmental and climatic conditions. We also include recent analyses of the occurrence and distributions of estrogens in different media and under different environmental conditions. Finally, we provide some consideration of the fate of steroidal estrogens and their relationship and interaction with humans, animals and plants.

2. Source of steroidal estrogens

The occurrence of natural estrogen hormones as minute concentrations in the environment has been examined by many scientists and is an emerging contamination issue. Worldwide, water has been polluted with steroid hormones with many released from sewage treatment plants and effluent from livestock feedlots. The dairy livestock industry has long-used a variety of growth-regulating steroids to enhance cattle growth rates, feed efficiency and to procure lean muscle mass. However, CAFOs have risk implications for the environment. For example, CAFOs involving both natural and synthetic steroids have a knock-on effect as animal manure has seeped into the aquatic environment. Steroidal estrogens used in CAFOs have been detected in faeces, liquid manure and solid waste collected from cattle, lagoon effluent, and in fertilizers applied directly to agricultural land (Biswas et al., 2013). Arguably, animal manure is the largest source of estrogen hormones in the natural environment. Certainly, poultry, cow and horse manure may contain the greatest amount of steroidal estrogens (Andaluri et al., 2012). About 49 tons of estrogens were excreted by farm animals in the USA in 2002. In the UK, total excretion of estrone (E1) and estradiol (E2) from the farm animal populations was 1315 and 570 kg/yr., respectively (Rayet al., 2013).

Dependent on published source, and on average, pregnant women excrete anywhere between 260-790, and 280-600 |g/day of estrone and 17(3-estradiol, respectively and a substantial 6000 to nearly 10,000 |g/day of estriol (Table 2). These levels are much higher than corresponding levels of these estrogens excreted by menopausal

Table 2

Average steroid estrogen excretion by humans (per person) |og/day. NDA, no data available.

E1 17ß-E2 E3 EE2 Reference

Pregnant women 787 277 9850 0 Kostich et al., 2013

Menopausal, with HRT 31.50 59.20 90.70 0

Menstruating woman 9.32 6.14 17.40 0

Women 7.00 2.40 4.40 NDA Andaluri et al., 2012

Menstruating females 3.50 8.00 4.80 NDA Hamid and Eskicioglu,

Adult male 3.50 1.83 3.21 NDA Kostich et al., 2013

Menopausal, no HRT 2.93 1.49 3.90 0

Menopausal females 2.30 4.00 1.00 NDA Hamid and Eskicioglu,

Males 1.60 3.90 1.50 NDA 2012

Female child 0.60 2.50 0.918 0 Kostich et al., 2013

Male child 0.63 0.54 0

Average excretion per 19.00 7.70 8100. 0.41 Laurenson et al., 2014

person

women on Hormone Replacement Therapy (HRT) treatment on a per person basis, but even this level is 1.7-fold higher than the average excretion rate per person of world population as a whole. Somewhat more predictably, rates of excretion in non-pregnant women, males and young children are progressively and substantially lower (see Table 2).

Municipal sewage treatment plants (MSTPs) are important sources of pollution by steroidal estrogens released into the environment. This is because MSTPs may not completely remove estrogens in the effluent, and therefore bio-solids and wastewater effluents containing significant concentrations of estrogens may be directly discharged to the natural environment (Andaluri et al., 2012; Belhaj et al., 2015; Pal et al., 2010; Pessoa et al., 2014). Municipal landfills are also sources of organic contaminants and may contain leachate with significant amounts of dissolved organic matter partly consisting of steroid hormones and other contaminants. The leachate is capable of infiltrating into groundwater (Li, 2014) (Fig. 2). Hospitals have been identified as yet another major source of steroidal estrogen pollution. Indeed, a few investigations revealed that steroidal estrogens, especially high levels of estriol, were found in all hospital effluent samples (Avbersek etal.,2011).

3. Occurrence of steroidal estrogens in the environment

Steroidal estrogens have been detected in effluents and influent from a variety of apartments of the environment; in particular, soil and water bodies at regions near Sewage Treatment Plants (STPs), Wastewater Treatment Plants (WWTPs) and animal manure. They can be found in groundwater, soil water, runoff water from agriculture sites and surface waters (Table 3).

The extremely high amount of the natural estrogen, E1, was obviously spotted in slurry-type sites followed closely by 17a- and then 17(3-E2. The picture is similar in slurry from dairy pits. Radioactive tracer studies in pigs and poultry reveal that 17(3-estradiol excretion is primarily in the faeces (58%), whilst 17a-estradiol and estrone (E3) are mostly in the urine of pigs (96%) and poultry (69%) (Hanselman et al., 2003). Hence, it is increasingly clear that these estrogens, as part of feed programmes associated with intensive animal husbandry, find their way into excreted products easily. Indeed, note the other instances of E1 in other agriculturally-linked sites (Table 3). Comparatively lower amounts of E1 are found in deep water sites whilst there are quite variable levels of the estrogens in STP/effluent. Nevertheless, Kjsr et al. (2007) did report 68.1 ng/L of E1 in deep groundwater (Table 3), which is sufficiently close to drinking water to cause alarm. Also, very conspicuous by their absence are hardly any measurements of E3 and in particular the synthetic EE2. This clearly prompts a more widespread effort to provide data on these potentially harmful estrogens from as many sites as possible and particularly from deep groundwater sites.

According to a National Sewage Sludge Survey of the US EPA, approximately 1,014,724,000 tons of solid waste, especially animal manure, contained an estimated 76 tons of estrogens. One clearly identified route for estrogens into the terrestrial environment is through the application of manure to agricultural land as fertilizer for crops. In manures, 17a-estradiol, 17(3-estradiol and estrone concentrations range from 6 to 462 ng/g of dry solids (Andaluri et al., 2012).

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A widespread practice is to convert manure into renewable energy such as biogas. In biogas digestate, estrogenic steroid levels were observed up to 1478 ng/g. A liquid or sold bi-product can be used as fertilizer (Rodriguez-Navas et al., 2013) clearly representing another potential source of estrogen pollution. Livestock excreta are also a source of natural estrogens in the aquatic environment. In run-off from manure to tile drainage systems, their maximum concentration can range from 2.5 to 68.1 ng/L (Kjffir et al., 2007). In the fresh water of the north USA, estriol was detected at 12-196 ng/L. In effluent and fresh water sources from European sites, estrone ranged from 1-5 to 12.4 ng/L, respectively. 17(3-estradiol in WWTPs and in rivers and fresh water in North America were 1 -22 ng/L and 0-4.5 ng/L, respectively (Pal et al., 2010). Also, in a study based in California, USA, steroidal estrogens were observed in 86% samples from surface water in pastures with a maximum 44 ng/L recorded (Kolodziej and Sedlak, 2007).

3.1. Human intake of estrogens

Justifiable concern has been expressed in the published literature concerning the possible presence of estrogens in drinking water and their consequent effects on human health (Gee et al., 2015). This has

been confirmed with our recent detection of steroidal estrogens in rural groundwater in the NE China that is used partially for public water supply (unpublished data). There are similar concerns about estrogen levels in natural waters and their effect on fish physiology and other aquatic wild life. Here we list publically available data on acceptable daily intake of estrogens in food for humans and the so-called "Predicted-no-effect concentrations" on aquatic wild life. We shall refer back to these figures where appropriate in relation to estrogen concentrations reported at various sites world-wide. However, it is worthwhile to comment on the paucity of data on the synthetic EE2 compared with the natural E1 and E2. Therefore the big question concerns the impact of steroidal estrogens on humans and eco-systems. We envisage there is a threshold level for estrogen intake posing no harm for human health and for the ecosystem as a whole.

3.2. Estrogens on a global scale

There is an interesting worldwide distribution of estrogens; the pattern of various types of estrogen may reflect sources of estrogens or specific environmental characteristics of that part of the world. We

Table 3

Summary of estrogen concentrations (ng/L) in the environment, generally ranked from high-to-low concentration. NDA, no data available.

Sample type E1 17a-E2 17ß-E2 E3 EE2 Reference

Slurry in swine pit 5900-150,000 4000-84,000 1800-49,000 NDA NDA Lietal., 2010

Swine farm effluent 5200-5400 650-680 1000-1500 2200-3000 NDA Franks, 2006

Slurry in dairy pit 2500-80,000 2000-5000 800-27,000 NDA NDA Lietal., 2010

Treated cattle feedlots 720 1100 1250 NDA NDA Bartelt-Hunt et al., 2012

Dairy farm waste water 370-2356 1750-3270 351-957 NDA NDA Lietal., 2010

Lagoon pond 650 NDA NDA NDA NDA Rodriguez-Navas et al., 2013

Biogas digestate 593 50 24 NDA NDA Rodriguez-Navas et al., 2013

Sow urine 416-490 NDA 85-97 127-193 NDA Zhang et al., 2014b

Grazing land water 78 31 18 NDA NDA Kolodziej and Sedlak, 2007

Swine manure 70 175 15 NDA NDA Rodriguez-Navas et al., 2013

Swine manure leachate 68.1 2.5 NDA NDA NDA Kjœr et al., 2007

1 m deep groundwater 68.1 NDA 2.5 NDA NDA Kjœr et al., 2007

STP/effluent 12-196 6.4-12.6 6.2-42.2 NDA 0.59-5.6 Palet al., 2010

Sea water NDA NDA 0.83 NDA 4.67 Palet al., 2010

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Fig.3. Worldwide distribution of estrogens in river and surface water sites. Each pie chart, comprises the natural estrogens: E1, E2, E3 and the synthetic EE2 as percentages of total at each site: (See Supplementary Fig. 1 and Supplementary Table 1).

reviewed the occurrence of various estrogen compounds mainly in river and surface water sites.

Fig. 3 portrays potential estrogen contamination of rivers and surface water on a global scale. Clearly, major occurrence of estrogens in river water is not a universal phenomenon but largely restricted to the American mid-west, to the eastern sea board of North America, to Mexico, Ecuador, Brazil and Chile, and to countries bordering or close to the Mediterranean basin of Europe, and to Asia and South Australia. Indeed, considerable swathes of the world comprise rivers that appear not to exhibit such levels of estrogen pollution, or, perhaps are areas for which we simply lack data. That said major areas of intense farming such as the mid-West of the USA and South Australia provide an immediate link to the rise in estrogen levels in rivers in those areas. Also of note is the north south divide of the Americas for the occurrence of

the synthetic EE2 in river water. In particular, in Brazil, it would seem that EE2 may be posing a serious pollution threat. The same can be said about the very large number of the Far East sites where high levels of EE2 have been recorded from river locations (Fig. 3). In a fresh water site at ARO-Volcani (Israel) estrone concentration was 0.6-1.1 ng/L whilst in a kibbutz at Revadim (Israel) it was 1.2-1.5 ng/L with waste water effluents rising to 2.3-3.3 ng/L (Shargil et al., 2015).

Estrogen compounds have also been detected in influent and effluent of sewage treatment plants (STPs) in several countries (Fig. 4). Average concentration of estrogenic steroids (E1, E2, E3 and EE2) in Italian STPs was 80,12,3 and 52 ng/L, respectively. The concentrations of E2 in influents of Japanese STPs ranged from 30 to 90 ng/L and 20 to 94 ng/L in autumn and summer seasons, respectively (Ying et al., 2002). In Beijing, one study showed that >40% of natural estrogens and 60% of

Fig. 4. Worldwide distribution of steroidal estrogens through WWTPs. Each pie chart comprises the natural estrogens: E1, E2, E3 and the synthetic EE2 as percentages of total at each site. (See Supplementary Fig. 2 and Supplementary Table 2.)

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Table 4

Acceptable daily intake for humans via food (|g/day) and Predicted-no-effect concentration for aquatic life (PNEC) (ng/L). NDA, no data available.

E1 17ß-E2 EE2 Reference

Adult/60 kg NDA 3 NDA Luetal., 2012

Child/10 kg NDA 0.5 NDA

Human/kg bw/day NDA 5 NDA Plotan et al., 2014

Mixed diet adult 0.1 0.1

Men 1 NDA NDA Shargilet al., 2015

Women 50 NDA NDA

Adult NDA 0.0041e 0.0028e Wenzel et al., 2003

Infant NDA 0.0016e 0.0011e

PNEC for aquatic NDA 2a NDA Anderson et al., 2012

wildlife (ng/L) NDA 5b NDA

NDA NDA 0.035c Laurenson et al., 2014

NDA NDA 0.5c Nagpal and Meays, 2009

100d 8.7d 0.1d Caldwell et al., 2012

a Long term PNEC b Short term PNEC c PNEC

d Reproductive stage, test species Oryzias latipes, NOEC e Via drinking water (2 L). All figures with superscripts are in unit of ng/L.

EE2 in waste water may be entering into receiving water. The average concentrations of E1, E2, E3, and EE2 in the receiving water ranged from 48 to 70 ng/L, 2 to 19 ng/L, 50 to 320 ng/L, and 6 to 7 ng/L, respectively (Zhou et al., 2012b); note the acceptable limits for human consumption of estrogens (see Table 4). In the largest wastewater treatment plant in Beijing, the maximum concentrations of E1, E2, E3, and EE2 were 74.2, 3.9, 5.1, and 4.6 ng/L, respectively (Zhou et al., 2012a).

Here the picture for North and South America is similar to that regarding river pollution but with notably high EE2 levels in Chile whereas it is at comparatively lower concentrations in North America. However, the profile for Western Europe is different for WWTPs compared with rivers, with the inclusion of the UK, France, Germany and Austria as countries in which estrogens are reaching pollution levels (Fig. 4). Generally, WWTP effluent levels of estrogens are similar to river levels in Asian countries and Australia. Once again, we emphasize that the distribution profiles in Fig. 4 reflect available data and may not necessarily be a true global picture. It may also reflect the differences in interpretation of environmental standards of the WWTP that are used worldwide.

4. Estrogen degradation and half-life

The half-life of an estrogen will depend on its rate of degradation, reflecting its initial quantity and that remaining after a measured period of time. Half-life can be determined by first order decay or regression curve kinetics whereas rate of degradation can be estimated directly from decay kinetics. Clearly, the longer the half-life of a pollutant, the more persistent it will be in the environment. Steroidal estrogens that are excreted by humans and animals have short half-lives. Because they are hydrophobic, their concentrations decrease significantly in the aqueous phase. Their half-lives were calculated as 2 to 6 days in water and sediments in a test batch (Ying et al., 2002). Degradation of

17ß-E2 and E1 occurred in English rivers with a half-life of 0.2 to 9 days at 20 °C (Jürgens et al., 2002) (Table 5).

In a groundwater system (aquifer sediments and groundwater fluid) under aerobic conditions, E2 degraded rapidly within 10 days. However, over the same interval, EE2 was not degraded but its concentration decreased from 1-0.62 |ag/g. Thus the synthetic estrogen was much more persistent in this environment than the natural one. Indeed, the halflife under aerobic conditions for E2 and EE2 was 2 and 81 days, respectively. Under anaerobic conditions, the two steroidal estrogens did not degrade clearly indicating that the oxidative state of the source has a critical bearing on half-life and rate of degradation (Ying et al., 2003). Half-lives also differ depending on the location of the detected estrogen. For example, in aerated soil, E2 and EE2 degraded within 15 days with a half-life of 3 to 4.5 days. However, in anaerobic soil, degradation was very slow and in which E2 had an estimated 24 d half-life (Ying and Kookana, 2005). So not only location but also the relative REDOX state of the sites of study can clearly affect half-life and rate of degradation of estrogens.

E1 and E2 are biodegraded under different REDOX conditions, with estrogens being more susceptible to biodegradation under biotic conditions. For example, some bacteria present in the environment can completely degrade estrogenic compounds into harmless products e.g. gram-negative Rhodococcus zopfii and Rhodococcus equi in sewage sludge. The aforementioned bacteria have the potential to degrade E2 within 24 h (Hamid and Eskicioglu, 2012; Khanal et al., 2006). Several other factors can affect the half-life and rate of degradation of estrogens in the environment: hydrophobic partitioning, covalent bonding, ligand exchange and migration to microsites on soil particles. In addition, these processes can also be affected by the concentration of organic contaminants that are absorbed on to soil particles and cannot be recovered by extraction procedures.

Estrogens such as E2 and EE2 in aquatic environments are also susceptible to breakdown by photocatalysis and photolysis. The extent of degradation by photolysis and photocatalysis depends upon an estrogen's chemical structure. Photolysis, biodegradation, and sorption are the likely leading attenuation pathways controlling the fate of E2 (17ß-estradiol) in surface waters (Petrie et al., 2015; Writer et al., 2011). Also, EE2 degradation was studied in a lake site in the USA. Under aerobic conditions, half-life was estimated as 108 days whilst there wasn't any biodegradation by microbes in the lake water. However, under natural sunlight, photo degradation accounted for a much shorter half-life of 23 h (Zuo et al., 2013). Further investigations are required to determine the impact of photolysis on organic contaminants in environmental conditions e.g. depth of river, shading from bankside vegetation.

5. Estrogen transformation cycle

As mentioned previously, estrone (E1), estradiol (E2), and estriol (E3) lie on interconnecting metabolic pathways (Casey et al., 2003; D'Alessio et al., 2014; Duncan et al., 2015; Goeppert et al., 2014; Goeppert et al., 2015). Indeed, microorganisms living in aerobic conditions can convert one estrogen to another (Fig. 5). For example, some microbes (e.g. nitrifying bacteria), can convert E1 to E3, and others

Table 5

Half-life (in days) of steroidal estrogens from different aquatic sources.

Medium

Oxygen status

17ß-E2

Reference

Natural soil Aire river water Calder river water Thames river water River water Sandy-loam Aquifer materials Natural water

Aerobic Aerobic Aerobic Aerobic NDA

Anaerobic

Aerobic

Aerobic

2.8-4.9

0.8-1.1

0.7-1.7

Biswas et al., 2013 Jürgens et al., 2002

Ying et al., 2002 Ying and Kookana, 2005 Ying et al., 2003 Zheng et al., 2011

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Estradiol Sulfate or Glucuronide Group (E2-3G) Estriol Sulfate or Glucuronide Group (E1-3G)

Fig. 5. Interconversion pathways of natural and synthetic estrogens.

degrade E1, E2 and EE2 (e.g Novosphingobium sp. in activated sludge) (Ma et al., 2016). Furthermore, the synthetic EE2 can be converted to E1 by Sphingobacterium sp. (Haiyan et al., 2007). Also, there is a diverse array of anaerobic bacteria that can transform one estrogen to another. For example, in lake water and sediment under anaerobic conditions, E2 was chemically transformed to E1 under methanogenic, sulfate, iron, and nitrate-reducing conditions but in contrast, EE2 degradation was not reported on (Czajka and Londry, 2006).

Many studies indicate that E1 (estrone) is the main degradation product of E2. For example, in a silt loam soil, E1 was a major product of E2 degradation under abiotic conditions (Xuan et al., 2008). However, note a racemization reaction between 17a-estradiol and 17(-estradiol via estrone occurred in waste water under anaerobic conditions (Zheng et al., 2012). Interestingly, in lake water and sediment, a racemization reaction can occur between E1 and 17a-estradiol. Moreover, EE2 transforms to E1 under all but nitrate-reducing conditions (Czajka and Londry, 2006).

Under artificial rainfall, a concentration decrease of 17a-estradiol was accompanied by an equivalent increase in estrone and 17(3-estradiol in superficial soil obtained from steer feedlots (Mansell et al., 2011) indicating the activity of microbial enzymes catalyzing these conversions. Similarly, rapid conversion of 17(-E2 to E1 occurs in the presence of swine manure colloids (Prater, 2012) and 17a-E2 to E1 in dairy waste disposal systems (Zheng et al., 2007). Prater et al. (2015) also noted reversible reactions between E1 and E2. Within 24 h, a reversible conversion from E2 to E1, and then back to E2 occurred in a swine manure colloidal suspension closed to the atmosphere (Prater et al., 2015). However, degradation of E2 to E1 does not always require biological interaction (Goeppert et al., 2014).

The rate of 17(-E2 degradation in soil increases steadily as soil moisture is increased so that in dry conditions estrogens may persist at higher levels. However, the estrogen concentrations also remained constant upon moistening of the soil by simulated rainfall (Mansell et al., 2011; Xuan et al., 2008). Stability of EE2 in the soil environment has

been further examined. Rapid dissipation of EE2 occurred in aerated soil, whilst in a separate study, bacterial assemblages were present capable of rapid degradation of EE2 under both aerobic and anaerobic conditions (Carr et al., 2011; Lorenzen et al., 2006; Sarmah and Northcott, 2008). Cajthaml et al. (2009) concluded that EE2 was decomposed slowly by anaerobic bacteria. The dissipation period could exceed 1000 days and the degradation was achieved under sulfate-, nitrate-, as well as iron reducing-conditions (Cajthaml et al., 2009).

6. Effects of steroidal estrogens on fish, domestic animals and human health

6.1. Aquatic wildlife

There is significant accumulated evidence that fish exhibit perturbed development in waters which receive the effluent from STPs (Hotchkiss et al., 2008). However, it is important to note threshold concentrations of toxicity by estrogens on fish life. In the U.S. watersheds, human derived estrogens have a short term predicted-no-effect concentration (PNEC) of 5 ng/L and a long term PNEC of 2 ng/L on fish (Anderson et al., 2012). Seemingly, EE2 is the most potent hormone with a PNEC of 0.1 ng/L for aquatic chronic toxicity (Laurenson et al., 2014).

More specifically, several studies demonstrated that elevated concentrations of natural and synthetic estrogens feminize male fish e.g. reduce testes size (Arnold et al., 2014; Tetreault et al., 2011), affect reproductive fitness (Rose et al., 2013), lower sperm count, induce the production of vitellogenin (VTG) (Kidd et al., 2007) and alter other reproductive characteristics (Van Donk et al., 2016). Additionally, EE2 caused a considerable reduction in fish biomass and interrupted the aquatic food chain (Hallgren et al., 2014). However a seven year microsatellite field study revealed that, remarkably, fish can overcome the effects of EE2 as evidenced by latent increases in fish population levels (Blanchfield et al., 2015). On the other hand, EE2 does have severe deleterious effects on other forms of aquatic life. For example, in a recent

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study, EE2 at 10 ng/L directly affected the heart function of bullfrog tadpoles (Salla et al., 2016).

6.2. Domestic animals

Phytoestrogens (isoflavones, which are structurally and functionally similar to 17(-E2) cause developmental abnormalities in domestic animals. These effects are manifest morphologically with cows exhibiting changes in teat length and color of the vulva (Burton and Wells, 2002). Some plants also contain sufficient concentrations of estrogens to cause reproductive alterations in domestic animals. For example, sheep grazed on the clover plant, which contains potent levels of phytoestrogens, develop permanent infertility, so called "clover disease" (Hotchkiss et al., 2008). The effect of estrogens can also impair vision. Intraocular eye pressure (IOP) varies from species to species in domestic animals but progesterone can increase the IOP in lions, and estrogen similarly in cats (Shemesh and Shore, 2012).

6.3. Humans

Estrogen hormones are crucial for human biology and physiology. They help regulate reproduction, cardiovascular function, bone strength, cognitive behavior, successful pregnancy and gastrointestinal systems. Arguably, the most widely discussed issue concerning estrogens and human health is HRT. This is where menopausal women can be administered estrogens to replace endogenous hormones that are no longer produced in adequate quantities to maintain normal health. The Joint FAO/WHO Expert Committee on Food Additives, evaluated 17(-E2 in relation to the HRT treatment in menopausal women. They found that adverse hormonal effects occurred at much lower than expected concentrations and subsequently established an acceptable daily intake (ADI) of 0-50 ng/kg body weight (bw) (Plotan et al., 2014). A no-observed-adverse-effect (NOEL) for humans of 0.3 mg/day (equivalent to 5 |g/kg bw/day) has been calculated by Plotan et al. (2014) but estrogens are capable of affecting human health as soon as above this safe level (see also, Table 4). However, we are surprised that these authors have used a value of 0.3 mg/day as an acceptable daily limit. This may need further study. In China, the estrogenic steroids, 17(-E2 and estrone, were detected in 53 out of 62 drinking water treatment works (DWTWs) and 31 out of 62 DWTWs from 31 major cities. The maximum detected concentrations were 1.7 ng/L and 0.1 ng/L for 17(-E2 and E1, respectively (Fan et al., 2013). To our knowledge, this is the first study on the occurrence of estrogens in drinking water that may represent a risk to human health.

Clearly, estrogens are essential for normal human physiology but can have serious adverse effects if allowed to accumulate in the environment and enter the human food chain. If consumed at levels above the safe thresholds they can increase the risk of cancer and induce cardiovascular diseases in humans (Wodawek-Potocka et al., 2013). Indeed supraoptimal levels of estrogens have been linked with increased incidences of breast cancer in females (Moore et al., 2016) and prostate cancer in men (Nelles et al., 2011), although cause-and-effect is hotly debated. Estrogens preferentially bind with receptor cells in breast tissues leading to cell proliferation that can ultimately form tumours. As noted by Liang and Shang (2013), the US National Toxicology Program listed estrogens as carcinogens. The predominant intracellular estrogen is 17(-E2. It binds with estrogen receptors (ER a and (3). ER a targets genes that promote cell proliferation or decrease apoptosis (cell death). A key cell cycle gene, cyclin D1 is expressed rapidly in estrogen treatments (Butt et al., 2005). In mice, ER a and ( have opposing effects on cell proliferation and apoptosis (Dupont et al., 2000). Post-surgery, breast cancer patients are often administered tamoxifen, a drug capable of blocking this selective binding of estrogens with the receptors or are treated with enzyme inhibitors or other agents that block the release of

estrogen at source. Whatever the exact link is between estrogens in the environment and breast cancer, water authorities world-wide include, or should include routine screening of estrogen concentrations (together with all EDCs) as part of their aim to deliver clean and wholesome water (Gee et al., 2015).

The risk of environmental estrogens on breast cancer was examined in 198 women at time of diagnosis. Sixteen organochloride pesticides and total xenoestrogen levels were measured and comparisons made with 260 unaffected women. A sub-group of leaner post-menopausal women showed an increased risk of breast cancer (Ibarluzea et al., 2004). More recently, exposure to environmental endocrine disrupting compounds was also correlated with cancer susceptibility (Trevino et al., 2015).

Steroidal estrogens in food and water can also induce premature menopause and affect reproductive development, also causing virilization in young women. Several studies also revealed that estrogens were involved in the decline of sperm counts and disorders of the male reproductive system and feminization of men (Bolong et al., 2009; Sumpter and Jobling, 2013). Steroidal estrogens singly or in combination with progesterone also reduce IOP after menopause in humans which might increase the risk of developing glaucoma (Shemesh and Shore, 2012). Besides phytoestrogens can also affect reproduction, the immune system and metabolism (Alexander, 2014). Accumulative evidence points clearly to serious health concerns regarding estrogens making it crucial to ensure that both estrogens from human and animal waste and phytoestrogens are not consumed in food and water at levels above the accepted NOELs.

7. Uptake and transport mechanisms in plant systems

The use of plants for phytoremediation of toxic environments is well known. Phytoremediation relies on some plants' capacities to adapt and grow in environments where few other eukaryote organisms can survive. Natural populations of weeds growing on rock faces, through cracks in paving stone and in desert conditions are just a few illustrative examples. Some plant species have also adapted to grow in soils contaminated with toxic metals. For example, the grass species, Festuca rubra, has several cultivars one of which is tolerant to toxic levels of zinc (Gomez et al., 2016) whereas others may be zinc sensitive. Other plants show remarkable tolerance to a range of toxic metals. For example, the alpine pennycress, Thlaspi caerulescens has multiple tolerance to cadmium, cobalt, copper, molybdenum, nickel, lead and zinc. The willow-related tree, Salix viminalis is another with tolerance to silver, selenium, manganese and zinc. Interestingly, this tree also tolerates polluted levels of petroleum products and organic solvents (Marmiroli and McCutcheon, 2003; Prasad, 2005; Schmidt, 2003). In contrast, and to our knowledge, there are fewer reports of plants capable of accumulating animal or synthetic estrogens: wetland macrophytes, leafy vegetables and algae together with poplar, maize and willow. For example, in a lab study, Scirpus validus (emergent wetland plant) and Populus deltoides nigra (wetland plant), could reduce the concentration of 17(-E2, E1, E3 and EE2 from the solution through transformation suggesting efficient uptake into root tissues (Bircher, 2011) (see Table 6).

Phytoaccumulating plants share the common property of up-take of potentially harmful molecules through transport systems that normally process nutrients but instead sequester toxic substances in the plant vacuole. Hence, plants have evolved a relatively unique method to take up and place toxic substances in locations that are not harmful to the plant's metabolism. They do this by accepting these substances through membrane bound pumps and carriers that normally take up nutrients that the plant requires. The extent to which uptake of organic matter follows the same pathway(s) is less clear.

Roots are the most essential part of plant for uptake of nutrients from soil and they also take up organic contaminants from both water

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Table 6

Phytoremediation of steroidal estrogens.

Species

Accumulation characteristics

Estrogen type

Reference

Chlorella vulgaris

Populus deltoids nigra, Scirpus validus

Lemna species

algal genera:

Anabaena cylindrica,

Chlorococcus,

Spirulina platensis,

Chlorella,

Scenedesmus quadricauda Zea mays,

Golden Cross Bantam (hybrid) Portulaca oleracea Salix exigua Arabidopsis thaliana (Lactuca sativa L.)

Biotransformation and bio concentration of steroidal estrogens Phytoremediation of natural and synthetic steroid growth promoters Removal of natural and synthetic estrogens from wastewater treatment system

Uptake and transformation of natural and synthetic estrogens by maize seedlings

Removal of phenolic endocrine disruptors Phytoremediation of pharmaceutical

Impact of estrogen on lettuce with biosolids and waste water effluent application

E2, E1 17ß-E2 EE2 17ß-E2, EE2, E1

17ß-E2, E1

17ß-E2 EE2

Lai et al., 2002 Bircher, 2011 Shi et al., 2010

Card et al., 2012; Card et al., 2013

Imai et al., 2007 Franks, 2006

Shargil et al., 2015

and soil. There are two main uptake mechanisms for plant uptake of organic contaminants: passive and active through the root system. In uptake studies of non-ionized contaminants from a solution culture, two steps were identified. Firstly, an equilibrium is established between the nutrient or pollutant concentration in the aqueous phase within the plant root and the external soil solution, and secondly, chemical sorption onto lipophilic bodies occurs. These solids contain lipids that attach in membranes and cell walls (Collins et al., 2006; Collins et al., 2011; Dodgen, 2014; Trapp and Legind, 2011).

Nonionic organic contaminants have the potential to pass cell membranes easily and thus have greater potential to be taken up by the roots. They tend to be transported in the roots by water flow driven by the water potential gradient and thus accumulate at a maximum concentration in the leaves (Fig. 6, the plant background from web) (Collins et al., 2011; Dodgen, 2014; Malchi etal., 2014). Indeed, organic (hydrophobic) contaminants have greater potential to partition into plant root lipids than hydrophilic contaminants. Mostly, the octanol-water partition coefficient (Kow, see Section 1)

is used as a surrogate measure of pollutant lipophilic tendency. A non-ionized contaminant with log Kow > 4 has a maximum potential for retention in plant roots. Indeed, pollutants with a log Kow higher than 3.5 are too hydrophobic to move through the vascular tissues (Card, 2011). Other additional parameters such as the contaminant's pKa, pH, ionic strength, biodegradation, and sorption might also affect uptake (Collins etal., 2011; Malchi etal., 2014).

The uptake of organic contaminants from the soil into plants is strongly affected by their concentration in the voids between soil and water. The concentration of these contaminants can be affected by: soil pH, dissolved organic carbon, and REDOX potential in the pore water which can indirectly influence the passive uptake of the organic contaminants. They can be attached to several components in soil including clays, iron oxides, and other organic matter. Many other factors are likely to be important, including: hydrogen bonding, surface complexion, and cation exchange. In addition, the partitioning behavior of the ionizable EDCs is highly susceptible to changes in soil pH, as changes in pH may alter the ionic fraction. Empirical relationships exist between

Fig. 6. Uptake and transport processes of organic chemicals in the soil-plant system.

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a chemical's lipophilicity and its affinity to sorption to soil organic matter (Collins et al., 2011; Dodgen, 2014).

7.1. Transport from the root to other plant parts

Plant root structure is well understood comprising the epidermis, cortex, endodermis and vascular tissue containing xylem and phloem. Water and solutes are moved upward from the root into other plant parts through the xylem by mass flow due to a pressure gradient created throughout the plant during transpiration. For contaminants taken up by plant roots to reach the xylem, they must pass through a number of layers: the epidermis, cortex, endodermis, and pericycle. At the endo-dermis all solutes must cross the cell membrane, and it is the combination of their aqueous solubility and their solubility in the lipid-rich cell membrane of the endodermis that affects their potential movement into roots from the soil pore water and later transport to other plant parts via the xylem (Collins et al., 2006; Collins et al., 2011). Water and solutes transported in the xylem may also diffuse laterally into nearby layers

Contaminant concentration might be high in plant shoots as a result of the equilibration of the aqueous phase and partitioning into lipophilic solids. Other influential factors include: rate of root uptake, concentration of lipophilic solids and the plant transpiration stream. There is potential for sorption to stem parts as the contaminants moves up the stem; this sorption becomes maximized with increasing lipophilicity (Collins et al., 2006).

8. Accumulation of estrogen in plants

A series of recent papers describe estrogen uptake studies in plants. Batch and continuous flow tests involving waste water indicated that algae and duckweed play a crucial role in the removal of estrogens (Shi et al., 2010). In maize seedlings, uptake of two natural steroidal estrogens, 17(-E2 and E3 and two synthetic estrogens was measured. All four were detected in roots at concentrations up to 0.19 |aM but only 17(-E2 was transported to the shoot (Card et al., 2012; Card et al., 2013). Sandbar willow and Arabidopsis thaliana also remove estrogens actively from solution. Both plants grown in estrogen-polluted medium eliminated 86% of the synthetic estrogen, 17a-ethynyl estradiol (EE2) in 24 h (Franks, 2006). In a hydroponic study in Osaka, Japan, one hundred different garden plant species were tested for phenolics and EDCs; Portulaca oleracea was the only effective phytoremediator. It removed EDCs having a phenol group, including 17(-estradiol (E2), within 24 h (Imai et al., 2007). In another study, steroidal estrogens were determined in fruits and vegetables obtained from local markets in Fort Pierce, FL, USA. Significant concentrations of estrogens were observed in the vegetables especially in lettuce. 17(-E2 in vegetables and fruits was 1.3 to 2.2 ^g/kg. According to the Joint FAO/WHO Expert Committee on Food Additives (JECFA), the toxic level for daily intake (ADI) of 17(-estradiol for a 60 kg adult is 3.0 ^g/day and that for a 10 kg baby is 0.5 ^g/day. Clearly, in this study 17(-E2 exceeded this limit for infants (Lu et al., 2012).

8.1. Effects of estrogens on plant growth

Various studies have examined the effects of exogenous steroid hormones on seed germination and plant development. For example, in potato (Solanum tuberosum L. cv. '¡wa') root growth and tuber size were reduced at 0.1 to 10 mg/L of E1,17(-E2 and E3, (Brown, 2006). On the other hand, maize seedling growth was consistently inhibited at 10 mg/L but was stimulated by 0.1 mg/L 17(-E2 (Bowlin, 2014). In tomato seedlings, estrone and 17(-estradiol at 1 |aM in Hoagland solution, reduced growth as well as root number (Janeczko and Skoczowski, 2011). However, in mung beans estrone and estradiol at low concentrations of 0.1 |jM augmented germination and vegetative

growth but were inhibitory at high concentrations (60 |aM) (Guan and Roddick, 1988). A stimulation of growth was also induced by E2 at 10-9 M in germinating chickpea. Hence, a fairly consistent theme is that estrogens at low concentrations could be beneficial in agriculture overcoming dormancy problems experienced by some plant species (Erdal and Dumlupinar, 2010).

Estrogens have other both positive and negative concentration-dependent effects on plant growth. In lentil, 17(-E2 treatment enhanced embryo growth and improved tolerance to cadmium and copper stress during germination (Chaoui and El Ferjani, 2013). However, in Arabidopsis thaliana, natural estrogens E1,17(-E2 and E3 at 0.1 |aM, reduced the number of generative plants (Janeczko et al., 2003). Also, the estrogenic hormone, androstenedione, maximized net photosynthetic rates. The impact of androstenedione was demonstrated during the rehydration of plants that had undergone a period of drought (Janeczko et al., 2012). Conversely, a recent study in Sweden highlighted the negative effects of EE2 (at 7 ^M) on growth and photosynthesis in the green alga, Chlamydomonas reinhardtii. They concluded that the discharge of EE2 in the waste water stream posed a deleterious effect not only by removing atmospheric CO2, but also in inhibiting algal growth. It was later suggested that further investigations are needed for the negative impacts of estrogen on plant growth (Pocock and Falk 2014).

8.2. Effects of estrogen on plant antioxidant activity

Reactive oxygen species (ROS) are generated as a normal product associated with plant cellular metabolism. A variety of environmental stresses cause excessive ROS production leading to progressive oxidative injury and ultimately, cell death. Detoxification associated with excess ROS is usually accomplished by an effective antioxida-tive system comprising non enzymic as well as enzymic antioxidants (Genisel et al., 2013; Sharma et al., 2012).

Enzymic antioxidants include superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPX), as well as enzymes of the ascorbate glutathione (AsA-GSH) cycle such as ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR). Ascorbate (AsA), glutathione (GSH), carotenoids, tocopherols, and phenolics serve as potent nonenzymic antioxidants within the cell (Erdal, 2012). In plants, ROS activation involves two different mechanisms (Fig. 7, adopted and redrawn after Sharma et al., 2012). ROS is generated in different organelles and cellular locations such as: chloroplasts, mitochondria, plasma membranes, peroxisomes, the apoplast, endoplasmic reticulum, and cell walls (Sharma et al., 2012).

Interestingly, several recent reports provide evidence that estrogens can alleviate some of the symptoms associated with toxic metal-induced oxidative damage. In maize and chickpea, exogenous an-drosterone treatment reduced significantly, oxidative damage caused from chilling stress by increasing the levels of antioxidant enzymes, including superoxide dismutase (SOD), guaiacol peroxidase (POX), catalase, ascorbate peroxidase (APX) and glutathione reductase (Erdal, 2012; Genisel et al., 2013). Similarly, (-estradiol has an ameliorative effect on growth of maize seeds suffering from salt-induced oxidative damage once again by enhancing antioxi-dant activity (Erdal and Dumlupinar, 2011a). Consequently MSH including progesterone, ( -estradiol and androsterone, significantly improved plant growth, resulting in increased levels of soluble protein and sugar (Erdal and Dumlupinar, 2011b). Root growth, lead content, protein content, amylase activity, and antioxidant activity were measured in wheat seeds under lead stress in the presence of 17(-estradiol (E2). Once again, the estrogen suppressed lead-induced oxidative damage. Also there was less DNA damage in wheat seedlings exposed to lead but treated with 17(-estradiol (Genisel et al., 2015). Furthermore, in bean seed, EE2 induced antioxidant enzyme activity and significantly decreased the extent of lipid peroxidation and lowered endogenous H202 levels (Erdal, 2009).

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Fig. 7. Schematic illustration of generation of reactive oxygen species (ROS) in plants.

9. Conclusions

In this review study we have examined the effects of exogenous estrogens on animal and human health, on pollution of aquatic systems and on plant growth and development. We have also tried to raise critical awareness of the route of potentially harmful estrogens through the food chain. We conclude that:

• Clarification is required about safe threshold levels of estrogens in the terrestrial, aquatic and human environments;

• Sewage treatment plants, wastewater treatment plants and sewage constituents used in manure constitute major potential sources of estrogen pollution;

• Global sites of estrogen release into rivers and from waste water plants are highly asymmetric and more data from more locations are required to test if this is a real effect;

• Half-lives of E1 and E2 are short and both can be biodegraded relatively rapidly but EE2 is more persistent in the environment;

• E1, E2, E3 and EE2 are easily transformable into each other by aerobic organisms but transformation rates are positively related to moisture content of soils;

• Fish, domestic and wild animal together with human health can be disrupted by rising levels of estrogens;

• There is a link between environmental estrogens and breast cancer that may be restricted to sub-sets of patients on a general weight-dependent basis;

• Plants synthesise phytoestrogens and take up mammalian-derived estrogens both actively and passively. Estrogens' hydrophobicity and li-pophilic properties facilitates relatively easy passage through plant membranes;

• Plants can accumulate estrogens in both roots and shoots;

• In a concentration dependent manner, estrogens can stimulate or inhibit plant growth and development and also they can ameliorate the ROS-induced damage caused by other stresses such as toxic metals.

Finally, we make the following specific points regarding estrogens in the environment, according to current literature review:

1. Estrogen should be listed as a toxic organic pollutant which is confirmed by several studies;

2. Many more data about estrogen levels in the natural environment from many more sites world-wide are urgently required;

3. A greater data pool should enable tests that model the accumulation of natural as opposed to synthetic estrogens in the environment and in particular at those sites close to water treatment and sewage disposal systems;

4. Estrogen pollution is becoming a vital environmental concern and has deleterious effects on human, animal and plant growth and development at significant levels. Attention to this issue is crucial and demands further in-depth investigation;

5. Establishing a causal link between increased presence of environmental estrogens and increased incidences of breast cancer requires more data;

6. The role of estrogens in biological systems is also ambiguous. In addition, further studies are also required to determine tolerance, because still the impact of estrogen-toxicity in many ecosystems is not clear.

Role of the funding source

We thank the National Natural Science Foundation of China (Grants:

41272255 and 41472237), Liaoning Innovation Team Project (no.

LT2015017) and Shenyang Sci-Tech Program (Grants F14-133-900,

F15-113-9-00).

Appendix A. Supplementary data

Supplementary data to this article can be found online at http://dx.

doi.org/10.1016/j.envint.2016.12.010.

References

Alexander, V., 2014. Phytoestrogens and their effects. Eur. J. Pharmacol. 741, 230.

Andaluri, G., Suri, R.P., Kumar, K., 2012. Occurrence of estrogen hormones in biosolids, animal manure and mushroom compost. Environ. Monit Assess. 184,1197-1205.

Anderson, P.D., Johnson, A.C., Pfeiffer, D., Caldwell, D.J., Hannah, R., Mastrocco, F., Sumpter, J.P., Williams, R.J., 2012. Endocrine disruption due to estrogens derived from humans predicted to be low in the majority of US surface waters. Environ. Toxicol. Chem. 31, 1407-1415.

Arnold, K.E., Brown, A.R., Ankley, G.T., Sumpter, J.P., 2014. Medicating the environment: assessing risks of pharmaceuticals to wildlife and ecosystems. Phil. Trans. R. Soc. Lond. B: Biol. Sci. 369. http://rstb.royalsocietypublishing.org.

ARTICLE IN PRESS

12 M.Adeel et al. / Environment International xxx (2016) xxx-xxx

Arnon, S., Dahan, O., Elhanany, S., Cohen, K., Pankratov, I., Gross, A., Ronen, Z., Baram, S., Shore, L.S., 2008. Transport of testosterone and estrogen from dairy-farm waste lagoons to groundwater. Environ. Sci. Technol. 42, 5521-5526.

Avbersek M., Somen, J., Heath, E., 2011. Dynamics of steroid estrogen daily concentrations in hospital effluent and connected waste water treatment plant. J. Environ. Monit. 13, 2221-2226.

Bartelt-Hunt, S.L., Snow, D.D., Kranz, W.L., Mader, T.L., Shapiro, C.A., Donk, S.J., Shelton, D.P., Tarkalson, D.D., Zhang, T.C., 2012. Effect of growth promotants on the occurrence of endogenous and synthetic steroid hormones on feedlot soils and in runoff from beef cattle feeding operations. Environ. Sci. Technol. 46,1352-1360.

Belhaj, D., Baccar, R., Jaabiri, I., Bouzid,J., Kallel, M., Ayadi, H., Zhou,J.L, 2015. Fate of selected estrogenic hormones in an urban sewage treatment plant in Tunisia (North Africa). Sci. Total Environ. 505,154-160.

Bircher, S., 2011. Phytoremediation of Natural and Synthetic Steroid Growth Promoters Used in Livestock Production by Riparian Buffer Zone Plants. M.Sc. Thesis. University of Iowa, U.SA

Biswas, S., Shapiro, C., Kranz, W., Mader, T., Shelton, D., Snow, D., Bartelt-Hunt, S., Tarkalson, D., van Donk S., Zhang, T., 2013. Current knowledge on the environmental fate, potential impact, and management of growth-promoting steroids used in the US beef cattle industry. J. Soil Water Con. 68, 325-336.

Blanchfield, P.J., Kidd, IKA., Docker, M.F., Palace, V.P., Park B.J., Postma, L.D., 2015. Recovery of a wild fish population from whole-lake additions of a synthetic estrogen. Environ. Sci. Technol. 49, 3136-3144.

Bolong, N., Ismail, A., Salim, M.R., Matsuura, T., 2009. A review of the effects of emerging contaminants in wastewater and options for their removal. Desalination 239, 229-246.

Bowlin, K.M., 2014. Effects of ß-estradiol on Germination and Growth in Zea mays L. M.Sc. thesis. Northwest Missouri State University, Maryville, Missouri, U.S.A.

Brown, G.S., 2006. The Effects of Estrogen on the Growth and Tuberization of Potato Plants (Solanum tuberosum cv. 'Iwa') Grown in Liquid Tissue Culture Media. M.Sc. Thesis. University of Canterbury, New Zealand.

Burton, J., Wells, M., 2002. The effect of phytoestrogens on the female genital tract. J. Clin. Pathol. 55, 401-407.

Butt, A.J., McNeil, C.M., Musgrove, E.A., Sutherland, R.L., 2005. Downstream targets of growth factor and oestrogen signalling and endocrine resistance: the potential roles of c-Myc, cyclin D1 and cyclin E. Endocr. Relat. Cancer 12,47-59 suppl..

Cajthaml, T., Kresinovä, Z., Svobodovä, K., Sigler, K., Sezanka, T., 2009. Microbial transformation of synthetic estrogen 17a-ethinylestradiol. Environ. Pollut. 157,3325-3335.

Caldwell, D.J., Mastrocco, F., Anderson, P.D., Länge, R., Sumpter, J.P., 2012. Predicted-no-effect concentrations for the steroid estrogens estrone, 17ß-estradiol, estriol, and 17a-ethinylestradiol. Environ. Toxicol. Chem. 31,1396-1406.

Card, M.L., 2011. Interactions Among Soil, Plants, and Endocrine Disrupting Compounds in Livestock Agriculture. Ph. D Thesis. The Ohio State University, U.S.A.

Card, M.L., Schnoor, J.L., Chin, Y.-P., 2012. Uptake of natural and synthetic estrogens by maize seedlings. J. Agric. Food Chem. 60, 8264-8271.

Card, M.L., Schnoor, J.L., Chin, Y.-P., 2013. Transformation of natural and synthetic estrogens by maize seedlings. Environ. Sci. Technol. 47, 5101-5108.

Carballa, M., Fink, G., Omil, F., Lema, J.M., Ternes, T., 2008. Determination of the solid-water distribution coefficient (K d) for pharmaceuticals, estrogens and musk fragrances in digested sludge. Water Res. 42, 287-295..

Carr, D.L., Morse, A.N., Zak J.C., Anderson, T.A., 2011. Microbially mediated degradation of common pharmaceuticals and personal care products in soil under aerobic and reduced oxygen conditions. Water Air Soil Pollut. 216, 633-642.

Casey, FX, Larsen, G.L., Hakk, H., Simunek J., 2003. Fate and transport of 17ß-estradiol in soil-water systems. Environ. Sci. Technol. 37, 2400-2409.

Chaoui, A., El Ferjani, E., 2013. ß-estradiol protects embryo growth from heavy-metal toxicity in germinating lentil seeds. J. Plant Growth Reg. 32, 636-645.

Collins, C., Fryer, M., Grosso, A., 2006. Plant uptake of non-ionic organic chemicals. Environ. Sci. Technol. 40, 45-52.

Collins, C.D., Martin, I., Doucette, W., 2011. Plant uptake of xenobiotics. In: Schroder, P., Collins, C.D. (Eds.), Organic Xenobiotics and Plants: From modeof action to Ecophys-iology. Springer, Heidelberg, pp. 3-16.

Czajka, C.P., Londry, K.L., 2006. Anaerobic biotransformation of estrogens. Sci. Total Environ. 367, 932-941.

D'Alessio, M., Vasudevan, D., Lichwa, J., Mohanty, S.K., Ray, C., 2014. Fate and transport of selected estrogen compounds in Hawaii soils: effect of soil type and macropores. J. Contam. Hydrol. 166,1-10.

Dodgen, L.K., 2014. Behavior and Fate of PPCP/EDCs in Soil-Plant Systems. Ph.D. Thesis. University of California Riverside, U.S.A.

Duncan, L.A., Tyner, J.S., Buchanan, J.R., Hawkins, S.A., Lee, J., 2015. Fate and transport of 17ß-estradiol beneath animal waste holding ponds. J. Environ. Qual. 44, 982-988.

Dupont, S., Krust, A., Gansmuller, A., Dierech, A., Chambon, P., Mark, M., 2000. Effect of single and compound knockouts of estrogen receptors a (ER a) and ß (ER ß) on mouse reproductive phenotypes. Development 127,4277-4291.

Erdal, S., 2009. Effects of mammalian sex hormones on antioxidant enzyme activities, H2O2 content and lipid peroxidation in germinating bean seeds. J. Fac. Agric. 40, 79-85.

Erdal, S., 2012. Androsterone-induced molecular and physiological changes in maize seedlings in response to chilling stress. Plant Physiol. Biochem. 57,1-7.

Erdal, S., Dumlupinar, R., 2010. Progesterone and ß-estradiol stimulate seed germination in chickpea by causing important changes in biochemical parameters. Z. Naturforsch. C 65, 239-244.

Erdal, S., Dumlupinar, R., 2011a. Exogenously treated mammalian sex hormones affect inorganic constituents of plants. Biol. Trace Elem. Res. 143, 500-506.

Erdal, S., Dumlupinar, R., 2011b. Mammalian sex hormones stimulate antioxidant system and enhance growth of chickpea plants. Acta Physiol. Plant. 33,1011-1017.

Fan, Z., Hu, J., An, W., Yang, M., 2013. Detection and occurrence of chlorinated byproducts of bisphenol a, nonylphenol, and estrogens in drinking water of China: comparison to the parent compounds. Environ. Sci. Technol. 47,10841-10850.

Franks, C.G., 2006. Phytoremediation of Pharmaceuticals With Salix exigua. M.Sc. Thesis Lethbridge, Alta. University of Lethbridge, Faculty of Arts and Science, Canada.

Gee, R.H., Rocket, L.S., Rumsby, P.C., 2015. Considerations of endocrine disruptors in drinkning water. In: Darbre, P.D. (Ed.), Endocrine Disruption and Human Health. Academic Press, London, N.Y. http://dx.doi.org/10.1016/B978-0-12-801139-3.00018-1.

Genisel, M., Turk, H., Erdal, S., 2013. Exogenous progesterone application protects chickpea seedlings against chilling-induced oxidative stress. Acta Physiol. Plant. 35, 241-251.

Genisel, M., Turk H., Erdal, S., Demir, Y., Genc, E., Terzi, 1., 2015. Ameliorative role of ß-es-tradiol against lead-induced oxidative stress and genotoxic damage in germinating wheat seedlings. Turk. J. Bot. 39,1051-1059.

Goeppert, N., Dror, I., Berkowitz, B., 2014. Detection, fate and transport of estrogen family hormones in soil. Chemosphere 95, 336-345.

Goeppert, N., Dror, I., Berkowitz, B., 2015. Fate and transport of free conjugated estrogens during soil passage. Environ. Pollut. 206, 80-87.

Gómez, J., Yunta, F., Esteban, E., Carpena, R., Zornoza, P., 2016. Use of radiometric indices to evaluate Zn and Pb stress in two grass species (Festuca rubra L. and Vulpia myuros L.). Env. Sci. Pollut. Res. 1-10.

Guan, M., Roddick, J.G., 1988. Comparison of the effects of epibrassinolide and steroidal estrogens on adventitious root growth and early shoot development in mung bean cuttings. Physiol. Plant. 73,426-431.

Haiyan, R., Shulan, J., ud din Ahmad, N., Dao, W., Chengwu, C., 2007. Degradation characteristics and metabolic pathway of 17a-ethynylestradiol by Sphingobacterium sp. JCR5. Chemosphere 66, 340-346.

Hallgren, P., Nicolle, A., Hansson, L.A., Brönmark, C., Nikoleris, L., Hyder, M., Persson, A., 2014. Synthetic estrogen directly affects fish biomass and may indirectly disrupt aquatic food webs. Environ. Toxicol. Chem. 33,930-936.

Hamid, H., Eskicioglu, C., 2012. Fate of estrogenic hormones in wastewater and sludge treatment: a review of properties and analytical detection techniques in sludge matrix. Water Res. 46, 5813-5833.

Hanselman, T.A., Graetz, D.A., Wilkie, A.C., 2003. Manure-borne estrogens as potential environmental contaminants: a review. Environ. Sci. Technol. 37, 5471-5478.

Hotchkiss, A.K., Rider, C.V., Blystone, C.R., Wilson, V.S., Hartig, P.C., Ankley, G.T., Foster, P.M., Gray, C.L., Gray, L.E., 2008. Fifteen years after "wingspread"—environmental endocrine disrupters and human and wildlife health: where we are today and where we need to go. Toxicol. Sci. 105, 235-259.

Ibarluzea, J.M., Fenanadez, M.F., Santa-Marina, L., Olea-Serrano, M.F., Rivas, M.F., Aurrekoettxea, J.J., Exposito, J., Lorenzo, M., Torne, P., Villalobos, M., Pedraza, V., Sasco, JA, Olea, N., 2004. Breast cancer risk and the combined effect of environmental estrogens. Cancer Causes Control 15, 591 -600.

Imai, S., Shiraishi, A., Gamo, K., Watanabe, I., Okuhata, H., Miyasaka, H., Ikeda, K., Bamba, T., Hirata, K., 2007. Removal of phenolic endocrine disruptors by Portulaca oleracea. J. Biosci. Bioeng. 103,420-426.

Janeczko, A., Filek, W., Biesaga-Koscielniak J., Marcinska, I., Janeczko, Z., 2003. The influence of animal sex hormones on the induction of flowering in Arabidopsis thaliana: comparison with the effect of 24-epibrassinolide. Plant Cell Tiss. Org. Cul. 72, 147-151.

Janeczko, A., Kocurek M., Marcinska, I., 2012. Mammalian androgen stimulates photosynthesis in drought-stressed soybean. Open Life Sci. 7, 902-909.

Janeczko, A., Skoczowski, A., 2011. Mammalian sex hormones in plants. Folia Histochem. Cytobiol. 43, 70-71.

Jürgens, M.D., Holthaus, K.I., Johnson, A.C., Smith, J.J., Hetheridge, M., Williams, RJ., 2002. The potential for estradiol and ethinylestradiol degradation in English rivers. Environ. Toxicol. Chem. 21, 480-488.

Khanal, S.K., Xie, B., Thompson, M.L., Sung, S., Ong, S.-K., Van Leeuwen, J., 2006. Fate, transport, and biodegradation of natural estrogens in the environment and engineered systems. Environ. Sci. Technol. 40, 6537-6546.

Kidd, K.A., Blanchfleld, P.J., Mills, K.H., Palace, V.P., Evans, R.E., Lazorchak J.M., Flick R.W., 2007. Collapse of a fish population after exposure to a synthetic estrogen. Proc. Nat. Acad. Sci. 104, 8897-8901.

Kjt£r, J., Olsen, P., Bach, K., Barlebo, H.C., Ingerslev, F., Hansen, M., Sorensen, B.H., 2007. Leaching of estrogenic hormones from manure-treated structured soils. Environ. Sci. Technol. 41,3911-3917.

Kolodziej, E.P., Sedlak, D.L., 2007. Rangeland grazing as a source of steroid hormones to surface waters. Environ. Sci. Technol. 41,3514-3520.

Kostich, M., Flick, R., Martinson, J., 2013. Comparing predicted estrogen concentrations with measurements in US waters. Environ. Pollut. 178,271-277.

Lai, K., Scrimshaw, M., Lester, J., 2002. Biotransformation and bioconcentration of steroid estrogens by Chlorella vulgaris. Appl. Environ. Microbiol. 68, 859-864.

Laurenson, J.P., Bloom, R.A., Page, S., Sadrieh, N., 2014. Ethinyl estradiol and other human pharmaceutical estrogens in the aquatic environment: a review of recent risk assessment data. AAPS J. 16, 299-310.

Li, W.C., 2014. Occurrence, sources, and fate of pharmaceuticals in aquatic environment and soil. Environ. Pollut. 187,193-201.

Li, Y., Hanwei Chunye, L., Liwe Ming, Y., Song, Z.F., 2010. Excretion of estrogens in the lives stock and poultry production and their environmental behaviors. Acta ecologica sinica 30,1058-1065.

Liang, J., Shang, Y., 2013. Estrogen and cancer. Ann. Rev. Physiol. 75, 225-240.

Lorenzen, A., Burnison, K., Servos, M., Topp, E., 2006. Persistence of endocrine-disrupting chemicals in agricultural soils. J. Environ. Eng. Sci. 5,211-219.

Lu, J., Wu, J., Stoffella, P.J., Wilson, P.C., 2012. Analysis of bisphenol A, nonylphenol, and natural estrogens in vegetables and fruits using gas chromatography-tandem mass spectrometry. J. Agric. Food Chem. 61, 84-89.

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M. Adeel et al. / Environment International xxx (2016) xxx-xxx 13

Ma, C., Qin, D., Sun, Q., Zhang, F., Liu, H., Yu, C.-P., 2016. Removal of environmental estrogens by bacterial cell immobilization technique. Chemosphere 144,607-614.

Malchi, T., Maor, Y., Tadmor, G., Shenker, M., Chefetz, B., 2014. Irrigation of root vegetables with treated wastewater: evaluating uptake of pharmaceuticals and the associated human health risks. Environ. Sci. Technol. 48,9325-9333.

Mansell, D.S., Bryson, RJ., Harter, T., Webster, J.P., Kolodziej, E.P., Sedlak, D.L., 2011. Fate of endogenous steroid hormones in steer feedlots under simulated rainfall-induced runoff. Environ. Sci. Technol. 45, 8811-8818.

Marmiroli, N., McCutcheon, S., 2003. Making phytoremediation a successful technology. Phytoremediation: Transformation and control of contaminants. In: McCutcheon, S., Schnoor, J.L. (Eds.), Phytoremediation: Transformation and Control of Contaminants. Wiley, N.J., U.S.A., pp. 85-119.

Moore, S.C., Matthews, C.E., Shu, X.O., Yu, K., Gail, M.H., Xu, X., Ji, B.-T., Chow, W.-H., Cai, Q., Li, H., 2016. Endogenous bstrogens, estrogen metabolites, and breast cancer risk in postmenopausal Chinese women. J. Nat. Cancer Inst. 108 (djw103).

Nagpal, N.K., Meays, C.L., 2009. Water Quality Guidelines for Pharmaceutically-active Compounds (PhACs): 17a-ethinylestradiol (EE2). Ministry of Environment, Province of British Columbia (Technical Appendix).

Nelles, J.L., Hu, W.-Y., Prins, G.S., 2011. Estrogen action and prostate cancer. Expert Rev. Endocrinol. Metab. 6,437-451.

Pal, A., Gin, K.Y.-H., Lin, A.Y.-C., Reinhard, M., 2010. Impacts of emerging organic contaminants on freshwater resources: review of recent occurrences, sources, fate and effects. Sci. Total Environ. 408, 6062-6069.

Pessoa, G.P., de Souza, N.C., Vidal, C.B., Alves, J.A., Firmino, P.I.M., Nascimento, R.F., dos Santos, A.B., 2014. Occurrence and removal of estrogens in Brazilian wastewater treatment plants. Sci. Total Environ. 490, 288-295.

Petrie, B., Barden, R., Kasprzyk-Hordern, B., 2015. A review on emerging contaminants in wastewaters and the environment: current knowledge, understudied areas and recommendations for future monitoring. Water Res. 72, 3-27.

Plotan, M., Elliott, C.T., Frizzell, C., Connolly, L., 2014. Estrogenic endocrine disruptors present in sports supplements. A risk assessment for human health. Food Chem. 159, 157-165.

Pocock, T., Falk, S., 2014. Negative Impact on Growth and Photosynthesis in the Green Alga Chlamydomonas reinhardtii in the Presence of the Estrogen 17a-Ethynylestradiol. PloS one 9:e109289. http://dx.doi.org/10.1371/journal.pone. 0109289.

Prasad, M.N.V., 2005. Nickelophilous plants and their significance in phytotechnologies. Braz. J. Plant Physiol. 17,113-128.

Prater, J.R., 2012. The Impacts of Colloidal Material on the Fate and Transport of 17 B-es-tradiol in Three Iowa Soils. Ph.D Thesis. Iowa State University, U.S.A

Prater, J.R., Horton, R., Thompson, M.L., 2015. Reduction of estrone to 17 (-estradiol in the presence of swine manure colloids. Chemosphere 119, 642-645.

Ray, P., Zhao, Z., Knowlton, K., 2013.17 emerging contaminants in livestock manure: hormones, antibiotics and antibiotic resistance genes. In: Kebreab, E. (Ed.), Sustainable Animal Agriculture. Cabi Internaional, Boston MA, U.S.A., pp. 268-283.

Rodriguez-Navas, C., Bjorklund, E., Halling-S0rensen, B., Hansen, M., 2013. Biogas final digestive byproduct applied to croplands as fertilizer contains high levels of steroid hormones. Environ. Pollut. 180, 368-371.

Rose, E., Paczolt, K.A., Jones, AG., 2013. The effects of synthetic estrogen exposure on premating and postmating episodes of selection in sex-role-reversed Gulf pipefish. Evol.Apps. 6,1160-1170.

Salla, R.F., Gamero, F.U., Rissoli, R.Z., Dal-Medico, S.E., Castanho, L.M., dos Santos Carvalho, C., Silva-Zacarin, E.C., Kalinin, A.L., Abdalla, F.C., Costa, M.J., 2016. Impact of an environmental relevant concentration of 17a-ethinylestradiol on the cardiac function of bullfrog tadpoles. Chemosphere 144,1862-1868.

Sarmah, A.K., Northcott, G.L., 2008. Laboratory degradation studies of four endocrine disruptors in two environmental media. Environ. Toxicol. Chem 27,819-827.

Schmidt, U., 2003. Enhancing phytoextraction. J. Environ. Qual. 32,1939-1954.

Shareef, A., Angove, M.J., Wells, J.D., Johnson, B.B., 2006. Aqueous solubilities of estrone, 17(-estradiol, 17a-ethynylestradiol, and bisphenol A. J. Chem. Eng. Data 51, 879-881.

Shargil, D., Gerstl, Z., Fine, P., Nitsan, I., Kurtzman, D., 2015. Impact of biosolids and waste-water effluent application to agricultural land on steroidal hormone content in lettuce plants. Sci. Total Environ. 505,357-366.

Sharma, P., Jha, A.B., Dubey, RS., Pessarakli, M., 2012. Reactive oxygen species, oxidative damage, and antioxidative defense mechanism in plants under stressful conditions. J. Bot. http://dx.doi.org/10.1155/2010/217037.

Shemesh, M., Shore, L., 2012. Effects of environmental estrogens on reproductive parameters in domestic animals. Israel. J. Vet. Med. 67,1.

Shi, W., Wang, L., Rousseau, D.P., Lens, P.N., 2010. Removal of estrone, 17a-ethinylestradiol, and 17ß-estradiol in algae and duckweed-based wastewater treatment systems. Environ. Sci. Pollut. Res. 17,824-833.

Shrestha, S.L., Casey, F.X., Hakk H., Smith, D.J., Padmanabhan, G., 2012. Fate and transformation of an estrogen conjugate and its metabolites in agricultural soils. Environ. Sci. Technol. 46,11047-11053.

Sumpter, J.P., Jobling, S., 2013. The occurrence, causes, and consequences of estrogens in the aquatic environment. Environ. Toxicol. Chem. 32,249-251.

Tetreault, G.R., Bennett, C.J., Shires, K., Knight, B., Servos, M.R., McMaster, M.E., 2011. Intersex and reproductive impairment of wild fish exposed to multiple municipal wastewater discharges. Aq. Toxicol. 104,278-290.

Trapp, S., Legind, C.N., 2011. Uptake of organic contaminants from soil into vegetables and fruits. In: Frank A. (Ed.), Dealing With Contaminated Sites. Springer, Heidelberg, Germany, pp. 369-408.

Trevino, L.S., Wang, Q., Walker, C.L., 2015. Hypothesis: activation of rapid signalling by environmental estrogens and epigenetic reprogramming in breast cancer. Reprod. Toxicol. 54,136-140.

Van Donk, E., Peacor, S., Grosser, K., Domis, L.N.D.S., Lürling, M., 2016. Pharmaceuticals may disrupt natural chemical information flows and species interactions in aquatic systems: ideas and perspectives on a hidden global change. In: de Voogt, P. (Ed.), Reviews of Environmental Contamination and Toxicology. Springer, Heildeberg, Germany, pp. 91 -105.

Wenzel, A., Müller, J., Ternes, T., 2003. Study on endocrine disrupters in drinking water. Final Report ENV.D.1/ETU/2000/0083. Schmallenberg and Wiesbaden, Germany.

Woclawek-Potocka, I., Mannelli, C., Boruszewska, D., Kowalczyk-Zieba, I., Wasniewski, T., Skarzynski, D.J., 2013. Diverse effects of phytoestrogens on the reproductive performance: cow as a model. Int. J. Endocrinol. http://dx.doi.org/10.1155/2013/650984.

Writer, J.H., Ryan, J.N., Keefe, S.H., Barber, L.B., 2011. Fate of 4-nonylphenol and ^-estradiol in the Redwood River of Minnesota. Environ. Sci. Technol. 46, 860-868.

Xuan, R., Blassengale, A.A., Wang, Q., 2008. Degradation of estrogenic hormones in a silt loam soil. J. Agric. Food Chem. 56, 9152-9158.

Ying, G.-G., Kookana, R.S., Dillon, P., 2003. Sorption and degradation of selected five endocrine disrupting chemicals in aquifer material. Water Res. 37,3785-3791.

Ying, G.-G., Kookana, R.S., Ru, Y.-J., 2002. Occurrence and fate of hormone steroids in the environment. Environ. Int. 28, 545-551.

Ying, G.G., Kookana, R.S., 2005. Sorption and degradation of estrogen-like-endocrine disrupting chemicals in soil. Environ. Toxicol. Chem. 24, 2640-2645.

Zhang, H., Shi, J., Liu, X., Zhan, X., Chen, Q., 2014b. Occurrence and removal of free estrogens, conjugated estrogens, and bisphenol A in manure treatment facilities in east China. Water Res. 58, 248-257.

Zheng, M., Wang, L., Bi, Y., Liu, F., 2011. Improved method for analyzing the degradation of estrogens in water by solid-phase extraction coupled with ultra performance liquid chromatography-ultraviolet detection. J. Environ. Sci. 23, 693-698.

Zheng, W., Li, X., Yates, S.R., Bradford, S.A., 2012. Anaerobic transformation kinetics and mechanism of steroid estrogenic hormones in dairy lagoon water. Environ. Sci. Technol. 46, 5471-5478.

Zheng, W., Yates, S.R., Bradford, S.A., 2007. Analysis of steroid hormones in a typical dairy waste disposal system. Environ. Sci. Technol. 42, 530-535.

Zhou, Y., Zha, J., Wang, Z., 2012a. Occurrence and fate of steroid estrogens in the largest wastewater treatment plant in Beijing, China. Environ. Monit. Assess. 184, 6799-6813.

Zhou, Y., Zha, J., Xu, Y., Lei, B., Wang, Z., 2012b. Occurrences of six steroid estrogens from different effluents in Beijing, China. Environ. Monitor. Assess. 184,1719-1729.

Zuo, Y., Zhang, K., Zhou, S., 2013. Determination of estrogenic steroids and microbial and photochemical degradation of 17a-ethinylestradiol (EE2) in lake surface water, a case study. Environ. Sci. Proc. Impacts 15,1529-1535.