Scholarly article on topic 'Determination of 210Po concentration in commercially available infant formulae and assessment of daily ingestion dose'

Determination of 210Po concentration in commercially available infant formulae and assessment of daily ingestion dose Academic research paper on "Agriculture, forestry, and fisheries"

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Abstract of research paper on Agriculture, forestry, and fisheries, author of scientific article — Ravi K. Prabhath, Sathyapriya R. Sreejith, Madhu G. Nair, D.D. Rao, K.S. Pradeepkumar

Abstract A study has been conducted to estimate the concentration of natural radioactive polonium in commercially available packaged infant food formulae available in Mumbai, India and the corresponding daily dose normalized based on its shelf life. Eleven most popular international brands of infant formulae were sourced from market and three aliquots from each sample were analysed for concordant results. Autodeposition method onto a silver planchet from hot dilute acid solution followed by alpha spectrometry was performed for estimation of polonium. Radiochemical recovery was ascertained by the addition of 209Po tracer. Radiochemical recovery of 209Po tracer was ranged from 14.7 to 98.1 %. The 210Po concentration in the samples was in the range of 0.08–0.23 Bq kg−1 on measured date and the corresponding daily dose, calculated on normalized date which is at mid-point of the shelf life of the sample, was ranged from 0.04 to 0.89 μSv d−1 as per the recommended daily consumption. The annual committed effective dose estimated based on the average of daily dose was found to be 150 μSv.

Academic research paper on topic "Determination of 210Po concentration in commercially available infant formulae and assessment of daily ingestion dose"

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Determination of 210Po concentration in commercially available infant formulae and assessment of daily ingestion dose

Ravi K. Prabhath*, Sathyapriya R. Sreejith, Madhu G. Nair, D.D. Rao, K.S. Pradeepkumar

Radiation Safety Systems Division, Bhabha Atomic Research Centre, Mumbai 400085, India

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ABSTRACT

Article history: Received 9 March 2015 Accepted 4 May 2015 Available online xxx

Keywords: Infant formulae

209Po tracer Daily dose

A study has been conducted to estimate the concentration of natural radioactive polonium in commercially available packaged infant food formulae available in Mumbai, India and the corresponding daily dose normalized based on its shelf life. Eleven most popular international brands of infant formulae were sourced from market and three aliquots from each sample were analysed for concordant results. Autodeposition method onto a silver planchet from hot dilute acid solution followed by alpha spectrometry was performed for estimation of polonium. Radiochemical recovery was ascertained by the addition of 209Po tracer. Radiochemical recovery of 209Po tracer was ranged from 14.7 to 98.1 %. The 210Po concentration in the samples was in the range of 0.08—0.23 Bq kg-1 on measured date and the corresponding daily dose, calculated on normalized date which is at mid-point of the shelf life of the sample, was ranged from 0.04 to 0.89 mSv d-1 as per the recommended daily consumption. The annual committed effective dose estimated based on the average of daily dose was found to be 150 mSv.

Copyright © 2015, The Egyptian Society of Radiation Sciences and Applications. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license

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

1. Introduction

United Nations Scientific Committee on Effects of Atomic Radiation (UNSCEAR) estimated the annual global average of natural radiation dose as 2.4 mSv in which ingestion of food and water contribute about 0.29 mSv (UNSCEAR, 2008). The main contributors are 40K, radionuclides of Uranium and Thorium series and 14C. Among the natural radioactive

uranium series, 210Po, the last radioactive element in the 238U series, is one of the radionuclide of radiological significance. The radiophysical properties of polonium isotopes are given below where Asp and Ea represent specific activity and alpha energy respectively (Health Physics Society, 2010).

* 208Po - T1/2 = 2.9 yrs, Asp = 21.8 TBq g"1, Ea = 5215 keV.

* 209Po - T1/2 = 103 yrs, Asp = 0.63 TBq g"1, Ea = 4882 keV.

* 210Po - T1/2 = 138 days, Asp = 166 TBq g"1, Ea = 5304 keV.

* Corresponding author. Tel.: +91 22 2559 8290; fax: +91 22 2550 5151. E-mail addresses: prabhathravi@gmail.com (R.K. Prabhath), rspri@barc.gov.in (S.R. Sreejith), madhugn@barc.gov.in (M.G. Nair), ddrao@barc.gov.in (D.D. Rao), pradeep@barc.gov.in (K.S. Pradeepkumar).

Peer review under responsibility of The Egyptian Society of Radiation Sciences and Applications. http://dx.doi.org/10.1016/j.jrras.2015.05.002

1687-8507/Copyright © 2015, The Egyptian Society of Radiation Sciences and Applications. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

It is estimated that the ingestion of 210Po contributes approximately 7% to the natural internal radiation dose (Bulman, Ewers, & Matsumoto, 1995) and about 18% of the average internal dose of the population is due to ingestion of 210Po along with its precursor 210Pb (Clayton & Bradley, 1995). Natural polonium i.e. (210Po) is radiologically toxic even in minute amount due to its high linear energy transfer (LET) and specific activity. It is believed that 210Po is almost as toxic as 239Pu and five-fold toxic as compared to 226Ra (National Research Council, 1988). The maximum permissible amount of 210Po by ingestion is 0.03 mCi (1.1 kBq) which is ~6.8 pg by weight and the maximum allowable concentration for soluble polonium compounds in air is about 2 x 10-11 mCi cm-3 (0.74 Bq m-3) (Los Alamos National Laboratory). Ingestion of about 50ngof 210Po is considered as a deadly dose (LD50 of 4 Sv - estimated from committed effective dose equivalent (CEDE) of0.51 mSv Bq-1 for 210Po for ingestion (Nuclide Safety Data Sheet, 2009) and 166 Bq g-1 specific activity of 210Po). In the-atmosphere, the main source of 210Po is the decay of 222Rn which originates from 238U as follows. (Values in parenthesis are the decay mode and half-life respectively).

222Rn (a, 3.8d) / 218Po (a, 3.1 m) / 214Pb (b-, 26.8 m) / 214Bi (b-, 19.9 m) / 214Po (a, 0.1643 ms) / 210Pb(b-, 22.3y) / 210Bi (b-, 5.013d) / 210Po(138d) / 206Pb(stable)

The polonium thus formed attaches to aerosols in the atmosphere electrostatically and deposited on earth's surface either by dry deposition or wash out. Polonium is then directly absorbed by plants through root system or by foliar absorption from the air. Another possible route of polonium in plants is the decay of 226Ra which they had already absorbed from the soil and water. Burning of fossil fuels, usage of tetra ethyl lead for internal combustion engines and excessive use of phosphate and other fertilizers have also contributed to the polonium inventory in the atmosphere (Karali, Olmez, & Yener, 1996; Pietrzak Flis & Skowronska Smolak, 1995; Santos, Gouvea, Dutra, & Gouvea, 1990). The radiological behaviour of polonium, its distribution, transport in environment and associated risk from its dietary intakes and smoking are well documented. It is believed that the affinity of polonium with high molecular weight proteins could be the reason for its accumulation in body as well as its easy transport through the food chain (Waska, Kim, Kim, Kang, & Kim, 2008). Higher concentration of 210Po in seafood items such as crab, mussels, fish, shrimp etc. supports this theory (Cunha, Bueno, Favaro, Maihara, & Cozzollino, 2001; Kannan, Iyengar, & Ramesh, 2001; Lee ets al., 2009; Uddin et al., 2012). Most of the polonium entering the body after ingestion reaches the gastrointestinal tract and is eliminated via excreta (Hunt & Allington, 1993; Stannard, 1964). The activity concentration of 210Po in different human tissues is approximated in the following order: hair > bone > liver = kidney > gonads > spleen = lung > muscle > heart = blood. Half of the total body burden is on bones and 17% of body burden is on muscles. The maximum daily excretion rate of polonium activity observed in feces was 18-50% within the third day of ingestion (Henricsson, Ranebo, Hansson, Raaf, & Holm, 2012). Polonium and its precursor, Lead in the plasma are distributed throughout the soft tissues of the body, and they accumulate in the liver and kidneys (Fellman, Ralston, Hickman, Ayres, & Cohen, 1994). International Commission on Radiation

Protection (ICRP) suggests that 210Po is generally distributed uniformly in the deposited tissues (ICRP, 1982). Due to the high incidence of lung cancer in smokers, it is believed that 210Po could be a reason for at least cigarette induced lung cancer as the concentration levels of this radionuclide is substantially high in tobacco products (Marmorstein, 1986). E.I Shabana et al. in their study suggested that about 30% of the 210Po in the blood samples of Saudi smokers can be attributed to the usage tobacco products (Shabana, Abd Elaziz, Al-Arifi, Al-Dhawailie, & Al-Bokari, 2000). Importance of polonium toxicity and associated radiation risk assessment can be so enormous that nearly 1024 residents were identified and scrutinized for possible potential risk of internal contamination due to exposure to contaminated environments in London in an incident of polonium poisoning in 2006 (Maguire et al., 2010). International Agency for Research on Cancer (IARC) has classified 210Po as a Group 1 human carcinogen (IARC, 2001). The importance of further research in biological effects of low level exposure to 210Po is well reviewed and explained by Ralph Seiler et al. (Seiler & Wiemels, 2012). Considering the case of infants, the major path of their intake is from their mother's milk and also from those commercially available infant formulae which is the only other feeding source at least upto their sixth month of age. Very few reports are available in case of polonium ingestion dose estimates for infants. Marko Strok et al. reported a concentration of 0.055-0.467 Bq kg-1 for 210Po in infant formulae samples from the vicinity of a former uranium mine in Slovenia (Strok & Smodis, 2011). According to the authors, consumption of these formulae as per dietary recommendations would lead to an annual effective dose of 50-450 mSv from 210Po alone which is approximately 67-72 % of the combined total ingestion dose from these samples. Similarly in Italian dietary items, Maria Assunta Meli et al. reports the committed effective dose from 210Po in infant milk products can be 21.1 mSv y-1 assuming an intake of 2.4 Bq y-1 which is about 5.57% of the total committed effective dose of 379 mSv y-1 from 210Po (Meli, Desideri, Roselli, & Feduzi, 2014). To our knowledge there is no data available in India for the inventory of natural polonium in packaged infant formulae.

So in order to calculate the ingestion dose of infants, monitoring the concentrations of radionuclides in their diet formulae is important. In that point of view, and also due to non-existence of data on 210Po in infant formulae in Indian scenario and also scanty data internationally, our study focus on the evaluation of 210Po in popular packaged infant formulae available in the local market of Mumbai, India and assessing the corresponding average daily dose, if ingested as per recommended daily consumption.

2. Materials and methods

2.1. Reagents and chemicals

Analytical grade acids were used in the present study. Nitric acid (69-71 %) was obtained from SD Fine Chemicals, Mumbai, India. Hydrochloric acid (36%) was obtained from Thomas Baker, Mumbai, India. Perchloric acid (70%) was obtained from Fluka, United States. Emplura grade hydrogen peroxide (50%)

was obtained from, Merck, India. Radioactive 209Po tracer was obtained from NPL, UK (Product code PMP 10030).

2.2. Samples

Eleven brands of popular infant formulae samples were obtained from markets of Mumbai, India and carefully stored in a cool, closed environment till further processing. Three ali-quots of approximately 50 g each from each sample were then taken in a pre-cleaned 1 Lbeaker. Each sample was added with 11 mBq of 209Po tracer and homogenized with 0.1 N HNO3, closed and kept overnight for equilibration. It was then added with 250 ml conc HNO3: conc HCl mixture (1:3), 100 ml (50%) H2O2 and 10 ml of HClO4. The samples were digested for 75 -100 h over a hot plate at 90 °C to avoid the volatilization of polonium. Due to the fat content in the formula, two layers comprising of aqueous part and fatty part were formed after digestion. These layers were separated with the help of a separating funnel and fat content layer was discarded. The clear aqueous layer was transferred to a pre-cleaned 400 ml glass beaker and evaporated to dryness under an Infrared lamp. The residue was redissolved in 200 ml of 0.5 N HCl and a pinch of ascorbic acid was added to minimize the interference of iron in autodeposition. Polonium from this solution was autodeposited onto a silver disc of 5 cm diameter with continuous stirring for 3 h at 90 °C as per the schematic diagram given in Fig. 1. After the autodeposition, the silver disc was removed and cleaned with methyl alcohol and dried at room temperature. These discs were counted for 24 h in a low background alpha spectrometer. The counting of the samples was completed within a period of 15 days after the sample processing to avoid the considerable decay of 210Po. The

radiochemical recovery of 209Po was in the range of 14.7-98.1 % with a mean of 56.9%. A typical plot of alpha spectrum of an infant formula (sample IF-8) is given in Fig. 2.

2.3. Counting system

Polonium autodeposited silver planchets were counted in Eurysis made alpha spectrometer equipped with a high resolution PIPS silicon semiconductor detector with approximate active area of 450 mm2 with depletion depth of 100 mm and counting efficiency of ~23% coupled with 1 k channel MCA (Multi-Channel Analyser). The background for a chemical blank which was prepared only with the reagents was about 2 counts in 24 h in the region of interest. The minimum detectable activity of the detector was 0.5 mBq per sample for 24 h of counting which was calculated using the Currie equation, assuming chemical recovery of 100% (Currie, 1968).

= ((4.65 x V2 + 2.7l) x 100)/(86400 x 23)z0.5 mBq

Results and discussion

Table 1 summarizes the details of packaged infant formulae. The shelf life of the infant formulae samples is one year from the date of manufacture. A new concept of normalized day which is the mid-point of the shelf life of the samples is introduced in this work for estimating the corrected activity on a common reference date and also for 210Po dose estimation. The importance of this concept is that, normally the samples near their expiry date may not be preferred by the consumers; likewise, freshly prepared infant formulae will

Fig. 1 - Autodeposition setup for 210Po.

Fig. 2 - Typical alpha spectrum of Po isotopes in an infant formula sample (sample IF-8).

not be available in the local market on the same month. So it is assumed that the likelihood of maximum consumption of the infant formulae is approximately in the sixth month from the manufacturing date. Table 2 gives the 209Po tracer recovery, 210Po concentration as on counting date and 210Po concentration as on normalised date in eleven commercially available infant formulae in Mumbai, India. It is also worth mentioning here that the brands are so popular that their use all over India can be safely assumed. The average concentration of 210Po was in the range of 0.08-0.23 Bq kg-1 on measurement date in the samples analysed. In commercial market there are two types of infant formulae available. First type is mainly based on milk only while the other variety is a mixture of milk, cereals and pulses. The range of 210Po in the formulae with cereals and pulses was 0.15-0.23 Bq kg-1 (mean of 0.15 Bq kg-1)

which was higher than those formulae based only on milk with concentration range 0.08-0.15 Bq kg-1 (mean of 0.11 Bq kg-1). No correlation was found between the fat content and the 210Po concentration in the samples. Table 3 gives the daily dose due to the ingestion of infant formulae for two age groups of infants. The daily dietary dosages recommended by manufacturer of these products were summarized in the third column of the table. The age dependent dose conversion factors for ingestion of 210Po were adopted from the publication-119 of International Commission on Radiation Protection (ICRP, 2012). The dose conversion factors for different age groups of infants (<1 year) and children (1 year) are 5.5 x 10-5 and 8.8 x 10-6 Sv Bq-1 respectively. The daily dose of 210Po from ingestion of infant formulae as per the recommended daily diet was in the range of 0.04-0.89 mSv d-1.

Table 1 - Details of packaged infant formulae samples.

Date of Date of expiry Date of Normalised Type of sample

Sample Manufacturing measuring date

IF-1 15-Feb-13 15-Feb-14 14-Jun-13 14-Aug-13 Milk powder

IF-2 15-May-13 15-May-14 23-Aug-13 11-Nov-13 Milk and cereals

IF-3 15-Feb-13 15-Feb-14 17-Sep-13 14-Aug-13 Milk and cereals

IF-4 15-Jun-13 15-Jun-14 1-Oct-13 12-Dec-13 Milk and cereals

IF-5 15-Jul-13 15-Jul-14 8-Oct-13 11-Jan-14 Milk and cereals

IF-6 15-Aug-13 15-Aug-14 13-Nov-13 11-Feb-14 Milk powder

IF-7 15-Sep-13 15-Sep-14 21-Nov-13 14-Mar-14 Milk powder

IF-8 15-Sep-13 15-Sep-14 16-Dec-13 14-Mar-14 Milk powder

IF-9 15-Oct-13 15-Oct-14 17-Dec-13 13-Apr-14 Milk powder

IF-10 15-Oct-13 15-Oct-14 19-Feb-14 13-Apr-14 Milk powder

IF-11 15-Sep-13 15-Sep-14 6-Mar-14 14-Mar-14 Milk powder

Table 2 - Average209Po recovery (Rec.),210Po concentration (conc.) and activity as on normalised date in infant formulae.

Sample

Aliquots (AQ#) taken for analysis

Average conc. (Bqkg-1)

Rec. Conc. (Bq kg-1) Rec. Conc. (Bq kg-1) Rec. Conc. (Bq kg-1)

Activity on normalised date (Bqkg-1)

(%) (%) (%)

IF-1 14.7 0.18 ± 0.04 40.9 0.17 ± 0.02 60.7 0.11 ± 0.01 0.15 ± 0.02 0.12 ± 0.02

IF-2 52.5 0.28 ± 0.02 32.7 0.24 ± 0.03 59.6 0.18 ± 0.02 0.23 ± 0.02 0.17 ± 0.02

IF-3 42.6 0.15 ± 0.02 67.1 0.16 ± 0.02 32.7 0.14 ± 0.02 0.15 ± 0.02 0.18 ± 0.02

IF-4 61.3 0.14 ± 0.01 65.4 0.17 ± 0.02 67.7 0.14 ± 0.01 0.15 ± 0.02 0.10 ± 0.01

IF-5 44.4 0.15 ± 0.02 78.8 0.13 ± 0.02 53.7 0.24 ± 0.02 0.17 ± 0.02 0.11 ± 0.01

IF-6 64.1 0.11 ± 0.01 64.7 0.15 ± 0.01 42.7 0.08 ± 0.01 0.12 ± 0.01 0.08 ± 0.01

IF-7 70.2 0.08 ± 0.01 43.2 0.13 ± 0.01 42.0 0.11 ± 0.01 0.11 ± 0.01 0.06 ± 0.01

IF-8 59.0 0.10 ± 0.01 52.5 0.09 ± 0.01 98.1 0.07 ± 0.01 0.09 ± 0.01 0.06 ± 0.01

IF-9 77.1 0.07 ± 0.01 58.0 0.13 ± 0.01 67.1 0.15 ± 0.01 0.12 ± 0.01 0.07 ± 0.01

IF-10 61.9 0.10 ± 0.01 63.1 0.10 ± 0.01 79.1 0.09 ± 0.01 0.10 ± 0.01 0.08 ± 0.01

IF-11 60.4 0.08 ± 0.01 - - - - 0.08 ± 0.01 0.08 ± 0.01

The estimated committed effective dose per annum by the ingestion of infant formulae, based on the average of daily dose would be 150 mSv. This reported annual dose is higher than the annual dose of 21.1 mSv reported by Maria Assunta Meli et al. and lower than the annual dose of 450 mSv reported by Marko Strok et al. A chart of the daily dose (mSv d-1) of the different infant formulae is given in Fig 3. From the plot it is evident that the infants near their sixth month are likely to receive more dose from ingestion of 210Po assuming the consumption of the formulae is as per the recommended daily usage by the manufacturer. For other age groups the corresponding average daily dose is lower except in one sample. Although recommended daily usage of this formula is approximately 74 g per day which is lower among others, two factors viz, the higher dose conversion factor and the 210Po concentration in this sample results in higher daily dose compared to others.

4. Conclusions

Eleven samples of the most popular commercially available infant formulae in Mumbai, India were estimated for 210Po concentration and the corresponding daily dose evaluated by the recommended daily usage. 209Po was added as a radiotracer for estimating the radiochemical recovery which was ranged from 14.7 to 98.1 % in average for analysed samples. The concentration of 210Po was ranged from 0.08 to 0.23 Bq kg-1 in the infant formulae samples. The concentration of 210Po in the infant formulae samples containing added cereals and pulses were higher than those formulae based only on milk. For different age group infants, the daily dose of 210Po, if consumed as per recommended by the manufacturer would range from 0.04 to 0.89 mSv d-1. The trend of daily dose increases as the age increases and reaches a maximum

Table 3 - 210Po activity, recommended daily use, DCF and daily dose calculated on normalized date.

Sample Recommended daily use 210Po activity on DCF (Sv Bq-1) Daily Dose

Recommended age group (gd-1) normalised date (mSv d-1)

(Bq g-1)

(1-2 weeks) IF-6 82.8 8.0E-05 5.5E-05 0.36

(1-2 weeks) IF-9 82.8 7.0E-05 5.5E-05 0.32

(3-4 weeks) IF-6 92 8.0E-05 5.5E-05 0.40

(3-4 weeks) IF-9 92 7.0E-05 5.5E-05 0.35

(2 months) IF-6 115 8.0E-05 5.5E-05 0.51

(2 months) IF-9 115 7.0E-05 5.5E-05 0.44

(3-4 months) IF-6 138 8.0E-05 5.5E-05 0.61

(3-4 months) IF-9 138 7.0E-05 5.5E-05 0.53

(5-6 months) IF-6 161 8.0E-05 5.5E-05 0.71

(5-6 months) IF-9 161 7.0E-05 5.5E-05 0.62

(6 months) IF-1 134.4 1.2E-04 5.5E-05 0.89

(6 months) IF-10 134.4 8.0E-05 5.5E-05 0.59

(7 months) IF-11 67.2 8.0E-05 5.5E-05 0.30

(6-10 months) IF-2 74.25 1.7E-04 5.5E-05 0.69

(8-10 months) IF-3 74.25 1.8E-04 5.5E-05 0.74

(10-24 months) IF-2 99 1.7E-04 8.8E-06 0.15

(10-24 months) IF-3 99 1.8E-04 8.8E-06 0.16

(10-24 months) IF-4 99 1.0E-04 8.8E-06 0.09

(12-24 months) IF-5 99 1.1E-04 8.8E-06 0.10

(12-24 months) IF-7 134.4 6.0E-05 8.8E-06 0.07

(12-24 months) IF-8 67.2 6.0E-05 8.8E-06 0.04

Fig. 3 - Chart of the daily dose on normalised date of the different infant formulae.

between 6th and 8th month of age and then decreases. This can be attributed to higher dose conversion factor and higher recommended daily usage. The committed effective dose per annum by the ingestion of infant formulae, estimated based on the average of daily dose will be 150 mSv.

Acknowledgement:

The authors would like to thank Dr. D. N. Sharma, Director, Health Safety and Environment Group, BARC for his kind support and encouragement in carrying out this work.

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