Tracing lead contamination in foods in the city of Kolkata, India Avijit ...

Tracing lead contamination in foods in the city of Kolkata, India

Avijit Das, KVSS Krishna, Rajeev Kumar, Anindya Das, Siladitya Sengupta & Joy Gopal Ghosh Environmental Science and Pollution Research ISSN 0944-1344 Environ Sci Pollut Res DOI 10.1007/s11356-016-7409-3

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Author's personal copy Environ Sci Pollut Res DOI 10.1007/s11356-016-7409-3

RESEARCH ARTICLE

Tracing lead contamination in foods in the city of Kolkata, India Avijit Das 1 & KVSS Krishna 1 & Rajeev Kumar 1 & Anindya Das 2 & Siladitya Sengupta 1 & Joy Gopal Ghosh 1

Received: 1 March 2016 / Accepted: 4 August 2016 # Springer-Verlag Berlin Heidelberg 2016

Abstract Lead isotopic ratios (LIR) of eight common food items, street dust, coal, diesel, sediments, lead ore and rainwater from India have been reported for the first time in this paper. This study characterized the source and extent of lead pollution in the different foodstuff consumed in Kolkata, a major metropolis of eastern India. The atmospheric lead input to the food items, sold openly in busy roadside markets of the city, has been quantified. The mean 207/206 and 208/206 LIRs of the eight food items ranged from 0.8847 to 0.8924 and 2.145 to 2.167, respectively. Diesel had the highest mean 207/206 and 208/206 values of 0.9015 and 2.1869, respectively, apart from the lead ore. The food items had a mean lead concentration between 3.78 and 43.35 mg kg−1. The two ratio scatter plots of all the different environmental matrices were spread linearly between the uncontaminated Ichapur sediment and diesel. The 207/206 LIRs of the coal with a mean of 0.8777 did not fall in the linear trend, while the street dust and food samples overlapped strongly. The rainwater sample had a 207/206 LIR of 0.9007. Contaminated sediments in Dhapa, the repository of the city’s municipal garbage, had a mean 207/206 LIR of 0.8658. The corresponding value Responsible editor: Philippe Garrigues Electronic supplementary material The online version of this article (doi:10.1007/s11356-016-7409-3) contains supplementary material, which is available to authorized users. * Avijit Das [email protected]

1

Laser Ablation Multicollector ICPMS (LAMCI) Laboratory, Geochronology& Isotope Geology Division, Geological Survey of India, Dharitri, Salt Lake, Kolkata 700091, India

2

Central Chemical Laboratory, Geological Survey of India, 15A&B Kyd Street, Kolkata 700016,, India

obtained from the sewage-fed vegetable grown there was 0.8058. The present study indicated that diesel was one of the main contributor to Pb pollution. The atmospheric lead contribution to the food items was in the range of 68.48– 86.66 %. Keywords Pollution . Market . Food . Kolkata . Lead isotopic ratios

Introduction Studies on the application of lead isotopic fingerprinting in environmental geochemistry as a versatile tool for its source tracing has been well recognised internationally (Komarek et al., 2008; Cheng and Hu, 2010; Sucharová et al., 2011). Lead is the most widely scattered environmental toxin, and its prolonged exposure can have serious human health implications causing damage to the kidneys, liver and hematologic systems ( Grandjean, 2010; Jusko et al. 2008; Lanphear et al. 2005). Children with their growing neural system and frequent hand-to-mouth behaviour are especially vulnerable because the accumulation of toxic concentration is inversely proportional to the lead intake (Gilman, 1990; Jain and Hu, 2006; Safi et al., 2006). In India, even though there exists a growing concern for environmental contamination associated with rapid urban development, lead exposure studies are very few. Lead has three radiogenic (208Pb, 207Pb, 206Pb) and one non-radiogenic isotope 204Pb. The latter has a constant abundance in the earth. The three radiogenic isotopes of Pb are daughter products of 238U, 235U and 232Th, respectively. As the isotopic composition of lead does not undergo any physicochemical fractionation, the isotopic ratios found in lead anywhere is the sum of the isotopic ratios from original

Author's personal copy Environ Sci Pollut Res

sources (natural or anthropogenic) and the inherent lead. The variations in isotope ratios can thus be used for source tracing, especially for distinguishing between natural and anthropogenic inputs (Walraven et al., 1997). In general, radiogenic 206 Pb/207Pb and 208Pb/207Pb ratios are commonly used as environmental tracers because of the relative abundances of these isotopes and the capability to analytically determine them accurately (Bollhöofer and Rosman, 2001; Li et al. 2012). It is also accepted that if a linear trend is obtained from these ratios in environmental samples, a mixing between two component end-members of geogenic and anthropogenic Pb can be quantified (Chen et al., 2005; Monna et al., 2000). Anthropogenic lead emissions along with other heavy metal toxins originate primarily from industrial and vehicular activities. Ingestion of food, drinking water along with inhalation of aerosols and urban street dust are the principal lead exposure pathways (USEPA 2006). To identify the Pb exposure from these pathways, stable isotopes of lead in different environmental media like vegetables, house dust, soil, PM10 and drinking water have been compared with body lead contamination in different studies (Liu et al. 2009; Yan et al. 2013). Furthermore, it has also been shown that by comparing the isotope ratios in bioaccessible lead rather than total lead with blood lead level (BLL), a more accurate way to identify the predominant Pb exposure pathway can be determined. Kolkata, in eastern India, is one of the four major densely populated metropolises of the country and also one of the most polluted cities in the world. According to data collected in 2010 by the Central Pollution Control Board (CPCB), Kolkata, along with Delhi, is among the worst affected Indian cities when it comes to air pollution. The highest number of lung cancer cases in India was reported from Kolkata, Delhi and Mumbai between 2009 and 2011. In the World Health Organization’s (WHO) ranking of cities by air pollution, Kolkata ranks 25th among a total of 1100 cities. There are three coal-based thermal power stations adjacent to the city, and public transport essentially consists of a large number of used, run-down buses and diesel operated taxis. A majority of the ubiquitous three-wheelers used by the local population are known to run on diesel to mitigate the cost incurred from expensive lead-free petrol. The overall pollution is compounded by prolonged construction activities like laying down of underground rail, the building of numerous bridges and flyovers and other small and medium industries in the city. Drinking and groundwater quality is bad, and the city scores very poorly in noise and light pollution as well. Unscientific garbage disposal has deteriorated the quality of greenery and parks of this city with teeming millions. Kolkata is also the largest generation point of e-wastes in eastern India without proper, scientific centres for recycling of such wastes. Recent studies on Pb and other heavy metal contamination of food items in Kolkata found elevated levels of metal contaminants

in vegetables grown in Dhapa, a century-year-old sewage disposal site of the city (Banerjee et al., 2010; Das et al., 2014). In this study, source identification of lead found in essential food items and in a popular medicinal herb (tulsi) sold in the markets of Kolkata has been attempted. Several potential lead emission sources have been considered in this study. Besides food items, coal, diesel, sewage contaminated sediments and a rain water sample have been analysed for lead contamination. As the food items sampled from the different markets were sold in the open, street dust were also analysed to find any possible correlation between the food and the airborne dust particles. The use of lead isotope systematic in environmental problems is very scanty in India. To our knowledge, this is the first environmental study of lead isotopic signatures of food items and Pb isotope content in coal, diesel, water and street dust of a major Indian city.

Sampling and analytical methods Study area Kolkata, situated on the banks of river Hooghly, is the capital of West Bengal state in the eastern part of India and is located between 88° 30′ E and 22° 33′ N. It is the third largest metropolitan city in India with a population of approximately 4.4 million inhabiting an area of 1480 km2. In comparison, London has an area of 1580 km2. Sandwiched between two clay layers, quaternary sediments consisting of clay, silt, sand and gravel underlie the city. It has a tropical climate with hot and humid summer with an average annual rainfall of 1582 mm. Pollution is a major concern of Kolkata as the level of SPM at 148 μg/cm3 is one of the highest in India (Bhadhuri 2013). Kolkata broadly extends in a narrow east-to-west dimension between the Hooghly River in the west and the Eastern Metropolitan Bypass in the east. The north-to-south alignment is roughly broken up into North Kolkata, which is the older part of the city, Central Kolkata, which is the main business and commercial area of the city and the newly expanding South Kolkata. With the gradual decline in industrial health of the city from the 1970s, only small and micro industries based on clothes, chemicals, paper and leather remain. The three industrial parks located in Salt Lake and Beliaghata in the of north Kolkata manufacture garments, toys, jewellery, sporting goods, electronics and telecommunication parts. Shyambazar, Alipur, Kasba, Maniktola and Behala are other places in the north and central Kolkata where plastic, printing and packaging, industrial paint, light diesel oil, lubricants, greases and automobile parts are manufactured. Kolkata is also a major recycling centre of electronic wastes in eastern India.


Kolkata’s public transport system is one of the cheapest in the whole world but is the major source of environmental concern. Besides the underground railway system, which was the first to be developed in South Asia and is presently being expanded, public transport consists of buses, taxis, three-wheelers and the hand-pulled rickshaws. There are approximately 80,000 three-wheelers, 60,000 taxis and 40,000 buses and a majority of these are old to very old and diesel operated. The majority of the three-wheelers run on diesel. Although the use of katatel made up of a mixture of kerosene and used diesel has been recently banned, it can be found outside the city. According to a UN report of 2006, Kolkata’s deteriorating air quality with an SPM value of 374 kg/m3 was mainly due to the toxic exhaust emissions of these three-wheelers and trucks. Sample collection Twelve markets covering the north, south, east and west of Kolkata were surveyed during August to November 2014 to collect eight food samples per market (Fig. 1, details in supplementary information S1). These included polished rice, red lentil (masoor dal), red spinach, chicken, fish (without scales), biscuits, spice (cumin seeds) and a common medicinal herb (holy basil or tulsi). As is common in Indian markets, the food items are sold in the open and except for the market in

Salt Lake location, the markets are located near major roads and traffic intersections. Considering that Dhapa has been the main solid waste disposal site for 100 years for the entire Kolkata municipality and that this area is known for garbage farming, three sediment and vegetable samples were collected from Bainchtola, Arupota and Khanaberia. Previous studies (Das et al., 2014) have reported high concentrations of heavy metals, especially lead in the vegetables grown in this waste disposal area and allegedly sold in Kolkata’s markets. Solid waste surface samples were collected in sealed polyethylene bags from a depth 0.3 m from the top. To compare the level of contamination in sediments and in vegetables found in Dhapa with that found in a relatively unpolluted area, a control site at Ichapur, located west of the Hooghly River, was selected and a sediment and vegetable sample was collected from there. Street dust is known to bear significant urban lead pollution burden and as reported in many studies, the burning of coal and automobile exhausts form a significant source of such environmental lead in road dust. Twenty-nine street dust samples (Fig. 1, S1) along with 15 coal samples and two diesel samples were collected to compare their lead isotopic ratios with that found in food. The street dust was collected from major roads of the north and south of Kolkata on June 10 and 11, 2014, before the arrival of the first seasonal rains. The dust samples collected were not specifically near the market places

Fig. 1 Map of West Bengal showing Kolkata and the sampling locations; grey markers are street dust locations (details in the supplementary information, S1)


but were selected adjacent to the major road crossings like BBD Bagh, Ultadanga, Esplanade, Ballygunje Phari, Topsia, Shyambazar, Moulali and Tollygunje Metro station. The samples were collected by brushing off the dust deposited on the leaves of plants growing on street dividers. Each dust sample was collected using a new brush and collected in clean polyethylene sample bags and sealed. The height of the plants was approximately above knee length, and only surface dust samples free of decomposed leaf remnants were carefully collected. To assess the presence atmospheric lead from the use of coal, eight coal samples from Raniganj and seven samples from Jharia were collected in sealed polyethylene sample bags and stored before further processing. Two diesel samples from the north and south Kolkata were also sampled. The samples were collected directly from the petrol filling stations. These were collected in clean, widemouthed amber-coloured 500-ml PDFE bottles and stored in a refrigerator before analysis. Similarly, one rainwater sample was collected in a clean PDFE bottle from the south of Kolkata in October 2014 and preserved by adding 2 % double-distilled nitric acid immediately before analysis. Lead isotopic ratios of Indian lead have not been reported till date. Eight galena samples collected from Alwar in Rajasthan were analysed for this purpose, and the ratios obtained were used for comparison with the ratios obtained from food, street dust, coal, rainwater and diesel. The crushed and finely ground samples were obtained in sealed sample bags for further analysis. Sample processing and Laboratory analysis Among the food items, rice, red lentil, snack and the spice samples were ground separately in a ceramic mortar pestle taking precaution to avoid cross-sample contamination. Vegetable, herb, fish and the meat samples were initially washed with distilled water. The vegetable and herb samples were at first air-dried for 24 h then dried again at 80 °C in an oven furnace for another 24 h before being ground to approximately ~200 mesh size powders. Small portions (about 5 g) of the washed meat and fish samples were cut using a clean ceramic knife, dried at 80 °C and then ground to a powder of ~200 mesh size. The sediment samples were dried at 40 °C for 2 days and then powdered to ~200 mesh size before chemical analysis. The coal samples were pulverised in a clean agate mortar and air dried to a constant weight in an oven furnace at 80 °C before further analysis. Digestion of the food samples was done in a class 10,000 clean room using an Anton Paar Multiwave 3000 Microwave digestion system using a three-sequence method (Table 1). 0.2 g of the sample was digested with 5 ml of doubledistilled nitric acid and 2 ml of hydrogen peroxide

Table 1 samples

Microwave program sequence for the digestion of food

Sequence no.

Power

Ramp

Hold

Fan

1

500 watt

10 min

10 min

1

2

650 watt

5 min

5 min

1

3

0 watt

5 min

5 min

2

(Suprapur, Merck), and the final solution was made up to 50 ml with the 18.2 MΩ Milli-Q water. Double distilled, concentrated (14.5 M) HNO3 was prepared in-house by subboiling distillation of reagent grade acids in quartz stills. The total time taken for the whole digestion was 40 min, including cooling of the Teflon tubes. The final pressure attained was 20 bars and the temperature attained was 190 °C. The digested solution was used for the analysis of lead and lead isotopic ratios.For coal analysis, 1 g of the powdered sample was mineralized slowly to ash at 1 °C per minute up to 450 °C in 10 h in an oven. After the ash content was determined gravimetrically, it was dampened with 18.2 MΩ water and 5 ml of 48 % HF and 0.5 ml of HClO3 was added before evaporating it to dryness. The residue was then dissolved in 2 ml of double-distilled, concentrated (14.5 M) HNO3 and made up to 100 ml with 18.2 MΩ water. Diesel samples were kept in a 30-ml Teflon vial and slowly evaporated at elevated temperature to 150 °C on a hot plate for 5 h. The residue was digested with 2 ml of 14.5 M HNO3 and 0.2 ml 30 % H2O2 at 160 °C with reflux. It was then further dried and re-dissolved in 2 ml of 5 % double-distilled nitric acid and made up to 50 ml with 18.2 MΩ water. Digestion of the sediment and galena samples was also done in Anton Paar Multiwave 3000 Microwave digestion system. For the sediment samples, a similar three-sequence method used previously for the food samples was used. 0.2 g of the sample was digested with 5 ml of 14.5 M HNO3 acid and 2 ml of HCl (Suprapur, Merck) and the final solution made up to 50 ml with the 18.2 MΩ Milli-Q water. For the galena samples, the same method was applied using 8 ml of 14.5 M HNO3 for 0.1-g sample. The rainwater sample was filtered using a 0.45-mm Whatman nylon syringe membrane and stored in a clean, acid-rinsed PFA (Savillex) bottle at 4 °C for later chemical analysis. It was then acidified with double-distilled 0.3 M HNO3 for the lead isotopic analysis. Lead isotopic measurements are usually done with thermal ionization or inductively coupled plasma mass spectrometry (TIMS or ICPMS). The ICP-MS instruments can be quadruple, time-of-flight and sector-based mass analyzers. The latter can be equipped with single (SC) or multiple collectors (MC). The determination of lead isotopic compositions of environmental matrices using quadruple based ICPMS with a calibration of the mass spectrometer and normalization of the


measured ratios of the four Pb isotopes by using NIST SRM 981 as an external standard have been reported widely (Liang et al. 2010; Oulhote et al. 2011). In this study, Pb isotope ratios were measured on a Nu plasma II, multi-collector inductively coupled plasma mass spectrometer (MCICPMS) by the direct aspiration of the sample solution taking into consideration the high concentration of Pb usually found in the dust. In addition, quality assurance and quality control of the analysis were assessed using duplicates and method blank control. Mass fractionation of Pb was corrected following the method described by White et al. 2000. The sample solutions were doped with known SRM-997 standard solution and were analysed following the standard-sample bracketing protocol. Isobaric interference from 204Hg on 204Pb was monitored, and necessary corrections were applied (White et al. 2000). NISTSRM 981 standard was analyzed after each of the eight samples to monitor the effect of mass fractionation. The mean values obtained for 208/204, 207/204 and 206/204 LIRs were 36.7138 (at 2σ value of 0.0443), 15.4973 (at 2σ value of 0.0153) and 16.9413 (at 2σ value of 0.0185), respectively. The range of the 208/204, 207/204 and 206/ 204 ratios cited in literature (Fig. 2) are 36.66710– 36.72190, 15.48180–15.49630 and 16.92950–16.94670, respectively, and the average values obtained in this study were well within the range of the reference values. The corresponding blank lead value obtained was 10.39 ng ml−1. Binary mixing model of lead isotope ratios The binary mixing model (Monna et al. 2000) of lead isotope ratios was used to calculate the relative contribution of each end member to Pb in the food items.

ð207=206Þ

X natural % ¼

ð207=206Þ Pb

ð207=206Þ

X anth % ¼

Pbanth − anth −

Pbfood −

ð207=206Þ Pb anth −

ð207=206Þ

Pbfood

ð207=206Þ Pb natural

ð207=206Þ

100;

100;

Pb concentration and 207/206 Pb isotope ratio (LIR) in food As shown in Table 2, among the food items, the 207/206 lead isotopic ratio (LIR) in rice ranged from 0.8731 to 0.8980 with a mean value of 0.8851 ± 0.0086. The maximum Pb concentration in rice was 14.39 mg kg−1 in the Khidirpur sample from the west of Kolkata. For the red lentil samples, the LIR was found to be between 0.8715 and 0.8946 with a mean value of 0.8857 ± 0.0073. The Pb concentration was between 1.82 and 7.44 mg kg−1 with the maximum found in the Tollygunje in South Kolkata. Locally made snacks had a Pb concentration range from 4.82 to 10.71 mg kg−1 with the maximum found in the sample collected from Gariahat. The corresponding 207/206 LIR was in the range 0.8756 to 0.8995 with a mean of 0.8924 ±0.0075. Vegetables sold in sampled markets had a mean Pb LIR value of 0.8846 ± 0.0144 and a Pb LIR range of 0.8553 to 0.8947. The Pb concentration ranged from a low 3.28 mg kg−1 to a very high value of 145.47 mg kg−1. Fish samples had a Pb LIR range from 0.8800 to 0.8973 with a mean value of 0.8900 ± 0.0057. The corresponding Pb concentration ranged from 1.33 to 17.80 mg kg−1. Chicken from the market at Garden Reach in the west of Kolkata had a high Pb concentration of 9.58 mg kg−1 with a corresponding Pb LIR range from 0.8786 to 0.8990. The corresponding mean value was 0.8915 ± 0.0070. The spice samples (whole cumin seeds) collected from the various markets had a Pb LIR range from 0.8743 to 0.8978 with a mean value of 0.8862 ± 0.0068. The Pb concentration had a high value of 31.25 mg kg−1 in the Tollygunje sample. Among the herb (tulsi) samples, the range of Pb concentration was from 8.92 to 33.27 mg kg−1. The corresponding Pb LIR ranged from 0.8839 to 0.8956 with a mean value of 0.8907 ± 0.0041. The coefficient of variation of the 207/206 Pb LIR values of the eight food samples decreased in the order of fish > vegetable > rice > red lentil > spice > snack > meat > herb.

ð1Þ Pb concentration and its isotope compositions in street dust

Pbnatural

ð207=206Þ Pb natural

Results

ð2Þ

where Xnatural and Xanth represent the percentage contributions (%) of uncontaminated and anthropogenic sources, respectively, and 207/206Pbanth, 207/206Pbnatural and 207/206Pbfood represent the 207/206 LIR in anthropogenic, uncontaminated and in the different food items, respectively. The highest 207/206 LIR obtained was 0.9015 for the diesel and the lowest was 0.7926 from the uncontaminated sediment at Ichapur.

The mean concentration of Pb found in the 29 sites was 383.2 mg kg−1 with a range from 23.82 mg kg−1 to a very high value of 2697.24 mg kg−1 at Amherst Street in north Kolkata. The 207/206 LIR value was between 0.8271 and 0.8998 with a mean of 0.8789 ± 0.0154, while the corresponding 208/206 value was between 2.001 and 2.169 with a mean of 2.12 ± 0.0318. Pb concentration and its isotope compositions in diesel The mean 207/206 and 208/206 LIRs of the two diesel samples was 0.9015 ± 0.0007 and 2.1869 ± 0.0024, respectively. The mean Pb concentration was 9.38 mg kg−1.

Author's personal copy Environ Sci Pollut Res Fig. 2 Comparison of 208/204 and 206/204 LIRs of NIST 981 obtained with some international references

16.94800

36.7300 HIRATA

16.94200

206/204

208/204

BELSHAW 36.7000 WHITE 36.6900 36.6800

BELSHAW

16.94000 16.93800

WHITE

16.93600

R.DEL RIO SALAS

16.93400

R.DEL RIO_SALAS

FEI_LI LI

16.93200

FEI_LI LI

36.6700

16.93000 THIS STUDY

36.6600 0

0.5

1

THIS STUDY

16.92800

1.5

0

0.5

1

1.5

The coefficient of variation among the three sediments with respect to the Pb concentration was 0.6393, whereas for the 207/206 and 208/206 LIRs, the values obtained were 0.0187 and 0.0108, respectively. The uncontaminated vegetable sample had a 207/206 LIR value of 0.6764 and a 208/206 LIR value of 1.5885. The total Pb concentration in the vegetable was 5.17 mg kg−1. For the contaminated vegetables collected from the three Dhapa sites, the mean 207/206 LIR was 0.8058 ± 0.0251 and 1.9322 ± 0.0596 for 208/206 ratio. The average Pb concentration was 16.83 mg kg−1 and the Bainchtola vegetable sample had the minimum with 13.24 mg kg−1 Pb concentration.

Pb concentration and its isotope compositions in coal, sediments and galena The uncontaminated sediment sample from Ichapur which was the control site had 207/206 and 208/206 LIR values of 0.7926 and 1.9484, respectively, with a total lead concentration value of 137.75 mg kg−1. The average 207/206 LIR for the three contaminated sites at Dhapa was 0.8658 ± 0.0162, while the value obtained for the 208/206 LIR was 2.0962 ± 0.0226. The average Pb concentration was 475.85 mg kg−1 with the minimum value of 197.09 mg kg−1 at Bainchtola and a maximum of 800.39 mg kg−1 at Arupota. Table 2

REHKAMPER &HALLIDAY

16.94400

REHKAMPER &HALLIDAY

36.7100

HIRATA

16.94600

36.7200

Summary of the lead isotopic ratios and total lead concentrations of the different environmental matrices. Pb (mg kg−1)

Sample id

207/206

208/206

Food (n = 12)

Mean

Min

Max

STDEV Mean

Min

Max

STDEV Mean

Min

Max

STDEV

Rice (Oryza sativa) Red lentil (Lens culinaris) Spice (Cuminum cyminum) Snack (-)

0.8851 0.8857 0.8862 0.8924

0.8731 0.8715 0.8743 0.8756

0.8980 0.8946 0.8978 0.8995

0.0086 0.0073 0.0068 0.0075

2.0998 2.0848 2.1289 2.1212

2.1871 2.1718 2.1734 2.1878

0.0221 0.0243 0.0154 0.0169

5.43 3.79 6.43 4.82

0.90 1.83 0.28 1.57

14.39 7.44 31.25 10.72

3.57 1.69 8.11 2.74

Vegetable (Amaranthus Gangeticus Linn.) Fish (Mustus uittatus) Chicken (Gallus gallus domesticus) Herb (Ocimum sanctum) Others Street dust (n = 29) Contaminated sed—Dhapa (n = 3) Uncontaminated sed— Ichapur (n = 1) Contaminated veg (n = 3) Indian lead ore (n = 8) Coal—Raniganj (n = 8) Coal—Jharia (n = 7) Rainwater (n = 1) Indian diesel (n = 2)

0.8846 0.8553 0.8947 0.0114

2.1473 2.1065 2.1588 0.0174

43.35

3.28

145.48

43.74

0.8800 0.8800 0.8973 0.0057 0.8915 0.8786 0.8990 0.0070

2.1595 2.1334 2.1857 0.0183 2.1672 2.1279 2.1873 0.0191

6.33 4.58

1.34 1.00

17.79 9.59

4.48 2.31

0.8907 0.8839 0.8956 0.0041

2.1576 2.1263 2.1832 0.0163

19.81

8.92

33.27

9.12

0.8789 0.8271 0.8998 0.0155 0.8658 0.8489 0.8811 0.0251

2.1200 2.0010 2.1690 0.0200 1.9322 1.8557 1.9851 0.0596

383.42 475.87

23.82 197.09

2697.24 800.39

1.32 304.24

0.7926 –

–

–

–

–

1.9484 –

137.75

–

–

–

0.8058 0.9659 0.8162 0.8396 0.9007 0.9015

0.8263 0.9663 0.8275 0.8573 – 0.9020

0.0251 0.0003 0.0097 0.0148 – 0.0007

1.9322 2.3095 2.0602 2.0946 – 2.1869

1.8557 2.3083 2.0175 2.0543 – 2.1852

1.9851 2.3102 2.0875 2.1308 2.1536 2.1886

16.83 449567.82 156.95 221.11 0.73 9.38

13.24 29996.79 85.47 96.76 – 8.76

19.24 786968.72 186.56 362.78 – 10.01

2.78 295113.88 41.41 86.02 – 0.88

0.7729 0.9655 0.8007 0.8191 – 0.9010

2.1495 2.1447 2.1508 2.1664

0.0596 0.0006 0.0230 0.0280 – 0.0024


For the eight coal samples collected from Raniganj, the mean 207/206 LIR was 0.8162 ± 0.0079 with a range from 0.8007 to 0.8275. The 208/206 LIR values had a range from 2.0175 to 2.0875 with an average value of 2.0602 ± 0.0215. The range and mean values of the 207/206 LIR for the seven coal samples from Jharia were 0.8191 to 0.8573 and 0.8396 ± 0.0148, respectively. The corresponding 208/206 LIR values were 2.0543 to 2.1308 and 2.0946 ± 0.0280. The eight galena samples had a mean Pb concentration of 44.96 % with a maximum value of 78.70 %. The average 207/ 206 LIR, the value was 0.9657 ± 0.0007 with a corresponding range from 0.9642 to 0.9663. The 208/206 LIR had a range from 2.3083 to 2.3103 with an average of 2.3096 ± 0.0006. The coefficient of variation of the 207/206 and 208/206 LIRs was 0.0003 and 0.0007, respectively.

Discussion There has been a number of recent studies on the correlation between atmospheric deposition on vegetables and their increased levels of heavy metal concentration in different parts of the world, including India (Azimi et al. 2003; Sharma et al. 2008). Atmospherically deposited metals may be absorbed directly through plant surfaces or indirectly through deposition onto the soil followed by root absorption (Harrison and Chirgawi, 1989). Leafy vegetables have been reported to accumulate substantially high amount of air-borne heavy metals (Eboh and Thomas, 2005). Many studies have demonstrated the imposition of anthropogenic Pb isotope signatures on food products. Studies of wine showed variable sources of introduced Pb and the process of making and storing vinegar introduced Pb contamination to a variable extent (Ndung'u et al., 2011). Airborne particulate pollution was shown to influence the Pb isotope composition of wines from the Czech Republic to varying degrees (Mihaljevic et al., 2006). In their study on tracing lead signatures in meat from three areas in the UK, the authors concluded that the Pb found in modern British meat from these areas was geogenic and showed no clear evidence of anthropogenic Pb (Evans et al., 2015). Interestingly, lead isotope fingerprinting done on Chinese vegetables (LiFei-Li et al., 2012) have shown that the 207Pb/206Pb and 208Pb/206Pb ratios in vegetables increased in the order of roots > stems > leaves > fruits. The 208/206 LIRs of all the eight types of food samples, when plotted against their 207/206 counterparts, showed a linear spread between the two extreme end members of galena and the uncontaminated sediment from Ichapur (Fig. 3). The plot of the mean lead concentrations of the food items and the corresponding mean 207/206 LIR is shown in Fig. 5. The 207/ 206 LIR of the food items overlapped with the corresponding isotopic ratios of the street dust and indicated a common source of origin of the lead burden in the different food items

and the urban dust. While the 207/206 LIR of the diesel, were found above the food as well as street dust, it was evident from the lead isotopic signatures of the coal samples from Raniganj and Jharia that their combustion did not contribute much to Kolkata’s environmental lead pollution. Lead isotopic characterization of sediments and vegetables in the waste disposal site at Dhapa The difference between the 207/206 LIR values of the sediment from the relatively uncontaminated site of Ichapur and the corresponding mean value of the sediments from the three villages of Dhapa (Arupota, Bainchtola and Khanaberia) reflected the degree of anthropogenic influence in lead pollution there. It has been established that the average 207/206 Pb LIR of the upper continental crust and different marine sediments around the world with minor variations is 0.8333 (Renberg et al., 2002, Zhu, 1995). In comparison, the value obtained for the Ichapur sediment was 0.7926. The range of 207/206 isotopic composition of Pb in the Dhapa sediments was 0.8489–0.8811. According to the Zhu et al. (2003), the reported range of 207/206 LIR values of Chinese soil from a natural background in the Indochina geochemical region was 0.8410 to 0.8278. Dhapa, administered by the Kolkata Municipal Corporation (KMC), has been the main waste disposal site of this city for the past 100 years and is a part of the 10,000-ha area of the famous Kolkata wetlands. An adjacent area near Dhapa called Topsia is one of the important e-waste and plastics recycling hotspots in Kolkata. The waste disposal system in Dhapa, in today’s consideration, is primitive and inadequate with no pre-treatment provided for the solid waste deposited. Compaction or composting is not practised after the separation of the waste into biodegradable and recyclable components. Dumping is practised on open land, with street sweepings and drainage cleanings laid over the garbage daily. A significant part of the waste is illegally used as compost for the adjacent farming activities. BGarbage farming^ practised thus can pave a way for untreated heavy metal toxins including lead in the food chain. According to a recent report for KMC (USEPA, 2010), the dumping in Dhapa comprised of food and garden/park waste combined (50.56 %), wood (1.15 %), paper and textiles combined (7.94 %) and all inert waste including construction and demolition products (29.60 %). Lead signature of the sediments here can be assumed to bear the individual signatures of these respective components. As shown in Fig. 4a, b, the correlation between the respective 207/206 LIRs of the Dhapa sediments and vegetables with the corresponding total lead concentration in the sediments and vegetables were very high (r = 0.98 and 0.99, respectively, p > 0.0001) (Fig. 5). In comparison, the correlation between the lead concentration in vegetables and sediment was weaker (r = 0.66). This confirmed that the source of lead in vegetables could not only be from the soil.

Author's personal copy Environ Sci Pollut Res Anthropogenic

Fig. 3 Scatter plot of 207/206 LIR against 208/206 of all the environmental samples Indian lead

Indian coal

Indian diesel

Geogenic

Atmospheric lead may be one of the possible sources. The mean 207/206 LIR of Dhapa vegetables at 0.8058 were found to be significantly lower than the corresponding mean value of the market vegetables at 0.8854 and the value of the Dhapa sediments at 0.8658. Similar 207/206 LIRs have been reported in sediments impacted by industrial and municipal wastewater discharges in Bohai Bay in China. The reported mean value was 0.8477 ± 0.0135 and 2.0997 ± 0.0180 for 207/206 and 208/206 LIRs.(Hu et al. 2015). The mean lead concentration in the Dhapa sediments at 475.87 mg kg−1 was higher than the optimum value set for soils by VROM (1994) and nearer to the value for industrial soils as specified by SEPA (1995). It was seen that soil near a burnt plastic dumpsite in Guiyu, China, had a lead concentration of 104 mg kg−1 (Leung et al., 2006). Similarly, streets near electronic recycling centres in New Delhi recorded a lead concentration in the range of 150–8815 mg kg−1 (Brigden et al., 2005). It was evident in this study that the market vegetables acquired the characteristic isotopic signatures of the city’s pollution sources from the Fig. 4 Plot of a 207/206 LIR of Dhapa sediments against total Pb and b 207/206 LIR of Dhapa vegetables against total Pb

similarity of their mean 207/206 LIR (0.8851) with that of the street dust (0.8789).The Dhapa vegetables have a lesser mean 207/206 LIR as they are grown in that part of the city where there are no major road intersections except for a major highway. Lead isotopic characterization of coal and diesel Significantly, the 207/206 LIR values of the Raniganj and Jharia coal did not overlap with the rest of the samples in the overall 207/206 against 208/206 LIR plot. The range of the 207/206 LIRs was from 0.8007 to 0.8396. In comparison, coal from Northern China and Shanghai had values of 0.8661 and 0.8771, respectively (Mukai et al., 1993, Zheng et al., 2004). Similarly, Indonesian coal had a mean value of 0.8449 compared to the mean 207/206 LIR of Raniganj and Jharia coal at 0.8162 and 0.8394, respectively. The mean 207/206 LIR of Raniganj coal was lower than that of Jharia and also less than that of the street dust, diesel and food samples. The effect of


LIR signified the anthropogenic influence in Kolkata’s environment. This value was higher than Chinese rainwater with comparable 207/206 Pb and 208/206 Pb ranges of 0.8547– 0.8593 and 2.098–2.109 (Li et al., 2012). Lead isotopic characterization of galena

Fig. 5 Mean lead concentrations (mg kg−1) against respective mean 207/ 206 ratios of food items

combustion of the Raniganj and Jharia coals in the adjacent Kolaghat Thermal Power Station on the overall lead pollution burden of food or street dust was, therefore, not prominent in terms of their 207/206 LIRs. One possible reason could have been the large distance between the power station and the markets. In general, source tracing of lead from coal would have been possible had a database of lead isotopic ratios of Indian coal existed. Such a database is currently being created in our laboratory. The mean 207/206 LIR value of diesel obtained directly from petrol filling stations in this study was 0.9015, and this value was the highest among all the 207/206 LIR values, after lead ore. Available data on lead isotopic ratios of petroleum fuel like diesel in Asia is limited. The reported value (Chang et al. 2015) of the LIRs of diesel used in Taipei was 2.105– 2.122 (208/206 Pb) and 0.8741–0.8643 (207/206 Pb). The corresponding values in Swiss diesel were 2.146 and 0.9009 (Cupelin, 2000). In any case, diesel thus contributed the most to lead pollution of the environmental samples including food and street dust in this study. The use of katatel or adulterated diesel has been banned in Kolkata. However, it is not uncommon to find it in the suburbs of Kolkata. This cheap variant of fuel used by three-wheelers is manufactured by mixing kerosene or used lubricants with diesel, and the exact composition of such diesel varies with the place. Significantly, the concentration of lead in the analysed diesel sample complied with the Bureau of Indian Standards specified value of 0.013 g/l (BIS petrol specifications IS 2796: 2000). However, the mean 207/ 206 LIR value was higher than Chinese vehicle exhaust (from leaded gasoline) at 0.9010 or Taiwanese diesel at 0.8692. Lead isotopic characterization of rainwater The rainwater sample had a 207/206 LIR of 0.9007 with the corresponding 208/206 value at 2.1536. The high 207/206

In this study, the galena samples were included not specifically for the purpose of source tracing. However, their position in the overall plot in Fig. 3 reflects the uniqueness of Indian lead ore isotopic signatures. The range of 207/206 and 208/206 LIRs found was 0.9659–0.9663 and 2.3095–2.3083, respectively. In comparison, the reported LIRs of the lead ores from Beishnan and Wanfanggon in China are (0.9440, 2.2533) and (0.9284, 2.2251), respectively (Cheng et al. 2010).

Lead isotopic characterization of food It has been reported that air exposed fruits and vegetables showed the highest lead enrichment factor relative to aluminium (Li et al., 2012). Importantly, it was also shown that atmospheric lead is a major source of contamination in leafy vegetables. In another study (Feng et al., 2011), it was found that in rice plants grown near an expressway, there was considerable Cd and Zn accumulation from the atmosphere via foliar uptake. In this study, the mean 207/206 LIR of the eight food items decreased in the order of snack > chicken > herb > fish > spice > red lentil > rice > vegetable. The range of the food LIRs was from 0.8847 to 0.8924, and these values overlapped with the LIR range of the street dust (0.8271–0.8998). Chicken, fish, vegetable, snack and the medicinal herb sold in the markets are produced locally in and around Kolkata, and the city is well known all over the world for its wide variety of street food. The mean LIR value of each food item reflected the complex mixture of individual LIR signatures of the original ingredients from which it was made, as in the case of the local biscuit, or its actual place of origin (rice, vegetable, meat, fish and herb) and the acquired environmental lead signatures on its way to the marketplace. In a marketplace, situated adjacent to a busy street, the chicken and fish were actually sliced in the open and then sold to the customers. The snack was made from flour, with the dough mixed with appropriate spice before being deep fried in oil. Polished rice, red lentil and spice (cumin seed) sampled from the different markets were stored in gunny bags or were at least kept covered. Also, the state of West Bengal does not produce cumin seeds, and the product is imported from Gujarat. Chicken and fish have similar, high mean values of 207/206 probably because these were sold openly and were much more exposed to dust and vehicular exhausts. Vegetables, as opposed to the basil leaves (herb) were initially washed to make them appear fresh


and then displayed for sale. This explained why the former had a lower mean 207/206 LIR value than the latter. Among all the sampled market places, the one at Salt Lake was comparatively unexposed to street pollution. The Salt Lake area is relatively a new locality and was developed with proper planning. More importantly, it is greener than market localities situated in north and south Kolkata. This could be the reason why a consistent correlation could be seen between the 207/206 LIRs and the total Pb found in rice, fish and chicken sold there (Fig. 6). Quantification of anthropogenic Pb in foods The quantification of anthropogenic Pb in the food stuffs of Kolkata markets is constrained by the absence of well-defined, accepted values of lead isotopic ratios of the end members relevant to the Indian context. In this study, the value of 207/206 lead isotopic ratio (0.7926) of the single Ichapur sediment representing natural Pb in the upper continental crust of India is close to the cited range (0.808 to 0.857) of the 207/206 Pb ratios belonging to an eroding continental crust (Millot et al., 2004). The 206/207 LIR of Chinese natural soils and sediments have a value of 1.2 or slightly higher than 1.2 (Zhang et al., 2007). In this study, therefore, while determining the percentage contribution of atmospheric lead in the food items, it was thought to be appropriate to have taken Fig. 6 Correlation between lead (mg kg−1) in rice, fish and chicken with 207/206 LIR

the 207/206 Pb ratio of 0.8333 as the value representative of our geogenic end member. On the other hand, diesel was chosen as the representative anthropogenic end member primarily because vehicular exhausts contribute significantly to atmospheric lead pollution besides coal combustion products and industrial emissions. Internationally, the reported 207/206 and 208/206 LIRs of vehicular emissions due to combustion of leaded gasoline ranged between 0.862–0.935 and 2.095– 2.198, respectively (Lahd Geagea et al., 2008). In India, leaded gasoline was phased out from 2000 (Singh and Singh, 2006), but neighbouring countries as Afghanistan, Iran and Myanmar still use leaded gasoline products. Additionally, there was a widespread use of adulterated diesel (katatel) by the three-wheelers of Kolkata till recently. Sturges and Barrie (1987) reported that the residence time of lead borne aerosols in the atmosphere is typically around 5 to 10 days. Thus, ‘historical’ lead from the combustion of diesel, adulterated or otherwise, would be significant source for the lead pollution load in the city’s food items. The application of the binary mixing model taking 0.8333 and 0.9015 as the 207/ 206 LIRs values of geogenic and anthropogenic end-members, respectively, showed that the contribution of atmospheric lead in the street dust was in the range of 68.48–86.66 %. In our study, the total lead concentration of the different food items sold in the market places may be ascribed to the soil, air, water of their production sites and also to aerial deposition

Author's personal copy Environ Sci Pollut Res Fig. 7 Two ratio plot of the mean 207/206 and 208/206 LIRs of different environmental matrices

during transportation and marketing. Sharma et al. (2008) have shown that the percent reduction of heavy metals in market vegetables sold in Delhi after washing varied between 23 and 68 %. This justified the fact that a major load of heavy metal contamination including lead in food products sold in open market places is from atmospheric deposits. The strong overlapping of the lead isotopic ratios of the street dust samples with the ratios obtained for food items as shown in this study supported this finding. Regardless of the inherent lead in the food matrix before it arrived in Kolkata’s markets, the city’s atmospheric lead burden is significantly high to influence it isotopically and compositionally. The two ratio plot of the mean 208/206 and 207/206 values of the different environmental matrices are shown in Fig. 7. Rainwater and emissions from diesel exhausts by different vehicles contributed primarily to the city’s atmospheric lead burden. The average 207/206 LIR value of diesel at 0.9015 was higher than that of rain water. The high anthropogenic lead contribution from the atmosphere to the different food items are shown in Fig. 8. The three food items which showed

the highest lead contamination from the atmosphere are the snack, chicken and herb with contributions as high as 86.66, 85.34 and 84.16 %, respectively. These are of local origin and hence are impacted more by the city’s pollution. Interestingly, vegetables and fish have lower percentage values of atmospheric lead contribution as these food items although sold openly are at least washed in water at the markets before being sold. For the present study, fly ash generated by the two thermal power stations adjacent to the city of Kolkata have not been sampled or analysed. The average 207/206 LIR of the Raniganj and Jharia coals was 0.8777, and if these coals are being utilised in the power stations, then their contribution to the lead burden in the market food is not high as compared to diesel. As the markets from where the food items were sampled are located near busy roads and traffic intersections, the 207/ 206 LIRs of both the street dust and food samples overlapped. Atmospheric lead in the form of diesel exhausts from vehicles was found to be the significant contributor in both these environmental matrices.

Conclusion

Fig. 8 Anthropogenic input (%) of atmospheric lead contribution to the food items

Lead isotopic ratios of different environmental matrices like coal, street dust, rain water and diesel were analysed to trace the source of lead pollution of the different food items sold in the markets of Kolkata. The average total lead concentration of the eight food items ranged from a low 0.28 mg kg−1 to a high 145.48 mg kg−1. However, the 207/206 LIRs were confined within the narrow range of 0.8847 to 0.8924. This range thus signified the unique lead isotopic signature of the city’s pollution level. The scatter plot of the two LIRs exhibited a


linear spread wherein the food and street dust samples overlap with each other between the Ichapur sediment and diesel as the geogenic and anthropogenic end members, respectively. The coal LIRs did not exactly fall on this linear plot. Raw food items sold in its roadside open markets in Kolkata are either exported from outside the state or transported from the city’s suburban districts. However, the accumulated atmospheric lead, derived mainly from diesel exhausts of the city’s traffic, had the dominant lead isotopic signature. This contribution of atmospheric lead to the overall lead contamination in the eight different food items ranged from 68.48 to 86.66 %. Acknowledgements This work is the outcome of the research project (RP/CHQMIV/2014/115) funded by the Geological Survey of India, Kolkata in April 2014. The authors would like to thank the Director General of the Geological Survey of India, Kolkata, for his kind permission to publish. Thanks are also due to Mr. Saikat Dutta, Assistant Chemist of the Central Chemical Laboratory, for his help in the sample preparation and digestion.

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