Raw food items sold in most city markets have Lead concentration far above the permissible limit and can permanently damage key human organs, a survey conducted by the Geological Survey of India (GSI) has found.
Samples of raw food items like 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), collected from 12 markets in the city showed a mean Lead (Pb) concentration between 3.78 and 43.35 mg/kg (average 23.56 mg/kg).
"The mean Lead concentration found in the raw food materials is very high compared to the threshold value of 2.5mg/kg specified by Food Safety & Standards Regulation (2011), India," senior scientist of the GSI, Avijit Das, who headed the group conducting the two-year study, said today.
As per the American and European standards, the current reference range for acceptable blood Lead-concentration in a healthy human being, without excessive exposure to environmental sources of Lead, is less than 0.05 mg/L for children whereas it is less than 0.25 mg/L for adults.
Prolonged exposure of lead, which is a highly toxic element, to humans can cause permanent damage to the kidneys, liver and hematologic systems.
Children are more at risk because lead exposure can reverse their brain growth and cause irreversible damage to their overall well being.
The study, conducted by leading scientists of the GSI, also found that about 75 per cent of the Lead contamination in the food items sold in Kolkata markets, were contributed by atmospheric Lead, mainly produced by the combustion of diesel.
Apart from collecting soil and vegetable samples from Dhapa ground, alongside the EM Bypass, for the study of Lead contamination, the scientists had also collected street dust samples from major roads of the northern and southern parts of the city for the study.
"Coal samples were collected from Jharia and Ranigunj to assess the presence of atmospheric lead from the use of coal while Galena (ore of Lead) samples from Alwar (Rajasthan) were brought to calculate the Lead Isotopic Ratio (LIR) of Indian lead," Das said adding, rain water and diesel samples were collected from city markets for the study.
"All these samples were collected to compare their LIR and lead concentration with that of the raw food items sold in Kolkata markets," he added.
To compare the level of contamination in sediments and vegetables found in Dhapa, soil and vegetable samples were collected from a relatively less polluted Ichapur (Control Site) in North 24 Parganas district.
The maximum Lead concentration in rice was 14.39mg/kg found in the samples collected from a market in Kidderpore in the western part of the city, the study said.
"The Lead concentration in red lentil samples collected from markets in Tollygunge in south Kolkata was found to be between 1.82 and 7.44 mg/kg," Das said.
Samples of vegetables sold in different markets also revealed a Lead concentration ranging from a low of 3.28 mg/kg to a very high value of 145.47 mg/kg while fish had a range of 1.33 to 17.80 mg/kg, he said.
Chicken collected from a market at Garden Reach in the city's port area showed a Lead concentration of 9.58 mg/kg.
"The whole cumin seeds samples collected from a market in Tollygunge area had a Lead-concentration value of 31.25 mg/kg. Among the herb (tulsi) samples, the range of lead concentration was from 8.92 to 33.27 mg/kg," Das said.
Vegetable samples from the three different sites in Dhapa showed an average Lead concentration of 16.83 mg/kg with the Bainchtola sample bearing the minimum with 13.24 mg/kg.
"The less contaminated soil and vegetable samples collected from Ichapur had a total Lead concentration value of 137.75 mg/kg for soil sample and 5.17 mg/kg respectively," it revealed.
The average Lead concentration in soil samples collected from the three sites at Dhapa was 475.85 mg/kg with the minimum value of 197.09 mg/kg at Bainchtola and a maximum of 800.39 mg/kg at Arupota.
The Lead concentration in locally made snacks were found to be in the range of 4.82 to 10.71 mg/kg with the maximum found in the sample collected from Gariahat in south Kolkata.
Das said the survey also found that the Lead concentration in street dust of the city was worrisome.
"The mean concentration of Lead found in the 29 sites of the city was 383.2 mg/kg with a range from 23.82 mg/kg to a very high value of 2,697.24 mg/kg at Amherst Street in north Kolkata," he said.
On ways to tackle the Lead contamination, Das said it could be done by minimising the use of diesel and by urging people to use green energy in vehicles.
"We must encourage the mass traffic movements by greener energy sources like LPG/CNG operated vehicles, battery operated electric cars, solar cars, increasing metro rail network," Das said.
The study was published in the peer reviewed International journals of "Environmental Science and Technology (2017) (online publication)" and "Environmental Science and Pollution Research (2016)".
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