The presence of a high concentration of lead has been detected in raw food items such as polished rice and fish, sold in city markets, says a team of Indian scientists.

The scientists have highlighted the linkages of the presence of the toxic substance with diesel combustion. The observations are based on recent studies carried out by a group of scientists lead by Avijit Das, Chemist of Geological Survey of India (GSI).

"The raw food items, sold near the streets of Kolkata, contain a mean lead concentration between 3.78 and 43.35 mg/kg (average 23.56 mg/kg) which is very high compared to the threshold value of 2.5mg/kg specified by Food Safety and Standards Regulation (2011), India," a statement from the Geological Survey of India said on Sunday.

The study also revealed that about 75 per cent of the lead contamination in the food items sold in Kolkata street markets, was contributed by atmospheric lead, mainly produced by combustion of diesel.

The current reference range for acceptable blood lead concentrations in healthy persons without excessive exposure to environmental sources of lead is less than 0.05 mg/L for children whereas, it is less than 0.25Amg/L for adults (as per American/European standards).

Lead (Pb) is a highly toxic element and its prolonged exposure 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 health system.

Samples of eight items -- 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) -- were collected from 12 roadside markets covering the north, south, east and west of Kolkata.

Soil and vegetables samples were collected from Dhapa Ground, alongside the EM Bypass, for the study of lead contamination while street dust samples were sourced from major roads north and south of Kolkata.

Coal samples from Jharia and Ranigunj were analysed for the presence of atmospheric lead from the use of coal.

The study also included analysis of galena (ore of lead) samples from Alwar (Rajasthan) to calculate the Lead Isotope Ratio (LIR) of Indian lead; rain water and diesel samples were collected from Kolkata.

LIR is a modern method used to ascertain the sources of lead exposure.

All these samples were collected to compare their lead isotopic ratios and lead concentration with that of food items sold near the streets of Kolkata.

To compare the level of contamination in sediments and vegetables found in Dhapa, soil and vegetable samples were collected from a relatively less polluted place called Ichapur (Control Site), located about 30 km north of Kolkata.

As far as the lead concentration in the street dust is concerned the findings are "worrisome".

The mean concentration of Pb found in the 29 sites was 383.2 mg/kg with a range from 23.82 mg/kg to a very high value of 2697.24 mg/kg at Amherst Street in north Kolkata.

"The study reveals that the accumulated atmospheric lead, derived mainly from diesel exhausts of the city's traffic, had the dominant lead isotopic fingerprints. This lead contamination can be arrested by minimizing the use of diesel and by encouraging the mass traffic movements by greener energy sources like LPG/CNG operated vehicles, battery operated electric cars, solar cars and increasing Metro rail network," the statement said.

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