Scientists have detected a plastic contaminant called bisphenol A (BPA) in hilsas in the Ganga’s lower stretches and the Hooghly’s estuary zone, signalling a potential health risk to humans, particularly children who eat this popular fish.

The study, the first to measure BPA concentrations in hilsas in the Ganga, has estimated that children who consume the standard recommended daily fish intake may receive 159 to 775 times the acceptable daily threshold of this contaminant.

But the scientists – from the Central Inland Fisheries Research Institute (CIFRI), Barrackpore -- also asserted that this was a preliminary study and there was “no evidence whatsoever” of any human harm yet.

BPA is commonly used in plastics found in food and beverage containers, tableware and other common household items.

Standard toxicity tests have indicated that exposure to BPA among humans is, normally, below the levels of concern for potential adverse effects. However, the European Food Safety Authority panel said in 2023 that BPA’s effects were worse than previously assessed (2015) and that even low exposure to the chemical could disrupt the endocrine and immune systems, apart from having other adverse effects.

The CIFRI scientists examined 184 hilsa specimens collected between March 2022 and February 2023 by fisherfolk from Farakka, Dhuliyan, Behrampore, Nabadwip, Balagarh, Tribeni and Barrackpore; and 163 specimens collected during the same period from Godakhali, Diamond Harbour, Kakdwip, Namkhana and Fraserganj in the estuary zone.

Their study revealed varying concentrations of BPA in the fish tissues, including the muscles. The highest levels were in the livers of adult male hilsas, intermediate levels in the muscles of reproductively active females, and the lowest levels in the livers of juveniles. The concentrations changed with the seasons, being the highest in May 2022 and the lowest in February 2023.

“Our objective was to assess the potential hazard to human health from BPA contamination in this queen among fishes,” said Basanta Kumar Das, CIFRI Barrackpore director, who led the study, published in the Journal of Hazardous Materials.

“But it is also important for us to assert that this was only a preliminary study and there is no evidence of any harm to humans from the hilsa yet,” he told The Telegraph.

Using the BPA concentrations in the fish, Das and his colleagues calculated the theoretical exposure levels to people. They assumed a person would consume on average 28 grams of fish a day -- the recommended intake under the guidelines of the National Institute of Nutrition, Hyderabad.

Their calculations suggest that the daily consumption of hilsas from any of these 12 sites would result in an estimated intake above the accepted threshold of 0.2 nanogram per kilogram body weight per day, set by the European Food Safety Authority panel, during the study period.

The theoretical ratios of the estimated daily intake to the accepted daily threshold among adults lay ranged between 174 to 189 at Barrackpore and 324 to 354 at Kakdwip. In children, the ratios ranged between 159 at Farakka and 775 at Kakdwip.

The findings are a “cause for concern” but are similar to results of studies from elsewhere in the world, including from Bangladesh where researchers at the Noakhali Science and Technology University too had documented BPA in hilsas.

The CIFRI scientists have underlined the need for the recycling and safe disposal of plastic waste and efforts by governments to treat urban runoff to prevent BPA and other pollutants from entering the waterways.

One encouraging finding, the scientists have said, was the relatively lower concentrations in the upper stretches than in the estuary region, which implies that high water flow levels can dilute BPA concentrations.