The aftermath

THE United States Environment Protection Agency has a four-day testing period to evaluate a pesticide's safety. A team studied the effect of the pesticide endosulfan. They concluded the four-day period is inadequate. It is the pesticide's impact after the four days that one should be worried about.

Endosulfan disrupts hormone functions and is banned in 60 countries. It is yet to be banned in India. A single dose between 1.3 ppb to 120 ppb can kill half the population exposed to it. USEPA classifies this range as highly toxic to very highly toxic. The team from the University of Pittsburg, USA, exposed tadpoles of nine frog species to a single dose of endosulfan. The findings, in the September issue of Environmental Toxicology and Chemistry, proved that the USEPA classification should be reset.

97 per cent of the leopard frogs died after they were transferred to clean water

All nine species were susceptible to endosulfan in varying degrees but leopard frogs suffered the most. An exposure to 60 ppb of endosulfan caused no deaths. When the tadpoles were transferred to clean water after the four-day period, almost all of them died. "This is the lag effect that is ignored. It is assumed that the chemical's impact disappears after you remove it," said Jason R Rohr, assistant professor at the University of South Florida.

Amphibians are sensitive to pollutants, said Rick Relyea, biologist from the University of Pittsburgh and one of the authors. If the insecticide cannot kill such susceptible species in four days, the test period is ineffective for less-sensitive species, he added.

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