Pesticides are commonly used in India but this comes at great cost to human health. The Centre for Science and Environment decided to investigate the matter and looked at the agricultural heartland of Punjab. It found that 15 different pesticides in the 20 blood samples tested from four villages in Punjab. But what is more important to find out is how much of pesticide in blood is ‘safe’. Does a safety threshold level exist? If yes, how do scientists — and the industry — compute it? As we delve into such questions, it becomes clear that science claims more, but understands much less.
All pesticides are tested to establish toxicity — a dose necessary to produce a measurable harmful effect — usually established through tests on mice, rats, rabbits and dogs. Results are then extrapolated on humans, and safe exposure levels predicted. The value commonly used to measure acute toxicity is LD 50 (a lethal dose in the short term; the subscript 50 indicates the dose is toxic enough to kill 50 per cent of lab animals exposed to the chemical). LD 50 values are measured zero onwards; the lower the LD 50 the more acutely toxic the pesticide. To illustrate, we compare DDT — most used in India up to the early 1990s — with monocrotophos, currently most used. DDT’ S LD 50 is 113 mg/kg; monocrotophos, 14 mg/kg. But let us never forget that lower LD 50 means higher acute toxicity.
Pesticides once ingested, accumulate in the body fat or pass through. Organochlorine pesticides, for instance, accumulate in body fat and blood lipids. These fat-soluble chemicals persist in the body for many years. CSE found that pesticide residues of DDE and DDT in the Punjab samples were 35 times and 188 times higher than in samples collected by US based Centre for Disease Control and Prevention which analysed blood and urine levels of 116 environmental chemicals.
CSE calls for urgent action to regulate use of pesticides. It calls for action to monitor human bodies –a biomonitoring programme – to ensure that this chemical invasion is stopped.