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♤ All pesticides are tested to establish toxicity — a dose necessary to produce a measurable harmful effect, it is 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, comparison of 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 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.