The Silent killer

Pesticides kill insects. Then, they poison animals and birds. Humans are hardly out of reach

 
Published: Friday 15 January 1999

The Silent killer

-- T he pesticide threat first emerged in the West, the us in particular. In the early 1930s, the Dutch elm disease spread across the us. A fungus disease spread by beetles, it proved fatal to trees, blocking their water-conducting vessels. In 1954, us farmers began spraying ddt to kill the beetles in a bid to curb the disease. But the pesticide soon affected robins, killing thousands of birds.

Then, in 1963, came Silent Spring , a landmark book by environmentalist Rachel Carson, which detailed how increased pesticide use affected bird population in the us , sometimes wiping out entire population and even species. Her emotive assessment of the situation -- how birds no longer heralded the onset of spring -- rang alarm bells across the nation. Many conservation measures were suggested and some adopted to ensure spring the welcome it has always enjoyed -- birds returning home after spending their winters in warmer locales. But these have not been enough. Though a few pesticides, such as ddt , dieldrin and chlordane, have been banned by the us and several European nations, the developing world is still at risk as these chemicals still enjoy widespread applications in these parts. India, for instance, has always persisted in using these deadly pesticides such as ddt even in its 'so-called' health programmes.

Toxins in the air...
Among the chemicals usually used as pesticides, organochlorines, including ddt, hch , aldrin, dieldrin, chlordane, are proven killers. ddt and dieldrin are the most dangerous because of their subtle and widespread effects on birds and the so-called 'benefits' they confer on human food supplies. To add to the problem, ddt, dieldrin and chlordane also belong to a class of chemicals called endocrine disrupters. These disrupt development of the immune, nervous and endocrine systems and are of serious concern as they affect cellular and molecular processes that regulate developmental, endocrine and immunological functions. Many of these even mimic and interfere with male and female hormones, modifying development and reproduction.

Throughout the late 1950s and the 1960s, us scientists experimented with ddt. These experiments indicated that when juvenile roosters were injected with the chemical, it led to reduced size of the male genitals (testis) and induced female appearance. In birds, ddt compounds may affect embryonic development by reducing egg shell thickness, as in the case of ducks, or by direct effects on the embryos. When eggs of Californian gulls ( Larus californicus ) and western gulls ( Larus occidentalis ) were injected with methoxychlor and ddt , these caused feminisation of male embryos. Endocrine disrupters also change mating and parenting behaviours in birds, say experts. Birds often eliminate organochlorines and heavy metals by sequestering them in their eggs, a phenomenon that, as mentioned, jeopardises the developing embryos. During the egg-laying period, the eggs receive half of the contaminants that are in the females' bodies (see cartoon: Dark duck tales ).

Moreover, ddt and its breakdown products, classified as Persistent Organic Pollutants ( pop s), are chemicals that take hundreds of years to disappear from the environment. These have even found their way to the polar regions borne by winds. They have caused serious health problems in human, bird and animal populations. Early leakage that might have contaminated land will continue to be a major threat for many years from now.

Organochlorines are severely detrimental to the survival and reproduction of wildlife, especially that of birds such as vultures, which are often indicate contamination in the environment. The first to get affected by the chemicals are vultures and other birds of prey, being on the top of food chain. Barbara Rutherford, policy coordinator, Water Pollution and Toxics at the Switzerland-based wwf international, once assessed the pesticide threat as "one of the great difficulties in identifying exactly how these chemicals (endocrine disrupters and other pesticides) affect birds, animals and humans is that the pattern of effects varies between species and compounds". "General conclusions can be drawn, however," she adds, "even one very low dose of an endocrine disrupter at a crucial stage in the development of an embryo is sufficient to cause irreparable damage." Further, Rutherford points out that the effects are transgenerational -- the gap between intake and effects could be as large as two generations.

...and within us
Studies conducted in Sweden, Canada and the us revealed a strong link between the incidence of a certain type of cancer called Non-Hodgkin's Lymphomas ( nhl ) and the use of pesticides. In Sweden for instance, frequent use of herbicides, such as 2,4-dichlorophenoxyacetic (2,4- d ) has been estimated to increase the risk of contracting nhl by 200-800 per cent.

According to N K Mehrotra, who was with the Industrial Toxicology Research Centre ( itrc ) in Lucknow, India, organochlorines such as toxaphene, hch , strobane, dieldrin and ddt are all known to cause lymphatic cancer in rats and mice, and most certainly in humans, too. Distressingly, these affect both birds and humans through the same channels: vector control, residues in food and in the environment.

In India, there is ample evidence that pesticides have affected birds and humans alike. And most Indians already have these chemicals inside them. A 1993 study conducted by the Indian Council of Medical Research ( icmr ) found alarming levels of pesticide in some 2,205 cow and buffalo milk samples collected from 12 states over a period of seven years ( Down To Earth , Vol 5, No 13). Detectable residues of alpha, beta and gamma isomers of hch -- or bhc , a pesticide known for its extreme toxicity -- were found in 87, 85 and 85 per cent of the samples respectively (See box: Fatal food ). The percentage of samples exceeding the scientifically-approved tolerance limits were 21, 24 and 28 in the case of alpha-, beta- and gamma- hch , respectively. The worst contamination was detected in samples of Andhra Pradesh ( ap ), Bihar and Uttar Pradesh. Dietary intake of beta- hch was about twice the acceptable daily intake ( adi ) among the high-income urban population in ap . ddt residues were detected in about 82 per cent of the samples. Some 37 per cent had ddt traces above the tolerance limit. Maximum levels of ddt residues were found to be 44 times the tolerance limit. States that recorded the maximum ddt levels were Maharashtra, with 74 per cent samples above the tolerance limit, Gujarat, with 70 per cent, ap, with 57 per cent, Himachal Pradesh, with 56 per cent and Punjab, with 51 per cent.

Even infant milk formula and bottled milk had pesticide residues. Of some 186 samples of 20 commercial brands of infant milk formula available in the market, 70 per cent showed ddt contamination and 90 per cent had hch -isomers. The results are frightening: children fed on instant formula would absorb quantities of beta- hch that are 90 per cent more than the adi .

Subscribe to Weekly Newsletter :

Comments are moderated and will be published only after the site moderator’s approval. Please use a genuine email ID and provide your name. Selected comments may also be used in the ‘Letters’ section of the Down To Earth print edition.