Snake in the grass

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Contaminant levels of pocs have been established in various foods in countries such as India, Thailand and Vietnam. Concentrations of a number of pocs exceed the recommended maximum residue limits set by the World Health Organisation (who) and Food and Agricultural Organisation (fao) for various food items in India. Overall intake of pocs exceed the acceptable daily intake (adi) only for a few pocs (aldrin and dieldrin). Concentrations of ddt and hch isomers found in blood, adipose (fat) tissues and breast milk in India are often between 10 and 100 times higher than those found in inhabitants of Europe or the us. Concentrations of pcbs in the blood are usually higher in individuals in Western nations as compared to those in tropical areas. Recent studies, however, indicate the presence of high concentrations of pcbs in blood samples of subjects residing in Bombay.

Though a number of studies report high concentrations of pocs in the biosphere, until now few studies have been conducted in developing countries to assess the adverse effects on ecosystems and human health, as the seriousness of the pesticides issue has not yet been given due importance in these areas.

One study observed the reproductive performance of 1016 couples, in which the males were occupationally exposed to pesticides. Compared to a control group of 1020 couples with similar social backgrounds, the study demonstrated a significant decrease in male fertility and a significant increase in abortions among wives of the exposed group. The frequency of live births decreased significantly and still-births, neonatal deaths and congenital effects showed a significant increase in the offspring of exposed males. Eighty percent of males in the exposed group showed ill-health effects. The study did not link these effects to a particular group of pesticides, since these workers were exposed to a large variety of them.

Studies conducted in 26 different countries between 1977 and 1993 revealed that the mean values of total pcbs exceeded the proposed who/fao recommendations. Mean concentrations for technical hch and technical ddt in breast milk in a variety of countries are also high, that a substantial percentage of the samples has most likely exceeded the adi recommendations (Turkey, Poland, Israel, France). (see table: Milk of human unkindness)

The results demonstrate that exposure and body burden in 'source' countries is generally higher than countries where these components are sparsely used or no longer used. This applies for tddt and thch in the tropical regions and for pcbs in the industrialised countries.

Studies to determine the toxicological aspects of several pocs have led to fresh insights, which may be sufficient to re-evaluate the existing norms and recommendations for these components.

ddt and its metabolites have been considered moderately toxic. At high concentrations, laboratory animals show liver damage (cell death), chemical changes in the heart muscles, adverse effects on the outer layer of the adrenal gland, thyroid and reproductive system.

Several estrogenic compounds have the potential of causing cancer in the genital tract of the elderly, and permanent effects have been reported to female offspring in relation to in utero (inside the uterus) exposure to estrogenic compounds. In the us, a correlation is suggested between the introduction of pocs and the increased rates of breast cancer by 57 per cent from 1950 to 1988. ddt accumulates in breast tumors, rather than in the adjacent healthy breast tissue.

A large study, involving 14,290 females was conducted in the us between 1985 and 1991. The presence of ddt in blood at levels between 2.0 and 19.1 nanogrammes/millilitre (ng/ml) showed a fourfold increase in the risk for breast cancer. In many countries, levels of POCs found in human blood are within this range or above.

A number of studies to establish serum ddt levels in India and Pakistan report mean dde concentrations of 870 ng/ml in Delhi, 37.3 ng/ml in Ahmedabad (rural India) and 8.6 ng/ml in rural areas of Baluchistan, Pakistan. Even in Germany, the mean ddt blood concentration of 135 residents living near the Elb river in Schleswig-Holstein was 5.7 ng/ml. Other communities in northern Germany showed mean blood ddt concentrations of 2.4 ng/ml.

pcbs are very well studied with respect to their toxicological effects. The reported effects include body weight loss, thymic atrophy, dermal disorder, hepatic damage, congenital malformations, reproductive toxicity and immunotoxicity.