Long-term hazards of exposure to chemicals

Most tests of chemical products, especially drugs and foodstuffs, are based on short-term effects, especially the LD-50 test which determines the amount of a substance fed to a test group of animals which will cause 50% of them to die within a given length of time (usually measured in days or weeks). Such short-term data is then used to set legal standards covering long-term exposure to lower levels of the chemical.

Exposure to chemical agents in the environment - in air, water, food and soil - has been implicated in numerous adverse effects on humans from cancer to birth defects. The 'old' poisons, such as lead and mercury, some industrial solvents and some pesticides, are still of concern in many parts of the world but there is a reasonable level of understanding of their effects and the measures needed to protect human health and the environment from them (although such measures are not always adequately implemented). There is far less knowledge about the toxicological effects of a number of new chemicals coming onto the market. These may be present in household products, cosmetics and even pharmaceuticals.

There is particular and growing concern about the threats that chemicals pose to children's health. The main problems include both acute exposure leading to poisoning and chronic, low-level exposures causing functional and organic damage during periods of special vulnerability, when neurological, enzymatic, metabolic and other systems are still developing. Exposure of unborn children to toxic chemicals may produce irreversible effects. For example, low levels of mercury have severe effects on the foetuses of pregnant mothers who ingest contaminated food. Recent research suggests that these chemicals may affect the ability of children to learn, integrate socially, fend off disease and reproduce (Colborn 1997).

Of the 80,000 pesticides and other chemicals in use today, 10 percent are recognized as carcinogens. Cancer-related deaths in the USA increased from 331,000 in 1970 to 521,000 in 1992, with as estimated 30,000 deaths attributed to chemical exposure.