Pesticides and the immune system

Robert Repetto presents evidence from his recent book Pesticides and the Immune System, which reveals potential health risks from pesticides. He discusses the possibility that exposure to pesticides at work and in the diet increases susceptibility to infectious diseases and certain cancers by suppressing the body's normal immune functions.

Exposure to pesticides can result in acute poisonings, birth defects, and some types of cancer. Now, scores of experimental and epidemiological studies have added immuno-toxicity to this list of health risks.
    More than a hundred experimental studies using accepted tests have shown that many widely used insecticides, herbicides and fungicides can alter the immune system and suppress normal immune system responses. These changes can reduce the body's normal resistance to bacterial, viral and other infections. Careful studies of diets of contaminated fish lead toward the same conclusion.
    What evidence there is from the few epidemiological studies of people exposed to pesticides reinforces these concerns. For example, farmworkers in the former Soviet Union, where pesticides were used heavily, showed immune system abnormalities and increased rates of infectious and chronic disease compared to people living away from districts of heavy pesticide use. Filipino rice farmers experienced rising mortality rates when pesticide use increased, although their wives and non-farming neighbours did not.
    In Northern Canada, native Americans eat mainly fish and other products in which organochlorine pesticides can accumulate. Their babies then take in these chemicals when breast feeding. It has been found that such babies show immune system deficiencies and higher rates of infectious disease compared to bottle-fed babies. Many such babies cannot even be vaccinated, since they do not produce sufficient antibodies.
    Though intensive, pesticide use is levelling off in OECD countries, but it is still increasing elsewhere. In Latin America, for example, pesticide use has almost tripled in the last 20 years, and is expected to continue rising as production of fruits, vegetables, and other commercial crops expands.
    Asia, whose rice crop alone accounts for 14% of global pesticide use, also represents a growing market. Scarce farmland and economic pressures to boost agricultural production have resulted in heavy chemical use to push up yields. After Japan, China and India are the largest Asian users. Despite substantial research in China on biological pest control methods, pesticide production more than doubled over the past decade to nearly 300,000 tons per year of active ingredient.
    Economic disruption in Central Europe and the former Soviet Union have led to a relative decline in pesticide use. Nonetheless pesticide consumption remains high in many regions. In 1994, roughly 80,000 tons of active ingredient were applied. Many of the pesticides that are still used in these areas have been banned or restricted in OECD countries and replaced by compounds that breakdown more quickly and can be applied in lower doses.
    Much can also be done to reduce unnecessary exposures. Farmworkers are often exposed by using inadequate equipment or by handling pesticides carelessly while mixing, loading or spraying chemicals. Other people are exposed by being near fields while spraying is underway, or soon afterwards. Even children are exposed when pesticide containers are stored improperly around the house or thrown away carelessly, or when food is not washed thoroughly before it is eaten. A recent study in Nicaragua, for example, found that 40% of farm children had lowered cholinesterase activity, one measure of organophosphate pesticide poisoning.
    The highest potential health risks from pesticide immunotoxicity arise in countries where much of the population still lives in rural areas and works in agriculture, where infectious and parasitic diseases are widespread, and where the coverage of the health services for rural people is incomplete. Malnutrition suppresses normal immunity, making affected people more susceptible to the consequences of immune suppression if exposed to pesticides. These conditions are widespread throughout many parts of the world.
    There is enough evidence linking pesticide exposure to immune system suppression in laboratory animals, wildlife and humans to justify much more comprehensive studies to clarify the risks. Along with further experimental research, more extensive epidemiological studies designed specifically to test for the immuno-suppressive effects of pesticides on vulnerable populations are needed. Such studies should be led by the World Health Organisation.
    Multilateral and bilateral aid agencies should support such research and expand efforts to improve pest management practices. Development assistance has been heavily invested in water supply, sanitation, and primary health care systems around the world to reduce the incidence of infectious diseases. Complementary programmes to eliminate environmental threats to the immune system could be a cost-effective method to insure the success of these on-going efforts. Pesticides now on the market should be tested much more thoroughly for their effects on the immune system. Testing requirements in most countries have not kept pace with advances in immunologic knowledge and technique.
    The over-riding concern, however, is public health. Infectious diseases account for most deaths in developing countries. If pesticides can weaken the immune system, then mortality rates from common infectious diseases may be much higher than need be but the added risks stemming from chemical exposure could easily remain undetected. Current knowledge warrants new research programmes and precautionary actions.

Robert Repetto and Sanjay S. Baliga, Pesticides and the immune system: the public health risks, WRI Publications, PO Box 4852, Hampden Station, Baltimore, MD 21211, US, Tel. +1 410 516 6963, Fax +1 410 516 6998.

Robert Repetto is the Vice President of World Resources Institute, Washington DC, US.