Pesticides Attack Immune System

After reviewing hundreds of studies from around the world, the Washington-based World Resources Institute (WRI) says that pesticides' apparent threat to the human immune system represents a "potentially serious risk to public health," especially in developing countries and the former Soviet Union.

Hundreds of millions of farm workers, farm households, and consumers may be at risk, according to WRI's new study, "Pesticides and the Immune System," released on March 1. Children are especially susceptible, the report says.

"This issue is too important to ignore," says Robert Repetto, co-author of 103-page report. "A well-functioning immune system is essential to life."

The principal conclusion of the report is that pesticides could be what Repetto calls "a hidden killer." That is because the immediate cause of a victim's death is normally a common infectious disease. But, according to Repetto, the "underlying problem" may have been the damage done to the immune system by exposure to pesticides.

"We are calling on the World Health Organization (WHO) to spearhead a large-scale research program into links between pesticides and damage to the immune system, and on major pesticide companies, multilateral banks, and the WHO's member governments to finance this important public health campaign," he says.

Studies reviewed by the WRI researchers and an advisory panel of top U.S. toxicologists were of three kinds: laboratory tests on animals, wildlife studies and human epidemiological studies.

While no one study conclusively proves the link between pesticides and damage to the human immune system, "together, they give ample cause for concern," according to Repetto.

Hundreds of studies have shown that many pesticides alter the immune system in experimental animals and make them more susceptible to disease by reducing the number of white blood cells and lymphocytes which kill bacteria and viruses. They also alter the development of the thymus and spleen, important organs which are tied to the immune system.

Among those that have this effect are organochlorines, such as DDT and chlordane; organophosphates, such as malathion; and carbamates, such as carbofuran and carbaryl.

In central Moldovia, where pesticides have been used heavily, Soviet researchers found that 80 per cent of children in rural areas had abnormal immunity and were at least twice as likely to suffer from contagious digestive and respiratory diseases than the general population.

And among northern Canada's isolated Inuit communities, which consume mainly fish and marine mammals that are heavily contaminated with pesticides, children and breast-fed infants showed clear immune-system deficiencies. They suffered meningitis and infections of the inner ear at 30 times the rate of U.S. children, according to the report.

Exposure to pesticides may also have been responsible for recent die-offs of seals in Europe, dolphins in the Mediterranean, the North Sea and the North Atlantic, and of beluga whales in the St. Lawrence Seaway in Canada, according to the report.

While all of these marine mammals apparently succumbed to common viruses, their carcasses showed high levels of pesticide residues which may well have reduced their resistance.

In one controlled test, seal pups captured off Scotland were fed uncontaminated fish for one year, after which half were fed herring from the pesticide-polluted Baltic Sea.

Initially, according to the Dutch scientists who conducted the study, the Baltic group of seals refused to eat the herring, which were intended for human consumption. After consuming it for some time, however, their immune system response was found to be three times weaker than that of the control group.

While such studies have important implications for the United States, Western Europe and Japan -- which together consumed about 62 per cent of the global pesticide market last year -- the lessons for developing countries are much more serious, according to the report.

The fastest-growing markets for pesticides are in Latin America and Asia, and the shift to export crops in all developing countries virtually assures higher demand.

At the same time, most developing countries do not regulate pesticide use nearly as strictly as in developed countries. In fact, many pesticides which have been banned for use in rich nations continue to be exported and used by poor countries.

These factors, combined with a much higher incidence of malnutrition, a younger and more rural population, and inadequate public health programs, make developing countries far more vulnerable to the immunological threats posed by pesticides, according to the report.

To deal with these threats, the report calls for much stronger government control of pesticide use, especially in developing countries, and new requirements that pesticide products be tested for immuno-toxicity before going on the market.

The WHO should take the lead in new research to address the link between pesticides and the human immune system the costs of which should be underwritten by the pesticide companies.

Multilateral development banks, like the World Bank, should also provide more support for integrated pest management systems, which reduce the need for pesticides, and to increase lending for water supply, sanitation and primary health care systems in developing countries.