Pesticides may challenge human immunity.

Many popular pesticides appear capable of compromising the body's ability to fight infection, an extensive study finds. If true, pesticide use "could be a hidden killer"-especially in developing countries, "where infections are a leading cause of death," says Robert Repetto, vice president of the Washington, D.C.-based World Resources Institute (WRI) and a coauthor of the new report.

Poor nutrition, bad sanitation, and inadequate instruction on how to use pesticides safely add to the vulnerability of farmworkers in these developing nations, he charges.

With colleague Sanjay S. Baliga, Repetto surveyed a broad range of scientific studies on the immunotoxicity of widely used pesticides-including organochlorines such as DDT, organophosphates such as malathion, and carbamates such as aldicarb. Though most of the studies tested laboratory animals, a few looked at the suppression of immunity in wildlife-such as harbor seals that had eaten Baltic herring tainted with high concentrations of organochlorines (SN: 7/2/94, p. 8).

The report also cites a host of studies from the former Soviet Union-one of the few regions where investigations have focused on pesticide-induced changes in human immunity. The WRI commissioned local scientists, such as Lyudmila Kovtyukh of the Academy of Sciences in Kishinev, Moldova (a republic between Romania and Ukraine), to track down and translate studies for English-speaking researchers.

One of Kovtyukh's reports found that water, soil, and many of the local crops around Kishinev carry pesticide residues exceeding what she calls "accepted standards." Children living in areas where pesticides had been most heavily applied experienced elevated rates of acute respiratory diseases (including pneumonia), skin disease, ear infections, tuberculosis, and dental caries. Adults also suffered from unusually high rates of infection. Scientists there documented suppressed T cells, white blood cells that help orchestrate or participate in immune defenses. The extent of T cell suppression corresponded to an individual's degree of pesticide exposure. The report also cites data from ongoing studies among Inuit children in the northern Hudson Bay area of Canada. Nursed on human milk laced with organochlorines, these children not only face a highly elevated risk of infection (SN: 2/12/94, p. 111), Repetto notes, but in some cases are so immunocompromised that they "can't be vaccinated, because they don't produce any antibodies."

Michael Luster, chief of toxicology at the National Institute for Occupational Safety and Health in Morgantown, W. Va., served as an adviser to the WRI team.

Although many of the cited studies were "weak," he says, the body of work overall certainly "raises a flag of concern."

Former Food and Drug Commissioner Donald Kennedy, now at Stanford University, believes the new study's major contribution is its weaving together of a host of disparate immunotoxicological studies with data on pesticide use "and the lack of care or instruction about that use that prevails in many developing countries." He told Science News, "I don't think the extent of this problem had been realized before-by anybody."

Other reports have linked pesticides to immune system problems, notes Albert Munson of the Medical College of Virginia in Richmond, but "this certainly is the most comprehensive one." It also highlights the social and educational factors that contribute to making this largely "a Third World problem," the immunotoxicologist says.

Munson contends that current U.S. requirements for testing the immunotoxicity of pesticides are essentially worthless. Repetto concludes that industrialized countries should require a stronger battery of such tests before they allow pesticides to be registered for use.

In fact, notes Sheryl Reilly of the Environmental Protection Agency in Arlington, Va., recommendations by Munson and other EPA advisors have already prompted the agency to begin drawing up new rules to do just that. She expects a proposal to be released this summer.