New research on health effects of pesticide exposure among agricultural workers

Matthew Keifer, Pacific Northwest Agricultural Safety and Health Center, University of Washington, Seattle, WA

Early pesticides, such as sulfur, arsenic, lead and copper were simple nonspecific toxins. Synthetic pesticides given to agriculture after WWII were still mechanistically general. Until recent advances resulted in chemicals targeting pest-specific susceptibilities, only the relative size of humans saved us from the same fate as the target pests.
Most early pesticide health effect studies focused on the epidemiology of acute poisonings, though the potential for long-term effects was recognized early and addressed in some studies. Many potential long-term changes, such as neurobehavioral, teratogenic, carcinogenic and psychiatric effects, were eventually addressed through study designs ranging from ecological to case-control. Numerous concerns, including endocrine disruption, chronic neurological effects, immunological impacts, and neurodevelopmental changes in children, call for creative technology and study designs.

Pesticide exposure and occupational health, in general, often don’t receive the same level of funding support as many non-occupational diseases, the U.S. Agricultural Health Study being a rare exception. However, nested case-control designs using large cohorts collected for other reasons may provide unique opportunities for pesticide health effects research. Participation in the early design phases of these studies is important to assure that the data being collected will be of use to investigators.

Pesticide health effects research demands a multidisciplinary approach. We will now include tools such as microarray technology, proteomics, and polymerase chain reaction to strengthen our epidemiological insight. These recent technical advances can provide markers of exposure, susceptibility, and effect, and will complement (and at times complicate) the basic tools of epidemiology. The critical weakness and the greatest challenge in long-term studies of pesticide health effects continues to be the characterization of long-term low-level and long past exposures. To date, new technology has not yet addressed this challenge.

We continue to deal with the old and the new. We ask “what have we done” in characterizing the effects of the ubiquitous residuals of past organochlorine excesses. The health effects of combined exposures remain a substantial, unresolved challenge. In developing countries, where the majority of pesticide-related health effects are suffered, the oldest, most dangerous chemicals remain in use. In contrast, the developed countries will see the first health effects of the newer “safer” pesticides. These new chemicals, with presumably pest-specific biological effects, may have unforeseen consequences on human health. In addition, the older cholinesterase inhibiting pesticides, which overlap mechanistically with war gasses, will continue to receive attention on a global level as nations unite to battle terrorism.

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