Development Of Risk Assessment Techniques For Soil Bioavailability And Bioaccumulation Of An Organophosphorus Pesticide

There is increased concern about the effects of organophosphorus (OP) pesticides on human and animal health. This class of chemicals has been shown to affect the immune function of macrophages and lymphocytes. Malathion, an OP compound, is one of the most widely used pesticides, applied to the environment at an annual rate of 4,486,000 in the US alone. While the most studied toxic effect of malathion is on cholinesterase in the nervous system, only a few studies have been conduced on its toxic effect on the immune system. A 1984 study observed that human occupationally exposed to OP compounds have marked impairment of neutrophil chemotaxis. These workers also had increased frequency of upper respiratory infections proportionate to the number of years of exposure to organophosphorus compounds. A 1983 study demonstrated a dose-response relationship to malathion induced chromosomal aberrations in mouse bone-marrow cells. A model was recently published in 1999 that demonstrated increased infectious disease susceptibility and mortality in amphibians externally exposed to field doses of an organophosphorus pesticide. Amphibians were selected as the model species for investigation because they are considered highly sensitive, environmental health indicator species that inhabit the aquatic and terrestrial interfaces. This research showed an increased susceptibility to bacterial infection in amphibians following pesticide exposure, strongly suggesting an effect on immune suppression that could correlate with reported effects in humans. This work demonstrates the need to integrate human and wildlife health research and models to better assess potential ecological risks, as some wildlife species may show effects that could be more subtle or later occurring in humans. It also shows the need for bioaccumulation and bioavailability studies to develop risk assessment techniques in this area. The objective of this project is to develop ecological risk assessment techniques for wildlife species to evaluate the soil bioavailability, bioaccumulation, and toxicity of organophosphorus pesticides.

Impact/Purpose

The objective of this project is to develop ecological risk assessment techniques for wildlife species to evaluate the soil bioavailability, bioaccumulation, and toxicity of organophosphorus pesticides. This research contains multiple phases including: 1) to determine the level of bioaccumulation of the organophosphorus pesticide, malathion, that may occur in earthworm from the exposed soil; 2) to determine the bioaccumulation of the organophosphorus pesticide, malathion in a secondary food chain consumer, the salamanders; 3) To assess behavioral changes in daily patterns (i.e. movement, burrowing. feeding); and 4) To assess survivability of these exposed species; and 5) To diagnostically assess and document any detectable effects on these species through pathology (gross and histopatholgy, electron microscopy, body and organ weights) and toxicology (cholinesterase levels, liver to body weight ratios).

Citation

U.S. EPA. Development Of Risk Assessment Techniques For Soil Bioavailability And Bioaccumulation Of An Organophosphorus Pesticide.