Potential uses of biomonitoring data: a case study using the organophosphorus pesticides chlorpyrifos and malathion

Abstract

Background: Organophosphorus pesticides such as chlorpyrifos and malathion are widely used insecticides. They do not bioaccumulate appreciably in humans and are rapidly metabolized and excreted in the urine. In nonoccupational settings, exposures to these pesticides are typically sporadic and short-lived because the pesticides tend to degrade in the environment over time; however, dietary exposures may be more chronic. Biologic monitoring has been widely used to assess exposures, susceptibility, and effects of chlorpyrifos and malathion; thus, the information base on these compounds is data rich. For biomonitoring of exposure, chlorpyrifos and malathion have been measured in blood, but most typically their urinary metabolites have been measured. For assessing early effects and susceptibility, cholinesterase and microsomal esterase activities, respectively, have been measured.

Objectives: Although many biologic monitoring data have been generated and published on these chemicals, their interpretation is not straightforward. For example, exposure to environmental degradates of chlorpyrifos and malathion may potentially increase f urinary metabolite levels, thus leading to overestimation of exposure. Also, the temporal nature of the exposures makes the evaluation of both exposure and effects difficult. We present an overview of the current biomonitoring and other relevant data available on exposure to chlorpyrifos and malathion and the use of these data in various environmental public health applications.

Figure 1

The structures of chlorpyrifos and malathion.

Figure 2

General metabolism and degradation of OP pesticides, where X = S or O, R₁ is typically CH₃ or CH₂CH₃, and R₂ is an organic moiety unique to the pesticide or pesticide pair. Additionally, side chains (R₂) with labile functional groups such as esters may hydrolyze to form carboxylic acid metabolites.