Toxicity evaluation of diazinon contaminated leaf litter.

Diazinon (O,O-diethyl O-[2-isopropyl-6-methyl-4pyrimidinyl] phosphothiate) is an organophosphate pesticide with widespread use on a variety of agricultural crops, such as fruit trees, corn, and tobacco (Burkepile et al., 2000). Approximately 6 million kg of diazinon are applied annually in the United States and, as a result, are a potential contributer to nonpoint source contamination of aquatic environments (Banks et al., 2003). Within these aquatic environments, decaying plant materials and leaf litter can be a prominent physical feature, especially during autumn (Webster and Benfield, 1986; Federle and Ventullo, 1990). These materials have extensive surface areas conducive to sorption of soluble organic contaminants (Pierce et al., 1977). This allows for the potential entry of these compounds into detrital food webs (Odum and Drifmeyer, 1978) resulting in potential effects on aquatic ecosystems (Forrow and Maltby, 2000). Despite the extensive presence of detrital material within some aquatic systems, such as wetlands, marshes, small streams, and heavily canopied rivers, ponds, and lakes, limited research or information exists on the influence of pesticide-contaminated detritus on aquatic ecosystems (Odum et al., 1969; Swift et al., 1988; Harrahy et al., 1994). With increasing use of constructed wetlands to mitigate nonpoint source contamination, there is a growing need to assess the role of detritus in understanding the fate and effects of various contaminants on nontarget aquatic organisms. This study presents an assessment of leaf litter contamination in a constucted wetland and a toxicity evaluation using a standard laboratory bioassay with the freshwater test organism, Hyalella azteca Saussure.