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Title: TOXICITY OF CHLORPYRIFOS ADSORBED ON HUMIC COLLOIDS TO LARVAL WALLEYE

Author
item PHILLIPS, TODD - IOWA STATE UNIVERSITY
item SUMMERFELT, ROBERT - IOWA STATE UNIVERSITY
item WU, JIGANG - IOWA STATE UNIVERSITY
item LAIRD, DAVID

Submitted to: Environmental Toxicology and Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2003
Publication Date: 8/4/2003
Citation: Phillips, T.A., Summerfelt, R.C., Wu, J., Laird, D.A. 2003. Toxicity of chlorpyrifos adsorbed on humic colloids to larval walleye. Environmental Toxicology and Chemistry. 45(2):258-263.

Interpretive Summary: Most agricultural chemicals are not particularly toxic to fish and other aquatic organisms, however these organisms are very sensitive to organophosphorous (Ops) insecticides which are widely used in agriculture to control insect pests. The Ops are very strongly adsorbed on soil particles and therefore once the Ops get into the soil they are believed to be no longer toxic. However, if a rain storm causes soil to erode from a field that was recently treated with Ops it is possible that the Ops could be transported with the eroded soil to a river or lake. We studied an OP known as Chlorpyrifos and discovered that when it is tightly bound to organic matter particles that are suspended in water that it is still toxic to very young walleye (1 to 16 days old). This study is important to farmers, environmentalists, the sport fishing industry, and regulatory agencies because the results demonstrate that contaminants adsorbed on suspended sediment can still be toxic and therefore should be considered when evaluating water quality.

Technical Abstract: After application, organophosphorus insecticides (Ops) are often strongly adsorbed to soil constituents. Because of their relatively low water solubility, Ops may be transferred from field to stream adsorbed on suspended solids. However, we are not aware of research done to evaluate the bioavailability (i.e. toxicity) of Ops transported on suspended solids to aquatic organisms. We conducted 48-h static toxicity tests to determine the toxicity of chlorpyrifos in aqueous solutions and adsorbed on calcium-saturated humic acid (HA) to three larval stages of walleye (Stizostedion vitreum). Three concentrations of chlorpyrifos adsorbed on HA, a HA control, and a chlorpyrifos-only treatment were tested. Fish that survived the 48-h static toxicity tests were analyzed to determine total cholinesterase (ChE) activity. Survival of all larval stages of walleye exposed to chlorpyrifos-HA complexes was less than that of walleye exposed to HA controls, which were non-toxic to walleye. Cholinesterase inhibition of larval walleye exposed to chlorpyrifos-HA complexes were similar to the ChE inhibition observed in larval walleye exposed to chlorpyrifos in the aqueous phase. These laboratory experiments indicate potential toxicity of chlorpyrifos-soil complexes to larval fish.