Submitted to: Archives of Environmental Toxicology and Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 30, 2002
Publication Date: N/A
Interpretive Summary: Understanding pesticide dissipation and loss processes from agricultural systems is important to ensure minimal exposure to native fauna in nearby enclosed ponds. Studies were conducted to follow dissipation processes of pesticides and exposure effects on larval amphibian in model laboratory and outdoor pond systems. Several concentrations of the herbicides atrazine and metolachlor and the insecticide chlorpyrifos were examined. Chlorpyrifos disappearance was rapid in all of the systems. No appreciable losses were apparent for either herbicide at high concentrations aquaria treatment. Some herbicide loss degradation was observed when using lower concentrations. The corresponding degradation products were observed. This information will be combined with the subsequent amphibian exposure studies. Together these studies will be used as inputs for establishing guidelines for total maximum daily loads (TMDLs) of commonly-used pesticides.
The work presented is phase I of a study to determine the toxic effects of a combination of commonly-used pesticides (atrazine, metolachlor, and chlorpyrifos) on amphibians that are likely to inhabit farm ponds. Dissipation processes are described for model laboratory and outdoor pond systems. Pesticide applications ranged from 2 and 2.5 ppm to 0.2 and 0.25 ppm, respectively, for atrazine and metolachlor. Chlorpyrifos was applied at 0.1 ppm in the outdoor macrocosms and 1.0 and 0.1 ppm in the aquaria. The herbicide was applied four weeks prior to the insecticide application to replicate conditions often encountered under field situations. Chlorpyrifos disappearance was rapid in all of the systems and followed a two phase sequence. Initial half-life values varied from 0.16 day to 0.36 days. A slower second phase loss pattern was observed except for one of the low herbicide treatments (1.86 day), while all the others were 17.6 to 27.4 days. For the herbicide dissipation studies, no appreciable loss was apparent even after one month for either herbicide in the high aquaria treatment. The half- life values for the lower herbicide aguaria treatments was 29.9 d and 13.7 d, respectively, for atrazine and metolachlor, and for the high herbicide treated pond these respective values were 48.4 and 28.8 days. Low levels of the degradation product of atrazine, CIAT and CEAT, were observed.