MP5 Agrochemicals and Pesticides
Monday, 14 November 2005: 8:00 AM - 5:30 PM in Exhibit Hall

(HAL-1117-712231) Effects of Dissolved Organic Material on the Fate of Selected Pesticides.

Haley, M¹, Davis, E¹, Anthony, J¹, Wershaw, R², Leenheer, J², Cox, L², ¹ U.S. Army, Edgewood Chemical Biological Center, Aberdeen Proving Ground, MD, USA² U.S. Geological Survey, National Research Program, Denver, CO, 80225

ABSTRACT- The persistence of Dicrotophos, Dichlorvos and Mevinphos in natural water is documented, however the effects on hydrolysis rates from potential catalysts in natural water, and the identification of subsequently generated degradation products are limited. Open literature suggests that dissolved organic carbon (DOC) substantially influence the degradation rates of pesticides. Many half-life determinations for organophosphorous compounds have been conducted in river and pond waters, however those waters were not well characterized. Thus the effects from DOC cannot be fully determined without additional water analysis. In this study, the half-life of selected pesticides was determined in distilled water, and a natural water from the Neversink Reservoir which is part of the New York City water supply. In addition to natural Neversink water, we treated subsamples with granular activated carbon (GAC) to reduced the DOC by 60%. These waters were used in fate studies to determine the effects of DOC on the degradation rates of the pesticides Dicrotophos, Dichlorvos, and Mevinphos. All the studies were conducted in darkness at room temperature. The initial concentration of pesticides was 100 mg/L, and the waters were analyzed using an Agilent 1100 Series HPLC. It was shown that in all waters tested, Dichlorvos degraded the quickest, followed by Mevinphos, and then Dicrotophos. The degradation rates of pesticides were determined both in buffered non-buffered (none added) water, and those maintained at a pH of 6.2 were degraded substantially faster than in non-buffered waters. The 60% reduction in DOC did not affect the degradation rates of the pesticides.

Key words: organophosphate pesticides, half-life, natural waters, DOC