Submitted to: Society of Environmental Toxicology and Chemistry Abstracts
Publication Type: Abstract only
Publication Acceptance Date: 11/15/1999
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: Chlorpyrifos is the most heavily used insecticide within the Chesapeake Bay watershed. A major transformation pathway controlling the fate of organophosphate compounds in the environment is hydrolysis. However, little is known of the actual degradation rates of chlorpyrifos under cpnditions found in the Chesapeake Bay. Natural water samples from representative sites in the Chesapeake Bay main stem were fortified with chlorpyrifos to determine hydrolysis rates under various natural conditions. Hydrolysis rates were analyzed as a function of salinity, pH, and concentrations of suspended particles, dissolved metals, total particulate carbon, and dissolved organic carbon (DOC) for determination of the dominant factors affecting the hydrolysis rate. Chlorpyrifos hydrolysis rates at 21 deg. C. in water samples from representative sites in Chesapeake mainstem were 0.0055, 0.0284, 0.0114, 0.0262, and 0.0151 day-1 for the Susquehanna, Choptank, Patuxent, and Pocomoke Rivers, respectively, which correspond to a half-life value of 126 days, 56 days, 24 days, and 27 days. Results indicated that chlorpyrifos decomposed primarily by base catalyzed hydrolysis to yield one major product, 3,5,6-trichloro-2 pyridonol (TCP). Copper catalysis was the dominant mechanism in chlorpyrifos hydrolysis under natural water conditions. A multiple-variable regression model was generated and yielded a significant correlation (r2 + 0.0994, t1/2 (day) = 3.30 x 105 x total Cu (mmo1/L) + 59.4 x pH - 293 at 21 deg. C). However more experimental data is needed for validation of the model in the future. This study will provide the first hydrolysis rate information for chlorpyrifos specifically in Chesapeake Bay waters, which is essential for understanding its fate in this important estuary.