Impact of animal -derived lagoon effluents on the fate of chlorpyrifos and metabolites in soils
Abstract
The increased use of animal- derived effluents for irrigation warranted an investigation of the impact of swine-, poultry-, and cow-derived lagoon effluents on the field-applied insecticide chlorpyrifos (O'O-diethyl O-(3,5,6-trichloro-2-pyridyl)phosphorothioate). Such effluents are often high in pH, electrical conductivity, microbial activity, and dissolved organic matter (DOM). In this study, the effect of effluent application on sorption, transport, and transformation of chlorpyrifos and metabolites was investigated using batch and column techniques. All DOM from lagoon effluents were found to have a strong affinity for chlorpyrifos and weak sorption to soil, resulting in reduced chlorpyrifos sorption by soil and enhanced mobility in the presence of DOM. The decrease in apparent retardation factors correlated well with decreasing DOM polarity and increasing DOM concentrations. However, retardation of chlorpyrifos for all soil-effluent combinations was still very large, thus transport remains limited. For the 3,5,6-trichloro-2-pyridinol (TCP), an organic acid and the primary metabolite of chlorpyrifos degradation in soils, mobility was impacted as a function of effluent-induced changes in pH, TCP's acid dissociation constant, and soil and effluent buffer capacities. Bicarbonate was the main source of effluent alkalinity (>97%) and subsequently a good way to estimate alkalinity. Aerobic degradation of chlorpyrifos by microbes was observed; however, effluents appeared to have only a minor effect on chlorpyrifos degradation in soils. In soils, both biotic and abiotic degradation contributed significantly to the overall dissipation of chlorpyrifos, with degradation rates being very soil-dependent. Laboratory studies with chlorpyrifos and TCP indicated effluent irrigation may result in enhanced downward movement of pesticides in selected scenarios. However, adjustments in the time and amount of each effluent irrigation event as a function of soil and pesticide type can minimize or eliminate the potential for enhanced pesticide transport and subsequent groundwater contamination.
Degree
Ph.D.
Advisors
Lee, Purdue University.
Subject Area
Environmental science|Agronomy|Soil sciences
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.