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ARS Home » Research » Publications at this Location » Publication #61767
Title: PERSISTENCE OF SEVEN PESTICIDES AS INFLUENCED BY SOIL MOISTURE

Author
item MOJASEVIC, MILICA - UNIV BELGRADE, YUGOSLAVIA
item Helling, Charles
item Gish, Timothy
item Doherty, Michael

Submitted to: Journal of Environmental Science and Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/4/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Predicting pesticide fate in soil requires knowledge of key processes such as degradation. An important parameter, soil moisture content, may affect degradation rates differentially, but rarely is this problem approached with a large matrix of applied pesticides. In this study, field results were compared with the same seven co-applied pesticides, laboratory-incubated at three moisture levels which encompassed the field extremes. All were adequately modeled by first-order kinetics, but some pesticides (especially triazines atrazine and cyanazine) were relatively insensitive to moisture changes equivalent to ca. 0.3-1 X field moisture capacity. The increasing order of soil persistence was carbofuran, cyanazine, metribuzin, alachlor, atrazine, ethoprop, and metolachlor. These results will be useful to scientists and regulators concerned with improved prediction of persistence and transport of pesticides in the soil environment.

Technical Abstract: Pesticides are often applied in combination, but their soil persistence is less often measured in this way. The present field and laboratory study determined relative persistence of five herbicides and two insecticides, co-applied, as a function of three soil water contents. Losses were modeled adequately by first-order dissipation, with no significant improvement by using a two-compartment model. The order of persistence in a silt loam, at 25% moisture, was carbofuran < cyanazine < metribuzin = alachlor < atrazine < ethoprop < metolachlor (t1/2 ranged from 7-91 days). Carbofuran degradation increased greatly from 12-25% soil moisture; atrazine was unaffected by 12-35%, whereas the remaining compounds showed limited increasing loss in wetter soil. Field-based persistence was more variable, but generally similar to lab rankings.