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ARS Home » Midwest Area » St. Paul, Minnesota » Soil and Water Management Research » Research » Publications at this Location » Publication #284509
Title: Acetochlor persistence in surface and subsurface soil samples

Author
item OLIVEIRA, RUBEM - University Of Maringa
item Koskinen, William
item GRAFF, CARRIE - University Of Minnesota
item ANDERSON, JAMES - University Of Minnesota
item MULLA, DAVID - University Of Minnesota
item NATER, EDWARD - University Of Minnesota

Submitted to: Water, Air, and Soil Pollution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/10/2013
Publication Date: 9/13/2013
Citation: Oliveira, R.S., Koskinen, W.C., Graff, C.D., Anderson, J.L., Mulla, D.J., Nater, E.A. 2013. Acetochlor persistence in surface and subsurface soil samples. Water Air And Soil Pollution. DOI: 10.1007/s11270-013-1747-2.

Interpretive Summary: Although degradation data for herbicides are essential in understanding their potential to be environmental contaminants and are indispensable inputs in computer-based modeling of the herbicides’ fate in the environment, most available data only concern laboratory studies and surface soils. The purpose of this study was to determine whether limited laboratory degradation studies can adequately represent variability in herbicide dissipation within a field or small watershed with varying physical and chemical soil properties. The herbicide acetochlor was chosen for this research due to its wide-spread use in agriculture. Soil samples, collected at two depths from four representative sites of a 31.4-ha field located in Blue Earth County, MN, were used to determine acetochlor dissipation under laboratory conditions. A field study was also carried out within a 16-ha watershed in Dakota County, MN in which 38 locations were sampled to obtain soil samples representative of the full range of soil properties found within the watershed. Acetochlor was applied for two consecutive years at 2.2 kg ha-1 and soil samples were collected and extracted periodically after herbicide spraying. In laboratory studies, time for 50% dissipation (DT50) ranged from 6.5 to 14 d in surface and from 20 to 27 d in subsurface samples. Field surface soil DT50 values for acetochlor dissipation were not significantly different for the two years, 5.7 and 7.7d. Although was slightly faster in the field as compared to the laboratory, the difference seems insignificant in view of the wide range in physical and chemical properties of soils in Minnesota. In both studies, acetochlor would be classified as slightly persistent. These data show that for acetochlor, laboratory dissipation studies can be representative of field dissipation. In both studies, acetochlor would be classified as slightly persistent. Also, inclusion of subsoil degradation data in mathematical models used for ground water risk assessment may significantly improve scientists’ and regulatory agencies’ capability to predict fate of acetochlor in soil and potential movement to ground water.

Technical Abstract: Although degradation data for herbicides are essential in understanding their potential to be environmental contaminants and are indispensable inputs in computer-based modeling of the herbicides’ fate in the environment, most available data only concern surface soils. Soil samples, collected at two depths from four representative sites of a 31.4-ha field located in Blue Earth County, MN, were used to determine acetochlor dissipation under laboratory conditions. A field study was also carried out within a 16-ha watershed in Dakota County, MN in which 38 locations were sampled to obtain soil samples representative of the full range of soil properties found within the watershed. Acetochlor was applied for two consecutive years at 2.2 kg ha-1 and soil samples were collected and extracted periodically after herbicide spraying. A bi-exponential decay model described acetochlor degradation. On average, dissipation of acetochlor in the first phase decreased by a factor of ~ 3 when soil samples were collected from depth 0.6-0.9 m, as compared to surface soil samples. For the second phase, dissipation rates were almost negligible for surface soil samples and ranged from negligible to 0.0375 for subsurface samples. DT50 ranged from 6.51 to 13.9 d in surface and from 20.3 to 26.7 d in subsurface samples. Variation by a factor of ~ 2 was also consistently found when DT50, DT75 and DT90 values for subsoil samples were compared to those found for surface samples. Field DT50 values for acetochlor dissipation were not significantly different for the two years, 5.7±2.5 and 7.7±4.5 d. For both years at all locations, DT50 values ranged from 2.9 to 12.6 d. Dissipation was slightly faster in the field (DT50 = 7 d; DT50 range = 2.9-12.6 d) as compared to the laboratory (DT50 = 11 d; DT50 range = 6.5-13.9 d), however the difference seems insignificant in view of the wide range in physical and chemical properties of soils in Minnesota. In both studies, acetochlor would be classified as slightly persistent. For acetochlor, laboratory dissipation studies can be considered representative of field dissipation. Also, inclusion of subsoil degradation data in mathematical models used for ground water risk assessment may significantly improve their capability of predict fate of acetochlor in soil and potential movement to ground water.