ARS | Publication request: Investigation of Anaerobic Herbicide Degradation in Agricultural Soils

Submitted to: American Society for Microbiology Annual Meeting
Publication Type: Abstract
Publication Acceptance Date: February 16, 2007
Publication Date: May 21, 2007
Citation: Chee Sanford, J.C., Sanford, R.A., Davis, A.S., Williams, M. 2007. Investigation of Anaerobic Herbicide Degradation in Agricultural Soils [abstract]. American Society for Microbiology Annual Meeting. Paper No. Q-161.

Technical Abstract: Anaerobic microbial pesticide degradation has received little attention, particularly in agricultural soils that receive routine inputs of halogenated herbicides. Seasonal rainfall in many regions can produce zones of periodic anaerobiosis in soil. Redox gradients within soil aggregates can also form microhabitats where the occurrence of anaerobic microbial processes can affect agrochemical fate. Here, we investigated the anaerobic fate of 2,6-dichlorophenol (DCP), bromoxynil, 2,4-D, atrazine, and dicamba in soils from the midwestern U.S. These soils originated from agroecosystems that are distinctly different in soil textures and climate, but similar in commercial corn and soybean crop management. The soils ranged from highly porous, predominantly sand with low organic matter, to primarily silt loam soils with fairly poor drainage. In anaerobic soil slurry microcosms with acetate as the electron donor, dechlorination of 2,6-DCP (125 µM) to phenol occurred in all samples after one month of incubation. Bromoxynil (100 µM) was completely debrominated to cyanophenol by 94% of the soil microcosms. After three months, 2,4-D was significantly degraded in 56% of the soil microcosms, with accumulation of an unknown metabolite. Atrazine was not significantly degraded. Multidimensional scale plots using Bray-Curtis similarity values of bacterial populations calculated from terminal restriction fragment (TRF) analysis of the 16S rRNA genes demonstrated that bacterial populations at each agroecosystem site were distinctly different. The results indicate a range of soils possess the potential for anaerobic microbial herbicide degradation, with reductive dehalogenation processes likely to occur.