|Kanissery, Ramdas Gopinath|
Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 8/10/2012
Publication Date: 8/10/2012
Citation: Sims, G.K., Kanissery, R. 2012. Transformation of herbicides under transient anoxia. In: Casteneda, S.F., Emerson, M.L., editors. Xenobiotics: New Research. Hauppauge, New York: Nova Science Publishers. p. 67-84. Interpretive Summary:
Technical Abstract: Resurgence in the use of soil-applied residual herbicides to augment performance of failing post-emergence herbicides has predictably reignited concerns over potential offsite movement, carryover damage onsite, or potential herbicide failure due to accelerated degradation. Many of the key processes in herbicide fate are relatively well-described, however, the bulk of our knowledge of herbicide transformation in soil is based on assumed aerobic conditions, which leaves gaps in our understanding of events taking place during transient saturation. Many areas of agricultural production are vulnerable to periodic flooding, which results in slower O2 replenishment, and thus promotes local anoxia. Variation in water content through its extremes modulates the bioavailability of substrates to microorganisms, as well as the dominant types of organisms and their associated activities (due to fluctuation of redox regime). Most information about anaerobic processes of herbicide degradation in soil has been derived from experiments performed under long-term submersion, however some studies have demonstrated significant impact of even transient soil saturation on herbicide degradation. A thorough analysis of available data is needed not only to address the current frequency of soil saturation events, but also anticipated changes in water regime as global climates shift. For example, in the American Midwest, projected changes in rainfall patterns are expected to have profound influence on soil water status and variability. Herein, we review literature available on herbicide fate processes as a function of soil water regime, including transient flooding. Examples are presented of herbicides undergoing degradation under denitrifying and iron-reducing conditions, which are most likely to be encountered under transient flooding. New findings are presented for reductive dehalogenation and potential for this process under transient flooding. Also described are water effects on the ecology and activities of herbicide-degrading microorganisms, as well as recent advancements in methodology available to address unanswered research questions in this area.