Title: Potential for bioavailability to limit degradation of herbicides in unsaturated soils Author
Submitted to: Society of Environmental Toxicology and Chemistry Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: February 8, 2007
Publication Date: March 14, 2007
Citation: Sims, G.K. 2007. Potential for bioavailability to limit degradation of herbicides in unsaturated soils [abstract]. Society of Environmental Toxicology and Chemistry Abstracts. p. 5. Technical Abstract: It is well established that biodegradation of organic compounds in soils can be limited by bioavailability if sorption reduces the pool of material available in solution. Bioavailability can also affect herbicidal function, reported herein in the complex processes of activation and degradation of the herbicide, isoxaflutole. Also reported is the observation that some ionizable herbicides, notably some of the acetolactate synthase inhibitors, do not readily penetrate bacterial cells when the compounds are in an ionized form. Since the neutral form of an herbicide is often the form preferentially sorbed to the soil solid phase, pH conditions that promote permeability may simultaneously promote sorption and thus reduce bioavailability for such compounds. In unsaturated soils, a very small portion of the soil pore space is likely to be inhabited by organisms with the ability to degrade a particular herbicide structure, thus, biodegradation in such matrices is accompanied by movement (presumably by diffusion) of material to pore space inhabited by appropriate organisms. This concept is consistent with observations made when soils are incubated under a range of water regimes, and was demonstrated using differently mixed soil systems to produce contrasting scenarios in which a substrate (atrazine) was either in close proximity to the degraders or dispersed throughout the pore space. Though atrazine degradation can also be affected by nitrogen nutrition, our observations with an atrazine spill site in Illinois suggests that the compound was degraded rapidly despite accumulation of inorganic N from the degradation process, with the primary constraint on degradation appearing to be bioavailability. It is apparent from the weight of evidence that the role of bioavailability in function and environmental behavior of herbicides remains an area of research need.