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Title:Bioavailability of metolachlor and glyphosate in aerobic and anaerobic soils
Author(s):Kanissery, Ramdas
Director of Research:Sims, Gerald K.
Doctoral Committee Chair(s):Kent, Angela D.
Doctoral Committee Member(s):Sims, Gerald K.; Metcalf, William W.; Yannarell, Anthony C.
Department / Program:Natural Res & Env Sci
Discipline:Natural Res & Env Sciences
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):Metolachlor
Glyphosate
Herbicide
Bioavailability
Aerobic Soil
Anaerobic Soil
Adsorption
Degradation
Mineralization
Stable Isotope Probing
Abstract:Metolachlor and glyphosate are two extensively used herbicides in the USA and throughout the globe. Despite the prevalence of anaerobic wet situations in the soil, the predictive capability for the environmental fate and bioavailability of these herbicides is based primarily on well-drained soil conditions. Anoxic events and flooding ubiquitous to agroecosystems may pose a threat for persistence and transport or conversely may facilitate herbicide degradation. This study was undertaken to explore the knowledge gap in the microbial bioavailability and degradation of metolachlor and glyphosate in aerobic and anaerobic soil conditions. Metolachlor retention pattern in the soils were significantly influenced by anaerobic conditions. Anaerobic soil incubations induced better degradation and mineralization of metolachlor in the range of soils evaluated, despite the differences in soil properties. The findings also confirmed the activity of microorganisms in the degradation and mineralization of metolachlor in the soils in spite differences in their soil properties and redox conditions. The anaerobic degradation and mineralization of metolachlor coincided with the iron (Fe) reducing conditions in soil namely Fe2+ formation and suggested a probable role of Fe in the microbial fate of metolachlor under such soil environmental conditions. Stable isotope probing (SIP) facilitated the identification of microorganisms responsible for the mineralization of metolachlor in aerobic and anaerobic soils. The 16S rRNA gene sequences of clones implied the role of organisms closely related to Bacillus spp. in aerobic and Acidobacteria in anaerobic mineralization of metolachlor in soils. Glyphosate also was influenced by soil redox conditions for bioavailability and mobility in soils. Contrary to metolachlor, the degradation and mineralization of glyphosate exhibited a slower kinetics in anaerobic soils compared to corresponding aerobic soils in all the soil types investigated. Glyphosate degradation was also deduced as a purely microbiological process as almost no degradation or mineralization occurred in sterile control soils. The addition of phosphate suppressed the adsorption of glyphosate in both aerobic and anaerobic soils and confirmed the widespread competition between glyphosate and phosphate for adsorption sites in soils. In summary, the results from this dissertation research clearly highlight the significance of aerobic versus anaerobic soil conditions as an important factor affecting the bioavailability of metolachlor and glyphosate in soils. The information generated from the current study could be applied towards efficacious use of metolachlor and glyphosate in soils and also for framing a viable strategy for the efficient clean-up of soils contaminated by these herbicides.
Issue Date:2014-05-30
URI:http://hdl.handle.net/2142/49688
Rights Information:Copyright 2014 Ramdas Kanissery
Date Available in IDEALS:2014-05-30
2016-09-22
Date Deposited:2014-05


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