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Title: TRIFLURALIN DEGRADATION UNDER MICROBIOLOGICALLY INDUCED NITRATE AND FE(III)REDUCING CONDITIONS

Author
item TOR, JASON - UNIV OF ILLINOIS
item XU, CAIFEN - UNIV OF ILLINOIS
item STUCKI, JOSEPH - UNIV OF ILLINOIS
item WANDER, MICHELLE - UNIV OF ILLINOIS
item Sims, Gerald

Submitted to: Journal of Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/8/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: Trifluralin is a soil-incorporated herbicide that is in common use in agronomic crops in the United States. Though not very susceptible to movement with water, trifluralin may move attached to soil particles and thus become associated with stream or lake sediments. Oxygen supply is usually limited in sediments. Previous research with trifluralin has shown that this herbicide is unusually easily degraded under anaerobic conditions (absence of oxygen). Such rapid degradation is probably not limited to lake sediments, but may also occur in the field. Vulnerability of trifluralin to anaerobic degradation is thought to explain the common failure of the herbicide to control weeds in wet fields. In this study, the role of iron-containing soil minerals in the rapid degradation of trifluralin was examined. The results showed that trifluralin degradation was most rapid when soil iron was being transformed (reduced) by microorganisms, and that conditions that prevented iron reduction slowed degradation of trifluralin. Reduced iron had no effect on trifluralin in pure water, but clay containing reduced iron caused rapid degradation of the trifluralin. The conclusion of this study is that rapid degradation of trifluralin in anaerobic environments, such as wet fields and stream sediments, is probably the result of the action of reduced iron minerals. The impact of this work is that these findings may be used by other scientists and extension personnel to develop improved effectiveness of this herbicide, and possibly for developing strategies for remediation of soils contaminated by unintentional spills.

Technical Abstract: Trifluralin (2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine) ranks among the most commonly used herbicides in the US. Extensive literature available on the environmental fate of trifluralin shows that the compound persists under most environmental conditions yet it is rapidly transformed under anaerobic conditions. Factors controlling fate of trifluralin in anoxic environments and the contribution of Fe(II) to its anaerobic degradation have been investigated. Experimental conditions employed were designed to emulate temporary flooding of upland soils, and utilized initially aerobic conditions. Trifluralin was rapidly degraded under anaerobic conditions in a range of midwest soils. Under iron reducing conditions, degradation kinetics among soils converged, suggesting a common mechanism. The presence of nitrate on oxygen suppressed trifluralin degradation. Degradation kinetics were faster under iron reducing conditions, and the addition of trifluralin appeared to result in reoxidation of Fe(II). Transformation of trifluralin under iron reducing conditions appeared to involve the soil solid phase, and was not limited by bioavailability. No reaction of trifluralin with dissolved Fe(II) was detected in the presence or absence of kaolinite under anoxic conditions. Reduced, Swa-1 smectite catalyzed rapid (30 h) transformation (72% of applied) of trifluralin to polar products. The results suggest that, as for other nitroaromatics, transformation of trifluralin in anoxic environments involves reaction with Fe(II) associated with the mineral phase. These results have implications for remediation of trifluralin-contaminated soil and may explain deactivation of this herbicide under flooded field conditions.