Trifluralin degradation under microbiologically induced nitrate and Fe(III) reducing conditions

Trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)- benzenamine] ran ks among the most commonly used herbicides in the United States. The compou nd persists under most environmental conditions, yet it is rapidly transfor med under certain anaerobic conditions. In this study, the fate of triflura lin in anoxic environments and the contribution of Fe(II) to its anaerobic degradation have been investigated. Trifluralin was rapidly degraded under anaerobic conditions in a range of soils representing typical agricultural usage in the Midwest. The presence of nitrate or oxygen suppressed triflura lin degradation. Degradation rate increased under iron-reducing conditions, and the addition of trifluralin appeared to promote reoxidation of extract able Fe2+. Transformation of trifluralin under iron-reducing conditions app arently involved the soil solid phase and was not limited by bioavailabilit y. In a soil-free aqueous system, no reaction of trifluralin with dissolved Fe2+ was detected in the presence or absence of kaolinite clay under anoxi c conditions. Reduced but not oxidized or reoxidized forms of purified ferr uginous smectite (sample Swa-1) catalyzed rapid transformation (72% of appl ied in 30 h) of trifluralin to polar products with a concomitant reoxidatio n of structural Fe in the clay. Results indicate that, as for other nitroar omatics, trifluralin is subject to reaction with Fe(II) associated with the minerals in anoxic environments.