Anoxic treatment of trifluralin-contaminated soil

Abstract

Amending anoxic soils with stoichiometric amounts of sodium acetate led to the complete transformation of trifluralin within the 45 day treatment period. Under these conditions, a maximum trifluralin transformation rate of 4.9 mg kg −1 of soil per day was estimated, which corresponded to a chemical half life of 11.9 days. Regression analyses indicated that the zero order rate model provided the best fit to the experimental data, suggesting that the trifluralin transformation rate is independent of concentration during acetate addition. Using radiolabeled trifluralin, it was determined that the principal contaminant transformation mechanisms were degradation and bound residue formation (i.e., irreversible adsorption). Volatilization and mineralization of trifluralin were found to be negligible over the 45 day treatment period. Using poisoned controls, it was determined that trifluralin transformation under acetate-amended conditions was biologically mediated. Amending trifluralin contaminated soils with stoichiometric amounts of iron sulfide resulted in complete trifluralin transformation within 24 hours of treatment. A maximum trifluralin transformation rate of 380 mg kg −1 of soil per day was estimated for this system, which corresponded to a chemical half life of 4.4 h. The rates of trifluralin transformation followed the first-order kinetic model during iron sulfide addition. Using radiolabeled trifluralin, it was found that chemical degradation was the principal removal mechanism. Neither volatilization nor mineralization was found to be a significant contaminant removal mechanism during iron sulfide treatment. Poisoned controls indicated that trifluralin transformation was mediated primarily by an abiotic chemical reaction mechanism. Additional study is required to clarify the rate limiting steps so that full scale soil treatment systems may be properly designed.