Abiotic Reduction of Pendimethalin and Trifluralin in Controlled and Natural Systems Containing Fe(II) and Dissolved Organic Matter

The environmental fate of dinitroaniline herbicides is poorly understood, despite their classification as Persistent Bioaccumulative Toxins by the U.S. Environmental Protection Agency. This study investigated the abiotic reduction of pendimethalin and trifluralin in controlled laboratory systems in the presence of Fe(II) and fulvic acids isolated from various surface waters and in sediment pore waters containing naturally abundant levels of dissolved Fe(II) and dissolved organic matter (DOM). It was found that Fe(II) was necessary for pendimethalin and trifluralin reduction to occur in controlled systems and that higher concentrations of DOM slowed Fe(II)-mediated reactions. Pendimethalin and trifluralin reduction in natural pore waters was roughly an order of magnitude slower compared to controlled Fe(II) DOM solutions, indicating that the reactive Fe(II) species responsible for reduction are concentration-limited in natural pore waters relative to controlled systems. The results show that caution must be exercised when extrapolating results from controlled system reactions to natural systems and that abiotic reduction of both trifluralin and pendimethalin is observed within 3-7 days in anaerobic sedimentary pore waters containing high concentrations of both dissolved Fe(II) and DOM.