Influence of Sediments on Concentrations of Fluridone and Penoxsulam in the Water Column and Sediment Pore Water.

Control of invasive aquatic plants is crucial for the maintenance of chemical, biological and ecological balances in many fresh water systems. Exposure of invasive plants to herbicides used for their control may be reduced by sorption to organic matter in sediments. Since granular herbicide formulations have closer contact with sediments (compared to liquid formulations), concentrations in the water column may be much lower. To test this hypothesis, microcosms containing sediments with < 1%, 6.4%, 19.7%, and 44% organic matter were treated with liquid and granular formulations of fluridone and penoxsulam. Herbicide concentrations in the water column and sediment pore water were monitored over 40 days. The presence of sediments (regardless of organic carbon content) significantly reduced concentrations of fluridone in the water column from the granular formulations relative to the liquid formulation. A similar, though less extreme, pattern was observed for penoxsulam in most of the organic carbon treatments.