Effect of temperature, disturbance and incubation time on release and degradation of atrazine in water columns over two types of sediments

The availability of sediment-bound atrazine to overlaying water is key in assessing its risk to aquatic organisms. A laboratory study was conducted to determine the potential release and degradation of sediment-bound atrazine in overlaying water columns. Sediments were generated from Cullen (1.3 % organic carbon, 38% clay) and Emporia (0.63% organic carbon, 12% clay) soils and were incubated at two temperatures (5 and 24 °C) for 336 days. The concentration of atrazine in the water columns was determined before and after disturbance of the sediments to simulate dredging of water bodies. At 5 °C, the release of atrazine from sediment to water columns was biphasic, whereby a short period of rapid diffusion was followed by a longer period of slow release. With no sediment disturbance, about 40% of the atrazine applied to sediment diffused into the water columns at 5 °C. At 24 °C, less than 15% of theapplied amount entered the water columns; this was due to the greater degradation rate of atrazine at this temperature. Initially, the disturbance of sediments caused greater amounts of atrazine to be released into the water columns at 5 °C, but disturbance caused no effect after 112 days. At 24 °C, the amount of atrazine released from sediments after disturbance was less than at 5 °C, and was minimal after 28 days. There was some diffusion of metabolites out of the Cullen sediment at 24 °C. In Emporia sediments however, metabolites were released only after disturbance of the sediment. Release of sediment-bound atrazine decreased with time and the decline was rapid at 24 °C, because of degradation of the herbicide. Disturbance of sediments, such as dredging, is unlikely to remobilize aged atrazine in warmer environments.