SPECIATION AND PARTITIONING OF ATRAZINE AND GAMMA-HEXACHLOROCYCLOHEXANE IN ESTUARINE WATERS

The partitioning behaviour and speciation of atrazine and gamma-hexachlorocyclohexane (gamma-HCH) in estuarine waters have been investigated. Particular emphasis was placed on evaluating the importance of pesticide binding to naturally occurring colloids and humic acids by using size-based speciation procedures such as equilibrium dialysis. Experiments using radiolabelled pesticides as model contaminants indicated that over the 24-h time frame of the experiments, the sorption of atrazine onto suspended sediments was not a significant process. Appreciable partitioning was only observed at high solids concentrations (> 80 g l-1) typical of close to the bed sediment/water interface. Determined log K(oc) values were in the range 1.68-1.94. Gamma-hexachlorocyclohexane partitioned appreciably onto suspended sediments at solids concentrations typical of the water column (log K(oc) 3.38-3.68). Equilibrium dialysis indicated that the two compounds showed little affinity for natural colloids or humic acids and were probably both present in true solution. The measured partition coefficients showed a dependence on salinity and particulate concentrations.