Fate of lindane in the aquatic environment: Rate constants of physical and chemical processes

Abstract

AbstractWater solubility, hydrolysis and photolysis rate constants, and sorption‐desorption partition coefficients were determined for lindane in three different natural water‐sediment systems, as well as in a Milli‐Q water and montmorillonite clay system. The aqueous solubility of lindane in surface waters at 25 ± 1°C ranged from 7.9 to 8.4 mg/L. In Milli‐Q water, lindane solubility was 9.2 mg/L. At α = 0.05, no significant difference was found between the values in different natural waters; however, the Milli‐Q water solubility did differ statistically. Lindane hydrolysis was found to be catalyzed by hydroxide and hydrogen ions. Neutral hydrolysis was relatively unimportant. Hydrolysis data followed first‐order kinetics with kh values of 74 × 10−4 h−1 at pH 9 and 7.4 × 10−1 h−1 at pH 5. Experimental hydrolysis half‐life (t1/2) in natural waters of pH 9.3 was comparable to the calculated value (92 h). Other natural water systems of pH 7.3 and 7.8 had t1/2 values greater than calculated values. Adjusted mid‐winter photolysis half‐life of lindane in Milli‐Q water was 1.56 × 103 h. Photolysis rate enhancement was noted in natural water of pH 9.3, possibly due to the alkaline hydrolysis side reaction. Photolysis rate retardation was noted in natural water of pH 7.3 and 7.8. Sorption‐desorption coefficient in Milli‐Q water‐montmorillonite clay was 1,259. Sorption coefficients for the natural systems ranged from 56 to 2,238. Results of the sorption‐desorption experiments indicate that the wide diversity of the characteristics of the natural water sediment systems considerably affect the lindane sorption‐desorption behavior.