Rates of Sorption and Partitioning of Contaminants in River Biofilm

Biofilms are believed to play a significant role in the fate and transport of contaminants in aquatic environments. However little is known about the rates of sorption ( k ) and partitioning ( K d ) of contaminants to biofilms. Studies of the latter were performed using mature biofilm cultivated in a roto-torque reactor. The reactor was flushed with river water containing a mixture of tetrabutyltin, p, p -DDT, diclofop-methyl, triallate, lindane, atrazine, parathion-methyl, and dimethoate in two experiments. The first experiment was conducted at a spiked level of 1 μg/L, and the second was conducted at 10 μg/L for each component. Apart from dimethoate, there was rapid depletion of all contaminants from the water phase within the first 5−10 min with sorption occurring by pseudo-first-order kinetics. In general, the mean values of k (10 - 4 min - 1 ) increased with water solubility and were 8, 70, 110, 180, 230, 370, and 100 for p, p -DDT, diclofop-methyl, triallate, tetrabutyltin, lindane, atrazine, and parathion-methyl, respectively. The values of log K d increased linearly with log K ow and decreased linearly with the log of the aqueous solubilities. In general, K ow values were significantly greater than the corresponding values of K d, indicating that partitioning of contaminants was not limited to lipophilic regions of the biofilm.