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 mu g/L, and the second was conducted at 10 mu g/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.