RESEARCH WATCH
BIODEGRADATION Rhizosphere impact Biodegradation of organic soil contaminants in the presence of plant roots may be the direct result of metabolism or cometabolism of the contaminant with other substrates provided by rhizodeposition. P A. Haby and D. E. Crowley studied 3-chlorobenzoate degradation in soils. Compared to unvegetated soils, soils in which plants were grown in the presence of 3-chlorobenzoate had a 40-fold increase in 3-chlorobenzoate metabolizers and a 250fold increase in cometabolizers but only a 12-fold increase of other types of bacteria After 2 to 3 days of incubation the relative number of tabolizers exceeded that of cometabolizers Results suggest that plants may augment degradation in sliehtly contaminated soils by providine an alternative substrate for cometabolism until a direct metabolizer DODUlation grows to a density that sienifi cantly affects the degradation rate After th t there may not be an influ ence by the rhizosphere, the authors
PCB accumulation by phytoplankton modeled A better understanding of how polychlorinated biphenyls (PCBs) accumulate in phytoplankton is essential for assessing their fate and transport in aquatic environments. R. S. Skoglund and co-workers developed a predictive kinetic model for PCB accumulation in phytoplankton that includes surface sorption, biomass dilution, and loss rate coefficients. The results contradicted the convention that PCBs accumulate in the lipid fractions of phytoplankton. In low-growth conditions predictions by both the kinetic model and an equilibrium partition-coefficient model were similar But during intense growth periods the kinetic mnripl achievpH values that agrepri with n h s e n / P f l fielrf v a l i i e s
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