Effect of concentration of organic chemicals on their biodegradation by natural microbial communities

Abstract

The effect of concentration of the biodegradation of synthetic organic chemicals by natural microbial communities was investigated by adding individual 14C-labeled organic compounds to stream water at various initial concentrations and measuring the formation of 14C02. The rate of degradation of p-chlorobenzoate and chloracetate at initial concentrations of 47 pg/ml to 47 μg/ml fell markedly with lower initial concentrations, although half or more of the compound was converted to C02 in 8 days or less. On the other hand, little mineralization of, 2,4-dichlorophenoxyacetate and 1-naphthyl-N-methylcarbamate, or the naphtol formed from the latter, occurred when these compounds were present at initial concentrations of 2 to 3 ng/ml or less, although 60% or more of the chemical initially present at higher concentrations was converted to C02 in 6 days. It is concluded that laboratory tests of biodegradation involving chemical concentrations greater than those in nature may not correctly assess the rate of biodegradation in natural ecosystems and that low substrate concentration may be important in limiting biodegration in natural waters.