Degradation of organic chemicals at trace levels in seawater and marine sediment. The effect of concentration on the initial fractional turnover rate

Abstract

The initial degradation rates of 14C-phenol, 14C-N, N-dimethyl formamide and 14C-MCPA was investigated in freshly collected (non-adapted) seawater and marine sediment. A rapid and sensitive tracer method was used to measure mineralization at the ppb — ppt level. For all three substances, the initial fractional turnover rate increased with decreasing concentration. This concentration effect did not follow Michaelis-Menten kinetics. The effect was largest for the degradation of phenol inmarine sediment, corresponding to a 500 times increase in the initial fractional turnover rate per 10 4 times decrease in the concentration with the lowest concentration being 500 ng/liter. It is concluded that • — The degradation kinetics for the substances tested considered a non-volume basis proceed most rapidly at small concentrations. • — Tests for biodegradation representing the natural environment should be carried out at concentrations very close to the environmentally relevant concentrations which are often below the ppb-level.