Effect of substrate concentration and organic and inorganic compounds on the occurrence and rate of mineralization and cometabolism.

Isopropyl N-phenylcarbamate (IPC) at 400 pg and 1 mug/ml was mineralized in samples of sewage, but only the lower concentration was mineralized in lake water samples in a 50-day period. IPC at 1 mug/ml disappeared from lake water, but it was converted to organic products. Mineralization of IPC at 400 pg/ml in lake water was enhanced by additions of inorganic nutrients or a mixture of nonchlorinated water pollutants but not by yeast extract or mixtures containing aromatic compounds or excretions of primary producers. The mineralization of 200 pg of 2,4-dichlorophenoxyacetate per ml of lake water was not affected by additions of low levels of yeast extract or compounds excreted by primary producers but was enhanced by low concentrations of mixtures of water pollutants. It is suggested that some chemicals that are found to be converted only to organic products, presumably by cometabolism, in tests using the concentrations commonly employed in laboratory evaluations may be mineralized at the lower concentrations prevailing in natural waters.