A sensitive and rapid method was developed to measure the mineralization of 14 C-labeled organic compounds at picogram-per-milliliter or lower levels in samples of natural waters and sewage. Mineralization was considered to be equivalent to the loss of radioactivity from solutions. From 93 to 98% of benzoate, benzylamine, aniline, phenol, and 2,4-dichlorophenoxyacetate at one or more concentrations below 300 ng/ml was mineralized in samples of lake waters and sewage, indicating little or no incorporation of carbon into microbial cells. Assimilation of 14 C by the cells mineralizing benzylamine in lake water was not detected. Mineralization in lake waters was linear with time for aniline at 5.7 pg to 500 ng/ml, benzylamine at 310 ng/ml, phenol at 102 fg to 10 mg/ml, 2,4-dichlorophenoxyacetate at 1.5 pg/ml, and di-(2-ethylhexyl) phthalate at 21 pg to 200 ng/ml, but it was exponential at several p -nitrophenol concentrations. The rate of mineralization of 50 and 500 ng of aniline per ml and 200 pg and 2.0 ng of the phthalate per ml increased with time in lake waters. The phthalate and 2,4-dichlorophenoxyacetate were mineralized in samples from a eutrophic but not an oligotrophic lake. Addition to eutrophic lake water of a benzoate-utilizing bacterium did not increase the rate of benzoate mineralization at 34 and 350 pg/ml but did so at 5 and 50 ng/ml. Glucose and phenol reduced the percentage of p -nitrophenol mineralized at p -nitrophenol concentrations of 200 ng/ml but not at 22.6 pg/ml and inhibited the rates of mineralization at both concentrations. These results show that the kinetics of mineralization, the capacity of the aquatic community to assimilate carbon from the substrate or the extent of assimilation, and the sensitivity of the mineralizing populations to organic compounds are different at trace levels than at higher concentrations of organic compounds.

The rates of mineralization of phenol, benzoate, benzylamine, p -nitrophenol, and di(2-ethylhexyl) phthalate added to lake water at concentrations ranging from a few picograms to nanograms per milliliter were directly proportional to chemical concentration. The rates were still linear at levels of <1 pg of phenol or p -nitrophenol per ml, but it was less than the predicted value at 1.53 pg of 2,4-dichlorophenoxyacetate per ml. Mineralization of 2,4-dichlorophenoxyacetate was not detected in samples of lake water containing 200 ng of the chemical per ml. The slope of a plot of the rate of phenol mineralization in samples of three lakes as a function of its initial concentration was lower at levels of 1 to 100 μg/ml than at higher concentrations. In lake water and sewage supplemented with <60 ng of 14 C-labeled benzoate or phenylacetate per ml, 95 to 99% of the radioactivity disappeared from solution, indicating that the microflora assimilated little or none of the carbon. The extent of mineralization of some compounds in samples of two lakes and sewage was least in the water with the lowest nutrient levels. No mineralization of 2,4-dichlorophenoxyacetate and the phthalate ester was observed in samples of an oligotrophic lake. These data suggest that mineralization of some chemicals at concentrations of <1 μg/ml is the result of activities of organisms different from those functioning at higher concentrations or of organisms that metabolize the chemicals at low concentrations but assimilate little or none of the substrate carbon.

Montmorillonite-benzylamine complexes were formed immediately upon addition of 20 pg to 20 μg of amine per ml of suspensions containing the clay. The extent of amine sorbed was a linear function of equilibrium amine concentration in lake water. Increases in the clay concentration decreased the percentage of the organic compound that was mineralized at amine levels of 20 pg to 200 ng, but not at 20 μg/ml. A larger percentage of the chemical was released from the complex during mineralization in the presence of high clay concentrations than in the presence of low clay concentrations. The rates of desorption and mineralization increased linearly with benzylamine levels up to 200 ng/ml. Montmorillonite did not enhance mineralization rates at amine levels of 200 ng/ml or lower, but it was stimulatory at 20 μg/ml. Except at high amine and clay concentrations, mineralization was more rapid than desorption during the early periods of decomposition when the amine concentration in solution was relatively high. However, relative to the microbial demand, desorption was more rapid during later periods of decomposition when the amine level in solution was very low. Mineralization of benzoate was not usually affected by montmorillonite, kaolinite, or glass beads. More than 90% of the carbon from benzylamine and benzoate was often mineralized when the substrate concentration was 250 ng/ml or less. After incubation of the chemical in lake water, none of the radioactivity from benzylamine was in the particulate fraction containing natural sediment and microbial cells. The data indicate that clay may have a significant effect on the microbial decomposition of low concentrations of certain organic compounds.

Isopropyl N -phenylcarbamate (IPC) at 400 pg and 1 μg/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 μg/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.

Resting cells of bacteria grown in the presence of diphenylmethane oxidized substituted analogs such as 4-hydroxydiphenylmethane, bis(4-hydroxyphenyl)methane, bis(4-chlorophenyl)methane (DDM), benzhydrol, and 4,4'-dichlorobenzhydrol. Resting cells of bacteria grown with benzhydrol as the sole carbon source oxidized substituted benzhydrols such as 4-chlorobenzhydrol, 4,4'-dichlorobenzhydrol, and other metabolites of 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (DDT), such as DDM and bis(4-chlorophenyl)acetic acid. Bacteria and fungi converted 1,l,1-trichloro-2,2-bis(4-chlorophenyl)ethane to 1,1-dichloro-2,2-bis(4-chlorophenyl)ethylene, 1,1-dichloro-2,2-bis(4-chlorophenyl)ethane, DDM, 4,4'-dichlorobenzhydrol, and 4,4'-dichlorobenzophenone. AsperglUus conicus converted 55% of bis(4-chlorophenyl)acetic acid to unidentified or unextractable water-soluble products. Aspergillus niger and Penicillium brefeldianum converted 12.4 and 24.6%, respectively, of 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane to water-soluble and unidentified products. 4-Chlorophenylacetic acid, a product of ring cleavage, was formed from DDM by a false smut fungus of rice. A. niger converted 4,4'-dichlorobenzophenone to 4-chlorobenzophenone and a methylated 4-chlorobenzophenone.