Rates of Mineralization of Trace Concentrations of Aromatic Compounds in Lake Water and Sewage Samples

Abstract

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.

Effect of aroclor 1248 concentration on the rate and extent of polychlorinated biphenyl dechlorination

“…This limitation was due to the inherent limit in microbial competence in dechlorinating congeners with certain Cl substitution patterns [2,10]. It is unclear whether this limit is also affected by PCB concentrations, because the microbial population or activity is often determined by substrate concentrations [11][12][13][14].…”

Quantitative assessment of herbicide decomposition at different initial concentrations

“…One obstacle in quantitative studies using I4C-labeled substances is how to define a rate constant from the nonlinear plots. The maximum rate (Boethling and Alexander, 1979) or the rate from the initial linear portion of the plots (Novick and Alexander, 1985;Rubin et al, 1982;Subba-Rao et al, 1982) have been used, and these rates were linear functions of co at low values of co with different chemicals under various conditions. The rate thus defined is probably equivalent to the rate constant k3, since the rate and the rate constant for a zero-order process are equivalent, and since k3 was also linear with low co.…”

Interpreting results from biodegradability tests of chemicals in water and soil

“…However, situations are known in which mineralization of a cosubstrate occurs. For example, Rubin et al [6] found that 95% of the radioactive carbon in labeled benzoic acid and phenylacetic acid that was added in low concentrations to samples of lake water or sewage was released as 14C02. Thus, a mineralization process similar to cometabolism may occur at low substrate concentrations.…”

“…Obligate oligotrophs cannot tolerate high carbon concentrations, whereas facultative oligotrophs are dormant under conditions of high carbon concentrations but are reactivated when the carbon level is reduced. In contrast, eutrophs are organisms that proliferate under conditions of high organic carbon but do not function at low organic carbon concentrations [6,7]. Thus, a chemical present at high concentrations would tend to be degraded by eutrophs but would be unaffected by oligotrophs.…”

“…Thus, it seems highly unlikely that results from these tests will provide good insight into the behavior of chemicals at trace concentrations in oligotrophic systems. For example, Rubin et al [6] reported that 2,4-D and di(2-ethylhexyl) phthalate (DEHP) did not --…”