Predicting the toxicity of substituted phenols to aquatic species and its changes in the stream and effluent waters.

The changes in the acute toxicity of 16 phenols toward Selenastrum capricornutum and Daphnia magna were examined as a function of their physical/chemical properties. The results demonstrated that phenols with a higher octanol-water partition coefficient (K(ow)) had a higher toxicity toward aquatic organisms. The toxicity of phenols was closely related to the log K(ow) values, with correlation coefficients of 0.93 (except for the nitrophenols) and 0.89 for S. capricornutum and D. magna, respectively. The changes in the phenols toxicities in the site waters (i.e., stream and effluent waters) were investigated by calculating the water effect ratios (WER) from the results of the toxicity tests in the site waters using D. magna. The results showed that the degree of ionization for each phenolic compound was altered by the differences in the dissociation constant (pK(a)), and the change in the toxicity could be predicted. Therefore, the WER should be considered when the toxicity of phenolic compounds is estimated in site waters. The quantitative structure-activity relationships (QSAR) study showed that the toxicity of the phenols to D. magna could be predicted by the hydrophobicity (log K(ow)) alone and by combining the log K(ow) with pK(a), while the toxicity to S. capricornutum was predicted by a combination of hydrophobicity (log K(ow)) and E(LUMO) (or pK(a)).

Estimating the combined effects of copper and phenol to nitrifying bacteria in wastewater treatment plants.

The inhibition of nitrification by phenol and copper mixtures was studied to investigate the differences between individual and mixture inhibition as the change of phenol and copper speciation due to their reactions. This study showed a decrease in the ammonium removal rate (k, first-order rate coefficient), indicating an increase in the relative % inhibition on nitrification, as the phenol and mixed liquor suspended solids (MLSS) concentrations were increased. In the case of copper, the ammonium removal rate decreased as the copper concentration increased and that of the MLSS decreased. This was attributed to the enhanced sorption of copper to heterotrophs at high MLSS concentrations. The relative % inhibition was plotted against free Cu2+ ions, which showed a close relationship. In the tests on copper and phenol mixtures, the mixture effects turned out overestimated by the calculation based on the additional chemical concentrations. In most Cu-phenol mixture tests, the presence of phenol as a complexation ligand caused a reduction of the inhibition rate to nitrifiers over the entire exposure range. Consequently, the prediction of nitrification inhibition in mixture environments, such as wastewater treatment plants, is influenced by the presence of a number of parameters that affect the activity of nitrifiers and, therefore, chemical speciation should be taken into consideration.