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A three-stage system was developed to automate a batchwise toxicity testing protocol designed for assessing wastewater toxicity to activated sludge. The three-stage system used the luminescent bacterium Shk 1. The three stages were cell storage, cell activation, and continuous toxicity testing. Shk 1 cells were stored in a bioreactor at 4°C when the system was not in use and activated in another bioreactor for use in toxicity tests conducted in a continuous manner. The system could quickly be switched between the "off" and "on" modes, and operation of the system was easy. The stability of the system, in terms of cell density and bioluminescence in the storage and activation bioreactors, and the response of the activated cells to a metal and an organic toxicant were studied. The feasibility of the system design was demonstrated by simulating zinc toxicity episodes in synthetic wastewater. The needs for further modifications and improvements of the system were discussed. [ABSTRACT FROM AUTHOR]

Statistical models have long been used for reliability analysis and risk assessment. In the present study, an accelerated life-test model was used to analyze a set of dose-time-response data obtained with the terrestrial isopod Porcellio scaber. Survival data were experimentally obtained by exposing P. scaber to diazinon (a nonpersistent insecticide) at six concentrations between 2 and 11.31 μg/g (toxicant/soil). Survival data are presented on a weekly basis. The accelerated life-test model assumed a log-normal distribution and constant variance across all diazinon concentrations. Model parameters were obtained by maximum likelihood estimation. The accelerated life-test model was compared to a toxicokinetics-based model reported in the literature. Survival predictions made by both models were compared with the observed data. Both the accelerated life-test model and the toxicokineticsbased model underestimated toxicity at a diazinon concentration of 8 μg/g. Overall, however, the accelerated life-test model outperformed the toxicokinetics-based model, with survival predictions closer to the observed data in most cases and a stronger correlation between predicted and observed survivals. However, as a statistical model, the accelerated life-test model did not reveal mechanistic information, and only statistical and distributional interpretations of its model parameters could be made. [ABSTRACT FROM AUTHOR]

A two-step classification algorithm was developed for the classification and prediction of the mechanisms of toxic action of phenols. The mechanisms considered were polar narcosis, weak acid respiratory uncoupling, pro-electrophilicity, and soft electrophilicity. The classification algorithm was based on linear discriminant analysis using molecular descriptors as discriminating variables. Polar narcosis/pro-electrophilicity was separated from weak acid respiratory uncoupling/soft electrophilicity in the first step. In the second step, polar narcosis was separated from pro-electrophilicity and weak acid respiratory uncoupling was separated from soft electrophilicity. Different molecular descriptors were involved as discriminating variables at different steps of the classification algorithm. This algorithm classified any given phenol as acting by one and only one of the four mechanisms considered. Compared to one-step classification models, the prediction accuracy of the two-step algorithm was higher for all four mechanisms involved. [ABSTRACT FROM AUTHOR]

Heavy metals are known to be inhibitory and toxic to the activated-sludge microbial community in biological wastewater treatment plants. Toxicity screening of aqueous mixtures of these heavy metal ions in plant influent could use both chemical and biological methods. As a biological method, luminescent bacterial bioreporters offer the advantages of a simple test procedure and rapid response. Current biologically based methods for screening aqueous streams for toxicity are labor-intensive, inaccurate, or difficult to use in continuous monitoring applications. In the present study, a system was developed that is simple and easily automated. This system is based on the bacterium Shk1, a genetically engineered bioluminescent Pseudomonad whose parent strain was originally isolated from activated sludge. Compared with other bioluminescence-based systems (specifically, the Microtox assay), the system of the present study more accurately reflects the effects of the toxicity of common metal ions on activated-sludge respirometry without being overly sensitive to typical constituents of wastewater. The use of Shk1 as a bioluminescent reporter for heavy metal toxicity testing for the application of wastewater treatment influent toxicity screening is presented in this study. [ABSTRACT FROM AUTHOR]