Ecotoxicological Effects Of Several Typical Organic Pollutants And Their Major Degradation Products

When classifying the efficacy of a treatment process for the removal of refractory organic pollutants in wastewater, the removal of the target compound or the total organic carbon (TOC) and chemical oxygen demand (COD) were used as the performance indicators in most studies. These parameters were not sufficient used on their own, since the formation of transient organic compounds, some of them more toxic than the starting one, should also be monitored. In addition, little information of the toxicity of the emerging persistent organic pollutants (POPs) and their degradation products is available. Hence, related investigation was warranted. The purpose of the present study is to characterize the toxicity changes during the treatment process of refractory organic pollutants, and to gain an insight into the toxicity mode of the emerging POPs and their degradation products. The results are expected to provide some scientific foundation for setting up the indicator system, which would focus on the ecotoxicological characterization and the evaluation of environmental safety of innovative wastewater treatment process.Photoelectrocatalysis with high oxidative efficiency is an emerging process for the removal of trace levels of refractory pollutants in water. In the present study, pentachlorophenol (PCP), one of the simple and typical polychlorinated aromatic hydrocarbons, was selected as the target compound. Ecotoxicological bioassays were conducted to characterize the photoelectrocatalytic process of PCP. Besides, toxicity of perfluorinated alkyl acids and their degradation products on green alga were investigated. The present study comprise of several parts as follows.(1) Toxicity changes during the photoelectrocatalytic process of PCP were investigated with alga growth inhibition test. The results demonstrate that PCP was effectively removed with a step down of toxicity. It seemed that no significantly toxic products to algae formed in the process. Moreover, photoelectrocatalysis was superior to direct photolysis and photocatalysis for both the removal of PCP and the reduction in toxicity.(2) Luminescence bioassay was employed to test the changes of acute toxicity during the photoelectrocatalytic process for the degradation of PCP. The results were similar to those of the alga toxicity test. It seemed that intermediates with significant levels of acute toxicity did not generate in photoelectrocatalytic process and photoelectrocatalysis was also superior to direct photolysis and photocatalysis for the removal of the acute toxicity of PCP. (3) Ethoxy resorufin-O-deethylase (EROD) induction activity mediated by aryl hydrocarbon receptor was tested during the photoelectrocatalytic process of PCP to monitor the generation of dioxin-like products. Moreover, chemical analysis was conducted to identify the PCDD/Fs congeners. Results illustrated that dioxins were generated during the photoelectrocatalytic process of PCP. The dioxin products could be removed by photoelectrocatalysis and as long as the reaction time was long enough, these compounds could be completely removed. Furthermore, photoelectrocatalysis was more efficient to remove the dioxin products than direct photolysis and photocatalysis. Results of bioassay were well correlated with that of chemical analysis, where bioassay-derived 2,3,7,8-TCDD equivalents (TEQ_bio) and chemical-derived 2,3,7,8-TCDD equivalents (TEQ_cal) were about of the same order of magnitude. The EROD induction bioassay used in this study was proved to be a sensitive and accurate method for indicating the presence of dioxins in the complex mixtures, which was suggested to be applied to the evaluation for the ecotoxicology and environmental safety of a treatment process(4) SOS/umu assay was conducted to investigate the genotoxic characteristics of PCP solution during the photoeletrocatalytic process and to evaluate the risk posed by the genotoxic products. Genotoxic intermediates formed in the process and then were removed after 120 min of reaction. However, reaction products formed in direct photolysis and photocatalysis process after 120 min of reaction still exhibited genotoxicity, further confirming that photoelectrocatalysis is superior to the other two with respect to environmental safety. Moreover, SOS/umu assay was suitable to evaluate the genotoxic characteristics of the photoelectrocatalysis process due to its simplicity and sensitivity. Hence it could be employed as part of the assessment system for the environmental safety of a treatment process.(5) The toxic effects of a series of perfluorinated alkyl acids (PFAAs) to the green alga Scenedesmus obliquus were investigated, including effects at the population and cellular level. Effects at the cellular level focused on the membrane function and were investigated by flow cytometry. Among the test compounds, perfluorooctane sulfonic acid (PFOS), perfluorododecanoic acid (PFDoA) and perfluorotetradecanoic acid (PFTeA) inhibited the algal growth, and PFOS, perfluorooctanoic acid (PFOA), PFDoA, and PFTeA induced an enhancement of the mitochondrial membrane potential (MMP) and cell membrane permeability in S. obliquus. Test compounds disturbed membrane properties at concentrations below those associated with algal growth inhibition. The effect of PFAAs on S. obliquus was related to an interruption on the membrane function. The response of S. obliquus increased with increasing length of the carbon chain for PFAAs belong to the same class and PFOS is more toxic than PFOA. Therefore, the toxicity of PFAAs will decrease during the treatment process according to the up-to-date reports concerning the removal of PFAAs.The combined toxicity of PFOS and other compounds were investigated. Although PFOS had a low toxicity to the growth of S. obliquus, it posed a significant effect on the toxicity of other compounds caused by the influence of PFOS on the algal uptake of these compounds. This effect was possibly due to the surface activity of PFOS and its interruption on the membrane of the algal cells. In the present study, PFOS exhibited a synergism or antagonism to the toxicity of other compounds.