Discrimination of typical cyclic compounds and selection of toxicity evaluation bioassays for coal gasification wastewater (CGW) based on toxicity mechanism of actions (MOAs).

This paper originally investigated toxicity discrimination of typical cyclic compounds and bioassays selection on toxicity evaluation for coal gasification wastewater (CGW) effluent with mechanism-oriented investigation. Initially, representative cyclic toxicants were selected and classified with quantitative structure-toxicity relationship (QSTR). Nitrogen heterocyclic compounds (NHCs) and polycyclic aromatic hydrocarbons (PAHs) were basically discriminated as nonpolar narcotics with significant correlation to hydrophobicity (p < 0.05, R = 0.8668-0.9635), while phenols were regarded as polar narcotics and reactive compounds due to slight correlation to hydrophobicity (p > 0.05, R < 0.5). Furthermore, specific mechanism of actions (MOAs) to various organisms revealed that phenols were discriminated as critical source of acute toxicity in CGW, with short-term visible and irreversible damage. However, NHCs and PAHs, which exerted accumulation toxicity rather than acute toxicity, might result in potential mutagenicity and unpredictable risk along the food chain. Afterwards, based on species sensitivity to typical toxicants and application in real CGW effluent, non-applicability of Chlorella vulgaris (C. vulgaris) was validated in toxicity evaluation. While Daphnia magna (D. magna) was suggested as a toxicity bioassay in entire effluent due to the highest sensitivity and applicability. Tetrahymena thermophile (T. pyriformis) might be applicable in effluent with low biodegradability due to similar evaluation results (TU = 8.90) to D. magna (TU = 6.67) in aerobic effluent. Finally, the relationship between toxicity and bioavailability based on typical pollutants and model species illustrated necessity for dualism toxicity-biodegradability investigation on CGW.