Zebrafish embryos ecotoxicity traceability of pharmaceutical wastewater during simultaneous...

Toxicity assessments based on transcriptomics and metabolomics at target organs are magnitude difference due to the tremendous variations in the sensitivity of receptor binding sites (subunits), which often require expensive instrumentation using quantitative whole-body autoradiography. In this study, zebrafish embryos combined with toxicity identification evaluation (TIE) and ECOSAR toxicity prediction were applied to monitor comprehensive toxicity changes of fermentation pharmaceutical wastewater (FPW) in the expanded granular sludge bed (EGSB) and the modified simultaneous nitrification-denitrification (SND) process. FPW with high toxicity (30.93 TU) was predominately detoxified (to 4.04 TU) in anaerobic EGSB process, in which chlortetracycline (CTC) was degraded via demethylation, dechlorination and ring-cleaving. TIE results showed that non-polar pollutants contributed to the major toxicity and existed in the whole process. The pH adjustment significantly influenced the toxicities of CTC and its mixture with NH₄⁺-N (M_CTC+NH4+) or NO₂^--N (M_CTC+NO2-) due to the hydrolysis and chelation. Noticeably, nearly no nitrite/nitrate were accumulated in SND treatment process, which greatly alleviated the toxicities of M_CTC+NH4+ and M_CTC+NO2- due to no generation of free ammonia and free nitrous acid. M_CTC+NH4+ exhibited antagonistic toxicity in all test pH, but M_CTC+NO2- converted from synergistic (pH i) to antagonistic (pH 7.5). This study deepened the detoxification mechanistic interpretations of FPW in the modified EGSB-SND process as well as related toxicity variation information.