A multi-endpoint approach to ecotoxicological assessment of wastewater polluted rivers using zebrafish

Freshwater bodies are often polluted by municipal wastewater discharges that degrade water quality while current river monitoring focuses primarily on physical and chemical parameters, neglecting ecosystem health assessments. Hence, this study uses zebrafish (Danio rerio) as a model organism to evaluate the ecotoxicological effects of wastewater contamination in the Musi River catchment with urban and rural land use. The river receives a combination of inputs from reservoirs, treated and untreated urban wastewater, industrial discharges, and agricultural runoff. Sampling locations were selected from upstream, within the city, and downstream stretches to assess the effects of these diverse pollution sources. Zebrafish embryos and larvae, exposed for up to 96 h post-fertilization (hpf) to water samples from the urban stretch, exhibited high mortality, delayed hatching, and increased teratogenicity. Significant effects on heart rate and cellular apoptosis were observed, while histopathological analysis revealed muscle disorganization, notochord malformation, yolk sac defects, and delayed eye and brain development at 96 hpf. Notably, water from the downstream site, despite lower pollution levels, still led to persistent tissue alterations. Most toxicity indicators differed significantly between stretches. Independent clustering of water quality and toxicity parameters separated stretches identically while linear discriminant analysis based on water quality parameters could classify the stretches with their contrasting toxicity. This study made comprehensive use of multiple biomarkers to assess river pollution typical for cities in developing nations. The findings demonstrate the potential of the Zebrafish Embryo-Larval Toxicity Test (ZELT) as an effective vertebrate model for ecological toxicity assessment of freshwater bodies worldwide.