The Capibaribe River provides water to a population of 1.7 million people in the Brazilian northeast, while receiving agricultural runoff and industrial and domestic effluents along its 280 km. The present study evaluated the ecotoxicity of surface waters along ten sites in rural and urban areas using zebrafish (Danio rerio) early‐life stages and related it to water quality indices and chemical abiotic variables. Lethality rates, delays in embryo‐larval development quantified by the general morphology score (GMS), and frequencies of developmental abnormalities were analyzed. A correlation was detected between zebrafish GMS and water quality index (WQI), sensitivity to domestic sewage contamination, and trophic state index, focused on eutrophication. These indices agreed in identifying a spatial pattern of smaller impact in terms of ecotoxicity, domestic sewage contamination, and eutrophication risk at three sites in rural areas (mean GMS 16.9), an intermediate impact at four sites with urban and agricultural influence (mean GMS 16.4), and greatest impacts at three more urbanized sites (mean GMS 14.9). Most frequent developmental abnormalities included noninflation of the swim bladder, delayed hatching, nonprotrusion of the mouth, blood stasis, and nondevelopment of pectoral fins. Toxic NH3 concentrations varied spatially, with higher concentrations in urban sites; and blood stasis correlated positively with NH3, suggesting a causal relationship. Polycyclic aromatic hydrocarbons were detected in both rural and urbanized sites, contributing to detected toxicity. The present study demonstrates the potential of zebrafish early‐life stages as an ecotoxicological model that may contribute to a better understanding of surface water quality and ecotoxicity in tropical river systems. Environ Toxicol Chem 2021;40:3063–3077. © 2021 SETAC

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The tropical estuarine guppy Poecilia vivipara was used to address fish early life stage toxicity caused by the antifouling contaminant tributyltin. Six-day-old P. vivipara were exposed for 7 d to control water and waterborne tributyltin at 15.8, 83.8, 716, and 818 ng tin (Sn) L-1. After exposure, swimming, feeding, growth, and eye histological endpoints were evaluated. Histopathological analysis of the retinal pigment epithelium (RPE) indicated alterations in pigment positioning at all tributyltin concentrations. A dose-dependent increase in photoreceptor layer disorganization and iris melanin hyperpigmentation was verified, and high frequencies of RPE invaginations and iris epithelial cell atrophy were observed even at the lowest exposure concentration of 15.8 ng Sn L-1. At the highest exposure level (818 ng Sn L-1) fish also presented reductions in swimming speed, swimming resistance, daily capture of Artemia nauplii, and growth in weight of 85, 60, 33, and 56% relative to controls, respectively. This association between retinal histopathology and reduced swimming and foraging behavior can reduce recruitment to the adult population.

Tropical rivers are the main destinations for tailings from urban, industrial and agricultural activities. The present study aimed to investigate if early stages of zebrafish (Danio rerio) development is a viable biological model to assess the toxicity of surface waters of tropical rivers, and whether that toxicity could be correlated to standard water quality indexes. Embryos were exposed to samples from 55 sites from 10 hydrographic basins of rivers in Pernambuco State, northeastern Brazil. Lethality rates, sublethal toxicity based on the general morphology score (GMS) and frequencies of abnormalities were analyzed. Significant mortality was observed in samples of 7 basins. The GMS indicated significant delay in embryo-larval development in 50% of the samples. Highest toxicity was detected in basins within Recife metropolitan area, where 61% of the samples caused sublethal toxicity. Most frequent developmental abnormalities included non-inflation of the swim bladder, delayed hatching and blood stasis. Highest frequencies of blood stasis were detected in samples with highest NH3 concentrations, corroborated by a positive correlation suggesting the existence of a causal relationship. A significant correlation was detected between water quality indexes and GMS with a greater toxic effect being observed in samples collected in areas of greater urban density and greater contamination by domestic sewage. This study demonstrates that the early stages of the zebrafish is a viable ecotoxicological model to assess the toxicity of surface waters and can contribute to a better understanding between the chemical composition and the adverse effects suffered by fish early life stages in tropical rivers.

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