Heavy metal bioaccumulation, stable isotope ratios, and human health risks of fishes from urban rivers in Haikou City, China

Despite its importance as a food source, toxic metals may also be transferred to humans by consuming contaminated fish, causing health risks. Studies on stable isotope ratios provide insight into contamination sources and how the pollutants get into the diet of aquatic organisms. Rivers provide fishes, which form a substantial human food source; hence assessing metal contamination in fish is vital. However, studies are limited on heavy metal contamination in urban rivers in Haikou City, China. Accordingly, this study assessed the heavy metal bioaccumulation and stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) in seven freshwater fish species collected from three urban rivers in Haikou City. The potential heavy metal human health risk was also assessed. Fish gills had significantly (p < 0.05) high Fe, Mn, Cu, Zn, Ni, Cd, Pb, and Co content than muscles. The metal content differed significantly (p < 0.05) regarding fish species type, feeding habits, and living habitat. For example, Anabas testudineus and Parachromis managuensis had the highest and lowest levels, respectively. Herbivorous fishes had the highest metal concentrations, while carnivores had the lowest. The isotope ratios ranged from -32.32‰ to - 14.47‰ for δ¹³C and 3.22‰ to 14.29‰ for δ¹⁵N, suggesting wide energy sources and trophic levels. Omnivorous fishes had a higher δ¹³C than carnivores and herbivores. Regarding living habitats, benthopelagic and demersal fishes had high values of δ¹³C and δ¹⁵N, respectively. The metal concentration correlated negatively with fish length and weight, suggesting a biological dilution. In contrast, Pb and Hg positively correlated with δ¹⁵N, indicating biomagnification along the food chain. The target hazard quotient (THQ) of As and Cr were > 1 in some fishes suggesting potential health risks. Generally, the hazard index (HI) of Anabas testudineus, Coptodon zillii, Mugil cephalus, Oreochromis niloticus, and Oreochromis mossambicus were above 1; thus, their consumption may impair human health. The study provides information on heavy metal contamination and bioaccumulation in fish, which is useful to inform public health and metal pollution control.