Bioaccumulation characteristics of mercury in fish in the Three Gorges Reservoir, China

Highlights: • Concentrations of Hg in fish muscle from the TGR ubiquitously fall below the safe fish consumption limit. • Muscle has the highest ability to accumulate Hg compared to the other organs (gill, heart, liver and swim bladder). • The short food web and the limited trophic magnification factor in the TGR explained the low Hg levels in predators. • No discernible "reservoir effect" was observed in the TGR within the initial few years after impoundment. Newly constructed reservoirs were recognized as hotspot of mercury (Hg) methylation, and then methylmercury (MeHg) accumulation in food chains. The risk of elevated MeHg concentrations in fish is one of the most important concerns in newly constructed reservoirs. The Three Gorges Reservoir (TGR) is one of the largest reservoirs in the world. However, the distribution and bioaccumulation characteristics of Hg species within the food chains and its potential ecological risk in the TGR remain poorly understood. In this study, 264 fish individuals covering 18 species were collected from the TGR. Total mercury (THg) and MeHg concentrations in different organs (gill, heart, liver, muscle and swim bladder) of fish species were analyzed; the values of δ¹³C and δ¹⁵N in fish muscle were determined as well to reveal the biomagnification properties of Hg in food chains. Our results showed that concentrations of THg (0.5–272 ng g⁻¹, w.w.) and MeHg (0.1–199 ng g⁻¹, w.w.) in fish muscle from the TGR ubiquitously fall below the safe fish consumption limit on Hg recommended by WHO (500 ng g⁻¹, w.w.) and the US-EPA Water Quality Criterion for MeHg (300 ng g⁻¹, w.w.). The short food web jointly with the limited trophic magnification factor in the TGR explained the relatively low Hg concentrations in predators. Among the five fish organs, muscle represented the highest Hg concentrations, followed by heart, liver, swim bladder, and gill, suggesting that muscle has the highest ability to accumulate Hg compared to the other organs. More importantly, no discernible "reservoir effect" was observed in the TGR within the initial few years after impoundment due to its special eco-environment including: 1) neutral and slightly alkaline pH and low dissolved organic carbon of water, 2) less vegetation coverage in inundated areas, 3) simple food web.