Heavy Metal Concentrations in Sediment, Water, and Fish Tissue From the Upper Salween River (Nujiang River In China)

The upper Salween River, named Nujiang River in southwest China, which is regarded as the least human-disturbed river in China and has been protected for ecological sustainability. Unlike the heavily polluted regions due to extensive anthropological activities, little research has been done on heavy metal bioaccumulation in this ecological-friendly river. However, understanding the environmental background value of bioaccumulation is essential for assessment of human disturbance. In this study, we conducted a systematic investigation of heavy metal concentrations in sediment, water, and fishes from the Nujiang River. To be specific, concentrations of multiple heavy metal elements in fish tissues including liver, kidney, heart, gill, and muscle of eight fish species were measured. Correspondingly, water samples and sediment samples were collected from the fish sampling sections for the heavy metal concentration analysis. Concentrations of Cu, Zn, Cd, Cr, Pb, and Ni in fish tissues, water samples, and sediment samples were detected applying the method of Atomic Absorption Spectroscopy (AAS). Therefore, the relationships between heavy metal concentrations in fish and in their habitat were revealed. Heavy metal concentrations in different fish species were compared to distinguish the dissimilarity owing to the differences in the types of fish habitat (inhabiting near the sediment or staying in the water column, preferring lentic flow or lotic flow) and feeding functions. The results showed that the heavy metal concentrations in slow-flow demersal benthic-feeding fishes were significantly higher than that in lotic pelagic omnivorous (herbivorous or planktivorous) fishes. Taking the local special species Schizothorax nukiangensis Tsao, which is omnivorous and torrent preference species as an example, the heavy metal concentrations in the different organs generally kept stable with slight fluctuation from the upstream to downstream. Thus, there was no significant correlation between heavy metal concentrations of fish organs and the concentrations in sediment and water. The indices of Estimated Daily Intake (EDI) and Target Hazard Quotient (THQ) were used to assess the human health risks caused by heavy metal bioaccumulation in fish in this area. It is indicated that it is risky in eating the fish internal organs even in the Nujiang River, which keeps favorable natural environment, while fish muscle eating is relatively safe (except high risk of Cr bioaccumulation).

Keywords: heavy metal, fish, environmental background value, bioaccumulation, upper Salween River