Mercury in piscivorous and detritivorous fish from the Teles Pires river basin, Southern Amazon

Mercury accumulation in fish can differ among species living in the same water body, and these differences can be related to their life cycle, feeding habits, and position in the trophic chain. The objective of this study was to evaluate the concentrations of total mercury (THg) in the muscle, liver, kidneys, and gills of the detritivorous fish Prochilodus nigricans, and the piscivorous fish Cichla mirianae, Hydrolycus armatus, and Hydrolycus tatauaia from the Teles Pires river basin. Collections were conducted in September 2015 (dry season) and May 2017 (ebb season). The THg concentrations in the liver of P. nigricans from the Teles Pires basin (1.05 standard deviation±1.24 mg.kg-1) and C. mirianae from the Peixoto river (0.46±0.26 mg.kg-1) were significantly higher than in the other tissues analyzed; for the other species, the concentrations in the liver and kidneys were similar. THg concentrations in the muscle were significantly higher (p=0.0002) in piscivorous fish (H. armatus 0.30 mg.kg-1; H. tatauaia 0.18 mg.kg-1; C. mirianae from the Teles Pires river 0.17 mg.kg-1 and from the Peixoto river 0.21 mg.kg-1) than in the detritivorous fish (P. nigricans from the Teles Pires basin 0.05 mg.kg-1), which was expected due to the biomagnification of mercury. The vast majority of specimens had THg concentrations in the muscle below that permitted for human consumption by the World Health Organization but, considering that the region has a high consumption of fish, the daily mercury intake exceeds the limit. The detritivorous fish P. nigricans presented the lowest THg concentrations in the muscle; therefore, it can be preferentially consumed by the general population, especially by sensitive groups (lactating women, infants, and children), and frequent consumers such as indigenous and riverine populations.