Seasonal variation of mercury in commercial fishes of the Amazon Triple Frontier, Western Amazon Basin

Artisanal and Small-scale Gold Mining (ASGM) has been spreading in the Western Amazon. ASGM is one of the main sources of pollution by anthropogenic mercury on the environment in the Amazon. Ecotoxicological approaches are important to monitoring aquatic ecosystems. They evaluate interactions among contaminants and living organisms and detect possible risks to animal and human health. The hydrological cycles of Amazonian rivers influence the fishery production. Depending on the period, the availability of mercury may also variate in these aquatic systems. This study aimed to monitoring mercury in commercial fishes from the Amazon Triple Frontier. Total mercury (THg) concentrations in muscle (MTHg), liver (LTHg), and gills (GTHg) of Hoplerythrinus unitaeniatus, Hoplias malabaricus, and Pterygoplichthys pardalis caught in the Western Amazon Basin were assessed during the ebb and flood periods. The determination of total mercury concentration in fish samples was done by Cold Vapor Atomic Absorption Spectrophotometry (CVAAS). In both periods, H. unitaeniatus and H. malabaricus presented the highest levels of THg in tissues. In the ebb period, H. unitaeniatus and H. malabaricus had higher levels of MTHg > LTHg > GTHg. All species of the flood period had higher levels of LTHg > MTHg > GTHg. Mercury concentrations of all tissues of H. malabaricus showed significant relationship with length and weight. In P. pardalis, negative length-GTHg and weight-GTHg relationship were observed as well as a negative weight-LTHg correlation. Liver presented the highest levels of THg found in this study. Some individuals of H. malabaricus presented MTHg above safe limits for consumption. These results suggest that fish and human exposure to Hg in the Western Amazon Basin is not constant throughout the year. The flood period seems to be critical for high Hg exposure. This information can be used to development of more specific public policies to reduce the risks of mercurialism in humans from Amazon Triple Frontier as well as impacts on fish diversity and fishery production of Solimoes-Amazonas Basin.