Selenium in sediment and food webs of the Tapajós River basin (Brazilian Amazon) and its relation to mercury.

BACKGROUND: We investigated Se levels along the Tapajós River basin - which is an important tributary of the Amazon River - and the possible antagonistic effect of Se in Hg availability. This is the first study to investigate Se transfer from abiotic to biotic compartments and along the food chain in aquatic ecosystems of the Amazon basin. METHODS: Se concentrations were measured in superficial sediment (n = 29), plankton (n = 28) and fishes (n = 121) along two stretches of the Tapajós River basin (Tapup/mi and Taplow), comprising approximately 500 km with different hydrological characteristics. RESULTS: Se concentrations in sediment were significantly higher in the Taplow (345-664 µg kg-1) than in the Tapup/mi (60-424 µg kg-1). The seasonal flooding of the Amazon River probably helps to carry selenium-rich sediment to the Tapajós mouth (Taplow stretch). We suggest that Se in sediment could decrease the bioavailability of Hg resulting in lower MeHg concentrations in fish, as observed in the Taplow (45-934 µg kg-1). Sediment and plankton were positively correlated in relation to their Se concentrations (r = 0.62; p = 0.001) suggesting that sediment can possibly be the main source of Se to plankton. Our data indicate Se uptake by primary consumers, as noted in phytoplankton levels. The decrease of Se concentrations along the food chain was also noteworthy. CONCLUSION: This work elucidates some aspects of Se biogeochemistry in the Amazon basin and shows its importance regarding Hg cycles in aquatic ecosystems.

Far-reaching cytogenotoxic effects of mine waste from the Fundão dam disaster in Brazil.

On November 2015, one of Brazil's most important watersheds was impacted by the mine waste from Fundão dam collapse in Mariana. The mine waste traveled over 600 km along the Doce River before reaching the sea, causing severe devastation along its way. Here we assessed trace element concentrations and cytogenotoxic effects of the released mine waste. Water samples were collected along the Doce River ten days after the disaster in two impacted sites and one non-impacted site. Sampling points were located hundreds of kilometers downstream of the collapsed dam. Water samples were used for trace element quantification and to run an experiment using Allium cepa to test cytogenotoxicity. We found extremely high concentrations of particulate Fe, Al, and Mn in the impacted sites. We observed cytogenotoxic effects such as alterations in mitotic and phase indexes, and enhanced frequency of chromosomal aberrations. Our results indicate interferences in the cell cycle in impacted sites located hundreds of kilometers downstream of the disaster. The environmental impacts of the dam collapse may not only be far-reaching but also very likely long-lasting, because the mine waste may persist in the Doce River sediment for decades.