Mercury levels in an environmentally protected estuarine area in Northeast Brazil: partitioning in the water column and transport to the ocean.

In this study, total Hg concentrations (HgT) were determined in the suspended particulate matter (SPM) and the dissolved fraction of the water column to evaluate their behavior through a gradient of physical-chemical parameters in a continuum between rivers and the Serinhaém River estuary of the Pratigi Environmental Protection Area, a pristine environment without point sources of Hg contamination, located in Northeast Brazil. Twelve points were sampled, forming a river-estuary transect, and two samplings were carried out (April and September 2019). Significant spatial and temporal effects were detected only for particulate HgT and not for dissolved HgT. Considering both samplings, the mean HgT concentrations in SPM were 1112 ± 824 and 44 ± 33 ng·g-1 in the river and estuary, respectively. Also, HgT concentrations in the dissolved fraction (1.61 ± 0.61 ng·L-1) were below the limits established by environmental agencies (CONAMA = 2 µg∙L-1 and USEPA = 1.4 µg·L-1). Salinity and SPM concentrations were important predictors of HgT in the water column (R2 = 0.81, p < 0.0001; R2 = 0.56, p < 0.0001, respectively). Mercury transport to the ocean through SPM was 2 kg∙year-1, 4000 times greater than the dissolved fraction.

Doce River Estuary: Geochemical Changes Following the Largest Tailing Spill in South America.

Accidents involving economic activities of great impact, such as mining, have caused massive environmental damage. In November 2015, the dam of Fundão, located in the city of Mariana, MG, broke and released 5 × 107 m3 of tailings in the nearby ecosystems, including the Doce River. The physicochemical changes that occurred in the Doce River estuary were analyzed, as well as the trace metal concentrations, both 1 day before and 1 month after the disaster. The analyses of the collected samples (water and sediment) showed changes to the physicochemistry regarding dissolved oxygen, SPM, and temperature (p = 0.008, 0.001, 0.036, respectively). It also detected metals (Fe and Al) in the dissolved fraction beyond the limits recommended by the Brazilian legislation. There was an increase in the total concentrations of Fe and Cd in the sediment after the rupture of the dam and a change in mobile metals (Al, Cd, Cr, Cu, Fe, Ni, Pb, and Zn), with higher concentrations of mobile metals being found closer to the ocean (p = 0.06356). After the rupture of the dam, there was a change in the granulometric fraction of the sediment, which became composed mainly of silt and clay. All of the results showed a change on the Doce River estuary, caused by the arrival of the tailings, which can result in future harmful effects with the release of metals present in the sediment and adsorbed to the particles. The changes to the sediment, such as changes in the granulometric fraction, can have negative consequences for the benthic community.