Distribuição da concentração de mercúrio em sedimentos de praias adjacentes a foz do Rio Doce, Espírito Santo, Brasil

Abstract

The disruption of the Fundão dam, in Mariana - Minas Gerais, occurred in November 2015, caused the spillage of a large amount of mining waste in the Rio Doce Basin. Mud spread along the river arriving its mouth in the northern of Espírito Santo. By the action of the sea currents, the mud has spread over the coast reaching important beaches for the local economy and areas of great environmental value. The present study aims to verify the distribution of mercury on the beaches adjacent to the mouth of the Rio Doce. The superficial sediments were collected in 11 sampling stations in July 2019 and 13 sampling stations in December 2019. The sampling was done in the regions of the berm, foreshore, shoreface and 5m and 10m isobates. Two sediment cores were collected in the isobath of ± 10m near the mouth of the Rio Doce. The samples after being collected were dried, sieved and quartered as stipulated by CETESB (2011). The determination of Hg was carried out using DMA-80 according to EPA 7374. In addition to the determination of Hg, the granulometry, CaCO3 content and organic matter content were also verified. The previous study of the chosen analytical method sought to investigate the preparation necessary for the analysis of Hg in addition to verifying as performance characteristics. The method performed good accuracy, good precision, LD = 0.11 µg kg-1 and LQ = 0.32 µg kg-1 . In general, the sample stations had concentrations between 0.10µg kg-1 and 68.97 µg kg-1 of Hg. Those values are below the limit established by CONAMA, which is 300µg kg-1 . In the sediment cores the variation in composition up to about 20 cm depth, after that, its composition becomes constant, indicating that the sedimentary exchange occurs up to that depth. The statistical study using PCA indicated a strong relationship between the levels of mud and organic matter with the concentration of Hg. The spatial distribution of Hg showed that the concentration of the metal increases in a north-south direction in the emerged portion of the beaches while in the submerged portion, a greater distribution is observed in the stations north of the mouth.