Dados da Submissão

Título

Occurrence and distribution of mercury in terrestrial systems (soil-sediment-water) of Itacaiúnas Basin, Brazilian Amazon

Texto do resumo

In the Amazon, mercury pollution is a great concern to human health and biota because of its well-known ability to biomagnify and bioaccumulate in the aquatic food chain, particularly in fish. Several studies reported mercury contamination in the Amazon and concluded that it resulted from natural sources as well as anthropogenic impacts. Nevertheless, there are still large areas of the Amazon that are poorly studied towards Hg contamination and little focus was made on the behavior of Hg in the multimedia soil-water-sediment system. This is true for the Itacaiúnas River Watershed (IRW), located in the Carajás region. The total Hg (THg) concentrations in stream and lake water, surficial stream and lake sediments, and surface and bottom soils of the IRW, which were sampled during 2017-2018, were defined to understand the pollution status and the source and distribution of Hg in different environmental media considering contrasts of geological domains and sub-basins, and to evaluate its potential ecological and human risk. Total mercury (THg) concentrations in both stream and lake water samples were very low (< 0.2 µg/L; CONAMA limit for Class II freshwater). Although, Hg content found in some of the soils (0.1 to 650 µg/kg) and stream sediments (0.1 to 270 µg/kg) samples can be higher than the upper crustal average values (56 µg/kg), accentuated enrichment was mostly found in lake sediments (80-590 µg/kg). When compared to the CONAMA limit in soil (Prevention Value - 500 µg/kg), only 1 soil sample from Parauapebas sub-basin and 4 sediment samples from Violão Lake exceeded that limit. The geochemical signature and spatial distribution of Hg shows a strong coherence between the surface and bottom soils, and both are also closely correlated with stream sediments. This is strong evidence that catchment soils are dominant drivers of variation of THg in stream and lake sediments. Furthermore, elevated Hg contents were registered mostly in the Itacaiúnas and Parauapebas sub-basins, both containing significant occurrence of mafic and intermediate metavolcanic and plutonic rocks. The whole data demonstrates that Hg in the IRW is largely derived from geogenic sources and anthropogenic effect is highly limited. The maximum enrichment of Hg in lake sediments correlates with that of organic matter with subordinate influence of catchment Al-enriched lateritic rocks. Multivariate statistical analyses show that Hg is strongly associated with total organic carbon (TOC), loss on ignition (LOI), and SO3, indicating that organic matter is the main factor controlling the distribution of Hg and the major cause of Hg enrichment in lake sediments. The ecological risk index revealed no risk for both water types. A low pollution risk from Hg was observed for most of the soil and sediments samples, except for 11% of lake sediment samples, which registered moderate risk. In case of non-carcinogenic health effect on either adults and children in terms of Hg contamination, there is no adverse effects on biota. However, considering the Hg bioaccumulation in the food chain and the possibility of changes in environmental conditions favoring Hg mobilization in the sediment-water interface, e.g., the impact of garimpos, it is relevant to maintain efforts of monitoring and to develop more comprehensive studies on THg cycling in different environmental media in the Carajás region.

Palavras Chave

Mercury contamination; soil-sediment-water system; Geogenic origin; Southeastern Amazonia; Carajás Province.