Risk Assessment of Mercury in Alta Floresta. Amazon Basin - Brazil

In the last 15 years gold mining activity has been the main source of the mercury (Hg) emissions into the atmosphere in the Amazon Basin. The first phase of gold production takes place in remote areas. In general the second one happens in the local urban area, where the gold is commercialized and sent to the great economic centers. In the last 3 years, this activity started to decline as a consequence of the high cost of the gold production but in the Municipality of Alta Floresta, the gold trade still plays an important role in the local economy. This paper addresses the assessment of the Hg exposure scenarios and their quantitative risk for inhalation of metallic Hg vapor and for ingestion of total Hg, using indirect exposure measurements, for different age groups of the urban area of Alta Floresta. This work took into account the field study which provided background information, such as characteristics of local and regional environment, Hg concentrations in different environmental media, and the character of the local urban population. The mean levels of Hg in the atmosphere of the urban area ranged from 210 ng/m³ to 880 ng/m³. Alta Floresta has no riverside population and there is a low fish consumption rate of 8 g/d among the general population. However, mercury levels in locally consumed carnivorous fish, ranged from 0.3 to 3.6 mg/kg, depending on the species and on the period of the year. The levels of mercury in soil surrounding the residential areas near the Hg emissions sources, ranged from 0.05 to 4.10 mg/kg. Hg in soil may represent an important source of mercury ingestion for local children up to 4 years of age. The mean Hazard Index estimated for the general adult population was 1.4. For the general population, regarding the number of persons exposed in the urban area, inhalation of metallic Hg vapor is the main route of exposure. The results for water ingestion for all groups are negligible. For families of fishermen the Hazard Index was estimated to be 9.3, with a contribution of 92% from fish ingestion.     

Atmospheric mercury and trace elements in the region of Alta Floresta in the Amazon Basin

In the early 1980's the Amazon region in the North of Brazil was the scene of the most intense gold rush in the history of Brazil. Metallic mercury (Hg) in gold mining activities is used to amalgamate particulate gold. The other sources of Hg emissions in Amazonian are tailing deposits and biomass burning of tropical forests and savannas. Total Hg concentrations in the urban area of Alta Floresta ranged from 20 to 5800 ng/m³. Indoor total Hg concentration in gold shops ranged from 250 to 40600 ng/m³. Particulate Hg accounts for 5 to 20% of total Hg in Alta Floresta. Through Factor and cluster analysis it was obtained a pattern of relationships between total Hg, fine and coarse mode particulate Hg, Pt, Pb, Ag and several other trace elements associated with the amalgamation process. A clear correlation was also observed with the fine mode biomass burning aerosol and coarse mode soil dust.