Luiz Drude de Lacerda

GLOBAL MERCURY EMISSIONS FROM GOLD AND SILVER MINING

Mercury has been used m gold and silver mining since Roman times. With the invention of the “patio” process in Spanish colonial America, silver and gold were produced in large scale, mostly in the Americas but also in Australia, Southeast Asia and even m England. Mercury released to the biosphere due to this activity may have reached over 260,000 t from 1550 to 1930, when silver reserves in Spanish colonial America were nearly exhausted and Hg-amalgamation was replaced by the more efficient cyanidation process Exceptional increases in gold prices and the worsening of social-economic conditions m the third world in the 1970s, resulted in a new gold rush in the southern hemisphere, involving over 10 million people in all continents, Presently, Hg amalgamation is used as a major technique for gold production in the South America especially the Amazon, China, Southeast Asia and in some African countries. Mercury inputs to the environment from this activity may reach up to 460 t yr−1. Compared with other anthropogenic Hg sources, gold mining is presently responsible for approximately 10% of the global anthropogenic Hg emissions, but has never been included m global models of Hg cycling in the biosphere. Further, most of the Hg released to the biosphere through gold and silver mining during the last 500 ,years, roughly 300,(100 t, may still participate in the global Hg cycle through remobilization from abandoned tailings and other contaminated areas.

Elevated mercury concentrations in soils, sediments, water, and fish of the Madeira River basin, Brazilian Amazon: a function of natural enrichments?

Previous site-specific investigations have found that mercury concentrations in water, sediments, and biota of the Brazilian Amazon are elevated above global averages, and that these concentrations are a direct result of widespread mercury amalgamation mining operations conducted by non-organized prospectors. In order to assess the regional impacts of Hg contamination from these non-organized gold mining activities, water, sediments, and fish were systematically collected in 1997 along a 900-km reach of the Madeira River. The sampling program extended from the Amazon River upstream to Porto Velho, the site of historic and ongoing mercury amalgamation mining. Mercury concentrations were found to be elevated above global averages in all sampled media. However, the geochemical data suggest that the high mercury levels are due largely to natural sources and natural biogeochemical processes, and that the impacts of anthropogenically released mercury from mine sites is relatively localized.

Metals reservoir in a red mangrove forest.

This study presents heavy metal concentrations and distributions in a mangrove forest in Sepetiba Bay, Rio de Janeiro. Sediments are the main reservoir of the total metal contained in mangrove studied: 99 percent for Mn; 100 percent for Fe; 100 percent for Zn; 99 percent for Cu; 100 percent for Cr and 100 percent for Pb and Cd. Rhizophora mangle biomass contained less than 1 percent of reservoir. Within the biotic compartment, perennial tissues accounted for almost all of the metals present in biomass. The results indicate that mangrove may act as an efficient metal trap in tropical coastal environments.

Factors affecting the hydrochemistry of a mangrove tidal creek, sepetiba bay, Brazil

We studied the porewater chemistry, and spatial and temporal variation of mangrove creek hydrochemistry. Except for nitrate porewater, the concentrations of nutrients we analysed were higher than for creek water. Groundwater is a source of silica and phosphate, whereas total alkalinity and ammonium are related to mangrove porewater migration to the creek. Open bay waters contribute chlorine, dissolved oxygen and elevated pH. The results also suggest that nitrate is related to nitrification inside the creek. During flood tides, salinity, chlorine, dissolved oxygen and pH increase, whereas total alkalinity decreases. This pattern is reversed at ebb tides. Silica, phosphate, nitrate and ammonium show an erratic behaviour during the tidal cycle. Tidal dynamics, precipitation events and nitrification inside the creek were identified as major control factors and an estimate of tidal exchanges indicate that the system is in an equilibrium state.

Mercury concentrations in inland waters of gold-mining areas in Rondônia, Brazil

Total mercury concentrations in water, sediments and fish from the gold-mining areas of Brazil, especially the Amazon region, are presented. Mercury concentrations were variable among rivers, with the highest values found in samples from tributary forest rivers. Concentrations in water samples varied between 0.1 and 8.6 micrograms l-1, while in bottom sediments they reached 19,800 micrograms kg-1. Concentrations in edible parts of locally consumed fish reached up to 2700 micrograms kg-1 wet wt, surpassing by almost five times the Brazilian advisory level for human consumption.

Trace metal retention in mangrove ecosystems in Guanabara bay, SE Brazil

Along contrasting environmental conditions (e.g., degree of trace metal contamination and mangrove forest structural development), sediments of Laguncularia racemosa-dominated mangrove stands in Guanabara Bay (SE Brazil) presented a trend of trace metal accumulation in forms with low potential of remobilization and biotic uptake. Concurrently, a relatively low transfer of sediment-bound metals to L. racemosa leaves was observed, which may moderate the metal export from the forests via leaf litter transport and the metal availability to enter in food chains based on leaf consumption.

Fish contamination and human exposure to mercury in Tartarugalzinho River, Amapa State, Northern Amazon, Brazil: a screening approach

This study reports for the first time, the Hg concentrations in the fish fauna of the Tartarugalzinho river basin - an important gold mining region in Amapa State, Northern Amazon - and evaluates human exposure to Hg due to fish consumption in the area. We analyzed 16 fish species (carnivorous and omnivorous) common in the aquatic environment of the Tartarugalzinho area and which are mostly consumed by the local population. Mercury concentrations in fish ranged from 35 µg.kg-1 to 1,225 µg.kg-1. Among the analyzed fish, 8 species (50%) presented Hg concentrations higher than 500 µg.kg-1, the U.S. Food and Drug Administration (FDA) Action Level for concentration of Hg in fish. No statistical difference was observed between Hg mean concentrations in carnivorous and omnivorous fish. Within a given species, Hg concentrations were positively correlated with fish size or weight. The Hg concentration ratio between fish and water showed values higher than 50,000. Human exposure was estimated through the daily Hg intake obtained through interviews with the local population on the amount and species of fish consumed and the Hg concentration in the fish. The estimated average daily intake was 114 µg.day-1. This amount is approximately one-half of the WHO recommended provisional tolerable Hg weekly intake. At screening level, it assumes that there is a level of exposure (e.g, USEPAs RfD = Reference of Dose) below which it is unlikely for even sensitive populations to experience adverse health effects. The estimated exposure level for adult humans (1.6 µg.kg-1.day-1) was nearly 5 times greater than Hg RfD (0.3 µg.kg-1.day-1). The results suggest a widespread Hg contamination in the local fish fauna. Due to high fish Hg concentrations and high fish intake by local population, environmental exposure to Hg is also high, presenting a health risk to population.

Mercury dispersal in water, sediments and aquatic biota of a gold mining tailing deposit drainage in pocone, Brazil

In the Pocone district, Brazil, Hg distribution was studied in a small watershed which drains tailings from a 10 yr old gold mining operation. Heavy regional rains are responsible for continuous weathering, thereby making it possible to transport Hg into the ecologically important Pantanal area. Mercury concentrations in creek sediments range from < 0.02 to 0.18 mg. kg−1. The highest concentrations occur close to the tailings deposit. Mercury concentrations in the water were always below the detection limit of the analytical method used (<0.04 µg. L−1). Suspended matter samples collected before, during and after a storm, showed a Hg peak value of 0.61 mg kg−1. about 30 min after the event. Dissolved Hg concentration still fell below the detection limit. Among the biota, molluscs accumulated moderately high concentrations of Hg, while macrophytes and fish did not. Mercury concentrations in molluscs were dependent on size, with larger animals presenting higher Hg concentration. We conclude that Hg present in the tailings shows low mobility and that its eventual transport into the drainage system is dependent on the erosion of fine material from the wastes during rains, resulting in a restricted contamination of the area and low Hg concentration in the biota.

The fate of trace metals in suspended matter in a mangrove creek during a tidal cycle

The variation of heavy metal content in suspended matter (SM) during tidal cycles in a mangrove creek is described. The stable isotope of carbon was used as a tracer for sources of SM to the system. During tidal cycles three patterns of metal variability were found. The first, represented by Fe, showed an irregular and small variability throughout the cycle; a second, represented by Mn, exhibited a sharp increase in concentration during the rising tide, coincident with the greatest variation of pH and Eh. The third pattern, including Cu, Cd, Pb, Ni, Cr and Zn, showed maximum concentration at the peak of the high tide, coincident with a shift in SM source. The stable isotope of carbon indicated that, during low tides, most of the organic carbon exported originated from mangrove plant detritus, while during the high tides organic carbon imported by the system was almost totally of marine origin. This shift of SM source is the principal parameter controlling metal fluxes through the system. Changes in water pH and Eh, and manganese precipitation, can also serve as a secondary control. Although the results strongly suggest that the metallic load of marine SM is being immobilized by the mangrove environment, mass balance studies are necessary to show whether a net accumulation of metals is actually occurring.

Iron and chromium transport and accumulation in a mangrove ecosystem

The export and import of Fe and Cr through a mangrove tidal creek and their further accumulation in bottom sediments were studied in a mangrove forest at the south coast of Rio de Janeiro State, Brazil. The mass balance after 4 tidal cycles showed a mean net accumulation of 891 g of Fe per tidal cycle and of 2.1 g of Cr per tidal cycle. This accumulation was due to the net import of large amounts of suspended material enriched in the two metals. Iron was buried in mangrove sediments as Fe sulfides while Cr burial was probably due to immobilization of refractory Cr-organic compounds.