Abstract. Mercury has born used in gold and silver mining since Roman times. With the invorrtion of the "patio" proo..'ss in Spanish colonial ,4.mtwiea, silver and gold were produced in large scale, mostly in the Americas but also in Aus~-alia. Southeast Asia and evon in 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 norly exhausted and Hg-amalgamation was replaced by the more eftlcient cyanidation process. Exceptiolaal increases in gold pric~ and the worsening of social-economic omditions in the third world in the 1970% resulted in a new gold rush in the southern herni.,q~here, involving over 10 million people in all continents. Prese~ly, Hg amalgamation is used as a major ttxtmique for gold production in the South Amerk.,'a especially the Amazcrt, China, Southeast Asia and in some African countries. Mercury inputs to the environment from this activity may reach up to 460 Lyr "l. Compared with other anthropogenic Hg sources, gold mining is presently responsible for approximatoly 10% of the global arrthropogenic Hg onissions, but has never born included in global models of Hg cycling in the bioephcre. Furthcr, most of the Hg released to the biosphere through gold and silver mining during the last 500 years, roughly 300,000 L may still participate in the global Hg cycle through remobilization fi'om abandoned tailings and other contaminated areas.

Soils and porewater of the rhizosphere of mangrove trees, Rhizophora mangle L. and Avicennia schaueria Leech., of the salt marsh grass Spartina alterniflora Loisel, and of unvegetated mud flats, were analyzed salinity, platinum electrode redox potential, organic matter content, sulfide concentrations, and the total changeable concentrations of trace metals (Fe, Zn, Cu, Pb and Cd). The study was conducted in a fringe m forest in Sepetiba Bay, Rio de Janeiro, Brazil. The rhizospheres differed in their biogeochemistry. Mud f Rhizophora soils were very reducing, with highest concentrations of sulfide. Avicennia soils showed t variability of the variables measured, with the rhizosphere changing from oxic to anoxic conditions. Spa on the other hand, were generally oxic, with very low sulfide concentration.The distribution of trace metals in these soils varied with the major physical and chemical characteris flat soils presented the highest total trace metal concentrations followed by mangrove soils and Spartina soils. exchangeable trace metals were similar among the different soils with the exception of Avicennia soils, wh their characteristic instability of redox conditions, presented much higher exchangeable trace metals conc RESUMO Solos e aguas intersticiais sob a influencia da rizosfera de arvores de mangue (Rhizophora mangle L. e Avicennia schaueriana Stapf & Leech.), de graminea de marisma Spartina alterniflora Loisel, e de areas sem vegetacao em planicies de lama, foram analizados em relacao ao pH, potencial redox, salinidade, teor de materia organica e concentraSao de sulfetos, e das concentraoces totais e trocaveis de metais traco (Fe, Zn, Cu, Pb e Cd), em uma floresta de mangue de franja na Baia de Sepetiba, Rio de Janeiro. Os resultados mostraram que a rizosfera das diferentes plantas mostraram diferenSas significativas em sua biogeoquimica. Os solos de planicie de mare e sob Rhizophora apresentaram-se mais redutores e com altas concentrac6es de sulfetos. Os solos sob Avicennia mostraram as maiores variaSoes dos parametros medidos, alternado condioces 6xicas e an6xicas. Por outro lado, os solos sob Spartina apresentaram-se geralmente 6xicos, com baixas concentra,ces de sulfetos.As concentraoces de metais traco tambem foram diferentes entre os diferentes solos, variando de acordo com as principais caracteristicas fisico-quimicas. Os solos de planicie de mare apresentaram as maiores concentraoces de metais totais, seguindo-se os solos de mangue e por ultimo os solos sob Spartina. Entretanto, as concentraoces trocaveis de metais traSo foram semelhantes para todos os solos, menos aqueles sob Avicennia, que devido a sua tipica instabilidade de potencial redox, apresentou a maiores concentrazces de metais trocaveis.

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The Guanabara Bay basin, SE Brazil, is shown as an experimental site to evaluate development and sustainability in coastal areas. We developed a Driver-Pressure-State-Impact-Response (DPSIR) framework in a practical context to integrate natural and socio-economic indicators. Sustainability reflects public policies towards the utilization of natural resources. Cost-benefit analysis (CBA) included in DPSIR evaluates losses and benefits resulting from such policies. CBA has some limitations due to the difficulty of valuating environmental goods and services. Instead of valuating them we propose to combine sustainability indicators and defensive expenditures for the implementation of public policies. This approach agrees with the environmental conservation paradigm implicit in sustainable development. It allows an estimation of the physical natural capital depreciation (PNCD), by using it to correct the gross domestic product (GDP) of the study area, and demonstrating the present non-sustainable characteristics of the current policies applied to the area.

Large quantities of mercury are being released into the waters of the Amazon and its tributaries by gold-mining activities. Large releases are also taking place into the air. In this paper, the fate of mercury released to the environment by gold mining in the Brazilian Amazon is reviewed. Mercury contamination is presently widespread in the Amazon region. A major source of mercury in the local environment is the burning of the gold–mercury amalgam, which releases from 30 to 150 t of mercury yearly into the Amazon atmosphere. Air samples collected close to mining sites showed extremely high mercury concentrations (up to 7.5 μg∙m−3). Inside gold-dealers' shops or in amalgam-burning stations, ambient air concentrations may reach 100 μg∙m−3. A secondary source is the discharge of metallic mercury into rivers during the amalgamation process. Sediment concentrations frequently range from 0.3 to 3.0 μg∙g−1 in contaminated sites. However, values as high as 19.8 μg∙g−1 have been reported in some sites. Waters of many rivers are also contaminated, although reliable data on dissolved mercury concentrations are still lacking. Local carnivorous fishes typically show mercury concentrations higher than 1.0 μg∙g wet wt.−1 in contaminated sites and methyl mercury represents over 90% of the total content. Human groups with fish-based diets frequently show evidence of mercury contamination, with high mercury concentrations in hair (up to 70 μg∙g−1). However, a reliable epidemiological study on the affected population still has to be carried out.Key words: mercury, gold mining, Amazon, sediments, aquatic biota, humans.

Small-scale gold mining is a significant source of Hg to the environment and may reach an annual input of about 450 t of Hg, mostly in South America, Russia and Asia. Countries of the Amazon Basin and Russia are the major contributors. On a regional scale, this source can contribute to more than 50% of the total Hg anthropogenic emission. Because of amalgam burning and bullion smelting under generally uncontrolled conditions, the majority of the emission is to the atmosphere. Therefore, on a global scale small-scale gold mining contributes about 20% of the total Hg atmospheric emissions from human activities. Most emissions occur in tropical developing countries. Preliminary results from research in the Amazon region suggest the Hg cycling in tropical rainforest environments is probably more dynamic and critical than in previously studied temperate environments, being strongly influenced by the existing ecological cycles and affected by land-use changes. At least two components of the Hg cycle can be identified. A short-term component, involving methylation of deposited Hg 2+ in aquatic systems and a long-term component, involving the re-emission of Hg deposited in soils particularly because of changes in soil use.

Global climate change interacts with regional alterations of land use in coastal basins and promotes rapid changes in the biogeochemistry of the coastal zone. These changes are generally stronger in extreme environments such as polar and semiarid regions. In these environments, biogeochemical changes result in a greater transfer of pollutants from the continent to the sea with resultant contamination of marine biota. In semiarid regions, there is a reduction in continental runoff and bulk pollutant transport, but paradoxically, there is an increase in the export of more bioavailable pollutants, resulting in higher contamination of the marine biota. In tropical latitudes, mangroves dominate coastal and estuarine environments and respond rapidly to environmental changes. The semiarid coast of Brazil is strongly affected by climate change. A major environmental response is altered hydrodynamics, generally involving decreasing continental runoff to the ocean, caused by reducing annual rainfall and damming of rivers. Also, strengthening of marine forcing due to heat accumulation in the South Atlantic Ocean and rising sea level pushes shelf and coastal waters into estuaries. Basin and oceanic processes undergo positive feedback, which causes an increase in the water residence time in estuaries, an extension of saline intrusion landward, accumulation of sediments in the inner reaches of estuaries, and the expansion of mangrove areas, particularly over the past 50 years. Expansion of mangroves means an expansion of sulfate reduction metabolism, which produces large amounts of dissolved organic carbon, characterized by a high capacity for forming organo-metallic complexes of high environmental significance. Dissolved and particulate Hg concentrations and fluxes are greater from the river to the estuary than from the estuary to the sea, producing an accumulation of particulate Hg in the estuary. Particulate Hg export may occur only during extremely rainy periods, and Hg is eventually deposited is shelf sediments, displaying low bioavailability. Export of dissolved, reactive, and DOC-bound Hg is practically nonexistent during rainy periods but increases by two orders of magnitude during the progressively longer dry periods. These highly bioavailable forms of Hg will enter food webs in the lower estuary and coastal areas, increasing contamination of the biota and human exposure to Hg.

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