ENVIRONMENTAL RESEARCH, SECTION A 77, 73Ð78 (1998) ARTICLE NO. ER983828 Gold Mining as a Source of Mercury Exposure in the Brazilian Amazon Olaf Malm Laborato« rio de Radioiso« topos Eduardo Penna Franca, Instituto de Biofõ«sica Carlos Chagas Filho, CCS, UFRJ, 21941-000 Rio de Janeiro, Brazil Received January 6, 1998 (50 AD) describes the mining technique for gold and Amalgamation has been used for more than 4500 silver with an amalgamation process that is similar years in mining processes. Mercury has been exten- to the one used today in many gold mining areas. sively used in South America by Spanish colonizers Final recovery of ®ne gold particles extracted was for precious metal recovery. It is estimated that always done through heating or burning of the amal- between 1550 and 1880, nearly 200,000 metric tonnes gam with high mercury emissions to the atmosphere of mercury was released to the environment. Dur- in many tropical countries, especially in South ing the present gold rush, Brazil is ®rst in South America but also in Asia and Africa where a new America and second in the world in gold production (with 90% coming from informal mining or garim- gold rush is occurring (Lacerda and Salomons, pos). At least 2000 tonnes of mercury has been re- 1997). In South America this procedure has ben used leased to the environment in the present gold rush. in countries like Brazil, Venezuela, Colombia, From the mid 1980s, environmental research has Bolivia, French Guyana, Guyana, Ecuador, and been carried out in impacted Amazon rivers, later Peru since the 1980s. followed by human exposure studies. The river The current gold rush in South America is the basins studied were the Tapajo« s, Madeira, and Ne- consequence of an increase in the gold prices during gro, but also some man-made reservoirs and areas the 1970s by a factor of 8 to 10, but also has a strong in central Brazil. The analyses mainly involved association with social and economic dif®culties, in- sediments, soil, air, ®sh, human hair, and urine. The cluding unemployment, poverty, etc. (Pfeiffer and results show high variability, perhaps related to Lacerda, 1988). biological diversity, biogeochemical differences in the river basins, and seasonal changes. High mer- Mercury was extensively used in South America cury values also occur in some areas with no known (mainly Mexico, Peru, and Bolivia) by Spanish colon- history of gold mining. The results available docu- izers for silver and gold recovery. It is estimated ment a considerable impact on environmental mer- that, from the middle sixteenth century (1550) to the cury concentrations and frequent occurrence of middle nineteenth century (1880), nearly 200,000 human exposure levels that may lead to adverse tonnes of mercury was released to the environment health effects. ( 1998 Academic Press (Nriagu, 1993). A release of 400 tonnes is estimated Key Words: mercury; amazon; air; ®sh; hair; for colonial Brazil during the same period (Lacerda, urine; human risk. 1997). Since the 1980s, Brazil has ranked as ®rst in South American gold production with annual pro- INTRODUCTION duction from 100 to 200 tonnes per year during the past 20 years 70 (with to nearly 90% coming from Artisanal goldmining is using simple processes to informal mining or garimpos), followed by Colombia, extract gold from secondary or primary ore bodies. Venezuela, Peru, and Bolivia. This production would Usually secondary deposits or very ®ne gold par- correspond to about 2000 to 3000 tonnes of mercury ticles need mercury for good gold recovery. The released into the Brazilian Amazon environment amalgamation process was known by the Phoe- during the present gold rush. These estimates are nicians and the Carthagians (2700 BC), who com- approximate, since formal gold production and mercialized mercury from the Almade« n mines in mercury imports were not well registered. Table 1 Spain. Caius Plinius in his ``Natural History'' shows some estimates of mercury released to the 73 0013-9351/98 $25.00 Copyright ( 1998 by Academic Press All rights of reproduction in any form reserved. 74 OLAF MALM TABLE 1 miners (Veiga, 1997). During the peak of the gold Estimated Mercury Input to the Environment Due to Gold rush the estimated number of miners in Brazil alone and Silver Mining was above 1,600,000 (Pfeiffer and Lacerda, 1988). Studies on mercury transport to water bodies, its Total input Annual input Period (tonnes) (tonnesper year) transformation to methylmercury, and the contami- nation of food chains, including human beings, are Spanish Colonial America 1554Ð1880 196,000 600 quite recent in South American countries. In the All North America 1840Ð1900 60,000 1,000 Colonial Brazil 1800Ð1880 400 5 middle 1980s environmental research began in the Amazon river basins. Brazilian Amazon 1979Ð1994 2,300 150 Investigations were mainly performed with sedi- Venezuela 1988Ð1997 360 40 Colombia 1987Ð1997 240 30 ments, soil, air, ®sh, human hair, and urine samples. Bolivia (Pando Department) 1979Ð1997 300 20 The most well studied river basins are the Tapajo« s, Madeira, and Negro, but some man-made reservoirs Philippines 1985Ð1997 200 26 Tanzania 1991Ð1997 24 6 and some areas in central Brazil have also been China 1992Ð1997 480 120 studied. These results will be brie¯y summarized here. Note. Data from Nriagu, 1993; Lacerda and Salomons, 1997; Veiga, 1997, and estimates from the author. RESULTS Different samples from distinct goldmining areas environment due to mining. If total mercury releases have helped in understanding the tropical mercury are considered, colonial environmental discharges cycle and identi®ed human exposure pathways and were about 600 tonnes per year, while currently possible risks. As a general result in the case of averaging about 150 tonnes per year. Mining of gold mercury vapor, resulting from burning or reburning and silver during the colonial period utilized mainly of gold amalgams, the main group of humans ex- primary ores but the current gold rush in the Ama- posed are the gold dealers in shops rather than the zon affects mainly secondary gold deposits (colluvial gold miners (garimpeiros), who work outdoors. In or alluvial gold reserves) in soils or river sediments, the case of methylmercury, the riverine populations where mercury releases during mining directly in- constitute the group at risk, as they depend on ®sh volve water bodies. as their main source of protein. The total number of miners is probably between The ®rst critical human exposure to mercury re- 200,000 and 400,000 within the Brazilian Amazon. sults from the burning of the amalgam, when a sig- Half as many are thought to exist in Colombia and ni®cant fraction of mercury emissions occur mainly Ecuador. For all Latin American countries combined, to the atmosphere. Table 2 summarizes the main the estimate is between 543,000 and 1,039,000 data on mercury in air from different studies. Very TABLE 2 Mercury Concentration (lgm23) in Air from Urban, Rural, or Occupational Exposures Origin/situation Average N Range Reference Rondoˆ nia Ð SW Amazon Urban, far from reburning areas Ð 7 (0.02Ð(0.66 Malm et al., 1991 Urban, nearby reburning areas 2.80 8 0.45Ð7.50 Occupational exposure during reburning in the dealer's shops 71.40 7 17.50Ð107.20 Occupational exposure during burning in the ®eld with various retorts 91.70 6 (10.24Ð296 Occupational exposure during burning in the ®eld without retorts 15,499 6 (42.29Ð59,600 Outlets with contrary water re¯ux for mercury recovery system 1,280 5 (120Ð5,162 Air samples close to waterfalls Ð 3 (0.14Ð0.50 Pocone« City (urban area) Ð Central Brazil Urban, nearby reburning areas Ð 10 (0.14Ð1.86 Marins et al., 1991 Above tailings 0.08 Tumpling et al., 1995 Alta Floresta City Ð South Amazon Occupational exposure during reburning in the dealer's shops 5.14 86 0.07Ð40.60 Hacon et al., 1995 Urban, far from reburning areas 0.61 152 0.01Ð5.79 GOLD MINING AND MERCURY EXPOSURE IN AMAZON 75 high air mercury concentrations are found when decline, thus reducing the number of primitive gold burning amalgam in open air. Fortunately this oc- shops, but perhaps also is the result of recommenda- curs at a low frequency (about once a week) in con- tions by a local physician, Dr. Fernando J. P. nection with gold mining. High mercury air values Branches. In Alta Floresta the values were signi®c- were found also in indoor areas in gold dealer shops antly lower (up to 70 lg/L; median value of 11.7 even without reburning activities. In our studies during the period from 1991 to 1995), but this is (Malm et al., 1995b) an average value of 71.50 lg´ a young city with newer and better ventilated shops m~3 was obtained, i.e., above the 50 lg´m~3 (Malm et al., 1997). maximum limit established by WHO (1991) for occu- Fish is the main source of methylmercury to hu- pational exposure. A more recent study (Hacon et al., mans. Piscivorous or carnivorous ®sh from several 1995) showed lower average values, perhaps due to goldmining areas show higher mercury concentra- decreased production rates. tions followed by ®sh from lower trophic levels such Inhaled metallic mercury is readily absorbed as omnivorous, detritivorous, and herbivorous spe- through lungs (more than 85%) and after some time cies. in the blood stream, part is oxidized and accumu- The former should be monitored as indicators of lated in the kidneys (WHO, 1991). The mercuric ion aquatic system contamination as well as for public is excreted through urine, which is the best indicator health reasons (Pfeiffer et al., 1993). There are of metallic mercury exposure and inorganic mercury around 200 different ®sh species of commercial im- body burden (WHO, 1991).