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Part1 Contaminated Sites
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Inorganic and organic geochemistry of waste material from the Idrija mercury mine, Slovenia CARINA ALCALA, JORGE E. SPANGENBERG & JOST V. LAVRIC Abstract: Ore smelter emissions, rock dumps and tailings are the major sources of Hg contamination in Idrija. Significant amounts of polycyclic aromatic hydrocarbons (PAH), persistent priority pollutants, are associated to the Idrija Hg ore. Natural PAH sources in the Idrija ecosystem include: i) pyrolytic PAH released from the outcropping or during mining exposed Hg ore, ii) PAH in the free oil staining the ore host rocks which have reached the oil window, and iii) PAH of biological origin (e.g., plants degradation, biosynthesis). Mining-related anthropogenic PAH originate from tailings containing pyrolytic hydrocarbons formed during roasting of the mercury-ore, and PAH emissions from the ore smelter. This study deals with the inorganic, organic molecular and isotope geochemistry of Idrija tailings. The studied materials include sediments and soils in vertical profiles to a depth of 200 cm in three old tailings and ore roasting sites, rock dumps, and fragments of clay retorts used for roasting of the Hg ore. A pristine locality near Idrija was sampled to assess the regional geochemical background. Thirty major (Si, Al, Fe, Mg, Ca, Na, K), minor (Mn, P, Ti, S) and selected trace elements were determined in all samples. The Hg content in tailings (n = 29) profiles decreases downwards from 7572 to the background value of 2 µg/g. The Hg content of retorts fragments (n = 5) range from 5300 to 12290 µg/g. Threshold values for pollutants in soils were exceeded also for As (up to 320 µg/g), S (up to 6700 µg/g), and Br (up to 750 µg/g). These elements concentrations are significantly correlated (r2 > 0.8) with Hg. High P2O5 concentrations (up to 5490 µg/g) in tailings and roasting sites samples likely originate from the phosphate rich Hg ore (mineralization in the fossiliferous Skonca beds). The distribution of n-alkanes in soil profiles ranges in C-chain length from C12 to C31 and shows an odd-over-even C number predominance in the range C21 to C31, and bimodality with peaks at C16-17 and C29. The shorter chain n-alkanes maximizing at C17 are typically attributed to algae and cyanobacteria, and the longer-chain n-alkanes with an odd-over-even predominance are generally attributed to terrestrial higher plants. The higher plant contribution decreases vertically. Only trace amount of PAH were measured in the soil samples. Fragment of clay retorts, found at the roasting sites, have an n-alkanes distribution similar to the surrounding soils, but contain high amounts of non-methylated PAH and sulfur aromatic compounds such as benzonaphtothiophene, chrysene, triphenylenothiophene, benzofluoranthenes, and benzopyrenes. These samples are depleted in low molecular weight (LMW) and alkylated aromatic compounds, found in the primary PAH assemblage of Idrija ore. Their δ13C values (~ 20 ) indicate their origin from annelation of LMW PAH during roasting of the ore. These results complement previous studies by the research group on the Hg-PAH association in the fossil hydrothermal vents of Idrija deposit, and permit to identify natural and anthropogenic source of pyrolytic organic pollutants. This study was supported by the SNSF (grants 2100-059198 and 200020-100401 to JES) and the University of Lausanne. We thank Ljuba Gantar from the Ecological laboratory of the Idrija mine for Hg analyses. Key words: Idrija, PAH, mine tailings RMZ-M&G 2004, 51
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Mineralogical/Geochemical sampling and mercury pollution at La Soterraña mine, Asturias, Spain ÁLVAREZ, RODRIGO1, LOREDO, JORGE1 & GARCÍA IGLESIAS, JESÚS1 1
E.T.S. Ingenieros de Minas, University of Oviedo, Independencia 13, 33004 Oviedo, Spain, e-mail:
[email protected]
Abstract: In abandoned mine sites a mineralogical and geochemical study of wastes is a necessary step in order to characterize them for a suitable management. At La Soterraña mine spoil heap (Asturias, northwestern Spain), the pyrite is quantitatively the most important sulphide. Its behaviour and destabilisation in supergenic conditions dominates the geochemistry of the spoil heap and, in consequence, the production of acidic leachates when rainwater enters in contact with the stored wastes. Mercury rich minerals are also quite abundant in the spoil heap, being total Hg content of representative samples very high (maximum values of 3,200 mg.kg-1 have been detected). As-rich minerals are usually associated to the mined ore and, in consequence, wastes from mining and metallurgical operations show high As contents (up to 50,348 mg.kg-1). Geochemical studies of wastes reveal a significant correlation coefficient between mercury and arsenic (r = 0.8767). According to geochemical data, mercury anomalies have been detected in atmosphere and soil at the site of the abandoned mine and spoil heap. Mercury concentrations in the atmosphere reaches a maximum value of 1.9 µg.m-3, and, in soils, the maximum value of total mercury concentration is 502 mg.kg-1. Key words: Mercury, Abandoned mining, Mineralogical studies, Geochemical studies, Spain.
INTRODUCTION The currently abandoned mining works constitute a significant part of Asturias’ mining heritage. “La Soterraña” mine was one of the most important mercury mines of Asturias (north-western Spain). It was operated successfully until 1972. The ore was roasted at the site of the mine by means of retorts and mercury vapour was condensed and collected. In the neighborhood of the mine, located in a valley and very near to the village of Muñón-Cimero (Pola de Lena), a big spoil heap, covering an area of about 15,000 m2, represents a potential pollution source for atmosphere, soils and waters. The abundant
rainfall and the abrupt topography of the site are important factors favoring the weathering of the ore and mercury and arsenic dispersion. From a geological point of view, the ore deposit is included in the low levels of the Asturian Central Coal Basin (Carboniferous age), and it is mainly associated to porosity zones induced by fracturation of carboniferous limestones. The mineralization appears either as lenticular stocks in the carboniferous limestones, either as irregularly distributed veinlets; occasionally it appears as disseminations in the enclosing limestones and sandstones (LUQUE, 1985). The ore paragenRMZ-M&G 2004, 51
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esis is constituted by cinnabar, native mercury, pyrite, marcasite, arsenopyrite, orpiment, and realgar, as primary minerals; and goethite, scorodite, and gypsum as main secondary minerals, in a gangue of quartz and calcite. From an environmental point of view, it is especially significant the presence of arsenic minerals in the ore deposit paragenesis (LOREDO, 2000). The study of the mimineralogical and geochemical characteristics of wastes stored in the currently abandoned spoil heap, allow knowing data about the potential capacity of these materials to form polluted leachates, and the possibility that mercury and/or arsenic can occur in significant concentrations in soils and waters.
RESULTS AND DISCUSSION The dispersion of mercury and/or arsenic from the spoil heap to the environment is enhanced by the abrupt topography of the
site, the great volume of mine wastes stored, and its proximity to streams. Mineralogical studies (on macroscopic and microscopic scales) of mine and metallurgical wastes have been accomplished. It has been observed an abundant presence of iron sulphides (pyrite). It presents from framboidal to massive texture, and the rate of decomposition varies with grain size. Pyrite frequently shows zoned idiomorphic crystals (Figure 1), with differences in resistance to weathering, probably related to the content in arsenic: the most intensively altered zones are located in the borders of the pyrite and they correspond with high contents in arsenic by microprobe analyses. Arsenopyrite, which is idiomorphic, is usually surrounding and replacing pyrite crystals. Excepted cinnabar, sulphides are generally in an advanced state of the oxidation process, with amorphous iron oxyhydroxides coatings, where goethite is the most abundant. The potential of these mine and metallurgical wastes to pollute the
Figure 1. Pyrite showing zones with different weathering degree. RMZ-M&G 2004, 51
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environment is enhanced by the presence of specific arsenic minerals such as arsenopyrite, orpiment, realgar, scorodite, and As-rich pyrite, because its destabilisation results in the liberation of arsenic to the environment, which is precipitated, in part, within the iron hydroxides.
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In order to know the presence of elements of high environmental relevance such as As, in pyrite and goethite, electron microprobe analyses of representative samples from the spoil heap have been made. The study of pyrite crystals by electron microprobe showed high As contents, reaching up to 4.93 % As (Table 1).
Table 1. Statistical analysis of data from electron microprobe analyses of pyrite and goethite from the spoil heap (n = number of samples).
Multielemental geochemical analyses of representative samples of wastes have been also made with the aim of quantifying the presence and total concentrations of ecotoxic elements. Samples of mine/metallurgical wastes contain high total mercury and arsenic concentrations, ranging from 317 to 3,200 mg.kg-1 and from 600 to 50,348 mg.kg1 , respectively. Geochemical data reveal a significant correlation between mercury and arsenic (r = 0.8767). In the spoil heap, mercury and arsenic concentrations in wastes increase with deep, in a general sense, and they decrease strongly in the argillaceous substratum (Table 2).
According to geochemical data, the representation of the mercury and arsenic anomalies in soils show similar distribution patterns, related to the dispersion from anthropogenic sources (mining and metallurgical works). Total mercury concentrations in soils vary from 4.18 to 501 mg.kg-1, and total arsenic concentrations vary from 32 to 19,940 mg.kg-1. Downgradient of the spoil heap, surface water reaches 7.4 µg.l-1 Hg and 137 µg.l-1 As. Mercury concentration in the atmosphere reaches 1.9 µg.m-3 at the site of the mine.
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Table 2. Vertical evolution of Hg and As contents in a trench (located at the bottom of the spoil heap).
Although mercury leaching from wastes seems to be a not important process, the dispersion of fine fractions of wastes may be the most important mercury dispersal mechanism through the years. In general, there is a strong tendency for mercury to sorb to nearly every available surface, including sediments and soil organic matter. The capacity of rain to erode fine particles, enriched with mercury, from the waste pile, is important and suggests that erosion is the main pathway of mercury contamination, followed by mercury transport associated with suspended particles.
CONCLUSIONS Thirty years after the abandonment of the mining and metallurgical works, it is evident that high concentrations of mercury and arsenic persist in the wastes stored in the spoil heap. The mineralogical study evidences the
presence of different pyrite phases, with different grade of reactivity and As content. Although mercury leaching from wastes is not a remarkable process, as consequence of its low solubility, the dispersion by gravity and wind of fine fractions constitutes a significant environmental pathway. On the other side, arsenic is dispersed by water and high concentrations of this element in surface waters have been detected. Geochemical anomalies are predominantly associated to the location of wastes disposal and smelting chimneys. Soils have been intensively affected by mercury and arsenic dispersions; they reach concentrations with 500 and 2,000 orders of magnitude respectively higher than the background geochemical levels in the area. Acknowledgements We acknowledge the support by the project PB-TBI01-07 from the Principado de Asturias Government.
REFERENCES LOREDO, J. (2000): Historic unreclaimed mercury mines in Asturias (northwestern Spain): Environmental approaches; In: Assessing and Managing Mercury from Historic and Current Mining Activities, Environmental Protection Agency, San Francisco, pp.175-180. RMZ-M&G 2004, 51
LUQUE, C. (1985): Las mineralizaciones de mercurio de la Cordillera Cantábrica; PhD. Thesis; Univ. Oviedo. Inedit.
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Mercury and antibiotic resistance in bacterial flora of sediments from Cartagena Bay, Colombia ARROYO B., ARZUZA O., YOUNG G., PUELLO M., MENDOZA K., JOHNSON B., PIERMATTEY J. AND OLIVERO J. Environmental and Computational Chemistry Group Master of Microbiology Program, University of Cartagena, Colombia
Abstract: Chlor-alcali plants are one of the most important mercury pollution sources of water ecosystems. In the late seventies, after the detection of the heavy metal in seafood and sediments, a factory located on Cartagena Bay, Colombia, was shut down. The aim of this study was to evaluate the actual presence of mercury in the food chain of this ecosystem and the impact on the local bacterial community. Mercury distribution on sediments, fish and crabs from this waterbody revealed that the metal has been biomagnified along the food chain. Levels of mercury in bottom sediments near the chlor-alkali plant were at least two orders of magnitude greater that those found in a control site. In addition, these mercury concentrations decreased toward the north following the freshwater stream of the Dique Channel. A survey of sediment-associated bacteria along the Cartagena Bay showed that Klebsiella ozaenae, Pseudomonas fluorescen and Pseudomona putida were mercuryresistant species. Bacterial resistance to antibiotics determined by the Kirby-Bauer method suggested that Pseudomona aeuriginosa was the species with broader resistance. Moreover, a close association between mercury or antibiotic resistance patterns and sampling site was not observed.
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Mercury in some lakes of the Southern Ural. Influence of former gold mining EDWARD N. BARANOV, TATYANA G. LAPERDINA, YURY G. TATSY Vernadsky Institute of Geochemistry and Analytical Chemistry, Kosygin Str., 119991, Moscow, Russia; E-mail:
[email protected]
Abstract: The mercury content in fish and bottom sediments in some lakes of the Uchala district, the Southern Ural located on gold mining areas was investigated. It was shown, mercury pollution of lake bottom sediments (80-20,000 ìg/kg) have been resulted from the mercury use at gold amalgamation. Correlation between the concentration of mercury in the perch (58.6-752 mkg / kg) and the level of mercury pollution of lakes, age and weight of fishes are established. In the most polluted the lake Kalkan the mercury content in the perch exceeded maximum permissible limit and so these fishes are represented a danger to the local population health. Key words: mercury pollution, gold mining, fish, bottom sediment
INTRODUCTION
MATERIALS AND METHODS
The intensive mercury pollution of the environment in the gold mining regions is one of the global ecological problems (LACERDA, 1998). The mercury use for these purposes in USSR was officially forbidden in 1990. However its intensive and long use has resulted in significant mercury pollution of gold mining regions. These mining activities in the Ural have more than a 250-years history. The mercury pollution of some lakes located in the Uchala district (the South Ural, the Republic Bashkortostan) was studied in during two years. Placer and ore gold deposits were mined in the watersheds of some lakes for a long time (KUTLIAKHMETOV, 2002).
The field works on the lakes Karagaikul, Kalkan and Urgun have included sampling the bottom sediments and fish species, which used by local population in the food. Mercury have been determined by cold vapor atomic absorption with use of microwave decomposition (fishes) or pyrolysis (bottom sediments) with preconcentration on the gold collector.
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The Karagaikul Lake was chosen as the background lake since there were not any gold ore deposits and placers mining into its watershed. A large gold placer was mined in the end of XIX century in the valley of the small river Zhuravka flowed in the running Kalkan Lake. In the northern part of the largest unflowing Urgun Lake the lake-alluvial gold placer was mined.
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As an assessment of mercury contamination of lake fish the mercury contents in the perch (Perca fluviatilis) was used. For these purposes 6, 7 and 4 fish specimens were sampled from the Kalkan Lake, the Urgun Lake and the Karagaikul Lake respectively. Their properties were age 2-3 years, size 15.5-18.5 cm, and weight (without viscera) 44-78 g.
RESULTS AND DISCUSSION It was determined the following contents of mercury in the perch specimens (wet weight): the lowest average 69.7 µg/kg from the Karagaikul Lake, the increased content 127.8 µg/kg from the Urgun Lake and the very high content 565 µg/kg from the Kalkan
Lake (Figure 1). The mercury concentrations in three specimens from the Kalkan Lake exceeded the maximum permissible level (MPL) equal 600 µg/kg and in two samples were close to the MPL. The difference between the mercury contents in the perch specimens correlates with mercury concentrations in the lake bottom sediments. The most extended (more than 12 km) and intensive (up to 1.3 mg/kg, the background level equals 0.012 mg/kg) streams of industrial mercury are formed in the lake sediments due to erosion of gravel dumps formed by the plants for processing gold ores. The streams formed due to gold placer mining are characterized by lower mercury contents (up to 0.2 mg/kg) and smaller extension. The
Figure 1. RMZ-M&G 2004, 51
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analysis of lake sediment cores has shown the largest coastal mercury anomaly in the Kalkan Lake at the mouth of the River Zhuravka where the mercury concentration amount to 0.3 mg/kg (at a background level 0.008 mg/kg). The more severe pollution is characteristic for silt sediments of the Kalkan Lake. The maximal contents (more than 20 mg/kg) are determined in silts located near 40 m from the Zhuravka Rivers mouth. The silt sediments with the high mercury concentrations (up to 2 mg/kg) are situated near this mouth and central running zone of the lake without bottom sediments. The mercury content in silt is decreased at moving off this zone.
REFERENCES DE LACERDA, L. D., SALOMONS, W. (1998): Mercury from
gold and silver mining: A chemical time bomb?; Berlin: Heidelberg, 146 p. KUTLIAKHMETOV, A. N. (2002): Mercury pollution of the landscapes due to mining enterprises of Bashkirian Transural; Ph.D. Thesis, Ecaterinburg, 25 p. (in Russian).
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CONCLUSIONS The obtained results on the mercury distribution in the bottom sediments of the Kalkan Lake have shown that the basic source of mercury supply is the River Zhuravka. The watershed of this river is strongly polluted by mercury used previously at gold mining. The dangerous bioaccumulation of mercury in a fish of some lakes of the Southern Ural resulting from gold mining was registered. It is the serious ecological and sanitary problem and the actual danger to the population health of gold mining territories.
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Formation and Degradation of (CH3)2Hg in Nuclear Waste Tanks NICOLAS S BLOOM1, ERIC VON DER GEEST1, ERIC M. PRESTBO1, WILLIAM WILMARTH2, AND DONNIE THAXTON2 Frontier Geosciences, 414 Pontius North Seattle, WA 98109 USA; E-mail:
[email protected] 2 Westinghouse Savanna River Company, Aikin, SC, 29808
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Abstract: As a result of cold-war era Pu production, we have inherited a legacy of hazardous caustic wastes that are now being evaporated prior to conversion to solids. This brew, heated over decades via radioactive decay, was recently found to be producing (CH3)2Hg. We found that (CH3)2Hg is stable in these alkaline solutions, despite being saturated with oxidizers such as nitrate and nitrite. Organic matter containing methyl groups was found to generate significant quantities of (CH3)2Hg over time-scales of days to months. Key words: Dimethyl Mercury, Nuclear Waste Tanks
INTRODUCTION As a result of the production of the A-bomb, large volumes of radioactive, Hg bearing waste were created. These wastes consist largely of a saturated solution of NaOH, NaNO3, and NaNO2, a result of the HNO3 dissolution of fuel rods. In the process, Hg was added as a promoter for the dissolution of the Al cladding surrounding the U/Pu fuel. Once the U and Pu were extracted, the solution was made basic to precipitate out transition metals, leaving a solution high in Hg and 137Cs. Due to the addition of process chemicals, such as antifoam agent, and the practice of mixing wastes, these tanks contain many other trace compounds (including carboxylic acids, alkanes, detergents, solvents, and traces of Fe-Mn hydroxide sludges). As a result of high temperatures, pH, and radiation levels, long chain organics oxidize to shorter carboxylates, ending ultimately with oxalate (C2H2O4). It is the goal
of the Westinghouse Savannah River Company (WSRC) to reduce the volume of these wastes by evaporation, with the residue eventually being converted to a vitreous solid. During evaporation, however, we found that large quantities of (CH3)2Hg, were being emitted from the evaporator.
RESULTS AND DISCUSSION Analytical Methods. Hg analyses were conducted using cold vapour atomic fluorescence spectrometric (CVAFS) detection (BLOOM AND FITZGERALD, 1988). Hg was determined by first oxidizing a sample aliquot with BrCl, then reducing with SnCl2, purging the liberated Hg0 onto a gold trap, and thermally desorbing it into the CVAFS detector for quantification (B LOOM AND CRECELIUS, 1983). CH3Hg was determined by ethylation, collection by purging onto Carbotrap, and then analysis by isothermal RMZ-M&G 2004, 51
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GC-CVAFS (LIANG ET AL., 1994). (CH3)2Hg was determined by direct purging onto Carbotrap, followed by GC-CVAFS (LINDBERG ET AL., 2001). Degradation Studies. Four matrices were simulated: (a) waste tank liquor, simulated as 7 M NaOH plus 1 M each of NaNO3 and NaNO2, (b) evaporator condensate, simulated by bringing deionized water to pH 10 using the waste tank liquor, (c) 0.01 M HCl (pH 2), and (d) 0.01 M HNO3 (pH 2). Experiments were done by filling 250 mL glass bottles with the various matrix solutions, spiking to a level of 1.61 µg L-1 of (CH3)2Hg, and then sealing the bottles and placing them in laboratory ovens set nominally at 40, 60, and 80 °C. The actual mean oven temperatures over the period of the experiment were 39 ± 2 °C, 65 ± 5 °C, and 83 ± 5 °C respectively. Over a period of up to a month, a fresh bottle was periodically withdrawn from the oven, shaken thoroughly, and after cooling, an aliquot quickly taken for (CH3)2Hg analysis.
In-Tank Formation Studies. To assess the potential for the production of (CH3)2Hg within the storage tanks, various matrix solutions (initially containing 10,000 µg L-1 Hg(II)) were incubated as above. In this case, an attempt was made to more realistically RMZ-M&G 2004, 51
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mimic the composition of the tank wastes. We prepared the basic tank waste matrix according to the proportions shown in Table 1 (the basic matrix contained only the inorganics, oxalate, and formate; the other organics and sludges being held as variables). The experimental set-up consisted of a 3x3x3 matrix of the temperatures, three levels of organics (none, 1,600 mg L-1 acetate, and acetate plus a mixture of site organics), and three categories of sludge addition (none, 1.00 g L-1 S-01 or S-02). The sludges were tested to see whether they could catalyze the formation of (CH3)2Hg. Both sludges were largely Fe/Mn oxy-hydroxides contaminated by traces of various other metals. Essentially, S-01 was elevated in Cu, Zn, Rh, and Ru, while S-02 was elevated in Pd, Ag, and Pb. At each time, a bottle was withdrawn from the oven, shaken vigorously, and then allowed to cool and settle for several hours prior to aliquoting for analysis of (CH3)2Hg.
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On the final day of the experiment, aliquots were taken of the shaken and centrifuged solutions, to assess the degree to which Hg attached to the suspended matter. In addition, aliquots of the supernatant liquid were analyzed at this time for CH3Hg. Stability of (CH3)2Hg. For each condition, (CH3)2Hg was plotted versus time, and fitted with the best exponential decay curve (Figure 1). In the case of the pH 2 solutions, decay occurred so rapidly that only 34 quantifiable concentrations were obtained, although good fits were still obtained. The best fit exponential equations (C0 = C1*10-at) were then used to calculate the decay half-lives, when C0/C1 = 0.5, as shown in Table 2. (CH3)2Hg appears to be most stable under the mildly alkaline conditions present in the condensate, and least stable when acidified with HNO3. For each matrix, we see approximately 2 fold decrease in stability for every
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10 °C increase in temperature. The relatively short half-life for (CH3)2Hg in the alkaline waste tank medium suggests that it must be continuously generated in situ to maintain the high concentrations which are emitted during evaporation. In several of the decay test samples, we measured the Hg speciation in the sample at the end of the study. In those cases, we observed that the primary product of decay in the acidified samples was CH3Hg, while in the case of the alkaline waste media, it was unaccounted for (presumed to be Hg0, which was not analyzed). In Tank Formation of (CH3)2Hg. In all of the test cases where organics were added, (CH3)2Hg was created (Figure 2) at a rate that appeared to be linear over the time of the experiment. We observed only small random differences in formation as a result of the presence or absence of the metal hydroxide sludges. Because of this, formation data were calculated as the mean and standard deviation of the three sludge conditions for each of the temperature and organics combinations. Since the rate of increase was lin-
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ear, results were calculated as a conversion rate (% yr-1) based upon the final observed concentrations (Table 3). From this we see that the biggest factor in the observed methylation rate was the type of organics present. The samples containing the mixture of organic compounds in addition to acetate were observed to methylate the Hg(II) at a rate 330 times greater than with acetate alone, even though the sum of additional organics was only about 30 % of the acetate concentration. Though we were unable to conduct tests on individual organic compounds, we suspect that the strongest methylator is PMDS. The methylation rate was also strongly dependent upon temperature, with a 3-fold increase in methylation rate for every 10 °C increase in temperature. At the end of the experiment, the solutions were analyzed for total and dissolved Hg, and CH 3Hg, as shown for the acetate spiked samples in Table 4. Surprisingly, a very large percentage (5090 %) of the Hg(II) initially present had been converted to CH3Hg, even
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if only small quantities of (CH3)2Hg had yet been produced. The high conversion of Hg(II) to CH3Hg was observed even under the mildest conditions (39 °C, acetate only). CH3Hg was not monitored at earlier times, so we have no kinetic data regarding the addition of the first methyl group. From the evidence that we do have, however, this first methylation appears to occur very rapidly compared to that of the second methylation step.
CONCLUSIONS These experiments open a fascinating window into the chemistry of Hg in these complex industrial liquors. We hope that in the future, additional funding can be secured to more fully elucidate the methylation potential of specific classes of organic compounds, the separate reaction rates for the first and second methylation step, the role played by the formation and loss of Hgo, and the effect of high levels of ionizing radiation on the overall reaction pathway.
REFERENCES BLOOM, N. S AND FITZGERALD, W. F. (1988): Anal. Chim. Acta. Vol. 208, pp. 151-161. BLOOM, N. S AND CRECELIUS, E. A. (1983): Mar. Chem. Vol. 14, pp. 49-59.
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LIANG, L., BLOOM, N. S, AND HORVAT, M. (1994): Clin. Chem. Vol. 40, No. 4, pp. 602-607. LINDBERG, S. E., WALLSCHLÄGER, D., PRESTBO, E. M., BLOOM, N. S., PRICE, J., AND REINHART, D. (2001): Atmos Environ., Vol. 35, pp. 4011-4015.
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Gold Mining and Mercury Pollution in The Ghanaian Pra River Basin, West Africa BONZONGO1* J.C., DONKOR1, A.K., NARTEY2 V.K., AND M.E. HINES3 Dept. of Environmental Engineering Sciences, University of Florida, Gainesville, Fl.32611 2 Dept. of Chemistry, University of Ghana, Legon-Accra, Ghana 3 Department of Biological Sciences, University of Massachusetts, Lowell MA 01854, USA
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Abstract: In this work, levels, speciation and the spatial/temporal distribution of Hg in the Pra River basin in southwestern Ghana were investigated, to assess the environmental impact of Hg introduced into waterways by artisanal gold mining operations. Surface water, sediment, soil and human hair samples were collected along longitudinal transects from locations upstream of known point sources down to the river delta, using ultraclean techniques and analyzed by CV-AFS. Our results show that total-Hg (THg) concentrations are very high in river waters (28 to 1961 ng/L), as well as in soil samples collected near sites of amalgam roasting (up to 185 mg/Kg or ppm). THg concentrations in reverine sediments ranged from very low values of about 0.011ppm to concentrations as high as 19ppm in the vicinity of mining sites. Overall, most sediment samples had rather very low THg as compared to published values from Hg-contaminated sites. Reported THg levels in human tissues were quite low as compared to proposed safe limits. MeHg was also detected in all samples, and in contrast to well-studied Hg contaminated systems in America and Europe, its levels in analyzed Ghanaian sediment samples were 2 to 3 times higher than most published values. Finally, laboratory experiments using riverine sediments were conducted to assess the potential rates of Hg methylation and MeHg demethylation in these tropical settings, and obtained data are presented. Key words: Gold mining, mercury, Ghana, and tropical ecosystems
INTRODUCTION The advent of gold mining in Ghana dates to the early 19th century, via British and other foreign investors, and was more capital intensive and large-scale mining (TSIKATA, 1997). Artisanal gold mining (AGM) by the local population predates the first recorded contact with Europeans in 1471 (TSIKATA, 1997), and for centuries, gold has been extracted mainly from alluvial deposits and from denuded outcrops and subsurface sediments along the side of dried-up valleys (DUMETT, 1998). AGM by amalgamation with metallic Hg in Ghana is believed to be
over 2000 years old. However, the severity of Hg in the Ghanaian environment has not been thoroughly examined to ascertain the extent of Hg contamination of water, soil and air, as well as the biogeochemical fate of released Hg. In these tropical ecosystems, Hg introduced to the environment from mining operations is likely to disperse over several miles as a result of high annual precipitation and transport via fluvial processes. Moreover, warm temperatures found year round and the high organic matter content characteristic of mostly forested watersheds would favor Hg methylation, and therefore, the bioaccumulation of dispersed Hg. RMZ-M&G 2004, 51
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The Pra takes its source from Kwahu section of the Southern Voltaian Plateau. It enters the Gulf of Guinea a few miles east of Shama, a small coastal town. Because of the intense gold mining activity that is taking place in the upper reaches of the river, there is concern for Hg contamination in the Gulf of Guinea, where intensive commercial fishing occurs.
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RESULTS AND DISCUSSION Mercury data from survey of different environmental compartments and those obtained from the literature are summarized in Tables 1 and 2. Results from Hg methylation and MeHg demethylation using sediments with increasing total Hg content are presented in Table 3.
Table 1: Sampling sites, sample description, and Hg concentrations in (1) the aqueous phase, sediments, and in soils MeHg was determined on solid samples only. Organic carbon content was determined as LOI
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Data in Table 1 indicate a clear evidence of Hg contamination in analyzed water, sediment and soil samples. Samples collected from the control site (i.e. not directly impacted by mining activities) have Hg concentrations similar to those reported as baselines in several non-contaminated systems. THg concentrations in water samples collected from mining-impacted sites span a range of values (17.25 1,961 ng L-1) similar to those reported for certain US-EPA superfund sites contaminated by historic mining operations such as the Carson River, in Nevada, or the Slovenian Idrija River, which has been impacted by historic mining of cinnabar.
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In the last decade, several studies using body indicators have focused on health risks associated with human exposure to Hg from AGM. In these studies, Hg levels have been determined in blood, hair and urine samples and compared with established safe limits to assess the potential for toxicity in Hg exposed populations. Table 2, summarizes published data on selected populations inhabiting regions with AGM activities in in the studied river basin. Overall, reported Hg concentrations span a wide range, but the average Hg concentration in these studied populations indicates exposure to Hg.
Table 2: Summary of published data on sites impacted by AGM in the Pra River Basin
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To assess the potential of sediments in these impacted Ghanaian systems to produce and degrade methyl-Hg, surface sediments (0-10 cm) were collected from 4 sites within a 1 km radius from a mining site. THg concentrations in these samples decreased as one moved away from the mining site (Table 3). Potential rates of methylation and demethylation were determined on wetsieved sediments using radiotracers as described in HINES ET AL (2002). The results presented in Table 3 show the following. (1) The potential to produce MeHg decreases with Hg content of the sample. This could
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be due to the dilution of the radioisotope, or simply to effect of Hg on microorganisms, or both. Demethylation patterns follow a similar trend and indicate the difference in demethylation pathways as shown by CH4 data. At lower THg concentrations, MeHg is fully degraded by oxidative pathways, while reductive degradation dominates at a much higher concentration. The sample with 12ppm of Hg showed no MeHg degradation and could suggest a higher probability of MeHg accumulation in sites with high Hg levels in these studied tropical ecosystems.
Table 3: Potential rates of Hg methylation and MeHg demethylation in sediment samples collected along a transect near a mining site in the Pra River Basin.
CONCLUSIONS Comparatively, the average Hg concentrations determined in human tissues collected from Ghana are lower than those reported for Brazil, where general sensory disturbance in humans have been detected. However, it is important to note that the Ghanaian new gold rush started only in late 1980s and early 1990s following the governments legalization of AGM. Since then, AGM has been on the increase and more people are expected RMZ-M&G 2004, 51
to engage in artisanal gold mining. Unless cleaner production methods and/or policy/ enforced-regulations are introduced, similar to the Brazilian Amazon, one could conclude that a catastrophe is in the making in Ghana. Acknowledgements This work was supported by a fellowship to AKD by the Compton Foundation and the UF Foundation
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REFERENCES B ABUT , M,, P OTIN -G AUTIER , M., T ELLIER , S., BANNERMAN, W., CASELLAS, C., RAMBAUD, A. (2001) Assistance in assessing and reducing mercury pollution emanating from artisanal gold mining in Ghana, Phase I: Part IIConduct of surveys on river systems and overall conclusions. United Nations Industrial Development Organization, US/GHA/99/128. BONZONGO, J.C., DONKOR, A. K., NARTEY, V. K. AND LACERDA, L. D. (2004). Mercury pollution in Ghana: A case study of environmental impacts of artisanal gold mining in sub-Saharan Africa In Facets of Environmental Geochemistry in Tropical and Sub-tropical Environments. Lacerda L.D. & Santelli, R.E. (eds.) Springer Verlag, Berlin, 135-153.
DUMETT, R.E. (1998) El Dorado in West Africa. Ohio University Press, Athens, Ohio, 396 p. HINES, M.E., HORVAT, M., FAGANELI, J., BONZONGO, J.C., BARKAY, T., MAJOR, E.B., SCOTT, K.BAILEY, E.A., WARWICK, J.J., AND W.B. LYONS, (2000). Mercury biogeochemistry in the Idrija River, Slovenia from above the mine into the Gulf of Trieste, Environmental Research, 83: 129-139. TSIKATA, F.S. (1997) The vicissitudes of mineral policy in Ghana. Resources Policy 23: 9-14
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Enhancement of selective indigenous sedimentary microbial populations and effect on mercury transformation: Implications for Development of Liners in Engineered Wetlands JEAN-CLAUDE BONZONGO AND JORGE M. GOMEZ Department of Environmental Engineering Sciences, P.O. Box 116450, University of Florida, Gainesville, FL 32611-6450, USA
Abstract: Constructed wetlands are being used increasingly for containment and/or treatment of urban/wastewater runoffs. In these man-made ecological settings, the benefits of flood mitigation are supplemented by water quality improvements, obtained by removing pollutants via physicochemical and biological processes. However, while wetlands do a very good job with most contaminants, they make the situation worse with mercury (Hg). This is illustrated by recent research on the biogeochemistry of Hg, which indicates that wetlands are important sources of methyl-Hg (MeHg), a lipophylic organic form of Hg that is highly toxic and readily bioaccumulated. In this work, empirical knowledge of redox chemistry is used in combination with sedimentary microbial biogeochemistry to explore ways for controlling Hg methylation in constructed wetlands and/or water retention basins via enhancement of selected indigenous microbial populations. We used sediment manipulations in laboratory experiments to establish the link between different TEAPs and sediment ability to produce or degrade MeHg. Our results point to Mn- and Fe-oxyhydroxides as terminal electron acceptors (TEAs) with potential to limit MeHg production/accumulation. The identified TEAs are currently used in a long term mesocosm experiments, where either artificially Mn/Fe-enriched soils or natural Fe-rich Georgia clay are used as liners to help establish predominant TEAs in simulated flow through wetland systems, and limit MeHg production and export through enhancement of indigenous Mn- and Fe-reducing bacteria. Key words: wetlands, TEAPs, mercury transformation, remediation
INTRODUCTION Constructed wetlands are being increasingly used for containment and/or treatment of urban runoff and wastewaters. This way of improving water quality is definitely more cost-effective than most options that are currently available. In these man-made ecological settings, the benefits of flood mitigation are supplemented by water quality improvements, obtained by removing pollutants via RMZ-M&G 2004, 51
physicochemical and biological processes. In wetland settings, heavy metals (e.g., Hg, Pb, Cu, Cd) and metalloids (e.g., As) could be sorbed onto particles and removed by sedimentation from the aqueous phase. Such a process would increase the residence time of these pollutants in sediments and limit their re-suspension in the overlying water (KING ET AL., 2002), therefore, in the out flowing water. However, an obvious concern for using constructed wetland to remove Hg is
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the potential for formation of MeHg (ZILLIOUX ET AL., 1993; ST. LOUIS ET AL., 1994; 1996; PORVARI AND VERTA, 2003). Wetlands are known sites of MeHg formation. This fact has been reported for sites located in boreal regions (e.g., ST. LOUIS ET AL., 1994; 1996), the Florida Everglades, and the Panthanal in South America (e.g., VON TÜMPLING ET AL., 1995; YOKOO ET AL., 2001). However, due to the potential of wetlands to support several aerobic and anaerobic biogeochemical processes that regulate transformation of pollutants, they are now increasingly used worldwide for pollutant abatement. It is therefore clear that the benefits of water quality improvement provided by wetlands could be diminished by a serious environmental problem, that of MeHg contamination of water resources. Therefore, appropriate measures should be taken to minimize MeHg formation while maximizing the ability of wetlands to treat water. In this study, we hypothesized that the coupling of Hg transformations with the decomposition of organic matter in sediments/soils leads to peaks and lows of MeHg as the pE of the system changes. Along the pE gradient, regions corresponding to such peaks and lows, if any, could be identified through laboratory incubation studies for use in mesocosm experiments simulating wetland settings.
RESULTS AND DISCUSSION Organic rich sediments were collected from a pristine wetland near the city of Gainesville in northern Florida, USA. In the laboratory, ambient THg and MeHg concentrations were determined by CV-AFS. The reactants and products of redox reactions were analyzed at the beginning and during
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the experiment by the following procedures. Sulfate and nitrate by ion chromatography (Dionex I320); Mn(II) after extraction in acidic copper sulfate solution and determination as outlined by LOVLEY AND PHILIPS (1988); Fe(III) and Fe(II) abundance by the ferrozine technique; and produced methane by GC-FID. To test the effect of different TEAPs on Hg transformations, sediment slurries were first completely depleted from the initial predominant TEAP by bubbling with N2:CO2 (95 % : 5 %) for 24 hours followed by an incubation in airtight container for a week in dark. The addition of a specific TEA to such slurry helped establish its predominance. All manipulations were conducted under controlled atmosphere in an anaerobic chamber. This approach is supported by prior findings reported by LOVLEY AND PHILIPS (1987) and its application to Hg studies by our research group to assess the role of predominant TEAPs in Hg methylation and MeHg degradation (WARNER ET AL., 2003). Depleted sediment slurries were separately amended with (i)-sodium nitrate, (ii) manganese oxide, (iii)-ferric hydroxide, (iv)sodium sulfate, and finally, (v) no addition to favor methanogenesis after complete depletion of all other TEAPsto ascertain the predominance of a new TEAP in sediments. Spikes were added to raise the ambient concentrations by a factor of 5 to 10. In comparison with controls (i.e., non amended slurries), slurries were spiked with cold inorganic Hg (in methylation experiments) and MeHg (in MeHg degradation experiments). Nitrate-reduction and Hg transformation to prepare nitrate-reducing treatments, aliquots of the above described depleted sediment slurry was first slightly oxidized by aeration. The idea is to start slightly aerobic RMZ-M&G 2004, 51
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in order to extend the occurrence on nitrate reduction in sodium nitrate spiked slurries. The oxidize slurry was then spiked with nitrate and either Hg or MeHg de-aerated solutions for methylation and demethylation experiments, respectively. Replenishment with de-aerated solution of sodium nitrate was conducted to maintain nitrate concen-
trations relatively constant. Control samples, not spiked with Hg species, were run in parallel with Hg-treated slurries and subtracted from Hg spiked data. Relevant geochemical parameters (e.g., dissolved nitrate, iron speciation, sulfate, methane, and MeHg) were measured versus time.
Figure 1. Selected trends of Hg methylation and MeHg degradation under Fe-and sulfatereducing conditions RMZ-M&G 2004, 51
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Mn(IV)-reducing sediments and Hg transformation Similar to nitrate reduction, aliquots of depleted sediment were inoculated with an anaerobic slurry of poorly crystalline synthetic MnO2 to establish Mn as predominant TEAP. Fe(III)-reducing sediments and Hg transformation To prepare iron-reducing sediments, ferric hydroxide was used and replenished whenever necessary. Sulfate-reducing sediments and Hg transformation Sulfate-reducing treatments were accomplished by Na2SO4 addition and replenished versus time to maintain levels at near starting concentration. Methanogenic-sediments and Hg transformationIn this last case, non-amended depleted sediments were used without further additions. Gas samples were taken periodically from the headspace using sterile N2flushed syringes and analyze by GC for methane determination. Due to space limitation, we have opted for Fe-reducing and sulfate-reducing conditions to illustrate the contrasting behavior of Hg transformation under specific predominant
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TEAs (Figure 1). For the tested sediments, our results indicate that under all tested predominant TEAPs, MeHg added to the slurry is degraded as shown in figures 1b and 1d, with a quite steady decreasing trend versus time. However, trends of MeHg production are less uniform. Hg methylation is highly favored under sulfate-reducing conditions (Fig. 1c) and methanogenis (not shown), while MeHg production seems to be limited under the predominance of the other three TEAs (only Fe-reducing conditions shown here, not the difference in scales). These results seem to confirm prior observations by MEHROTRA ET AL. (2003) obtained from pure cultures of Desulfobulbus propionicus, and field observations by WARNER ET AL. (2003). Therefore, one can speculate that the combination of high demethylation and low methylation potential rates under Mn- and Fereducing could be used towards the development of a redox buffer approach aimed at limiting MeHg production and accumulation in sedimentary environments. Acknowledgements This work was supported by grant # R827168-01-0 form US-EPA, Occidental Chemical, and UF Foundation.
REFERENCES KING, J. K., MICHELE HARMON, S., THERESA, T. FU AND JOHN B. GLADDEN (2002): Mercury removal, methyl mercury formation, and sulfate-reducing bacteria profiles in wetland mesocosms; Chemosphere 46(6), pp. 859-870. LOVLEY, D. R. AND PHILIPS, E. J. P. (1987): Competitive mechanisms for the inhibition of sulfate reduction and methane production in the zone of ferric iron reduction in sediments; Appl. Environ. Microbiol 53, pp. 2636-2641.
LOVLEY, D. R. AND GOODWIN, S. (1988): Hydrogen concentrations as an indicator of the predominant terminal electron accepting reactions in aquatic sediments; Geochimica et Cosmochimica Acta 52(12), pp. 2993-3003. MEHROTRA, A. S., HORNE, A. J. AND SEDLAK, D. L. (2003): Reduction of net mercury methylation by iron in Desulfobulbus propionicus (1pr3) cultures: Implications for engineered wetlands; Environ. Sci. Technol. 37(13), pp. 3018-3023. RMZ-M&G 2004, 51
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PORVARI, P. AND VERTA, M. (2003): Total and methyl mercury concentrations and fluxes from small boreal forest catchments in Finland; Environmental Pollution, 123 (2): 181-191. ST. LOUIS, V. L., RUDD, J. M. W., KELLY, C. A., BEATY, K. G., BLOOM, N. S., FLETT, R. J. (1994): Importance of wetlands as sources of methylmercury to boreal forest ecosystems; Can. J. Fish. Aquat. Sci. 51, pp. 1065-1076. ST. LOUIS ET AL. (1996): Production and loss of MeHg and loss of total-Hg from boreal forest catchments containing different types of wetlands; Environ. Sci. Technol. 30: 2719-2729. VON TÜMPLING, W., WILKEN, R. D. AND EINAX, J. (1995): Mercury contamination in the northern Pantanal region Mato Grosso, Brazil; Journal of Geochemical Exploration 52(1-2), pp. 127-134
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WARNER, K. A., RODEN, E. E. AND BONZONGO, J. C. (2003): Microbial Mercury Transformation in Anoxic Freshwater Sediments under Iron-Reducing and Other Electron-Accepting Conditions; Environ. Sci. Technol. 37(10), pp. 21592165. YOKOO, E. M., VALENTE, J. G., SICHIERI, R., AND SILVA, E. C. (2001): Validation and Calibration of Mercury Intake through Self-Referred Fish Consumption in Riverine Populations in Pantanal Mato-grossense, Brazil; Environmental Research, 86(1), pp. 88-93 ZILLIOUX, E. J., PORCELLA, D. B., AND BENOIT, J. M. (1993): Mercury cycling and effects in freshwater wetlands ecosystems; Environ. Toxicol. Chem. 12, pp. 2245-2264.
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Mercury Contamination in Fish from Gold Mining Areas in The Amazon Region and Human Health Risk Assessment ZULEICA C. CASTILHOS1, SAULO RODRIGUES-FILHO1, ANA PAULA RODRIGUES1, 3, ROBERTO C. VILLAS-BÔAS1, MARCELLO M. VEIGA2, CHRISTIAN BEINHOFF2. 1
CETEM, Centre for Mineral Technology, Av. Ipê, 900, 21941-590, Rio de Janeiro, Brazil,
[email protected]; 2 UNIDO, United Nation Industrial Development Organization, Vienna International Centre, P.O. Box 300, A-1400, Vienna, Austria; 3 Fluminense Federal University, Department of Geochemistry, Niterói, Brazil.
Abstract: The main objective of this work is to conduct an assessment of the magnitude of mercury contamination in fish from the target Amazonian region influenced by gold mining areas and perform the human health hazard assessment due to fish consumption. It was investigated the mercury levels in fish from all 11 sites in two areas: 4 sites in São Chico and 7 in Creporizinho area. The results showed that total mercury in fish from São Chico (2.53±3.91 µg/g) is significantly higher than in fish from Creporizinho area (0.36±0.33 µg/g). The most contaminated sites are located in São Chico, São Chico reservoir and Buriti mining site, in Creporizinho. By employing the mercury risk assessment to human health due to fish consumption, the results suggest that possibly in all sites, except in reference area (Chico Chimango creek), populations are subject to potential hazards, being site A2 the most evident case of mercury pollution. Although the estimated by single compartment-model and verified blood and hair Hg concentrations in local population are lower than values (∼200 µg.l-1 and 50 µg.g-1) associated with adverse effects on nervous system, manifested as an approximately 5 % increase in the incidence of paraesthesia, it is important to realize that there are some individuals with higher levels of mercury in blood and hair in São Chico area. The estimated blood and hair Hg concentration in Creporizinho fall closer to the observed. Keywords: Amazonian fish, mercury, gold mining, human health hazard
INTRODUCTION The present work describes part of the results achieved in two small scale gold mining areas in the Brazilian Amazon - São Chico and Creporizinho - as part of the environmental and health assessment (E&HA) conducted by the Centre for Mineral Technology (CETEM) with the colaboration of the Evandro Chagas Institute (IEC), under the general coordination of the United Na-
tions Industrial Development Organization (UNIDO). The E&HA is a part of the GEF/ UNIDP/UNIDO Global Mercury Project Removal of Barriers to the Introduction of Cleaner Artisanal Gold Mining and Extraction Technologies. The main objective of this work is to conduct an assessment of the magnitude of mercury contamination in fish from the target Amazonian region influenced by gold minRMZ-M&G 2004, 51
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ing areas and perform the human health hazard assessment due to fish consumption. Fish sampling was conducted in August 2003, at two study areas, at São Chico and at Creporizinho mining sites or “garimpo” areas. Both areas are located inside of the Mineral Tapajós Reserve, State of Para, between the cities of Jacareacanga and Itaituba, where the mining sites are distributed alongside the tributaries of the Tapajós river. However, these two areas belong to two distinct hydrographic basins: Jamanxin river basin and Crepori river basin, respectively.
RESULTS AND DISCUSSION The São Chico mining site is located 5 km distance from the Transgarimpeira road. The village consists of 63 houses and 134 individuals, being 41 % of garimpeiros. From the beginning of the very first gold mining activity in 1963, the village has shown two main periods of prosperity, one in the end of the 80´s, and other in the end of the 90´s, when gold rich primary deposits were discovered. Nowadays, exploitation of primary gold ore is over, being gold production in São Chico almost restricted to the reprocessing of tailings produced during the 80´s. Creporizinho is a typical gold mining village with an estimated population of 1000 inhabitants.The mining sites of Papagaio, Areal, Tabocal and Bofe are located near the village, where alluvial gold has been explored, and from the middle of 90’s exploration of primary started. Nowadays, alluvial gold is rare, being mining of lateritic soil, primary ore and reworking of tailings common all over the area. RMZ-M&G 2004, 51
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A total of 234 fish specimens of 16 species were collected: 73 specimens belonging to 13 species in São Chico and 161 specimens of 11 species in Creporizinho. A total of 7 common species could be collected in both areas (acari, cará, curimatã, mandi, piau, piranha and traíra). It was investigated the mercury levels in fish from all 11 sites belonging to two areas: 4 in São Chico (A1-flooded open pits; A2-São Chico reservoir, A3-flooded open pit near Rosa stream; A4- Conrado inflow and Novo river) and 7 in Creporizinho (A5-Papagaio mining site; A6- Tabocal mining site, A7-Buriti mining site; A9- Porto Alegre, Crepori river; A10- Crepori river upstream of Creporizinho inflow; A11- Chico Chimango creek, clear water near the Creproizinho inflow into the Crepori river). It should be stressed that was not easy fishing near the garimpo’s areas, mainly by high turbidity from mining activities, which has as a consequence, fish avoidance. The results show that total mercury in fish from São Chico (2.53±3.91 µg/g, n=73) is higher than in fish from Creporizinho area (0.36±0.33 µg/g, n=161; p