HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Tomazelli, A. C. Articles by Horvat, M. Search for Related Content PubMed PubMed Citation Articles by Tomazelli, A. C. Articles by Horvat, M. Agricola Articles by Tomazelli, A. C. Articles by Horvat, M. Related Collections Surface Water Quality Toxic Trace Metals Ecological Risk Assessment Heavy Metals Water Pollution

TECHNICAL REPORTS

Heavy Metals in the Environment

Mercury Distribution in Medium-Size Rivers and Reservoirs of the São Paulo State (Southeast Brazil)

^a Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Dep. de Biologia, Av. dos Bandeirantes, 3900-CEP, 14040-901 Ribeirão Preto, SP, Brazil
^b Centro de Energia Nuclear na Agricultura, USP, Piracicaba, SP, Brazil
^c Dep. of Environmental Sciences, Joef Stefan Institute, Ljubljana, Slovenia

^* Corresponding author (andrea_tomazelli{at}yahoo.com.br)

Received for publication October 25, 2005.

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
The aim of this work was to investigate mercury (Hg) levels in six meso-scale watersheds (Upper Paranapanema, Aguapeí, Peixe, São José dos Dourados, Mogi-Guaçu, and Piracicaba) of the São Paulo state to contribute to a more comprehensive understanding of Hg contamination in Brazil. Water, sediment, bivalves, and fish samples were collected during 2001 at 11 sites. Fish were also collected in the Jurumirim and Salto Grande Reservoirs which are 39 and 52 yr old since impoundment, respectively. Results showed that Hg concentrations were low in almost all samples, except fish from Jurumirim Reservoir (total mercury [T-Hg] = 1.14 ± 0.55 mg kg^–1 wet wt.). In spite of industrialization and high population, the results showed that there was no important source of Hg contamination in the investigated areas. The higher concentrations found in fish from Jurumirim seem to be the result of processes that favor Hg mobilization and methylation as a consequence of the impoundment of the reservoir area. The same levels were not observed in the Salto Grande Reservoir, probably because these are no longer significant due to the long time since the impoundment. To understand the dynamics of methylmercury (MeHg) production and its accumulation in fish, further studies are needed in the Jurumirim Reservoir. The results show that even at low T-Hg concentrations in sediment and water, concentrations in fish can reach values that pose concerns for consumption. This emphasizes the importance of designing an optimized biomonitoring program that can provide warning of biogeochemical conditions that promote formation of MeHg.

Abbreviations: MeHg, methylmercury • T-Hg, total mercury

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
IN THE PAST FOUR DECADES, a great number of studies about environmental mercury (Hg) contamination worldwide were performed. They have shown how human activities have greatly modified the natural cycling of Hg. These studies confirmed the high toxicity of Hg to plants and animals and its ability for bioaccumulation through aquatic and terrestrial food chains (Boudau and Ribeyre, 1997; Horvat et al., 2003). In addition, the advances in analytical techniques have also enabled the assessment of Hg at very low concentrations permitting a better understanding of its role in the environment and human health.

Although there is a vast literature dealing with Hg pollution in aquatic systems around the world, in Brazil there is a lack of information on Hg distribution. Generally Hg contamination in aquatic systems is mainly documented for the Amazonian region where this element is used for gold amalgamation in mining activities (Martinelli et al., 1988; Pfeiffer et al., 1991; Malm et al., 1997; Guimarães et al., 1999) and specific natural biogeochemical processes are also responsible for the enhancement of Hg bioavailability (Roulet et al., 1998; Fostier et al., 2000; Lechler et al., 2000; Fadini and Jardim, 2001). In other regions of Brazil, studies concerning Hg contamination are sparse and concentrated in areas such as Pantanal (Lacerda, 1992; Callil and Junk, 2001; Leady and Gottgens, 2001) and coastal areas of the state of Rio de Janeiro in the southeast region of Brazil (Marins et al., 1998; Lacerda et al., 2001), and others (i.e., Moraes et al., 1997; Pestana et al., 2000).

Human activities, mainly those involving medical and solid waste incineration, oil, coal, and gold mining, represent significant emission sources of Hg to the environment. Around 50% of the total Hg emission to the Brazilian atmosphere is attributed to mining activities (Lacerda, 2003). On the other hand, in highly industrialized and populated regions, aquatic Hg contamination could be the result of atmospheric deposition and Hg release directly into the aquatic system from point and diffuse sources, such as waste disposal and agricultural soil lixiviation, (Schroeder and Munthe, 1998; United Nations Environment Programme-Chemicals, 2002). In the last 10 yr, several studies have demonstrated the increasing importance of diffuse sources on Hg contamination in aquatic systems (Lacerda and Marins, 1997; Balogh et al., 1998; Lacerda and Salomons, 1999). Therefore, it is also important to investigate regions with no clear point sources of contamination, looking for areas potentially contaminated by diffuse Hg sources or with specific characteristics for Hg mobilization, methylation, and bioaccumulation.

São Paulo is the most industrialized and densely populated state of Brazil. In recent years, many problems associated with water quality degradation have been documented for some rivers (Krusche et al., 1997; Ballester et al., 1999; Martinelli et al., 1999a, 1999b; Daniel et al., 2002), but there are only a few studies regarding the significance of metallic contaminants (Salomão et al., 2003; Tavares et al., 2003; Tomazelli et al., 2003; Fostier et al., 2005). In some areas such as the eastern and southeastern areas of the state there are no Hg concentrations data, emphasizing the necessity of monitoring this toxic element to establish background concentrations and to identify areas contaminated by diffuse sources.

Thus, the aim of this work was to investigate Hg concentrations in water, sediments, fish, and bivalves in six meso-scale watersheds of the São Paulo state to contribute to a more comprehensive understanding of Hg contamination in Brazil. The purpose of this study was to compare the concentrations of Hg detected in the studied areas with the data available in the literature, and to highlight possible contaminated areas.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Study Area
Six meso-scale watersheds in the São Paulo state, Brazil were selected (Fig. 1): Upper Paranapanema, Aguapeí, Peixe, São José dos Dourados, Mogi-Guaçu, and Piracicaba. These watersheds encompass rivers with different degrees of anthropogenic impacts such as urbanization, agricultural uses, and input of domestic and industrial effluents (Table 1). The Piracicaba River Basin is the most populated watershed (3400000 inhabitants) with a population density of 340 inhabitants km^–2. On the other extreme the Upper Paranapanema River Basin shows the lowest population density with 31 inhabitants km^–2 (Martinelli et al., 2002). This population distribution relates to the amount of biochemical oxygen demand (BOD) released into the rivers (Table 1). In all watersheds there are remarkable land cover alterations, with a shift of the natural vegetation for agricultural, forestry, and urbanized areas (Silva, 2002). Pasture is the main land cover in the majority of the watersheds (São José dos Dourados, Aguapeí, Peixe, Turvo, and Piracicaba), ranging from approximately 20% in Mogi-Guaçu up to approximately 75% in the Aguapeí River Basin. In the Upper Paranapanema watershed forest is the predominant land cover. Interestingly, the principal forestry area in the whole study is in this watershed (12% in the entire study drainage basin) which can be a threat to the remaining original vegetation. The production of sugarcane occurs mainly in the Mogi-Guaçu (almost 40%) and Piracicaba (35%) watersheds. Piracicaba (6%), Mogi-Guaçu (2%), and Peixe (1%) watersheds were the most affected by urban land cover (Silva, 2002).

View larger version (33K): [in this window] [in a new window]   Fig. 1. Sampling sites in the São Paulo state. Site 2 is the Jurumirim Reservoir and Site 13 is the Salto Grande Reservoir. Samples collected in each site: 1. bivalve, sediment, water; 2. fish; 3. sediment, water; 4. sediment, water; 5. fish, sediment, water; 6. bivalve, sediment, water; 7. bivalve, fish; 8. sediment, water; 9. sediment, water; 10. bivalve, fish, sediment, water; 11. sediment, water; 12. bivalve, fish, sediment, water; 13. fish; 14. bivalve, sediment, water.

Water samples (n = 60) were collected at the surface (0.5-m depth) in 1-L cleaned PET bottles according to Fadini and Jardim (2000). Samples were acidified with 1% v/v HNO₃ (final concentration) and stored at 4°C until further laboratory processing. Total mercury (T-Hg) was determined in nonfiltered water samples 3 d after sampling.

Sediments
Sediment samples (n = 61) were collected by using an Ekman Birge grab. Samples were placed in polyethylene bags and frozen until analysis. In the laboratory, sediments were wet-sieved and the fraction lower than 63 µm freeze-dried (–40°C) to a constant weight and homogenized in an agate mortar. The water content in samples was recorded. All data are expressed on a dry weight basis. No experiments were made to check for volatilization losses during freeze-drying of sediment, bilvalves, and fish samples. It was assumed that there were no Hg losses during this step.

Fish and Bivalves
Only carnivorous fish were collected as indicators of Hg biomagnification in the trophic chain (Lebel et al., 1997; Malm et al., 1997). Fish species sampled included Cynopotamus humeralis (Saicanga or Cadela), Hoplias malabaricus (Traíra), Megalonema platana, Salmimus hilarii (Tabarana), Salminus maxillosus (Dourado), and Serrasalmus sp. (Piranha). Samples (n = 132) were obtained from local fisherman, placed into polyethylene bags, deep-frozen, and stored. In the laboratory, their weight and length were recorded, and fish specimens were identified. Muscle samples were carefully placed in polyethylene vials and deep-frozen. The muscle samples were then freeze-dried (–40°C) to a constant weight.

Bivalve specimens (Anodontites trapesialis, Anodontites crispatus, Castalia undosa undosa, Corbicula fluminea, Diplodon fontaineanus, Diplodon sp, and Fossula fossiculífera; n = 222) were manually collected. Bivalves are known to be sedentary aquatic organisms and were selected to identify the presence of Hg at sampling locations. For this reason, monitoring of Hg in bivalves complements the analysis of Hg in fish, which mainly accumulates monomethylmercury. Bivalves are recognized to accumulate high metal concentrations in their tissues, representing efficient environmental biomonitors of metals (Phillips, 1980; Tomazelli et al., 2003). After sampling, the specimens were deep-frozen (–20°C) and stored in polyethylene bags. In the laboratory, the specimens were thawed at room temperature and removed from their shells. Their viscera were washed with deionized water to remove any sediment residue. Thereafter the samples were partially dried on a filter paper and weighed. The soft tissue of each animal was ground, homogenized, and freeze-dried to a constant weight.

Dry fish and bivalve samples were ground in liquid nitrogen using a model 6800 cryogenic mill (SPEX, Metuchen, NJ, USA) as described elsewhere (Santos et al., 2002). The water content in fish and bivalve samples was recorded. All results for bivalves and sediments are expressed on a dry weight basis.

Total Mercury Determination
Total mercury was determined by cold vapor atomic fluorescence spectrometry (Merlin Mercury Fluorescence Detector, P.S. Analytical, UK) using 2% m/v SnCl₂ (bubbled with purified argon for 30 min) for reduction of divalent to elemental Hg.

Water samples were treated with HCl, KBr, and KBrO₃, according to PSA (1995). Immediately before the measurement the excess of KBr/KBrO₃ was reduced with hydroxylammonium hydrochloride solution (12% m/v).

Sediment samples were digested using a microwave-assisted method in closed vessels (Milestone, Ethos 1600). Samples were decomposed in duplicate according to the following procedure: 200 mg of dried and ground material was accurately weighted in the TFM vessels of the microwave oven and then 3.0 mL of HCl plus 1 mL of HNO₃ were added. After decomposition, the TFM microwave vessels were cooled, the digest was transferred to a 25-mL volumetric flask, and the volume filled to the mark with high purity water. Any solid silica was left in the volumetric flask, with careful sampling of the supernatant solution by adjusting the depth of the capillary of the auto-sampler arm of the Hg analyzer.

Fish and bivalve samples were digested according to a modified method based on Bloom (1992). Samples were decomposed in duplicate by wet decomposition in a block digestor according to the following procedure: 100 mg of dried and ground material was accurately weighted, transferred to a 50.0-mL borosilicate digestion tube and 3.5 mL of HNO₃ plus 1.0 mL of H₂SO₄ were added. Cold fingers were adapted to the digestion tubes which were kept overnight at room temperature. Thereafter, digestion tubes were slowly heated in a digestion block up to 100°C and maintained at this temperature for 8 h. After cooling down to room temperature, 2.5 mL 0.2 mol L^–1 BrCl was added and the volume was filled up with water. Just before analysis the excess of BrCl was reduced with hydroxylammonium hydrochloride (12% m/v).

Methylmercury Determination
Methylmercury (MeHg) was determined in fish samples from the Jurumirim and Salto Grande Reservoirs at the Department of Environmental Sciences, Joef Stefan Institute (Ljubljana, Slovenia) according to Liang et al. (1994), Liang and Horvat (1996), and Logar et al. (2000). The method is based on formation of volatile ethylated Hg compounds (derivatization by sodium tetraethylborate), room temperature adsorption on a Tenax trap, desorption and gas chromatographic separation of the ethylated derivatives, pyrolisis and detection by cold vapor atomic fluorescence spectrometry (CVAFS). Before ethylation, about 50 to 200 mg of dry and ground fish tissue was accurately weighed and transferred to 50-mL screw-capped Teflon vials. Thereafter, 2 mL of 25% KOH/methanol solution were added and the mixture was heated in an oven for 3 h at 80°C. The digest was cooled and diluted with methanol before analysis according to the sample mass and concentration of the Hg species. When the digests were not analyzed on the same day as digestion, they were reheated for 1 h at 80°C in an oven before analysis to release any MeHg and Hg²⁺ bound to particles.

Data Quality
During sampling, subsampling, storage, and analytical measurements, samples only came into contact with carefully cleaned materials. Samples only came into contact with purified nitric and chloridric acids by subboiling distillation [Analytical reagent-grade HNO₃ and HCl (Merck, Rio de Janeiro, Brazil) was distilled in quartz subboiling stills (Kürner, Rosenheim, Germany)]. To avoid contamination, sample preparation was performed in a Class 10000 (ISO Class 7) environment. Solutions were stored in Class 100 (ISO Class 5) laminar flow hood. During Hg determination the resulting Hg vapor was trapped in a potassium permanganate solution.

Field and laboratory blank solutions were regularly checked. Blanks were prepared as samples with high purity deionized water (resistivity > 18.2 M cm) obtained by a Milli-Q water purification system (Millipore, Bedford, MA, USA). The mean value of blank samples (n = 3) were subtracted from the sample mean value and the uncertainty of the net result was equal to the square root of the sum of the squares of the individual uncertainties of blank and sample measurements. Certified reference materials were employed to verify the accuracy of the results. A list of the reference materials used for accuracy checking is presented in Table 2, as well as the results obtained for T-Hg and MeHg.

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

The present data for T-Hg in water samples were correlated with data for total and fine suspended sediment (TSS and FSS) and dissolved organic carbon (DOC) obtained from Salomão (2004) who analyzed samples from the same study area and collected in the same campaign. No correlation was observed between T-Hg in water samples and these variables, which is in contrast with other studies reported elsewhere (Hurley et al., 1995; Tavares et al., 2003; Fostier et al., 2005).

Low Hg concentrations were observed for most sediment samples when compared with data for others areas in Brazil and the world (Table 4). Total mercury concentrations in sediment samples were lower than those reported for contaminated areas, such as the river Elbe (Germany; Brügmann, 1995), some areas of the river Madeira (Amazon, Brazil; Pfeiffer et al., 1991), river Soa (Slovenia; Horvat et al., 2002), and the Province of Guizhou (China; Horvat et al., 2003) (Table 4). Only one sample (from the Peixe basin) contained values higher than the PEL (probable effect level) from Canada (Environment Canada, 2002). Total mercury concentrations observed in the present work were similar to background concentrations reported for nonimpacted areas in the São Paulo state, such as the concentrations found in rivers located in protected areas of the state (Salomão et al., 2003).

However, MeHg concentrations differed between fish from the Salto Grande and Jurumirim reservoirs. The former showed significantly lower concentrations. This may be due the fact that Salto Grande is older than Jurumirim Reservoir (Table 7). Fostier et al. (2005) collected carnivorous fish samples (Hoplias malabaricus) in the Salto Grande Reservoir between 1996 and 1997, and reported mean concentrations of T-Hg around 0.593 ± 0.168 mg kg^–1 wet wt., which is higher than the values measured in the present study (0.106 ± 0.077 mg kg^–1 wet wt.). This can be attributed to a decrease in MeHg production in the reservoir over the past years.

The high Hg concentrations observed in fish from Jurumirim Reservoir can be associated with the processes occurring in the reservoir after its impoundment. The increase of MeHg in fish of new reservoirs has been well documented in the literature for temperate, subartic, and tropical ecosystems (Porvari, 1995; Bodaly et al., 1997; Neumann et al., 1997; Porvari, 1998; Bodaly and Fudge, 1999; Ikingura and Akagi, 2003). Mobilization of MeHg bound to soil and organic matter into the water column during flooding and filling of the reservoir has been considered the cause of increased Hg bioavailability in fish in new reservoirs (Morrison and Therien, 1995). Other studies have attributed elevated fish Hg levels to enhanced MeHg production in the reservoir system because of increased microbial activity due to the decomposition of submerged organic matter soon after flooding (Rogers et al., 1995).

Although these high Hg concentrations in fish from the newly formed reservoirs have been well documented, the duration of elevated fish Hg concentrations is often hard to predict. In reservoirs from the northern hemisphere the duration of elevated Hg concentrations can be decadal, probably most commonly 20 to 30 yr for predatory fish and 15 to 20 yr for omnivorous fish (Verdon et al., 1991; Bodaly et al., 1997; Porvari, 1998).

On the other hand, Ikingura and Akagi (2003) reported that fish Hg levels in Tanzanian reservoirs were very low (total Hg = 0.001 to 0.14 mg kg^–1 wet wt.), almost 3 to 22 times lower than the average concentrations reported in carnivorous fish species from Tucuruí (Aula et al., 1995; Porvari, 1995), Balbina (Kehrig et al., 1998), and Jurumirim (this study) reservoirs, among the tropical regions. According to the authors, "in the Tanzania scenario, it is possible that fish Hg levels have fallen to background concentrations since the reservoirs are all very old (19 to 35 yr), or the dynamics of Hg cycling in the reservoirs did not favor high levels of Hg bioaccumulation in fish."

At the time of sampling in the Jurumirim Reservoir (2001), it was 39 yr since the impoundment, and the levels of MeHg in fish samples were still very high. This is rather different from the observations of the authors cited above who found that MeHg concentrations decreased before 30 yr on average. On the other hand, the Salto Grande Reservoir was 52 yr old and the levels of MeHg in fish samples were low. The fact that physical-chemical conditions in the Jurumirim Reservoir were still promoting methylation at the time of the sampling campaign resulting in the elevated concentrations in carnivorous fish may be related to the dimension of the impounded area. This is much bigger in Jurumirim (449 km²) than in Salto Grande (13 km²). Fish Hg concentrations have been correlated with lake size in Sweden (Halanson et al., 1988) and Ontario (McMurtry et al., 1989; Bodaly et al., 1993). However, to get a better picture of the Hg accumulation over the food chain, it is necessary to collect sediment and bivalves samples in the reservoirs, as well as other primary and secondary data. This investigation should proceed in future studies, since exposure of inhabitants that eat fish with MeHg caught in the reservoir may cause health problems in sensitive population groups, such as pregnant women and children.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Mercury concentrations were low in almost all samples analyzed, except fish from the Jurumirim Reservoir. These results clearly show that there are no important sources of Hg contamination in the areas investigated, and the slightly higher Hg concentrations in some samples may have been due also to natural heterogeneity of the samples and diffuse sources of Hg, such as atmospheric deposition and agriculture. The higher concentrations of Hg and MeHg found in fish from the Jurumirim Reservoir seem to be a result of processes that favor MeHg production due to the impoundment of the area for the reservoir building. To understand the dynamics of production of MeHg and its accumulation in fish, further studies are needed in the Jurumirim Reservoir.

The results of this study show that in aquatic systems the concentrations of T-Hg in water and sediments are of limited use in quantifying the potential risk to humans and wildlife. Even at low concentrations of Hg in these environmental compartments, concentrations of Hg in fish can reach values that are unsafe for consumption. It is therefore strongly recommended that any surveying program related to Hg should include speciation of Hg in all environmental compartments studied. As this may be difficult from the analytical point of view, an alternative approach may be to design an optimized biomonitoring program that can provide an alert for biogeochemical conditions that promote formation of MeHg that is easily accumulated and biomagnified, such as for example, measurements of Hg concentrations in sediment samples, selected fish species, clams, or other biological species.

	ACKNOWLEDGMENTS

 
The authors are grateful to FAPESP for financial support (grant No. 99/07966-9, 99/05279-4), and to the Department of Environmental Sciences of the Joef Stefan Institute (Ljubljana, Slovenia), especially technical assistance of Dr. Martina Logar for help in methylmercury determinations. Our gratitude is expressed to many friends from CENA (USP, Piracicaba) for help during sampling and analytical procedures.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

• ANVISA. 1998. Agência Nacional de Vigilância Sanitária. ANVISA, Brazil. Available at http://www.anvisa.gov.br/legis/portarias/685_98.htm (verified 28 Aug. 2006).
• Aula, I., H. Braunscheweiler, and I. Malin. 1995. The watershed flux of mercury examined with indicators in the Tucuruí Reservoir in Pará, Brazil. Sci. Total Environ. 175:97–107.
• Ballester, M.V., L.A. Martinelli, A.V. Krusche, R.L. Victoria, M. Bernardes, and P.B. Camargo. 1999. Effects of increasing organic matter loading on the dissolved O₂, free dissolved CO₂, and respiration rates in the Piracicaba river basin, southeast Brazil. Water Res. 33:2119–2129.
• Balogh, S., M. Meyer, and K. Johnson. 1998. Diffuse and point source mercury inputs to the Mississipi, Minnesota, and St. Croix Rivers. Sci. Total Environ. 213:109–113.
• Bloom, N.S. 1992. On the chemical form of mercury in edible fish and marine invertebrate tissue. Can. J. Fish. Aquat. Sci. 49:1010–1017.
• Bodaly, R.A., and R.J.P. Fudge. 1999. Uptake of mercury by fish in an experimental boreal reservoir. Arch. Environ. Contam. Toxicol. 37(1):103–109.[CrossRef][Web of Science][Medline]
• Bodaly, R.A., J.W.M. Rudd, R.J.P. Fudge, and C.A. Kelly. 1993. Mercury concentrations in fish related to size of remote Canadian Shield lakes. Can. J. Fish. Aquat. Sci. 50:980–987.
• Bodaly, R.A., V.L. St. Louis, M.J. Paterson, R.J.P. Fudge, B.D. Hall, D.M. Rosenberg, and J.W.M. Rudd. 1997. Bioaccumulation of mercury in the aquatic food chain in newly flooded areas. p. 259–287. In A. Sigel and H. Sigel (ed.) Metals ions in biological system: Mercury and its effects on environment and biology. Marcel Dekker, New York.
• Boudau, A., and F. Ribeyre. 1997. Mercury in the food web: Accumulation and transfer mechanisms. p. 289–319. In A. Sigel and H. Sigel (ed.) Metals ions in biological system: Mercury and its effects on environment and biology. Marcel Dekker, New York.
• Brügmann, L. 1995. Metals in sediments and suspended matter of the river Elbe. Sci. Total Environ. 159:53–65.[CrossRef]
• Callil, C.T., and W.J. Junk. 1999. Concentração e incorporação de mercúrio por moluscos bivalves Anodontites trapesialis (Lamarck, 1819) e Castalia ambigua (Lamarck, 1819) do Pantanal de Poconé-MT, Brasil. Biociências 7(1):3–28.
• Callil, C.T., and W.J. Junk. 2001. Aquatic gastropods as mercury indicators in the Pantanal of Poconé region (Mato Grosso, Brasil). Water Air Soil Pollut. 319:319–330.
• Costa, M.C., E.P. Paiva, and I. Moreira. 2000. Total mercury in Perna perna mussels from Guanabara Bay-10 years later. Sci. Total Environ. 261:69–73.[CrossRef][Medline]
• Daniel, M.H.B., A.A. Montebelo, M.C. Bernardes, J.P.H.B. Ometto, P.B. Camargo, A.V. Krusche, M.V. Ballester, R.L. Victoria, and L.A. Martinelli. 2002. Effects of urban sewage on dissolved oxygen, dissolved inorganic and organic carbon, and electrical conductivity of small streams along a gradient of urbanization in the Piracicaba River Basin. Water Air Soil Pollut. 136:189–206.
• Environment Canada. 2002. Canadian Environmental Quality Guidelines: Canadian Sediment Quality Guidelines for the protection of aquatic life. Environment Canada, Gatineau, Quebec.
• Fadini, P.S., and W.F. Jardim. 2000. Storage of natural water samples for total and reactive mercury analysis in PET bottles. Analyst 125:549–551.
• Fadini, P.S., and W.F. Jardim. 2001. Is the Negro River Basin (Amazon) impacted by naturally occurring mercury? Sci. Total Environ. 275:71–82.[CrossRef][Medline]
• Fostier, A.H., M.B. Falótico, E.S.B. Ferraz, A.C. Tomazelli, M.S.M.B. Salomão, and L.A. Martinelli. 2005. Impact of anthropogenic activity on the Hg concentrations in the Piracicaba river basin (São Paulo State, Brazil). Water Air Soil Pollut. 165(1–4):371–392.
• Fostier, A.H., M.C. Forti, J.R.D. Guimarães, A.J. Melfi, R. Boulet, C.M. Espirito Santo, and F.J. Krug. 2000. Mercury fluxes in a natural forested Amazonian catchment (Serra do Navio, Amapá State, Brazil). Sci. Total Environ. 260:201–211.[CrossRef][Medline]
• Guimarães, J.R.D., A.H. Fostier, M.C. Forti, A.J. Melfi, H. Kehrig, J.B.N. Mauro, O. Malm, and J.F. Krug. 1999. Mercury in human and environmental samples from two lakes in Amapá, Brazilian Amazon. Ambio 28:296–301.
• Halanson, L., A. Nilsoon, and T. Anderson. 1988. Mercury in fish in Swedish lakes. Environ. Pollut. 49:145–162.[CrossRef][Medline]
• Harada, M. 1995. Minamata disease: Methylmercury poisoning in Japan caused by environmental pollution. Crit. Rev. Toxicol. 25(1):1–24.[Web of Science][Medline]
• Horvat, M. 1996. Mercury analysis and speciation in environmental samples. p. 135–159. In W. Bayens, R. Ebinghaus, and O. Vasilev (ed.) Global and regional mercury cycles: Sources, fluxes, and mass balance. NATO ASI Series (21). Kluwer Academic Publ., Dordrecht.
• Horvat, M., V. Jereb, V. Fajon, M. Logar, J. Kotnik, J. Faganeli, M.E. Hines, and J.-C. Bonzongo. 2002. Mercury distribution in water, sediment, and soil in the Idrijca and Soa river systems. Geochem. Explor. Environ. Anal. 2:287–296.
• Horvat, M., N. Nolde, V. Fajon, V. Jereb, M. Logar, S. Lojen, R. Jacimovic, I. Falnoga, Q. Liya, J. Faganeli, and D. Drobne. 2003. Total mercury, methylmercury, and selenium in mercury polluted áreas in the province Guizhou, China. Sci. Total Environ. 304:231–256.[CrossRef][Medline]
• Huggett, D.B., J.A. Steevens, J.C. Allgood, C.B. Lutken, C.A. Grace, and W.H. Benson. 2001. Mercury in sediment and fish from north Mississippi lakes. Chemosphere 42:923–929.
• Hurley, J.P., J.M. Benoit, C.L. Babiarz, M.M. Shaffer, A.W. Andren, J.R. Sullivan, R. Hammond, and D.A. Webb. 1995. Influences of watershed characteristics on mercury levels in Wisconsin rivers. Environ. Sci. Technol. 29:1867–1875.
• Hurley, J.P., S.E. Cowell, M.M. Shafer, and P.E. Hughes. 1998. Tributary loading of mercury to Lake Michigan: Importance of seasonal events and phase partitioning. Sci. Total Environ. 213:129–137.
• Ikingura, J.R., and H. Akagi. 2003. Total mercury and methylmercury levels in fish from hydroelectric reservoirs in Tanzânia. Sci. Total Environ. 304:355–368.[CrossRef][Medline]
• Kehrig, H.A., M. Costa, I. Moreira, and O. Malm. 2001. Methylmercury and total mercury in estuarine organisms from Rio de Janeiro, Brazil. Environ. Sci. Pollut. Res. Int. 8(4):275–279.[Medline]
• Kehrig, H.A., O. Malm, H. Akagi, J.R.D. Guimarães, and J.P.M. Torres. 1998. Methylmercury in fish and hair samples from the Balbina Reservoir, Brazilian Amazon. Environ. Res. 77:84–90.[Medline]
• Krusche, A.V., F.P. Carvalho, J.M. Moraes, P.B. Camargo, M.V.R. Ballester, S. Hornink, L.A. Martinelli, and R.L. Victoria. 1997. Spatial and temporal water quality variability in the Piracicaba River Basin, Brazil. J. Am. Water Res. Assoc. 33:1117–1123.
• Lacerda, L.D. 1992. Trace metals distribution in sediment profile from remote lakes in the Pantanal Swamp, Central Brazil. Geochem. Brasil 6(2):103–109.
• Lacerda, L.D. 2003. Updating global Hg emissions from small-scale gold mining and assessing its environmental impacts. Environ. Geol. 43:308–314.
• Lacerda, L.D., F.C.F. Depaula, A.R.C. Ovalle, W.C. Pfeiffer, and O.Malm. 1990. Trace metals in fluvial sediments of the Madeira River watershed, Amazon, Brazil. Sci. Total Environ. 97–98:525–530.
• Lacerda, L.D., and R.V. Marins. 1997. Anthropogenic mercury emissions to the atmosphere in Brazil: The impact of gold mining. J. Geochem. Explor. 58:223–229.
• Lacerda, L.D., R.V. Marins, H.H.M. Paraquetti, S. Mounier, J. Benaim, and D. Fevrier. 2001. Mercury distribution and reactivity in waters of a subtropical coastal lagoon, Sepetiba Bay, southeast Brazil. J. Braz. Chem. Soc. 12(1):93–98.
• Lacerda, L.D., and W. Salomons. 1999. Mercury contamination from new world gold and mine tailings. In R. Ebinghaus, R.R. Turner, L.D. Lacerda, O. Vasiliev, and W. Salomons (ed.) Mercury contaminated sites. Springer-Verlag, Berlin.
• Leady, B.S., and J.F. Gottgens. 2001. Mercury accumulation in sediment cores and along food chains in two regions of the Brazilian Pantanal. Wetlands Ecol. Manage. 9:349–361.
• Lebel, J., M. Roulet, D. Mergler, M. Lucotte, and F. Larribe. 1997. Fish diet and mercury exposure in a riparian Amazonian populations. Water Air Soil Pollut. 97:31–44.[Medline]
• Lechler, P.J., J.R. Miller, L.D. Lacerda, D. Vinson, J.C. Bonzongo, W.B. Lyons, and J.J. Warwick. 2000. Elevated mercury concentrations in soils, sediments, water, and fish of the Madeira river basin, Brazilian Amazon: A function of natural enrichments? Sci. Total Environ. 260:87–96.[CrossRef][Medline]
• Liang, L., N.S. Bloom, and M. Horvat. 1994. Simultaneous determination of mercury speciation in biological materials by GC/CVAFS after ethylation and room-temperature precollection. Clin. Chem. 40:602–607.[Abstract/Free Full Text]
• Liang, L., and M. Horvat. 1996. A simple solvent extraction technique for elimination of matrix interferences for determination of methylmercury by GC/CV AFS after ethylation. Talanta 43:1883–1888.
• Lodenius, M., and O. Malm. 1998. Mercury in the Amazon. Rev. Environ. Contam. Toxicol. 157:25–52.[Medline]
• Logar, M., M. Horvat, I. Falnoga, and V. Stibilj. 2000. A methodological study of mercury speciation using dogfish liver CRM (DOLT-2). Fresenius' J. Anal. Chem. 366:453–460.[CrossRef][Medline]
• Malm, O. 1998. Gold mining as a source of mercury exposure in the Brazilian Amazon. Environ. Res. 77:73–78.
• Malm, O., F.J.P. Branches, H. Akagi, M.B. Castro, W.C. Pfeiffer, M. Harada, W.R. Bastos, and H. Kato. 1995. Mercury and methylmercury in fish and human hair from the Tapajos river basin, Brazil. Sci. Total Environ. 175:141–150.[CrossRef][Medline]
• Malm, O., J.R.D. Guimarães, M.B. Castro, W.R. Bastos, J.P. Viana, F.J.P. Branches, E.G. Silveira, and W.C. Pfeiffer. 1997. Follow-up of mercury levels in fish, human hair, and urine in the Madeira River and Tapajós basins, Amazon, Brazil. Water Air Soil Pollut. 97:45–51.[Medline]
• Manly, R., and W.O. George. 1977. The occurrence of some heavy metals in populations of the freshwater mussel Anodonta anatina (L.) from the River Thames. Environ. Pollut. 14:139–154.
• Marins, R.V., L.D. Lacerda, H.H.M. Paraquetti, E.C. Paiva, and R.C. Villas Boas. 1998. Geochemistry of mercury in sediments of a sub-tropical coastal lagoon, Sepetiba Bay, Southeastern Brazil. Bull. Environ. Contam. Toxicol. 61:57–64.[CrossRef][Web of Science]
• Martinelli, L.A., M.V. Ballester, A.V. Krusche, R.L. Victoria, P.B. Camargo, M. Bernardes, and J.P.H.B. Ometto. 1999b. Land cover changes and ¹³C composition of riverine particulate organic matter in the Piracicaba river basin (Southeast region of Brazil). Limnol. Oceanogr. 44:1826–1833.
• Martinelli, L.A., J.R. Ferreira, B.R. Forsberg, and R.L. Victoria. 1988. Mercury contamination in the Amazon-a gold rush consequence. Ambio 17:252–254.
• Martinelli, L.A., A.V. Krusche, R.L. Victoria, P.B. Camargo, M. Bernardes, E.S. Ferraz, J.M. Moraes, and M.V. Ballester. 1999a. Effects of sewage on the chemical composition of Piracicaba river, Brazil. Water Air Soil Pollut. 110:67–79.[CrossRef]
• Martinelli, L.A., A.M. Silva, P.B. Camargo, L.R. Moretti, A.C. Tomazelli, D.M.L. Silva, E.G. Fischer, K.C. Sonoda, and M.S.M.B. Salomão. 2002. Levantamento das cargas orgânicas lançadas nos rios do Estado de São Paulo. Biota Neotropica 2(2). Available at http://www.biotaneotropica.org.br (verified 29 Aug. 2006).
• Mason, R.P., W.F. Fitzgerald, and F.M.M. Morel. 1994. The biogeochemical cycling of elemental mercury: Anthropogenic influences. Geochim. Cosmochim. Acta 58:3191–3198.[CrossRef][Web of Science]
• Mason, R.P., J.M. Laporte, and S. Andres. 2000. Factors controlling the bioaccumulation of mercury, methylmercury, arsenic, selenium, and cadmium by freshwater invertebrates and fish. Arch. Environ. Contam. Toxicol. 38:283–297.[CrossRef][Web of Science][Medline]
• Maurice-Bourgoin, L., I. Quiroga, J. Chincheros, and P. Courau. 2000. Mercury distribution in waters and fishes of the upper Madeira rivers and mercury exposure in riparian Amazonian populations. Sci. Total Environ. 260:73–86.[CrossRef][Medline]
• McMurtry, M.J., D.L. Wales, W.A. Scheider, G.L. Beggs, and P.E. Dimond. 1989. Relationship of mercury concentrations in lake trout (Salvelinus namaycush) and smallmouth bass (Microplerus dolomieui) to the physical and chemical characteristics of Ontario lakes. Can. J. Fish. Aquat. Sci. 46:426–434.
• Moraes, L.A.F., E. Lenzi, and E.B. Luchese. 1997. Mercury in two fish species from the Parana River floodplain, Parana, Brazil. Environ. Pollut. 98:123–127.[CrossRef][Medline]
• Morrison, K.A., and N. Therien. 1995. Changes in mercury levels in Lake Whitefish (Coregonus clupeaformis) and northern Pike (Esox lucius) in the Lg-2 Reservoir since flooding. Water Air Soil Pollut. 80(1–4):819–828.
• Neumann, C.M., K.W. Kauffman, and D.J. Gilroy. 1997. Methylmercury in fish from Owyhee Reservoir in southeast Oregon: Scientific uncertainty and fish advisories. Sci. Total Environ. 204:205–214.[CrossRef][Medline]
• Pestana, M.H.D., P. Lechler, M.L.L. Formoso, and J. Miller. 2000. Mercury in sediments from gold and copper exploitation areas in the Camaquã River Basin, southern Brazil. J. S. Am. Earth Sci. 13:537–547.
• Pfeiffer, W.C., O. Malm, C.M.M. Souza, L.D. Lacerda, E.G. Silveira, and W.R. Bastos. 1991. Mercury in the Madeira River ecosystem, Rondonia, Brazil. For. Ecol. Manage. 38:239–245.
• Phillips, D.J.H. 1980. Quantitative aquatic biological indicators: Their use to monitor trace metal and organochlorine pollution. Applied Science Publ., London.
• Porvari, P. 1995. Mercury levels of fish in Tucuruí hydroelectric reservoir and in River Moju in Amazonia, in the state of Para, Brazil. Sci. Total Environ. 175:109–117.
• Porvari, P. 1998. Development of fish mercury concentrations in Finnish reservoir from 1979 to 1994. Sci. Total Environ. 213:279–290.[CrossRef][Medline]
• PSA. 1995. Method for total mercury in drinking, surface, ground, industrial and domestic waste waters and saline waters: Methods of analysis, Manual. PS Analytical, Ltd, Orpington, Kent, UK.
• Redmayne, A.C., J.P. Kim, G.P. Closs, and K.A. Hunter. 2000. Methylmercury bioaccumulation in long-finned eels, Anguilla dieffenbachia, from three rivers in Ontago, New Zealand. Sci. Total Environ. 262:37–47.[CrossRef][Medline]
• Rogers, D.W., M. Dickman, and X. Han. 1995. Stories from old reservoirs: Sediment Hg and Hg methylation in Ontario Hydroelectric developments. Water Air Soil Pollut. 80(1–4):829–839.[CrossRef]
• Roulet, M., M. Lucotte, R. Canuel, I. Rheault, S. Tran, Y.G. De Freitos Gog, N. Farella, R. Souza do Vale, C.J. Sousa Passos, E. De Jesus da Silva, D. Mergler, and M. Amorim. 1998. Distribution and partition of total mercury in waters of the Tapajós river basin, Brazilian Amazon. Sci. Total Environ. 213:203–211.
• Salomão, M.S.M.B. 2004. Biogeoquímica de rios do Estado de São Paulo com bacias de drenagem apresentando diferentes características de ocupação do solo. Ph.D. thesis. CENA, Universidade de São Paulo, Brazil.
• Salomão, M.S.M.B., A.C. Tomazelli, D.M.L. Silva, and D. Santos. 2003. Heavy metals in tropical small catchments in the São Paulo State, Brazil: A first step towards the establishment of regional "background" levels. J. Phys. IV 107:1181–1184.
• Santos, D., Jr., F. Barbosa, A.C. Tomazelli, F.J. Krug, J.Á. Nóbrega, and M.A.Z. Arruda. 2002. Determination of Cd and Pb in food slurries by GFAAS using criogenic grinding for sample preparation. Anal. Bioanal. Chem. 373:183–189.[CrossRef][Web of Science][Medline]
• Schroeder, W.H., and J. Munthe. 1998. Atmospheric mercury–an overview. Atmos. Environ. 32:809–822.
• Silva, A.M. 2002. Mapeamento da cobertura do Solo para as bacias hidrográficas Alto Paranapanema, Aguapeí, Peixe/Santo Anastácio e São José dos Dourados, a partir de imagens de satélite. Report FAPESP 00/12.939-0. FAPESP, São Paulo, Brazil.
• Tavares, G.A., J.R. Ferreira, C.E.D. Magalhães, N.C. da Silva, and M.H.T. Taddei. 2003. Mercury in the Moji-Guaçu river basin, S.P-Brazil: The link between marginal lagoons and river contribution, assessed by Pb-210 dating profiles. Ambio 32:47–51.[Medline]
• Tomazelli, A.C., L.A. Martinelli, W.E.P. Avelar, P.B. Camargo, A.H. Fostier, E.S.B. Ferraz, F.J. Krug, and D. Santos, Jr. 2003. Biomonitoring of Pb and Cd in two impacted watersheds in southeast Brazil, using the freshwater mussel Anodontites trapesialis (Lamarck, 1819) (Bivalvia: Mycetopodidade) as a biological monitor. Braz. Arch. Biol. Technol. 46(4):671–682.
• United Nations Environment Programme-Chemicals. 2002. Global mercury assessment. UNEP Chemicals, Geneva.
• USEPA. 2003. National sediment quality survey. Appendix D. Screening values for chemicals evaluated. Available at http://www.epa.gov/ostwater/cs/vol1/appdx_d.pdf (verified 29 Aug. 2006).
• Verdon, R., D. Brouard, C. Demers, R. Lalumiere, M. Laperle, and R. Schetagner. 1991. Mercury evolution (1978–1988) in fishes of the La Grande hydroelectric complex, Quebec, Canada. Water Air Soil Pollut. 56:405–417.
• Watras, C.J., K.A. Morrison, and N.S. Bloom. 1995. Mercury in remote Rocky Mountain lakes of Glacier National Park, Montana, in comparison with other temperate North American regions. Can. J. Fish. Aquat. Sci. 52:1220–1228.

This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Tomazelli, A. C. Articles by Horvat, M. Search for Related Content PubMed PubMed Citation Articles by Tomazelli, A. C. Articles by Horvat, M. Agricola Articles by Tomazelli, A. C. Articles by Horvat, M. Related Collections Surface Water Quality Toxic Trace Metals Ecological Risk Assessment Heavy Metals Water Pollution