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MERCURY IN THE SEDIMENT OF PELOTAS RIVER BASIN, BRAZIL

ABSTRACT

Many studies have determined the concentration of trace elements in river sediments in Brazil. Notwithstanding, mercury assessments are scarce, especially because of exclusive extraction techniques and expensive analysis techniques. Still, this element is known for its toxicity, persistence, and bioaccumulation, making its presence in the environment an important factor for biota and human health. For this reason, the objective of this study was to determine the mercury concentration in the sediment of the Pelotas River basin, located on the border of the states of Santa Catarina and Rio Grande do Sul. The sediment was collected at eight locations of the Pelotas basin and, after drying, the mercury was quantified by atomic absorption spectrometry based on the Zeeman-background correction, coupled to a pyrolysis reactor. The mercury concentrations in the sediments of the Pelotas River varied from 40.5 ng g-1 to 62.0 ng g-1 and presented a positive correlation with the fraction of silt and clay. The concentrations of mercury found in sediments of the Pelotas River basin have a low probability of negatively affecting the biota. Nonetheless, given the persistence and bioaccumulation potential of this element, the aforementioned region needs further studies to quantify the risks it may cause on the local biota and human health.

KEYWORDS
heavy metal; trace element; multivariate statistics

INTRODUCTION

During the last few years, research in the field of sedimentology has been focused on sediment production, quantification, and transportation (Sousa et al., 2012Sousa GB, Martins Filho MV, Matias SSR (2012) Perdas de solo, matéria orgânica e nutrientes por erosão hídrica em uma vertente coberta com diferentes quantidades de palha de cana-de-açúcar em Guariba - SP. Engenharia Agrícola 32(3):490-500. DOI: http://dx.doi.org/10.1590/S0100-69162012000300008
http://dx.doi.org/10.1590/S0100-69162012...
; Vanzela et al., 2014Vanzela LS, Grecco DLG, Costa Neto JN, Santos GO (2014) Evaluation of sediment production and siltation in a small earth dam in Fernandópolis, SP. Engenharia Agrícola 34(5):912-924. DOI: http://dx.doi.org/10.1590/S0100-69162014000500010
http://dx.doi.org/10.1590/S0100-69162014...
; Cerquetani & Martins Filho, 2006Cerquetani GE, Martins Filho MV (2006) Rotina computacional e equação simplificada para modelar o transporte de sedimentos num Latossolo Vermelho Distrófico. Engenharia Agrícola 26:617-626. DOI: http://dx.doi.org/10.1590/S0100-69162006000200032
http://dx.doi.org/10.1590/S0100-69162006...
). Additionally, studies have concentrated on the impacts of contaminated sediments on the environment, especially because sediment is considered the main fixator and carrier element in aquatic environments (Pejman et al., 2015Pejman A, Bidhendi GN, Ardestani M, Saeedi M, Baghvand A (2015) A new index for assessing heavy metals contamination in sediments: A case study. Ecological indicators 58:365-373. DOI: http://dx.doi.org/10.1016/j.ecolind.2015.06.012
http://dx.doi.org/10.1016/j.ecolind.2015...
; Cembranel et al., 2017aCembranel AS, Frigo EP, Sampaio SC, Mercante E, Reis RRDos, Remor MB. (2017a). Residue analysis of organochlorine and organophosphorus pesticides in urban lake sediments. Engenharia Agrícola, 37(6), 1254-1267. doi: 10.1590/1809-4430-eng.agric.v37n6p1254-1267/2017
https://doi.org/10.1590/1809-4430-eng.ag...
). Among the main contaminants, mercury (Hg) has received special attention because of its high toxicity, environmental persistence, and bioaccumulation potential, which negatively affects humans and environments worldwide (Kim et al., 2016Kim K, Kabir E, Jahan SA (2016) A review on the distribution of Hg in the environment and its human health impacts. Journal of Hazardous Materials 306:376-385. DOI: http://dx.doi.org/10.1016/j.jhazmat.2015.11.031
http://dx.doi.org/10.1016/j.jhazmat.2015...
).

Countless human activities contribute to increase Hg concentrations in the environment, including coal-based thermoelectric plants, incineration of organic products, gold mining, industrial manufacturing processes of organochlorine products, caustic soda, batteries, thermometers, fluorescent light bulbs, and their disposal, along with the production of drugs and fungicides (Kim et al., 2016Kim K, Kabir E, Jahan SA (2016) A review on the distribution of Hg in the environment and its human health impacts. Journal of Hazardous Materials 306:376-385. DOI: http://dx.doi.org/10.1016/j.jhazmat.2015.11.031
http://dx.doi.org/10.1016/j.jhazmat.2015...
). As an illustration, when Hg based pesticides are applied to crops, these areas are considered major sources of Hg to watercourses and groundwater.

In aquatic environments, microorganisms can transform Hg into methylmercury (CH3Hg), considered even more toxic than the original element. Consequently, this substance accumulates in the tissue of aquatic animals in higher quantities than those found in the environment. The toxic effect of Hg on humans and other living organisms depend on factors such as chemical form, environmental concentration, exposure routes, and vulnerability of the exposed organisms (Kim et al., 2016Kim K, Kabir E, Jahan SA (2016) A review on the distribution of Hg in the environment and its human health impacts. Journal of Hazardous Materials 306:376-385. DOI: http://dx.doi.org/10.1016/j.jhazmat.2015.11.031
http://dx.doi.org/10.1016/j.jhazmat.2015...
). In humans, elevated concentrations of Hg can cause neurological, nephrological, immunologic, cardiac, and reproductive disturbances, along with genetic problems and reduction of cognitive functions (Oliveira et al., 2013Oliveira GA, Rocha GC, Macedo JAB, Britto MC (2013) Percepção de risco à contaminação por mercúrio em uma antiga área de garimpo de ouro em descoberto/MG. Revista de geografia 2(2):1-6.; Gibb & O'leary, 2014Gibb H, O'leary KG (2014) Mercury exposure and health impacts among individuals in the artisanal and small-scale gold mining community: A comprehensive review. Environmental Health Perspectives 122:667-672. DOI: http://dx.doi.org/10.1289/ehp.1307864
http://dx.doi.org/10.1289/ehp.1307864...
).

Several studies have already determined the concentrations of trace elements in river sediments in Brazil, notably Melo et al. (2012)Melo VF, Andrade M, Batista AH, Favaretto N, Grassi MT, Campos MS (2012) Chumbo e zinco em águas e sedimentos de área de mineração e metalurgia de metais. Química Nova 35:22-29. DOI: http://dx.doi.org/10.1590/S0100-40422012000100005
http://dx.doi.org/10.1590/S0100-40422012...
, Santos et al. (2013)Santos JS, Souza FM, Santos MLP (2013) Distribuição de Zn, Pb, Ni, Cu, Mn e Fe nas frações do sedimento superficial do rio Cachoeira na região sul da Bahia, Brasil. Química Nova 36:230-236. DOI: http://dx.doi.org/10.1590/S0100-40422013000200005
http://dx.doi.org/10.1590/S0100-40422013...
, Botero et al. (2014)Botero WG, Souza SO, Santos OS, Oliveira LC (2014) Influência das substâncias húmicas de sedimentos na biodisponibilidade de metais para o sistema aquático. Química. Nova 37:943-949. DOI: http://dx.doi.org/10.5935/0100-4042.20140164
http://dx.doi.org/10.5935/0100-4042.2014...
, and Voigt et al. (2016)Voigt CL, Silva CP, Campos SX (2016) Avaliação da bioacumulação de metais em Cyprinus carpio pela interação com sedimento e água de reservatório. Química Nova 39:180-188. DOI: http://dx.doi.org/10.5935/0100-4042.20160014
http://dx.doi.org/10.5935/0100-4042.2016...
. Nevertheless, studies involving Hg are scarce, especially because of the complex technical requirements of exclusive extraction and the high costs of analyses (Franklin et al., 2012Franklin RL, Bevilacqua JE, Favaro DIT (2012) Organic and total mercury determination in sediments by cold vapor atomic absorption spectrometry: methodology validation and uncertainty measurements. Química Nova 35:45-50. DOI: http://dx.doi.org/10.1590/S0100-40422012000100009
http://dx.doi.org/10.1590/S0100-40422012...
). Some of the noteworthy studies are: Siqueira & Aprile (2012)Siqueira GW, Aprile FM (2012) Distribuição de mercúrio total em sedimentos da plataforma continental Amazônica: Brasil. Acta Amazonica 42:259-268. DOI: http://dx.doi.org/10.1590/S0044-59672012000200012
http://dx.doi.org/10.1590/S0044-59672012...
; Hortellani et al., (2013)Hortellani MA, Sarkis JES, Menezes LCB, Bazante-Yamaguishi R, Pereira ASA, Garcia PFG, Maruyama LS, Castro PMG (2013) Assessment of metal concentration in the Billings Reservoir sediments, São Paulo State, Southeastern Brazil. Journal of the Brazilian Chemical Society 24:58-67. DOI: http://dx.doi.org/10.1590/S0103-50532013000100009
http://dx.doi.org/10.1590/S0103-50532013...
; Almeida et al., (2014)Almeida R, Bernardi JVE, Oliveira RC, Carvalho DP, Manzatto AG, Lacerda LD. Bastos WR (2014) Flood pulse and spatial dynamics of mercury in sediments in Puruzinho lake, Brazilian Amazon. Acta Amazonica 44:99-105. DOI: http://dx.doi.org/10.1590/S0044-59672014000100010
http://dx.doi.org/10.1590/S0044-59672014...
; Araujo et al. (2015)Araujo BF, Almeida MG, Rangel TP, Rezende CE (2015) Distribuição e fracionamento do hg em sedimentos do rio Paraíba do Sul – RJ, Brasil. Química Nova 38:30-36. DOI: http://dx.doi.org/10.5935/0100-4042.20140268
http://dx.doi.org/10.5935/0100-4042.2014...
; Remor et al. (2015)Remor MB, Sampaio SC, Damatto SR, Castilhos ZC, Stevaux JC, Vilas Boas MA, dos Reis RR (2015) Geochemistry of the Upper Paraná River floodplain: study of the Garças Pond and Patos Pond. Journal of Radioanalytical and Nuclear Chemistry 305:409-418. DOI: http://dx.doi.org/10.1007/s10967-015-4021-9
http://dx.doi.org/10.1007/s10967-015-402...
; Rocha et al., (2015)Rocha ARM, di Beneditto APM, Pestana IA, Souza CMM (2015) Isotopic profile and mercury concentration in fish of the lower portion of the rio Paraíba do Sul watershed, southeastern Brazil. Neotropical Ichthyology 13:723-732. DOI: http://dx.doi.org/10.1590/1982-0224-20150047
http://dx.doi.org/10.1590/1982-0224-2015...
; and Sahoo et al. (2015)Sahoo PK, Souza-Filho PWM, Guimarães JTF, Silva MS, Costa FR, Manes CLO, Oti D, Silva Júnior RO, Dall'agnol R (2015) Use of multi-proxy approaches to determine the origin and depositional processes in modern lacustrine sediments: Carajás Plateau, theasternAmazon, Brazil. Applied Geochemistry 52:130–146. DOI: http://dx.doi.org/10.1016/j.apgeochem.2014.11.010
http://dx.doi.org/10.1016/j.apgeochem.20...
.

The Pelotas River basin is a very fragile area, known for its high hydroelectric and industrial potential and intense agricultural activities. Looking to improve the quality of this environment and to prevent its exposure to highly dangerous chemical agents, environmental diagnoses are performed in order to propose management measures and to remediate areas already contaminated or with high contamination risks. Overall, this study aimed to determine the concentrations of Hg in the sediment of the Pelotas River basin.

MATERIAL AND METHODS

Study area

The Pelotas River basin is located on the border of the Brazilian states of Santa Catarina and Rio Grande do Sul (Figure 1). The Pelotas River is the main affluent of the Uruguay River, composing one of the largest basins of Southern Brazil. It possesses a 13,227 km2 drainage area, 62% in the state of Santa Catarina, and 38% in the state of Rio Grande do Sul. The climate of the region is considered temperate, with average yearly rainfall of 1623 mm, distributed throughout the year, but having higher concentrations from May to September.

FIGURE 1
Study area geographic location, land use and sediment sampling points within the Pelotas River drainage basin.

The soil was classified using the Spatial Analysis Tools from the ArcGIS 10 software. Images were used from the Digital Elevation Models, belonging to the TOPODATA project of the Brazilian National Institute for Spatial Research (INEP). The use of soil used in areas of influence was classified by using images from an orbital sensor taken on January 30, 2014, by the Landsat 8 satellite. The classification was done in a supervised manner, using the Maximum Likelihood algorithm from the SCP (Semi-Automatic Classification Plugin) plugin of the open source QGIS software, version 2.14.5. Figure 1 illustrates the soil use classes, wherein pastures occupy 52.79% of the total area of influence, followed by vegetation (45.16%), agriculture (0.92%), and urban area (0.46%). Furthermore, the basin houses industrial activities such as timber, pulp & paper, construction, and agriculture. The hydroelectric potential becomes apparent due to the extremely wavy relief and the presence of the Machadinho and Barra Grande hydroelectric power plants (HPP), as well as the possibility of installing the Pai Querê and three other HPPs, which are under licensing process now.

Sample collection and preparation

Sediment samples were collected from eight sites within the Pelotas River basin, using a Petersen sampler. Six locations in the Pelotas River (PEL 00, PEL 01, PEL 02, PEL 03, PEL 04, PEL 05) and two in its tributaries (TRI 01 – Contas River and TRI 02 –São Sebastião do Arvoredo Stream) (Figure 1). Five samples were collected from each location, constituting a composite sample by the norms of ANA (National Water Agency). Sampling was carried out in February 2014, a period with the lowest annual rainfall average. This is important because the fine river sediments are deposited during the dry season, and are washed away during the rainy season. Thus, only one yearly sampling during the dry season is sufficient for analysis (ANA, 2011ANA – Agência Nacional De Águas (2011) Guia nacional de coleta e preservação de amostras: água, sedimento, comunidades aquáticas e efluentes líquidos. ANA, 326p.). After collecting the samples, they were transported in a refrigerated vehicle (4 °C) and later dried out in an enclosed area, away from the sun and at room temperature.

Physicochemical analyses

Particle size analyses were conducted with a combination of sedimentation and sieving procedures, according to the NBR 7181/1984 standard of the Brazilian Association of Technical Norms (ABNT). The total organic carbon (TOC) was determined by the modified Walkley-Black method (Coser et al., 2012Coser TR, De Figueiredo CC, Ramos MLG, Jannuzzi H, Marchão RL (2012). Recuperação de carbono obtida por três métodos em frações da matéria orgânica de Latossolo sob consórcio milho forrageiras, no Cerrado. Bioscience Journal 28:91-97.).

The chemical elements were only quantified in the silt + clay fraction (<63 μm), as recommended by the World Health Organization (WHO, 1982WHO – World Health Organization (1982) Micropollutants in river sediments. WHO, 85p.). In order to do so, after drying, the sediment samples were sieved through a PVC and nylon sieve with a 63 μm mesh net.

The elements aluminum (Al), iron (Fe), and manganese (Mn) were extracted on a wet basis, using the 3050B method of USEPA (UNITED STATES ENVIRONMENTAL PROTECTION AGENCY). This extraction method was developed to quantify the fractions of metals that could become environmentally available. After extraction, these elements were quantified by flame atomic absorption spectrometry (FAAS). Data accuracy was evaluated by the analytical methods for IAEA 356 and IAEA 433 certifications as reference materials (marine sediment), which were in line with the results at the 95% confidence level.

Total mercury (Hg) was quantified by atomic absorption spectrometry based on Zeeman-background correction, with a pyrolysis reactor. First, the solid sample (sediment) is thermally disrupted, and then the Hg vapor is measured (Castilhos et al., 2006Castilhos ZC, Rodrigues S, Rodrigues APC, Villas-Boas RC, Siegel S, Veiga MM, Beinhoff C (2006) Mercury Contamination in Fish from Gold Mining Areas in Indonesia and Human Health Risk Assessment. Science of the Total Environment 368:320-325. DOI: http://dx.doi.org/10.1016/j.scitotenv.2006.01.039
http://dx.doi.org/10.1016/j.scitotenv.20...
; Fiori et al., 2013Fiori CS, Rodrigues APC, Santelli RE, Cordeiro RC, Carvalheira RG, Araújo PC, Castilhos ZC, Bidone ED (2013) Ecological risk index for aquatic pollution control: a case study of coastal water bodies from the Rio de Janeiro State, southeastern Brazil. Geochimica Brasiliensis 27:24-36.). The accuracy of these data was evaluated by comparing it to Mess-3 sample (marine sediment), i.e. certified reference material, checking the consistency of at least 95%.

Data analysis

Sediment particle-size analyses were interpreted through the ternary diagrams of Shepard (1954) and Pejrup (1988) to determine texture and hydrodynamics, respectively. These interpretations were performed in the R environment using the RYSGRAN package (Gilbert et al., 2012Gilbert ER, Camargo MG, Sandrini-Neto L (2012) Rysgran; Grain size analysis, textural classifications and distribution of unconsolidated sediments; R package version 2.0.).

The set of sediment physicochemical variables was summarized in a Principal Component Analysis (PCA) by the PCORD 5.0 software. This assessment reduces the set of original variables into a set of Principal Components (PC), looking to maintain the maximum variability of the original set. PCA was performed on the Pearson correlation matrix of variables, adopting the broken-stick retention criterion, i.e. with eigenvalues higher than those randomly expected (Jackson, 1993Jackson DA (1993) Stopping Rules in Principal Components Analysis: A Comparison of Heuristical and Statistical Approaches. Ecology 74:2204-2214. DOI: http://dx.doi.org/10.2307/1939574.
http://dx.doi.org/10.2307/1939574....
). To interpret the meaning of retained PCs of original variables, only Pearson correlation coefficients higher than 70% were considered (Jolliffe, 1986Jolliffe IT (1986) Principal component analysis New York, Springer. 487p.).

RESULTS AND DISCUSSION

Particle size analysis was used to classify the sediment samples by texture and hydrodynamics (Figure 2). The Shepard Diagram (Figure 2A), on the other hand, displays the texture variability among locations. The PEL 02 site showed a silty clay texture, while PEL 01 and PEL 04 had sandy silty clay textures and PEL 00 a silty clayey sand texture. Both TRI 01 and PEL 03 sites had a clayey sandy textures while TRI 02 revealed a sandy clayey silt texture and PEL 05 a silty sand texture.

FIGURE 2
Textural composition and hydrodynamics of the bottom sediments of the Pelotas River. A: Shepard Diagram. B: Pejrup Diagram.

The hydrodynamics in PEL 00, PEL 03, PEL 05, and TRI 02 was high according to the Pejrup diagram (Figure 2B). On the other hand, PEL 01, PEL 02, PEL 04, and TRI 01 presented moderate hydrodynamics. The sites with elevated hydrodynamics had higher proportions of sand, from about 52% to 72%. In high hydrodynamic-energy environments, fine particles remain suspended and then transported to environments with lower energy levels, where they are sedimented (Noronha-D'mello & Nayak, 2015Noronha-D'mello CA, Nayak GN (2015) Geochemical characterization of mangrove sediments of the Zuari estuarine system, West coast of India. Estuarine, Coastal and Shelf Science 167:313-325. DOI: http://dx.doi.org/10.1016/j.ecss.2015.09.011
http://dx.doi.org/10.1016/j.ecss.2015.09...
).

Figure 3 exhibits the PCA for the set of physicochemical variables of sediments. According to the broken-stick criterion, two PCs were considered for the analysis; they comprised 69.22% of the total variability. In the positive quadrant, the PC 1 is composed of the variables sand, Al, and gravel; yet, in the negative one, it is composed of the variables clay, silt, and Hg (Figure 3). The PC 2 in the negative quadrant is composed of the variables Mn and Fe. Conversely, TOC was taken as uninterpretable by the broken-stick criterion, thus presenting lower variability among the locations than the random variability (Jackson, 1993Jackson DA (1993) Stopping Rules in Principal Components Analysis: A Comparison of Heuristical and Statistical Approaches. Ecology 74:2204-2214. DOI: http://dx.doi.org/10.2307/1939574.
http://dx.doi.org/10.2307/1939574....
). Therefore, no significant statistical difference among the sampled locations was registered. The PC 1 separated the sites into three groups: the first, formed by PEL 03 and PEL 05, which had the highest results for sand, Al, and gravel; the second, by PEL 02, TRI 02, and PEL 01, where the highest levels of clay, silt, and Hg were found; and the third, by PEL 00, TRI 01, and PEL 04, with intermediate values for the variables included in PC 1 (Figure 3). PC 02 separated PEL 02 from the rest of sites since it had the highest levels of Mn and Fe, and the lowest concentrations of the variables forming PC 02 (Figure 3).

FIGURE 3
Principal Component Analysis (PCA) of the physicochemical variables of sediments from the Pelotas River.

The positive correlation between the finer portion of sediments (silt and clay) and Hg contents (Figure 3) is due to the larger surface area of fine particles, increasing their adsorption capacity (Oliveira et al., 2011Oliveira LC, Botero WG, Santos A, Cordovil MCO, Rocha JC, Silva HC (2011) Influência das características físicoquímicas dos solos no ciclo hidrobiogeoquímico do mercúrio na região do Rio Aracá – AM. Química Nova 34:1303-1308. DOI: http://dx.doi.org/10.1590/S0100-40422011000800002
http://dx.doi.org/10.1590/S0100-40422011...
; Cembranel et al., 2017bCembranel AS, Sampaio SC, Remor MB, Gotardo JT, Rosa PMD (2017b). Geochemical Background in an Oxisol. Engenharia Agrícola 37(3):565-573. DOI: http://dx.doi.org/10.1590/1809-4430-eng.agric.v37n3p565-573/2017
http://dx.doi.org/10.1590/1809-4430-eng....
). Thus, clay is considered an important factor for Hg adsorption in soils and sediments (Araujo et al., 2015Araujo BF, Almeida MG, Rangel TP, Rezende CE (2015) Distribuição e fracionamento do hg em sedimentos do rio Paraíba do Sul – RJ, Brasil. Química Nova 38:30-36. DOI: http://dx.doi.org/10.5935/0100-4042.20140268
http://dx.doi.org/10.5935/0100-4042.2014...
). The PCA shows the lack of correlation between Hg and the contents of TOC, Al, Fe, and Mn. In this experiment, only the fractions of elements environmentally available were quantified, confirming the association between most of the Hg found and the fine portion of sediments (silt and clay). This result points out the complexing minerals as absorbent agents for Hg, albeit they are commonly unavailable for reactions with the aquatic environment, i.e. there is a low probability of it being incorporated by the aquatic biota (Araujo et al., 2015Araujo BF, Almeida MG, Rangel TP, Rezende CE (2015) Distribuição e fracionamento do hg em sedimentos do rio Paraíba do Sul – RJ, Brasil. Química Nova 38:30-36. DOI: http://dx.doi.org/10.5935/0100-4042.20140268
http://dx.doi.org/10.5935/0100-4042.2014...
).

By observing the PCA results, it seems that the largest fraction of Hg found in sediments is in its least reactive form (adsorbed to complexing minerals), which is hardly available to the ecosystem. Elements of anthropogenic origins are predominantly found in sediment parts that are more unstable, which are vulnerable to small environmental changes (Bartoli et al., 2012Bartoli G, Papa S, Sagnella E, Fioretto A (2012) Heavy metal content in sediments along the Calore river: relationships with physical-chemical characteristics. Journal of Environmental Management 95:S9-14. DOI: http://dx.doi.org/10.1016/j.jenvman.2011.02.013
http://dx.doi.org/10.1016/j.jenvman.2011...
). Hence, we believe the largest fraction of Hg in sediments from the Pelotas River is most likely of geogenic origin. However, thorough studies in this region are still necessary to confirm these results.

Figure 4 shows the Hg concentrations in the sediment of the Pelotas River. The locations presenting higher concentrations (PEL 01, PEL 02, PEL 04, and TRI 02) were the same that had higher quantities of fine sediments (silt and clay) and moderate hydrodynamics (Figure 2). This supports the results obtained in the PCA (Figure 3), which showed a correlation of Hg concentrations with silt and clay fractions.

FIGURE 4
Mercury concentrations in the bottom sediments of the Pelotas River.

The Hg concentrations in the bottom sediments of the Pelotas River varied from 40.5 ng g-1 to 62.0 ng g-1 (Figure 4; Table 1). Our findings were compared to those of other studies in Brazilian river environments, as shown Table 1. In general, the highest levels of Hg found in this research were lower than were those reported by other authors. Furthermore, according to the CONAMA resolution n° 454/2012 (Brazilian National Environmental Committee), Hg concentrations lower than 170 ng g-1 (level 1) have smaller probabilities of adversely affecting the biota and only those above 486 ng g-1 (level 2) could. Therefore, the concentrations found in the Pelotas River show a low probability of risk to the biota. Nevertheless, Castro et al., (2016)Castro NSS, Braga CM, Trindade PAA, Giarrizzo T, Lima MO (2016) Mercury in fish and sediment of Purus River, Acre State, Amazon. Cadernos Saúde Coletiva 24:294-300. DOI: http://dx.doi.org/10.1590/1414-462x201600030142
http://dx.doi.org/10.1590/1414-462x20160...
demonstrated the bioaccumulation potential of Hg when studying the Purus River. These researchers found Hg concentrations between 38 and 65 ng g-1 in the sediment of the Purus River, while in carnivorous fish muscle, it reached up to 5384 ng g-1, with an average of 927 ng g-1. This outcome demonstrates the high toxicity, persistence, and bioaccumulation potential of this element. In this context, it is important to emphasize the need for further studies to quantify the risks to aquatic biota and human health in the Pelotas River basin.

TABLE 1
Mercury concentration in sediments of river environments in Brazil.

CONCLUSIONS

This study found no correlation between human activities and mercury concentrations in the sediment of the Pelotas River basin and its tributaries. The mercury concentrations found in the sediment have little chance of causing adverse effects on local biota. Yet, the high toxicity, persistence, and bioaccumulation potential of mercury emphasizes the need for further investigations in this region with the purpose of quantifying risks it may cause to aquatic biota and human health.

ACKNOWLEDGEMENTS

The authors would like to thank the financial aid provided by the CNPq (Brazilian Committee for Scientific and Technological Development), CAPES (Coordination for the Improvement of Higher Education Personnel), UNIOESTE (Western Paraná State University), and PGEAGRI (Post-graduation Program in Agricultural Engineering).

REFERENCES

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    » http://dx.doi.org/10.1590/S0044-59672014000100010
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    » http://dx.doi.org/10.5935/0100-4042.20140268
  • Bartoli G, Papa S, Sagnella E, Fioretto A (2012) Heavy metal content in sediments along the Calore river: relationships with physical-chemical characteristics. Journal of Environmental Management 95:S9-14. DOI: http://dx.doi.org/10.1016/j.jenvman.2011.02.013
    » http://dx.doi.org/10.1016/j.jenvman.2011.02.013
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    » http://dx.doi.org/10.5935/0100-4042.20140164
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    » http://dx.doi.org/10.1016/j.scitotenv.2006.01.039
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Publication Dates

  • Publication in this collection
    Jan-Feb 2018

History

  • Received
    07 Apr 2017
  • Accepted
    03 Sept 2017
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