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Aquatic Geochemistry ISSN 1380-6165Volume 18Number 5 Aquat Geochem (2012) 18:445-456DOI 10.1007/s10498-012-9169-0

Mercury in the Waters of the Jundia River,SP, Brazil: The Role of Dissolved OrganicMatter

Enelton Fagnani, Jos RobertoGuimares & Pedro Srgio Fadini

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ORI GIN AL PA PER

Mercury in the Waters of the Jundia River, SP, Brazil:The Role of Dissolved Organic Matter

Enelton Fagnani Jose Roberto Guimaraes Pedro Sergio Fadini

Received: 12 November 2010 / Accepted: 20 April 2012 / Published online: 26 May 2012 Springer Science+Business Media B.V. 2012

Abstract Many developing countries have regions of high demographic density, whereuntreated residuary waters from different sources are often discharged into rivers, streams

and other water bodies. This paper discusses the reducing action of organic matter of

anthropic origin on the mercury redox cycle in the Jundia River impacted by discharged

wastes, and on the Pira River, a non-impacted water body. The total mercury concen-

trations in these locations vary from 1.7 to 32 ng L-1 in the former and from 0.6 to

10.6 ng L-1 in the latter. Dissolved organic carbon concentrations of up to 68.3 and

6.5 mg L-1 were observed, confirming the higher impact on the Jundia River. It was

found that an inverse correlation between the concentration of dissolved organic carbon

and total mercury was stronger in the Jundia River, given that it receives higher organic

loads, suggesting that organic matter exerts a reducing action on mercury, which is

released as gas into the atmosphere. This correlation was not observed in the Pira River,

where the organic matter of natural origin is probably not sufficiently labile to act intensely

upon the Hg redox cycle, favoring the metal transport.

Keywords Mercury redox cycle Jundia River

1 Introduction

Mercury is a chemical element known for its toxicity and ability to bioaccumulate and

biomagnify (Drott et al. 2008), presenting a complex biogeochemical cycle which is not

fully understood (Ravichandran 2004; Fitzgerald et al. 2007). The various chemical species

E. Fagnani J. R. GuimaraesFaculdade de Engenharia Civil, Arquitetura e Urbanismo, Universidade Estadual de Campinas(UNICAMP), POB 6021, Campinas, SP 13083-852, Brazil

P. S. Fadini (&)Departamento de Qumica, Universidade Federal de Sao Carlos (UFSCAR), POB 676, Sao Carlos, SP13565-905, Brazile-mail: psfadini@ufscar.br

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of mercury include elemental mercury, Hg (0), the inorganic forms, Hg(II) and Hg(I),

mainly chlorides and sulfates, and the inorganic forms such as methylmercury, MeHg.

Methylmercury is formed mainly in anoxic waters and sediments (Covelli et al. 2008),

and its presence in water is controlled by methylation and demethylation process (Morel

et al. 1998). In some animals, MeHg is retained in fatty tissues, but liposolubility does not

explain the bioaccumulation in fish muscles. In this case, the intestine wall is responsible

by the absorption (Boudou and Ribeyre 1997).

In sulfidic sediments, Hg(II) complexes with sulfur and enters the cellular membrane as

soluble neutral HgS where it undergoes methylation (Benoit et al. 1999). Once methyl-

mercury is formed, its solubility is facilitated in large quantities of dissolved organic matter

(DOM), increasing its concentration in the aqueous phase (Ravichandran 2004), and it can

subsequently be destroyed (demethylation) by both abiotic and biotic processes (Morel

et al. 1998).

In aquatic environments, mercury fluxes occur at the water/atmosphere and water/

sediment interfaces. In the atmosphere, mercury exists predominantly in gaseous form as

Hg(0), but also as divalent reactive gaseous mercury (RGM) or as particulate mercury,

which is RGM adsorbed in particles suspended in the air, such as soot, dust and marine

aerosols. The passage of mercury from air to water may be the result of dry deposition

(Fang et al. 2010), wet deposition or invasive fluxes of Hg(0) that occur when water is

undersaturated in relation to the atmosphere (Jardim et al. 2010; Silva et al. 2006, 2009a,

b). A contribution of mercury in aquatic environments may also occur through silting

processes (Liu et al. 2008).

Intercompartmental mercury fluxes are affected by natural phenomena such as volca-

nism, rainfall, wind velocity, solar intensity and temperature, and by anthropic interven-

tions linked to industrialization, mining and the use of fossil fuels, among others. These

phenomena, in turn, cause changes in pH, redox conditions and in the concentrations of

sulfides, organic matter, oxyhydroxides and carbonates in the water column and sediments,

influencing strongly and impacting the benthic and microbial community (Hatje et al.

2009; Hung et al. 2009; Zhong and Wang 2008).At the water/atmosphere interface, solar ultraviolet (UV) radiation can induce photo-

chemical modifications in mercury speciation (Peters et al. 2007), an action that is variable

during the day (Garcia et al. 2005a, b; Jardim et al. 2010). Humic and fulvic acids, the

predominant forms of aquatic organic carbon (De Oliveira et al. 2007), are able to reduce

Hg(II) to Hg(0), and the latter is carried easily from the water column to the atmosphere,

decreasing the methylation and bioaccumulation potential of the water body as was

observed in rivers of the Amazon region and described by Jardim et al. (2010). On the

other hand, organic matter contains acid sites, such as carboxylic and phenolic acids, which

are able to complex metals and, particularly in the case of mercury, thiols, sulfides and

other reduced sulfurated groups, rendering the metal unavailable for chemical redox

reactions and anchoring it in the water column (Barringer et al. 2006; Chadwick et al.

2006), thereby increasing the bioaccumulation potential.

Dissolved organic matter is the most important phase related with the transportation of

mercury in water. Its complexing capacity is due mainly to reduced sulfur functional

groups such as thiols, which are present in minor quantities but which act as strong metal

ligands (Haitzer et al. 2003). The type and lability of dissolved organic matter may imply

complexation mechanisms of adsorption and even interfere in the mercury redox cycle

through the formation of H2O2, which can both oxidize and reduce mercury species

depending on the pH. In an acid medium, the proton competes for the acid sites of DOM,

causing it to lose much of its metal-complexing potential and leaving the Hg free to

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undergo methylation, since the pKa of the thiol groups is higher than the pH values

frequently found in acid waters (Haitzer et al. 2003).

Methylation is favored (Bisinoti et al. 2007) by microbiological growth in more labile

and degradable DOM. However, if sufficiently labile, this same organic matter can act

directly upon mercury, reducing it chemically and preventing it from remaining in the

water (Lalonde et al. 2004; Silva et al. 2009a, b; Jardim et al. 2010). Hence, speciation

processes are governed not only by the quantity but also by the type of DOM (Han et al.

2006). That is why several methodologies involving molecular fluorescence have been

proposed to elucidate the composition and formation kinetics of HgDOM complexes in

the environment, using three-dimensional techniques and fluorescence quenching titration

(Wu et al. 2004; Fu et al. 2007).

When positive correlations are found between Hg and DOM concentrations in a water

body (Dennis et al. 2005), this usually means that the Hg originates from floodable areas

and soils rich in organic matter and leaches into the water body under study (Akerblom

et al. 2008). However, when Hg comes predominantly from atmospheric sources, this

correlation with organic matter is not always unequivocal (He et al. 2007).

In waters containing high concentrations of mercury comparatively to humic acids, the

latter usually promote the chemical reduction of the metal. Conversely, when the con-

centration of humic acids is very high, three important events occur. The first of these

events is inhibition of the photochemical reduction of Hg due to the lower penetration of

the solar radiation as a result of the dark color of the water; the second is the ability of

humic acids to complex the metal (ODriscoll et al. 2006); and the third is that the direct

oxidation of DOM by UV radiation may also produce hydroxyl radicals (OH) that are able

to oxidize Hg(0) into Hg(II) (Whalin et al. 2007).

Because the behavior of the HgDOM system varies in each region, studies were

conducted in the Jundia River watershed in the state of Sao Paulo, Brazil, to looking for

insights into the linkage between DOM and Hg in this location. The present study therefore

focused on the Jundia River, several stretches of which are impacted by domestic and

industrial effluents, and the Pira River, an important tributary that supplies water for

human consumption (Fadini et al. 2004), pointing out for a hypothesis that the organic

matter of anthropic origin have a reductor agent role over the mercury on its cycle.

2 Methods

2.1 Area Descriptions

The Jundia River, which is approximately 110 km long and drains an area of 1,114 km2, is

located in a highly industrialized region of the state of Sao Paulo (PCJ 2007). This intense

industrialization will soon make it imperative to find alternative sources of water supply for

the cities located in this hydrographic basin, which is home to approximately one million

people.

In this context, the Jundia River stands out as a strategic water resource. However, at

the moment, it is the recipient of industrial and urban wastewaters from innumerable

sources, often without any type of treatment.

The National Environmental Agency, a Brazilian federal legislative body, classifies

water bodies into four categories, where class 1 indicates non-impacted waters and class 4

indicates waters highly impacted by humans (CONAMA 2005). Due to its high level of

contamination, the Jundia River is classified according to this index as class 4 along most

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of its length and independently of the time of year. On the other hand, the Pira River, a

tributary of the Jundia River and also an object of study, can be classified as class 2 due to

the quality of its waters.

2.2 Sampling

Three (03) water sampling sites were selected in the Jundia River and one (01) in the Pira

River, its main tributary. The abbreviations and coordinates of the four sampling sites are,

respectively, CLP (S = 238 12.3800; W = 468 47.0190), downstream from a metal work-shop in the city of Campo Limpo Paulista; DIST (S = 238 8.1550, W = 478 12.6740), anindustrial district in the city of Indaiatuba; SALTO (S = 238 12.6150, W = 478 17.5300), atthe mouth of the Jundia River in the city of Salto; and PIRAI (S = 238 11.0170, W = 47814.7860), which is close to the mouth of the Pira River in the city of Indaiatuba.

The CLP site is marked by strong human occupation, both domestic and industrial,

notably by the presence of a metal workshop. The DIST site is characterized by a high

diversified and active industrial park. The SALTO sampling site shows a strong presence

of domestic sewage and industrial effluents, including effluents from timber beneficiation,

and paint and varnish factories. PIRAI is the most well-preserved site in terms of vege-

tation and intensity of sewage disposal.

Field sampling was based on protocols described in the literature by Fadini and Jardim

(2000, 2001), which provide guidelines on clean procedures for the collection, preserva-

tion, transportation and storage of samples.

To determine the dissolved organic carbon (DOC), the water samples were collected in

glass jars with polyethylene lids, which were previously washed in a solution containing 20

volume % of sulfuric acid, rinsed in ultrapure water and dried. The jars containing water

samples were then double-bagged and stored on ice in thermal boxes until the moment of

analysis, which occurred within no more than 48 h. Duplicate samples were collected at

each sampling site.

2.3 Determination of Total Mercury (THg)

During all the time, clean techniques were used, including gloves use, extractions inside

class 100 fume hood, samples storage in double plastics bags, blanks control, and carrying

out of analytical calibration curves at each analysis session and sample determinations in

triplicate, where the standard deviations were in the range of 5 %. Preparation of the water

samples for total mercury determination involved oxidizing all the Hg species into Hg2?,

using BrCl, as described by Bloom and Crecelius (1983) and by Fadini and Jardim (2001).

The samples were allowed to settle for 2 h, and the clarified supernatant was injected into

the equipment. In an extractor, the Hg2? was reduced with stannous chloride, purged with

N2 and amalgamated in a quartz column packed with gold-coated sand. Quantification was

performed by two-stage amalgamation and thermal desorption, followed by detection in

the Cold Vapor Atomic Fluorescence Spectrometry, CVAFS (Brooks Rand mercury

detector).

2.4 Determination of Dissolved Organic Carbon (DOC)

Carbon was quantified in a Shimadzu TOC-5000A total organic carbon analyzer, which

operates under the principle of high temperature catalytic oxidation (HTCO) at 680 C.

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The samples were allowed to settle for 2 h, and the clarified supernatant was injected into

the equipment. Results with standard deviation minor than 2 % were obtained.

3 Results and Discussion

The variables of total mercury (THg) and dissolved organic carbon (DOC) were quantified

and monitored at the various sampling points during the period of August 2007December

2008. Figure 1 and Table 1 show the THg results.

As can be seen from the data in Fig. 1 and Table 1, the samples collected in the Pira

River presented the lowest HgT contents, as well as the lowest amplitude of variation

among the results. This finding suggests that Hg contamination is lower and predominantly

of diffuse origin, characterizing the region as less impacted. The Jundia River presented

consistently higher concentrations of THg than the Pira River at all its sampling sites.

In the period between January and April 2008, water samples collected in the region of

the Industrial District of Indaiatuba (DIST) presented a peak in the values of THg on one

22/08

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10121416182022242628303234

Tota

l Hg

(ng L-

1 )

Sampling date

CLP SALTO DIST PIRAI

Fig. 1 Concentration of THg in water samples between August 2007 and December 2008

Table 1 Minimum, maximum and mean concentrations of THg in waters between August 2007 andDecember 2008

Site THg (ng L-1)

Min Max Mean SD and RSD

CLP 2.0 22.5 8.2 6.4 (78 %)

DIST 1.7 32.0 7.0 6.6 (95 %)

SALTO 2.1 17.2 5.2 3.6 (70 %)

PIRAI 0.6 10.6 2.1 1.9 (88 %)

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occasion, characterizing pointwise discharges of effluents containing the metal in question,

whose source was not identified.

No clear and systematic correlation was identified between the seasons of the year and

the values of total mercury found in the water bodies under study, probably due to the

anthropic influence that mischaracterizes the possible natural relations that might be

observed (Caron and Lucotte 2008).

Figure 2 and Table 2 show the DOC findings.

The highest concentrations of dissolved organic carbon (DOC) were found close to the

mouth of the Jundia River in the municipality of Salto, SP (SALTO). This region is highly

urbanized and has a large industrial park, which are factors that directly influence the

composition of the Jundia River in terms of organic matter. The lowest DOC concen-

trations were found in the Pira River (PIRAI). The DOC concentrations were usually

found in the following increasing order: PIRAI \ CLP \ DIST \ SALTO, a relationshipthat is valid for any time of the year.

In an attempt to gain an understanding of how DOC may interact with THg in the waters,

correlations between these two variables were tested for each sampling site throughout the

28/08

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DO

C (m

g L-1 )

Sampling date

CLP SALTO DIST PIRAI

Fig. 2 Concentration of DOC in water samples between August 2007 and December 2008

Table 2 Minimum, maximum and mean concentrations of DOC in water samples between August 2007and December 2008

Site DOC (mg L-1)

Min Max Mean SD and RSD

CLP 4.6 10.5 7.1 1.5 (21 %)

DIST 5.1 13.3 9.4 2.2 (23 %)

SALTO 7.8 68.3 28.6 17.7 (62 %)

PIRAI 1.7 6.5 3.3 1.2 (35 %)

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period of this study. Figures 3, 4, 5 and 6 illustrate how the variables of THg and DOC

correlated.

There is a positive correlation between THg and DOC in the PIRAI site, as illustrated in

Fig. 3. Because the site is relatively well preserved, it is assumed that the humic and fulvic

acids originating from the degradation of natural organic matter may basically present two

distinct effects on THg: complexation or chemical reduction (Ravichandran 2004). At the

PIRAI site, as in other water bodies rich in humic and fulvic acids (Dong et al. 2009;

Khwaja et al. 2010), the organic matter can complex mercury. Thus, the metal will have a

strong tendency to remain in the water column, acquiring good mobility along the river

course, rather than a transfer between the compartments waterair (volatilization and

photochemical reduction) or watersediment (sulfide precipitation and/or adsorption).

1 2 3 4 5 6 7

0

2

4

6

8

10

12

r = 0.577

Tota

l Hg

(ng L-

1 )

DOC (mg L-1)

Fig. 3 Variation in theconcentration of THg as functionof DOC in the samples from thePIRAI sampling site (September2007December 2008).Significant correlation atp = 0.05 was observed

4 5 6 7 8 9 10 110

5

10

15

20

r = 0.05

Tota

l Hg

(ng L-

1 )

DOC (mg L-1)

Fig. 4 Variation in the concentration of THg as function of DOC in the samples from the CLP sampling site(September 2007December 2008). No significant correlation was observed

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Sampling data from the region of the CLP site presented slightly positive or null

correlation coefficients, suggesting that the concentration of THg is not affected system-

atically by the concentration of DOC. This weak correlation between THg and DOC is

probably due to competition between the reducing action of the organic matter (OM) of

anthropic origin and the complexing capacity of OM of natural origin (Jardim et al. 2010).

The CLP sampling site did not show a clear correlation between DOC and THg,

probably because this site is little impacted and lacks sufficient contents of labile organic

matter to trigger a significant process of Hg reduction and its release into the atmosphere.

Several types of industrial and domestic wastewaters are discharged into the Jundia

River in the region of the industrial district of Indaiatuba (DIST). What is noteworthy is the

inverse correlation from the one found in the Pira River, that is, the higher the content of

4 6 8 10 12 14

0

5

10

15

20

25

30

35

r = - 0.338

Tota

l Hg

(ng L-

1 )

DOC (mg L-1)

Fig. 5 Variation in theconcentration of THg as functionof DOC in the samples from theDIST sampling site (September2007December 2008).Significant correlation atp = 0.10 was observed

0 10 20 30 40 50 60 700

2

4

6

8

10

12

14

16

18

r = - 0.352

Tota

l Hg

(ng L-

1 )

DOC (mg L-1)

Fig. 6 Variation in the concentration of THg as function of DOC in the samples from the SALTO samplingsite (September 2007December 2008). Significant correlation at p = 0.10 was observed

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organic matter, the lower the amount of mercury found. Based on an analysis of these data,

it seems feasible to suggest that the nature of the organic matter found in the region of the

industrial district differs considerably from that found in the Pira River because, rather

than concentrating mercury in the water compartment, it appears to effect a phase transfer,

probably into the atmosphere, in the form of elemental Hg via reduction of the Hg2?

cations. In this case, the complexing capacity of the natural organic matter is supplanted by

the reducing capacity of the organic matter of anthropic origin.

An analysis of the results obtained from monitoring the samples collected at the mouth

of the Jundia River in the municipality of Salto (SALTO) revealed a mercury dynamics in

the presence of organic matter analogous to that found in the industrial district of In-

daiatuba (DIST). This finding is an indicator that the organic matter in this region plays a

similar role to that found in the industrial district, chemically reducing mercury and

releasing it into the atmosphere. This correlation followed the same trend during the entire

study, that is, an increase in DOC corresponded to a lower concentration of THg.

Data obtained in previous works presented and published in 24th Brazilian Meeting of

Sanitary and Environmental Engineering (Fadini and De Lima 2007), revealed the ten-

dency of waters from Jundiai River to photoreduce dissolved mercury to elemental state.

Dissolved gaseous mercury (DGM) measurements were carried out in waters displaced in

transparent bottles spiked with Hg in pH ranged from 3.7 to 8.2. The organic matter was

responsible for the Hg reduction, corroborating to our main hypothesis.

This set of data on correlations between THg and DOC allows us to put forward the

hypothesis that, in a practically non-impacted environment such as that of the Pira River,

the organic matter appears in the form of large complex and stable molecules, that is,

humic and fulvic acids of natural origin, which are able to anchor mercury in the water

column. At sites strongly impacted by human activities, such as industrial parks, as is the

case of the Jundia River in the industrial district of Indaiatuba, as well as at its mouth in

the city of Salto, the more labile organic matter possesses reducing properties that are

responsible for releasing mercury from the water column into the atmosphere in the form

of Hg0. This, therefore, is evidence of the fact that organic matter plays an important and

differentiated role, depending on the characteristics of the contributions upstream from the

sample collection site.

Within the scenario of complexity of the biogeochemical cycle of mercury, the infor-

mation presented in this paper highlights the fundamental role not only of organic matter

but also, and particularly, of its origin. DOM may or may not be responsible for keeping

mercury in the water column, influencing the global cycle of this metal, since, if it is

released into the atmosphere, Hg0 will have a mean residence time of 1 year in this

compartment, and hence, will be the object of intercontinental transport (Schroeder and

Munthe 1998). The results found in this study are consistent with those observed for DOM

of natural origin and with differentiated lability that exists in the Negro River, in the

Brazilian Amazonian region (Jardim et al. 2010).

Table 3 summarizes the correlations found between DOC and THg at the various

sampling site in the Jundia River basin, as well as a suggestion of the probable mecha-

nisms of interaction between the metal and organic matter present at those sites.

4 Conclusions

The correlations between dissolved organic carbon (DOC) and total mercury (THg) in the

waters of the Jundia River basin observed in this study indicated that dissolved organic

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matter (DOM) plays differentiated roles with respect to mercury dynamics, as a function of

the anthropic impact at each sampling site. Although an increment was found in the

organic load from upstream to downstream of the Jundia River, the DOM exhibited a

differentiated reducing action on the mercury in stock. In the Pira River, which is less

impacted, the DOM promotes chemical complexation of THg in the water column, facil-

itating its transport along the watercourse. In contrast, in the Jundia River, in the industrial

district of Indaiatuba and close to its mouth (SALTO), the DOM plays the role of chemical

reducer, transforming Hg(II) into Hg(0) and favoring its evasive flux at the water/air

interface. A weaker correlation was observed at the sampling site located in Campo Limpo

Paulista (CLP), probably due to the lower lability of the organic matter at this point, which

receives a low load of OM of anthropic origin.

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CLP Inconclusive

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atmosphere

SALTO DOC :, THg ; Chemical reduction of Hg2? to Hg0, with resulting release into the

atmosphere

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Mercury in the Waters of the Jundia River, SP, Brazil: The Role of Dissolved Organic MatterAbstractIntroductionMethodsArea DescriptionsSamplingDetermination of Total Mercury (THg)Determination of Dissolved Organic Carbon (DOC)

Results and DiscussionConclusionsReferences