Geochemical Distribution of Copper and Zinc in the Aquatic Sediment of Nyolo Spring Water at Karangploso

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Geochemical Distribution of Copper and Zinc in the Aquatic Sediment of Nyolo Spring Water at Karangploso

Malang East Java

Anis Khoirun Nisa¹, Barlah Rumhayati¹*, and Andi Kurniawan²

1Chemistry Department, Faculty of Science, Brawijaya University, Malang, Indonesia

2Faculty of Fisheries and Marine Science, Brawijaya University, Malang, Indonesia

*Corresponding email: [email protected]

Received 3 December 2018; Accepted 28 January 2019

ABSTRACT

Aquatic sediment has a role for heavy metals sink. Understanding the geochemical fractions of heavy metals in the aquatic sediment can predict the mobility and reactivity of heavy metals fractions that can induce environmental problems. The aim of this study was to determine the distribution of geochemical fractions of copper and zinc in aquatic sediment of Nyolo spring. Sediments samples were taken from five locations along the spring. Geochemical fractions of copper and zinc were extracted using BCR (Community Bureau of Reference) sequential extraction method. The concentration of these metals in each extract was analyzed using AAS. The result showed that overall the sediment consisted of zinc at a higher concentration than copper. Amongst the geochemical fractions, copper and zinc were found dominantly at an oxidizable fraction. As the first fraction, Zn was more bioavailable than copper for biological uptake. Furthermore, based on the Risk Assessment Code (RAC) value, the aquatic sediment of Nyolo Spring was low risk to the Zn and Cu contaminations at most sites, except for Zn in Site III showed a medium risk. This metals fraction will potentially available for organism uptake with the changing of pH sediment or overlying water.

Keyword: copper, zinc, Nyolo spring, BCR sequential extraction method

INTRODUCTION

Heavy metals are one of the environmental pollutants that are very dangerous because of their toxicity, abundance, and easily accumulated by various aquatic organisms [1], thus they pose a serious threat to the aquatic ecosystem [2]. Copper and zinc are important elements for organisms for physiological and reproductive functions [3], besides, these metals are micronutrients needed for growth and development in small quantities [4]. Excessive intact of zinc in the human body may lead to vomiting, abdominal pains, lethargy, and nausea, while high concentrations of copper may cause anemia, liver and kidney damage, and acute or chronic damage to the nervous system [1]. These metals enter into aquatic ecosystems through domestic waste, fertilizers, and pesticides, or atmospheric decomposition. The changes of physical and chemical conditions such as pH, redox potential, salinity, organic matter as complexing agents, and particulate matter are controlled by the chemical form and mobility of heavy metals in the aquatic environment. Metals that are insoluble in water can be adsorbed by suspended particles and accumulate in sediments [5].

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Sediment is an important ecological component in the aquatic environment and functions as a sink for heavy metals. Sediments have been known as environmental indicators because of their large capacity to combine and accumulate heavy metals [6]. Naturally, heavy metals can enter into water sediments through weathering of soil and rocks, besides heavy metals also enter through anthropogenic activities such as domestic, agricultural and industrial waste. Availability and mobility of heavy metals in the aquatic environment depend on the chemical form and interaction of metals with the solid phase of the sediment. Thus, knowing their chemical form can determine the potential for their remobilization of heavy metals into water bodies [5].

The interaction between metals ion and solid phase of sediment affect mobility and availability of heavy metal in sediment [2]. Heavy metals are retained in the solid phases by ion exchange, precipitation, adsorption, or chelate formation so the metals are available in geochemical fractions. The geochemical fraction of heavy metals in aquatic sediment provides detailed information about the origin, occurrence, biological and physicochemical availability, mobility, and transport of heavy metal [3]. Technically, the fractions can be determined after sequential extraction. The Community Bureau of Reference (BCR) sequential extraction scheme divides heavy metals in a sediment into four geochemical fractions including acid-soluble fraction (exchangeable and bound to carbonates), an acid- reducible fraction (bound to Fe-Mn oxides), an oxidizable fraction (bound to organic matter), and residual fraction [4–6]. According to Ma [7], the remobilization ability from anthropogenic sources is indicated by an acid-soluble fraction. Heavy metals in the acid- soluble fraction are easily released into water bodies; therefore, it can establish their contamination factor to the aquatic environment. The potential of sediment as a source of heavy metals contamination can be determined by the value of risk assessment code (RAC).

Whereas the bioavailability of heavy metals to the aquatic environment can be determined by the amount of acid-soluble fraction, acid-reducible fraction, and oxidizable fraction. A residual fraction is not available for biota because heavy metals are strongly bound to silicate mineral.

Nyolo spring water, located in Karangploso Malang, is a source of natural water used by local residents for domestic activities and its channel used as agricultural irrigation. Changing of land use around the spring becomes agricultural and residential land could cause erosion.

This change of land use is strongly bound to the anthropogenic activities that could cause increasing sedimentation and heavy metal concentration subsequently [8]. The main objective of this study was to determine the distribution of geochemical fractions of copper and zinc in the aquatic sediment of Nyolo Springwater, therefore the potential of the sediment for the heavy metals contamination in the water bodies of the spring can be predicted.

EXPERIMENT Sampling area

The sediment samples were collected in the Nyolo spring water, Karangploso Malang, East Java, in March 2018. A total of five sites for sediment samples were collected in the Nyolo spring water and its channel, as shown in Table 1 and Figure 1. Sites I and II were located at the upper stream of Nyolo spring, meanwhile, site III, IV, and V were located at downstream of Nyolo spring.

Sediment samples were collected about 1 kg from each site by using core sampler, respectively. Three random samples were taken from each site, homogenized, and composited samples were stored in polyethylene bags. Furthermore, the sediment samples were stored and kept in a cool box at 4^oC until reaching the laboratory for further analysis.

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Table 1. The coordinates point of sampling sites

Site(s) Latitude Longitude Annotation

I II III IV V

7°52'44.84"S 7°52'44.92"S 7°52'51.78"S 7°52'53.29"S 7°52'52.75"S

112°37'20.22"E 112°37'18.63"E 112°37'24.39"E 112°37'25.73"E 112°37'23.86"E

Upper stream of Nyolo spring Upper stream of Nyolo spring

Curah Glogo Curah Glogo Curah Lang-lang

Figure 1. Sampling sites of Nyolo Spring, Karangploso Malang Chemicals and instrumentation

All reagents used for analysis were analytical reagent grade unless otherwise stated. All standards, reagents, and samples were kept in polyethylene containers. Acetic acid (glacial, Merck), hydroxylammonium chloride (Merck), hydrogen peroxide (30%, PT. Smart Lab), ammonium acetate (Merck), and nitric acid (v/v) (65%, JT Baker) were used to extract sediment samples. Heavy metals determination in the sediment samples were performed using an Atomic Absorption Spectrometry (AAS, Shimadzu AA-6200) with hollow cathode lamps having resonance lines for Cu and Zn at 213.9 nm and 324.7 nm, respectively.

Physical and chemical characterization of sediment samples

All physical and chemical properties of sediment analyzed for this research were conducted using available standard method [9-10]. These included pH; redox potential; cation exchange capacity (CEC); grain size; organic matter concentration; total iron (Fe) concentration; and total manganese (Mn) concentration. The standard method from Tanah [9]

was used to analyze the pH of sediment, redox potential, cation exchange capacity (CEC),

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grain size, and organic matter concentration of sediment samples. Total iron (Fe) and total manganese (Mn) concentration were measured using an Indonesian National Standard (SNI) method [10].

Sequential extraction

The sequential extraction procedure modified by Fathollahzadeh and Nemati [4,6] was performed in the present study (Table 2).

Table 2. Sequential extraction steps of sediment fractionation

Step Fraction Reagent(s)

F1 F2 F3 F4

Acid-soluble

(e.g. exchangeable, carbonates) Acid-reducible

(e.g. Fe-Mn oxide) Oxidizable

(e.g. organic matter) Residual

(e.g. non-silicate bound metals)

Acetic acid, 0.11 M

NH2OH.HCl 0.5 M at pH 1.5

H2O2, 8.8 M, then CH3COONH4, 1.0 M at pH 2 Aqua regia (HCl : HNO3 = 3 : 1)

All extractions were shaken for 16 hours at room temperature at 200 rpm, using a mechanical shaker. Furthermore, the extracts were separated from solid residue by centrifugation for 20 minutes at 3000 rpm, the resulted supernatant liquid was transferred into a polyethylene volumetric flask then ready for AAS analysis. The residue washed by adding 20 mL of deionized water and shaken for 15 minutes, then centrifuged for 20 minutes at 3000 rpm. The residue decanted and used for the next extraction.

Table 3. Physical and chemical properties of Nyolo spring sediments.

Sites

Parameter pH CEC (NH4OAc 1.0

M pH 7, meq/100g)

Redox potential

(mV)

Organic matter

(%)

Sand (%)

Silt (%)

Clay (%)

I 7.1 22.41 312 5.34 44 28 28

II 6.9 11.32 325 4.74 44 28 28

III 6.8 34.05 326 5.71 50 17 33

IV 6.9 37.56 323 4.95 31 32 37

V 7.0 17.12 327 4.62 61 32 7

RESULT AND DISCUSSION

Distribution of copper and zinc in the sediments of Nyolo spring

The bioavailability of metals in the sediment depends on their distribution between solid and solution phase. This distribution was affected by the physical and chemical condition of sediment. The result of physical and chemical conditions of Nyolo spring given by Table 3.

The distribution of copper and zinc concentration was determined for each extraction steps in the sediment shown in Figure 2.

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Figure 2. Distribution percentage of heavy metals in sediment fraction: (a) copper; (b) zinc Acid-soluble Fraction (F1). Heavy metals in acid-soluble fraction present in ionic form, bound to carbonates and the exchangeable. The metals in this fraction are held by weak electrostatic adsorption shows most mobile and available to biota in the aquatic environment thus this fraction considered an indicator of water pollution [11]. Metals remobilization can occur due to adsorption-desorption reactions and lowering of pH [1]. Metals in this fraction are authigenic and contributed by anthropogenic source [12].

As shown in Figure 2, the distribution percentage of zinc in the acid-soluble fraction was higher than copper in all sites. Zinc concentration in F1 were 0.360 mg/kg to 3.520 mg/kg for all sites, while copper concentration were 2.53 mg/kg to 18.59 mg/kg. The concentration of copper and zinc in acid-soluble fraction affected by pH changes. Based on Table 3, the pH of sediment samples was around 6.8-7.1 indicated slightly acid to moderated neutral. At this pH range, copper and zinc form metal ions (Cu²⁺ and Zn²⁺) and inorganic complexes (Cu(HCO3)⁺, Cu(CO3)22-, CuCO3, and ZnCO3, Zn(HCO3)⁺) that has high concentration and solubility as dissolved metals. The high quantity of zinc as dissolved metals (Zn²⁺) rather than copper (Cu²⁺) show the higher concentration of zinc in acid soluble fraction than copper.

This result appropriated with Kayastha [3], that showed the abundance of Zn rather than Cu in acid-soluble fraction.

Correlation of copper and zinc in fraction 1 to their dissolved in water is displayed Figure 3. The zinc concentration in Fraction 1 had a positive correlation with a dissolved copper concentration in the water body, otherwise had a negative correlation with dissolved zinc concentration. While copper concentration in Fraction 1 had low correlation with dissolved copper and zinc in water. This shows the high concentration of zinc in acid-soluble fraction increasing the concentration of dissolved copper but decreasing dissolved zinc concentration in the water body. Conversely, based on low correlation value (r²), the concentration of copper in this fraction did not affect the concentration of dissolved copper and zinc in the water body.

Based on the measurement of dissolved copper and zinc concentration in water bodies shows that the concentration of dissolved copper in Nyolo spring water was higher than dissolved zinc. Thus, the concentration of dissolved copper had a positive correlation with zinc concentration in the acid-soluble fraction. The pH changes of sediment can affect the solubility of metals in Fraction 1. Decreasing of sediment pH can be increasing solubility of

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zinc in acid-soluble fraction, which is remobilizing to water bodies. The high concentration of zinc and copper in this fraction is probably due to anthropogenic sources like domestic sewage, fertilizer, or pesticides, which entered the sediments as absorbed ions or carbonate species.

Figure 3. Correlation of copper and zinc concentration in Fraction 1 to the copper and zinc concentration in water. (a) copper; (b) zinc.

Acid-reducible Fraction (F2). Metals in this fraction bound to Fe and Mn oxides. This fraction referred to as sink for heavy metals. Metals bound to Fe-Mn oxides as a combination of precipitation, adsorption, surface complex formation, and ion exchange [16]. Metals in acid-reducible fraction can be affected by the changes of pH and the redox potential of sediment. Based on Figure 2, the distribution percentage of copper and zinc concentration was 0.30 to 7.68 mg/kg and 1.74 to 7.5 mg/kg, respectively.

Figure 4. The concentration of Fe and Mn in all sediment sites

Fe and Mn oxides in sediment have large surface area thus it is considered as predominant sorbent and found to have high significant positive loadings for metals [13]. Under oxidizing condition (as seen in Table 3), Fe(II) is rapidly oxidized to Fe(III), which will hydrolyze to

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insoluble FeOOH precipitate and Mn(II) formed hydroxides, MnO2 [14], its act potentially as a sorbent for zinc and copper. Fe and Mn total concentration in the aquatic sediments of Nyolo spring water illustrated in Figure 4.

Based on Figure 5, there was a slightly positive correlation of Zn (F2) and a negative correlation of Cu (F2) with the sediment redox potential. It means that increasing sediment redox potential has a low contribution to the increasing concentration of Zn (F2), but it may lead to the decreasing of the copper as the second fraction. It means increasing redox potential affecting Fe and Mn oxides adsorption to copper in this reducible fraction instead of zinc. Conversely, under reducing conditions metal tends to unstable and associated with sulfide, organic matter, and carbonate. The adsorbed heavy metals may be released when the aquatic sediment conditions became increasingly reducing [15].

Figure 5. The concentration of sediment redox potential to the Zn and Cu concentrations in acid-reducible fraction (F2)

Oxidizable Fraction (F3). Metals in this fraction were associated through complexation or bioaccumulation process with various organic matters such as living organism, detritus or coatings on minerals particles [16]. As shown in Figure 2, the distribution percentage of Cu (F3) were 1.875 mg/kg to 7.827 mg/kg for all sites, while Zn (F3) were 0.19 mg/kg to 94.38 mg/kg. The second most abundant concentration of copper and zinc were found in the oxidizable fractions. Metals associated with oxidizable fraction are tended to remain in sediment for longer periods but could be mobilized by the decomposition process [16]. The reaction between metal ions and organic ligand form a species, which can precipitate or absorbed on sediment materials. The concentration of metals in this fraction can be affected by redox potential, organic matter, cation exchange capacity, and particle size of sediment.

Metals can be mobilized to the aquatic environment when aquatic sediment conditions became increasingly oxidizing [17]. Based on redox potential value, the sediment of Nyolo spring water tends to oxidize. Under the oxidizing condition, metals in the oxidizable fraction (F3) can be mobilized to water bodies corresponding decomposition process of organic matter so the metals will be bound to carbonates [18,19]. It was shown in Figure 6a that there was a negative correlation between Cu (F3) and Zn (F3) with the potential redox. It indicates that the redox potential of sediment has a contribution to the release of heavy metals as the third fraction.

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As shown in Figures 6 b-d that the availability of Zn (F3) and Cu (F3) in the sediment was positively correlated to the particle size, cation exchange capacity (CEC) and organic matter content, except for Zn (F3) which had a slightly negative correlation to the CEC. The organic matter and clay particles had a positive correlation with the concentration of copper and zinc in Fraction 3. Sediment with the finer particles size (clay particle) contains high organic matter content. The finer grain particles generally contain a higher concentration of metals because of their large surface area and high adsorption capacity [20]. Thus more heavy metals are exchanged and increasing the value of cation exchange capacity of sediment.

Organic matter commonly composed by humic and fulvic acid. Humic acid can interact with metal ions, oxides and hydroxides minerals since it contains active functional group such as carboxyl (-COOH), -OH phenolic compounds, and –OH alcoholic. Therefore, humic acid interacts with metal ions by complexation and chelation [21]. Organic substances exhibit a high degree of selectivity for divalent ions compared to monovalent ions in sediments.

Copper usually found strongly associated with the organic matter due to the high stability constant of the copper-organic compound. From the correlation below (Figure 6b-d) showed that the concentration of copper in the oxidizable fraction was more stable than zinc. This result is in accordance with the research from Filgueiras [16] that showed the stronger binding of copper-organic complex than zinc-organic complex in sediment.

Figure 6. Correlation of: (a) sediment redox potential; (b) clay particle; (c) CEC; and (d) organic matter content to the Zn and Cu concentrations in F3.

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Residual Fraction (F4). Metals in this fraction are the most stable and least bioavailable of all the chemical fraction of sediment [11]. Metals were occluded in the crystal lattice of silicate and well-crystallized oxide minerals [22], thus, it was hard to release to the water body. The source of this metal in the residual fraction is related to litoghenic source such us soil or rock weathering. Based on percentage distribution (Figure 2) copper and zinc were mostly concentrated in the residual fraction. These result indicated that copper and zinc have the strongest association with the crystalline structures of the minerals and they are stable under natural conditions with low mobility [6].

Risk Assessment Code (RAC)

Metals associated with first three fractions (F1+F2+F3) of sequential extraction were considered as readily to potentially bioavailable metals (non-resistant fraction) to the aquatic environment [5], while metals in the residual fraction (F4) (resistant fraction) are considered as non-bioavailable metals. As shown in Figure 7, the percentage of bioavailable copper was higher than zinc, about 40% and 36%, respectively. This indicates that copper is potentially more bioavailable and easy to release to water body than zinc. This result appropriate with the previous study from Remor [23] that copper was more potentially bioavailable than zinc in aquatic sediment.

Figure 7. Total percentage bioavailable and a non-bioavailable fraction of copper and zinc

Table 4. RAC values of copper and zinc for all sites

Site Cu Zn

RAC (%) Values RAC (%) Values

I 7 Low risk 7 Low risk

II 10 Low risk 8 Low risk

III 2 Low risk 17 Medium risk

IV 6 Low risk 9 Low risk

V 3 Low risk 7 Low risk

Heavy metals in acid-soluble fraction (F1) is the most mobile and most ready to release to the aquatic environment [1]. Metals bound to this fraction mainly caused by anthropogenic source thus this fraction considered as a pollution indicator. To assess sediment potential as a source of a contaminant in the aquatic environment of the Nyolo spring, the Risk Assessment

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Code (RAC) was calculated. The risk assessment code defined as the metals exchangeable and/or bound to carbonate fraction (% F1 for BCR method) [6], was determined for copper and zinc metals, and the value interpreted inappropriately with the RAC classification. Table 4 shows the result of RAC value of the acid-soluble fraction (% F1). Based on Table 4, the sediments generally showed low risk for Cu and Zn, except for Zn at Site III. It may cause by using chemical fertilizer, which contains mostly zinc metals that entered to the water body.

Based on this result, the aquatic sediment of Nyolo Spring water showed a low risk for the bioavailability of copper and zinc in the aquatic environment. The sediment will have a high risk to the aquatic environment when there is the changing of sediment pH.

CONCLUSION

The distribution of copper and zinc in the geochemical fractions in aquatic sediment of Nyolo spring water showed that less than 50% of copper and zinc were in the bioavailable fractions (non-resistant). Copper and zinc in these fractions can be available for biota and became an environmental risk. The speciation of copper followed the order: F4 > F3 > F2 >

F1. Meanwhile, the following order of zinc speciation are F4 > F3 > F1 > F2. The sediment samples show low risk for copper and zinc with RAC values <10%, except for Zn at site III show medium risk with RAC value about 17%. This condition can be varied depends on the pH changes of sediment.

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