The Bioavailability and Risk Potential of Copper and Zinc of Soil as An Indicator Heavy Metals Contamination in The Aquatic

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The Bioavailability and Risk Potential of Copper and Zinc of Soil as An Indicator Heavy Metals Contamination in The Aquatic

System in Sumber Nyolo, Karangploso, East Java

Rifnida Azmi Fitratian¹, Barlah Rumhayati^1*, Andi Kurniawan²

1Chemistry Department, Faculty of Mathematics and Natural Science, Brawijaya University, Malang, Indonesia, 65145

2 Faculty of Fisheries and Marine Science, Brawijaya University, Malang, Indonesia, 65145

*Corresponding email: [email protected]

Received 1 December 2018; Accepted 28 January 2019

ABSTRACT

The bioavailability potential of heavy metals in the soil can be used as an indicator of heavy metals pollution in an aquatic system. Soil samples were collected from five sites at the upper and downstream of the Sumber Nyolo by using grab sampling. Samples were pretreated before metals analysis. Geochemical fractions of Cu and Zn were extracted using the Community Bureau of Reference (BCR) modified technique and followed by Cu and Zn analysis using Atomic Absorption Spectroscopy. Based on percent distribution, Cu was dominant in the form of a resistant fraction (F4) (57%), while Zn was dominant as a nonresistant fraction (F1, F2, and F3) (59). As the first fraction (F1) that is referred as the bioavailable fraction, Cu (13%) was more potentially released from soil to water body than Zn (4%), thus Cu was more bioavailable. Based on correlation with physical-chemical properties of soil, Cu and Zn will be released when there is increasing of soil redox potential, increasing of cation exchange capacity and changes of pH to an acid condition.

Furthermore, the Risk Assessment Code value for Cu and Zn in soil from Sumber Nyolo were 0.13% and 0.04%, respectively. This indicated that soil in Sumber Nyolo has no potential in providing Cu and Zn in the water body. Thus, physical-chemical properties of soil can be used as indicators of availability of heavy metals in a water body.

Keyword: Copper and Zinc, Geochemical Fraction, Physical-Chemical Properties, Soil

INTRODUCTION

Soils are the reservoir for many harmful constituents elemental and biological, including heavy metals and trace metals [1]. The presence of heavy metals in the soil must be identified where the source of heavy metals originates, which can be derived from a natural source and anthropogenic sources (human activities). Bioavailability and mobility of metals are related, then the higher the concentration of mobile toxic metals in the soil column which increase the potential for a water body, plant uptake, and animal or human consumption [2].

Sumber Nyolo which is located in the agroforestry area, surrounded by forest and agricultural plants, in Ngenep, Karangploso, East Java is one of the springs that used by local people as irrigation purposes, a drinking water source, and other domestic purposes. The external inputs of bioavailable metals to forest soils are atmospheric deposition, from the use of fertilizers, pesticides, and animal manure, while the internal input is in the form of

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weathering of soil minerals. The external and internal inputs of bioavailable metals which may occur in the soil around the Sumber Nyolo may cause the accumulation of heavy metals in the soil. Interaction of solid phase of soil with the aquatic environment may release the bioavailable metals from the soil, as a result, elevate heavy metals concentration in the water column.

Heavy metals commonly found in contaminated soil are lead (Pb), chromium (Cr), cadmium (Cd), copper (Cu) and zinc (Zn). Copper and zinc are essential heavy metals that are micronutrient heavy metals in the soil for plant growth [3]. Copper is an essential heavy metal used by plants and animals. In the soil, copper is strongly fixed by organic matter, iron (Fe), manganese (Mn) and clay minerals. Copper mostly found as complex compounds with organic matter. Copper phases in soil important are copper soluble and can be exchanged, these phases play a role in contaminating water body [4]. Meanwhile, zinc concentration in the soil depends on the concentration of organic matter, soil texture (particle size) and pH.

Zinc is positively correlated with organic matter, clay content and cation exchange capacity [4]. Zinc soluble phase in the soil is contaminant for a water body. Dissolved zinc can reduce the pH of water which affects the chemical process of other compounds in the water body.

In soil, heavy metals exist in various chemical forms, which exhibit different physical and chemical behaviors with respect to their chemical interactions, mobility, biological availability, and potential toxicity. Determination of geochemical fractionation of heavy metals in soils is important to assess their potential toxicity, a threat to the ecosystem, and source (natural or anthropogenic source) [5]. The accumulation of heavy metals in the resistant fraction is an indication that they originate from the natural process, while accumulation in the non–resistant fraction indicates they originate from anthropogenic source [6]. Metals may be present in the soil several different physicochemical fractions, including sinks for soluble or exchangeable trace elements in the environment, iron–manganese oxides, bound to organic matter, sulfides, and a mineral fraction (residual) [7].

To determine the potential risk of soil using the Risk Assessment Code (RAC). RAC classification based on the percentage of metal in the carbonate and exchangeable fraction [8]. This was important because the fractions introduced by anthropogenic activities were typified by the adsorptive, exchangeable and bound to carbonate fractions. These fractions were weakly bonded metals that could equilibrate with the aqueous phase and thus became more rapidly bioavailable [8].

This research was aimed to determine the distribution of geochemical fractions of heavy metals copper and zinc in the soil, the correlation of soil chemical-physical properties to the availability of heavy metal fractions in water bodies and to determine the potential risk of soil to the bioavailability of heavy metals copper and zinc in Sumber Nyolo.

EXPERIMENT

Chemicals and Instrumentation

All the reagents used to digest samples were analytical reagent grade. These reagents included nitric acid 65% (Merck) and hydrochloric acid 32% (Merck). Most reagents used for sequential extraction were of analytical grade and supplied by Merck. Copper(II) nitrate (Merck) and zinc(II) sulfate (Merck) were used to prepare copper and zinc standard solutions.

These reagents included glacial acetic acid, hydroxylamine hydrochloride and ammonium acetate (Merck), also of analytical grade was provided by Chem Lab.

Volumetric glasses were used to prepare a standard solution and extracting solution.

Instrumentation used included digital pH meter (ATC PH–009) (l)), ORP meter (Kedida CT–

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8022), soil grab sampler, water sampler, 150 mesh and 200 mesh sieve, oven (Memmett), shaker, centrifuge (Hettich) and atomic absorption spectrometer (Shimadzu AA-6200).

Collection of Samples

Sampling was conducted in March 2018 by collecting soil and water from five sites (Table 1 and Figure 1) at the upper and downstream of the Sumber Nyolo. Sites I and II were located at the upper stream of the Sumber Nyolo. Site III, IV and V were located at Curah Glogo and Curah Lang-lang.

Soil samples were collected about 1 kg from each site by grab sampling method. Soil samples were stored in the dark plastic bag. Water samples were collected from the same site as soil sample collection by using a water sampler and stored in polyethylene bottles. All samples were kept cool and put in a cool box at 4^oC during shipping back to the laboratory.

Table 1. The Coordinate Points of Sampling Location No Sampling

Location

Coordinate Point

Located Latitude Longitude

1 Site I 7°52'41.30" S 112°37'20.22” E The upper stream of the Sumber Nyolo Site II 7°52'44.20" S 112°37'17.40" E

2 Site III 7°52'50.90" S 112°37'22.40" E Curah Glogo and Curah Lang-lang Site IV 7°52'53.00" S 112°37'25.70" E

Site V 7°52'52.90" S 112°37'21.25" E

Figure 1. Malang Regency Map and Sampling Location from Sumber Nyolo, Karangploso, East Java

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Analysis of Physical and Chemical Properties

Soil samples were dried in an oven at temperature 105–110 ^oC, sieved through a 150–200 mesh screen (after removing stones or other debris) and stored in polyethylene bottles until further use. All physical and chemical properties of soil investigated in this research were conducted using the available standard method. These included redox potential and pH were measured in mixtures at a 1:5 (material/water) ratio; Cation Exchange Capacity (CEC);

organic matter concentrations; and the percentage distribution of sand, silt and clay.

Sequential Extraction Procedure BCR (Community Bureau of Reference) for Soil Samples

Four stages sequential extraction method was performed on soil samples using the modified BCR protocol [9-11]. Four fractions were separated in four steps as follows:

Step one: exchangeable or bound to carbonate fraction (F1). This refers to the bioavailable fraction. Acetic acid 0.11 M (40 mL) was added to 1 g of dried samples and shook by mechanical shaking for 16 h at room temperature. The extracts were then separated from the residues by centrifuging for 15 min at 2000 rpm. Subsequently, the supernatant was decanted.

Step two: The acid reducible fraction (F2). This fraction was bound to Fe–Mn oxides in soil. Residue from step the 1 was extracted with 40 mL of NH2OH·HCl (pH 1.5 with HNO3 2 M), and re-suspended by mechanical shaking for 16 h at room temperature. The extracts were then separated from the residues by centrifuging for 15 min at 2000 rpm and the supernatant was decanted.

Step three: The oxidizable fraction (F3), i.e. the metals fraction that is bound to the organic matter in the soil. Residue from step was added 10 mL H2O28.8 M and digested for 1 h at room temperature. The contents were then heated on a water bath at 85^oC for 1 h and evaporated to near dryness. Step 3 was performed twice. Finally, 50 mL of 1 M NH4CH3COO (pH 2 with HNO3 2 M) was added to the cool residues and then residues were shaken with mechanical shaking for 16 h at room temperature. Subsequently, the supernatant was decanted.

Step four: Residual fraction (F4). Residues from step 3 were digested with aqua regia (HCl: HNO3) at ratio 3:1. The contents were heated on a water bath at 85^oC until evaporated to near dryness. After cooling, the residues were dissolved in HNO3 0.5 M. Then analyses were carried out by AAS to determine the content of Cu and Zn for step one until step four.

Statistical Analysis

Statistical software SPSS 16.0 was applied to determine the mean concentrations and standard deviation of heavy metals from sampling sites [12]. Relationships of heavy metals concentrations in soil were tested by Pearson correlation analysis. Statistical significance was tested at 95% confidence level.

Evaluation of Potential Soil as a Source of Heavy Metal Contaminants

Risk Assessment Code (RAC) is an assessment index of the risk of heavy metal existence on the environment based on the geochemical fraction of heavy metal interaction with soil particle which is potentially absorbed by the organisms [5]. Risk Assessment Code was obtained by calculating the percentage of exchangeable and bound to carbonate fraction in soil [13]. The index can be defined in five classes, there is no risk when F1 BCR fraction is lower than 1%, the risk is low for the range 1–10%, the risk is moderate for the range 11–

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30%, high risk for the range 31–50%, and very high risk for F1 BCR fraction greater than 50% [14].

RESULT AND DISCUSSION

Distribution of Copper and Zinc in Soil from Sumber Nyolo

Heavy metals are found in the different interaction mechanism in soil. Understanding the geochemical fractions of heavy metals in soil can predict the bioavailable concentration for microorganism uptake and risk potential of soil as heavy metals contaminant sources.

Distribution of heavy metals in the soil is controlled by reaction of heavy metals in the soil, namely: (1) adsorption, desorption, and ion exchange, (2) mineral precipitation and dissolution, (3) aqueous complexation, (4) biological immobilization and mobilization, and (5) plant uptake [15]. Heavy metals in soil were fractionated into four geochemical fractions including; acid–soluble fraction (exchangeable and bound to carbonates) (F1), a reducible fraction (bound to Fe–Mn oxides) (F2), oxidisable fraction (bound to organic matter) (F3), and residual fraction (F4). Heavy metals in F1 to F3 generally come from anthropogenic sources, while heavy metals bound to residual fractions (F4) generally come from natural sources [16].

Figure 2. Concentrations of copper and zinc in soil from Sumber Nyolo as F1(a), F2(b), F3(c), and F4(d)

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Figure 2. shows the concentrations of copper and zinc fraction in the soil of Sumber Nyolo. It can be seen that overall the concentration of zinc in the soil was higher than the concentration of copper for investigated sites.

Percentage distribution of each heavy metal shows the percentage of heavy metal in each fraction compared to the total amount of metals contained in the soil. Percent of metal distribution can show how much potential metal can be released into the water body from the amount of metal found in the soil. The percentage distribution of copper and zinc in each geochemical fraction can be seen in Figure 3.

Figure 3. Percentage distribution of geochemical fraction of copper (a) and zinc (b) in soil from Sumber Nyolo

Exchangeable or bound to carbonate fraction (F1). Most metals introduced by human activity are present in the exchangeable and carbonate fractions. This fraction includes weakly adsorbed metals retained on the solid surface by relatively weak electrostatic interaction, metals that can be released by ion exchange process and metals that can be coprecipitated with carbonates present in many types of soil [17]. These fractions are a loosely bound phase and bound to changes with environmental factors such as pH [18]. The concentrations of copper in five sites were 12.7 mg/kg (36%); 3.19 mg/kg (6%); 9.11 mg/kg (12%); 11.42 mg/kg (10%); 5.6 mg/kg (4%) (Figure 2a and Figure 3). While the concentrations of zinc for each site is 6.56 mg/kg (1%); 23.17 mg/kg (5%); 45.11 mg/kg (13%); 3.1 mg/kg (0.5%); 24.56 mg/kg (3%) (Figure 2a and Figure 3). Based on percent distribution of geochemical heavy metals, overall in all site the concentration of copper higher than zinc. The exchangeable fraction is the most mobile and the most readily bioavailable. This situation poses a higher risk to the environment. The release of heavy metals from this fraction to water body depends on soil solution pH. Proportionally, the heavy metals followed the pattern of Cu > Zn. It means, copper in the acid-soluble fraction is considered to be bound the weakest, and therefore the most mobile metals, so copper is more easily release into a water body.

Reducible fraction or bound to Fe–Mn oxides (F2). Iron and manganese oxides are the best scavengers of heavy metals and sorption by these oxides tend to control copper, manganese, and zinc solubility in soil [19]. This fraction consists of metals bound to Fe–Mn oxides that can be released if the soil changes from the oxic to the anoxic state, which could

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be caused by the activity of microorganisms present in the soil [20]. The concentration of total Fe in the soil of Sumber Nyolo was higher than the concentration of Mn total (Figure 4).

Concentrations of Fe and Mn total in the soil of Sumber Nyolo were 12781.53 mg/kg and 1024.42 mg/kg, respectively. It could be predicted that Fe oxides acted as the sorbent for Zn and Cu. Based on Table 2, soils in Sumber Nyolo were in oxidized condition with a potential soil reduction of 321 mV. In the oxidized condition, Fe and Mn in soil were in the form of Fe–Mn oxides so that it has the potential as an absorber for Cu and Zn metals. Figure 2b and Figure 3, showed the concentration and distribution of copper and zinc. Distributions of copper for each site is 3.54 mg/kg (10%); 3.28 mg/kg (6%); 4.69 mg/kg (6%); 8.37 mg/kg (7%); and 19.24 mg/kg (15%). While distributions of zinc in five sites were 164.16 mg/kg (32%); 20.76 mg/kg (4%); 2.06 mg/kg (1%); 267.94 mg/kg (39%); and 47.79 mg/kg (5%).

Distribution of heavy metals in reducible fraction showed concentration zinc higher than copper (Fig.2b and Fig.3). Higher levels of the reducible fraction of zinc can be attributed to the affinity of this metal to metals associated with manganese and iron oxides or hydroxides [11].

Table 2. Physical and Chemical Properties in Soil from Sumber Nyolo

Location pH ORP (mV)

Particle Size Cationic Exchange Capacity (CEC)

(me/100g)

Organic Matter

(%) Sand

(%) Silt

(%) Clay

(%) Classification

I 7.4 310 34 30 36 Clay Loam 29.44 4.19

II 7.3 315 35 13 52 Clay 23.62 4.05

III 6.9 322 28 42 30 Clay Loam 30.21 4.55

IV 6.9 325 29 41 30 Clay Loam 27.87 3.67

V 6.9 335 20 25 55 Clay 31.97 4.55

Mean 7.1 321 29 30 40 28.62 4.20

Figure 4. Concentrations of Fe and Mn Total in soil of Sumber Nyolo

Oxidizable fraction or bound to organic matter fraction (F3). In this fraction, heavy metals are assumed to stay in the soil for longer periods but may be immobilized by the decomposition process [18]. The organic fractions released in the oxidizable is not considered very mobile or available since it is thought to be associated with stable high molecular weight

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humic substances that release small amounts of metals in a slow manner [16]. Based on Figure 2c and Figure 3, concentrations of copper in five sites were 12.9 mg/kg (36%); 4.14 mg/kg (8%); 35.9 mg/kg (46%); 22.25 mg/kg (19%); and 20.34 mg/kg (16%). While concentrations of zinc in five sites were 25.33 mg/kg (5%); 356.74 mg/kg (71%); 76.53 mg/kg (22%); 13.71 mg/kg (2%); and 669.54 mg/kg (71%). The distribution of heavy metals in the oxidizable fraction showed the concentration of zinc was higher than copper. Heavy metals in F3 are strongly influenced by organic matter content and particle size of soil. In site II and V, the concentration of zinc is higher than the other stations. This is possible because of the effect of higher CEC and organic matter concentrations at site II and V compared to stations I, III, and IV. While copper may be bound to various forms of organic matter, including detritus and coatings on mineral particles, and will only be released in the soluble form under strongly oxidizing conditions [17].

Residual fraction (F4). The residual fraction is concerned the most stable and least bioavailable of all the chemical fractions of the soil. In this fraction, metals are bonded in the crystal lattice of silicates and well–crystallized oxides minerals [21]. Heavy metals associated with this fraction are not likely to be released under normal environmental condition, that is the nonlabile (resistant) fraction. The percentage distribution of geochemical F4 showed concentration copper higher than zinc in all stations except site I and III (Figure 2d and Figure 3), respectively. Residual phase serves as a useful tool in the assessment of the long- term potential risk of heavy metals or toxic metals entering the biosphere [22]. Metals associated with the residual fraction are likely to be incorporated in aluminosilicate minerals [11]. Minerals in the residual fraction are strongly bonded to metals and do not represent an environmental risk.

The amount of heavy metals concentrations from F1, F2, and F3 showed heavy metals derived from anthropogenic source (labile fraction or nonresistant), while F4 was heavy metals that can be carried out in soil (nonlabile fraction or resistant). It can be seen from Fig.

5, that copper in soil was mostly found as a resistant fraction (57%) while Zn was found as a non-resistant fraction (59%). The high percentage of zinc as non-resistant fraction may due to the use of phosphate fertilizer in the Sumber Nyolo which uses zinc as a micronutrient in phosphate fertilizer.

Figure 5. Comparison of heavy metals in the resistant and non-resistant fractions

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Table 3. Correlation Coefficients (r) between Heavy Metals in Soil and Physical-Chemical Properties of Soil and Water

* significant at the 0.05 level Parameters

Soil Water

pH ORP CEC Particle size Organic Matter Fe

Total Mn

Total pH ORP EC TDS C.

Organic Cu Zn Sand Silt Clay

Cu F1 0.105 -0.271 0.379 0.155 0.755 -0.829 -0.271 -0.248 -0.240 0.41 -0.461 0.638 -0.422 -0.336 0.568 -0.32 Cu F2 -0.601 0.908* 0.615 -0.927* -0.035 0.494 0.336 0.401 0.903* -0.393 0.263 0.345 -0.264 0.81 -0.838 -0.69 Cu F3 -0.761 0.446 0.659 -0.528 0.854 -0.589 0.398 -0.134 -0.212 0.611 -0.652 0.618 0.671 0.173 -0.148 -0.714 Zn F1 -0.432 0.216 0.193 -0.286 0.047 0.095 0.764 -0.377 -0.297 0.126 -0.055 -0.311 0.933* -0.055 -0.189 -0.829 Zn F2 0.099 -0.075 -0.005 0.153 0.42 -0.494 -0.78 0.424 0.103 0.305 -0.395 0.687 -0.72 0.137 0.173 0.636 Zn F3 -0.243 0.605 0.164 -0.6 -0.628 0.923* 0.471 0.225 0.755 -0.704 0.665 -0.345 0.326 0.555 -0.75 -0.048

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Correlation Physical and Chemical Properties in Soil of Sumber Nyolo with Bioavailability Heavy Metals of Copper and Zinc in Water Body

The presence of heavy metals in the soil at Sumber Nyolo is strongly influenced by environmental conditions. The presence of soil physical and chemical properties plays an important role in the presence of heavy metals in soil. The correlation between the physical and chemical properties of the soil with the concentration of copper and zinc in geochemical fraction can be determined by statistical analysis methods, in this case, the determination was made using Pearson’s correlation analysis [9]. Pearson’s correlation which is a parameter measurement and will produce correlation coefficients that serve to measure the strength of a linear relationship between two variables.

Pearson’s correlation coefficient matrix among the selected heavy metals is presented in Table 3. The results of the Pearson’s correlation test show that not all parameters have a significant correlation with other parameters, but it must be remembered that the value of the correlation coefficient is small (not significant) does not mean that the two variables are not interconnected. As shown in Table 2, all soil samples were indicated slightly acid to moderate neutral with the average range being pH of 7.1. At this pH, heavy metals could be in precipitated form rather than the soluble form. It means the bioavailability of the heavy metals were relatively low. As shown in Table 3, all heavy metals fraction have a negative correlation with pH. pH greatly affects the mobility of F1 in the soil. Metals corresponding to the exchangeable and carbonate fraction usually represent a small portion of the total metal content in the soil. Acidification that occurs in anoxic soil during aeration mainly affects the carbonate content because carbonates are dissolved when the soil is acidified [17]. Copper at pH below 5 and zinc at pH below 7 will be soluble form in soil [4]. So at low pH, copper and zinc will be released to the water body.

Copper and zinc have a positive correlation with cation exchange capacity (CEC) but the correlation coefficient is small. Copper showed a higher positive correlation to CEC than the correlation of Zn. This is because the possibility of sorption of Cu ions is greater than that of Zn ions. Maximum sorption capacity for the metals followed Cu²⁺> Zn²⁺. Higher capacity for sorbing Cu²⁺ than Zn²⁺is an effect for the electron structure Cu²⁺ because Cu²⁺ has one unpaired electron on its 3d orbital and has more active polarization and higher affinity to the anionic site. Sorption also depends on the ionic radius, ion charge, electron structure, and hydration of bound metal [23]. The higher CEC of the soil will increase the concentration of copper. So copper will be easily released.

It can be seen from Table 3. Copper at F2 has a significant positive correlation with redox potential (ORP), and percentage of clay. It means the higher the redox potential of the soil will increase the concentration of copper. In addition, when the oxidation-reduction potential (ORP) increase, metals bound to the organic matter could be degraded, leading to a release of soluble trace metals [24]. However, the concentration of Cu and Zn as F3 showed at a high level instead of the F2 concentration of Cu and Zn (Figure 3). It means that redox potential was more correlated to the copper and zinc as F2 than to the metals as F3.

The concentrations of organic matter are closely related to the particle size of soil. The soil has a different percentage of particle size will have different content of organic matter.

Generally, soil with a finer particle size will be followed by an increase in the amount of organic matter. At Table 3, showed that there is a significant positive correlation between the percentage of clay with the concentration of zinc fraction 3 (Zn F3). The particle size of soil affects the ability of the soil to bind and exchange cations, the finer the particle size of soil so the higher the content of organic matter on the soil. Based on Pearson's correlation above, copper and zinc have a positive correlation with organic matter but the correlation coefficient

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is small. Organic matter in the soil is more correlated with copper than zinc. This suggests that copper preferred to form complexes with the binding ligands present in the organic phases of the soil. The concentrations of Cu associated with organic phases were relatively high (Figure 3) and found 16%–46% of the total Cu in the soil.

Association of copper with the oxidizable fraction gradually increased with the rising total copper loading in the soil. However, there was a decrease in copper association with Fe–Mn oxides phases with increasing total copper loading in the soil [6]. It indicates that copper higher affinity for the oxidizable fraction than the reducible fraction in soil. It has been reported that copper has a strong affinity for the binding sites of organic phases in soils and dissolved organic carbon in natural systems [16].

Evaluation of Soil Potential Risk as a Source of Heavy Metal Contaminants

The risk assessment code (RAC) is used to gain additional insights into the assessment of the environmental risk of trace metal pollution of soil [25]. RAC determines the availability of soil metals by applying a scale to the proportions of the metals in bioavailable fraction.

This is imperative because the metals concentrations attributed to anthropogenic activities remain loosely held to the soil as exchangeable and bound to carbonate fraction (F1) which could be released to aquatic phase and/or could be taken by plants or animals, causing environmental toxicity [13-14]. Evaluation of potential soil in Sumber Nyolo using the RAC can be seen in Table 4.

Table 4. Risk Assessment Code in Soil from Sumber Nyolo Heavy

Metals Site RAC Risk Category Heavy

Metals Site RAC Risk Category

Cu (%)

I 0.36 No Risk I

Zn (%)

I 0.013 No Risk I

II 0.06 No Risk I II 0.05 No Risk I

III 0.12 No Risk I III 0.13 No Risk I

IV 0.10 No Risk I IV 0.005 No Risk I

V 0.04 No Risk I V 0.03 No Risk I

Mean 0.13 Mean 0.04

Based on the calculated RAC resulted for sites I to V (Table. 4) at each site has a low RAC value, both for copper and zinc. According to this approach the percentage of each metal bound to the exchangeable and carbonates fraction (F1), the RAC classification suggests that soil which could release a percentage less than 1% could be characterized as nonharmful for the environment. It means, copper and zinc in soil from Sumber Nyolo have no potential in providing Cu and Zn in the water body, because the majority of the copper and zinc was in nonlabile (resistant) or residual fraction. The low availability of these metals is due to its low solubility at neutral pH in the soil.

Based on Table 4, the average RAC value of copper is higher than zinc. RAC value for copper and zinc in soil from Sumber Nyolo were 0.13% and 0.04%, respectively. Thus copper in the soil is more risk of contaminating aquatic system than zinc and this is also influenced by physical-chemical properties of soil in Sumber Nyolo. This is consistent with the study of Anitra et. al. [26] which states that copper has the highest mobility because is able to diffuse rapidly and has high solubility [27].

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CONCLUSION

Heavy metals, copper and zinc, can be released into the environment depending on the physical and chemical properties of soil. Based on the percentage of distribution geochemical fraction, copper concentration as the exchangeable and carbonate fraction (F1) was higher than zinc concentration (F1). This means copper was more bioavailable than zinc, therefore copper was easily release to the water body, while a high concentration of copper and zinc from the anthropogenic source were found dominantly at the oxidizable fraction. Based on correlation with physical-chemical properties of soil, copper and zinc will be released when there is increasing of soil redox potential, increasing of cation exchange capacity and changes of pH to an acid condition. The Risk Assessment Code index indicating that the copper and zinc in the soil are not harmful to the water body. Based on the results obtained it can be concluded that by understanding physical-chemical properties of soil which are positively correlated with copper and zinc nonresistant fraction in soil, soil can be an indicator of the availability of copper and zinc in a water body.

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