Environ Sci Pollut Res DOI 10.1007/s11356-015-4618-0

RESEARCH ARTICLE

Geochemical fractions and risk assessment of trace elements in soils around Jiaojia gold mine in Shandong Province, China Feifei Cao 1 & Linghao Kong 2 & Liyuan Yang 1 & Wei Zhang 1

Received: 9 February 2015 / Accepted: 26 April 2015 # Springer-Verlag Berlin Heidelberg 2015

Abstract Soils located adjacent to the Jiaojia gold mine were sampled and analyzed to determine the degree of which they were contaminated by trace elements (Hg, As, Cd, Pb, Cu, and Zn) in Shandong Province, China. All 18 samples exhibited mean Hg, As, Cd, and Pb concentrations in excess of local background values, while the mean concentrations of Cu and Zn were below the background values. In addition, the concentrations of trace elements in gold smelter (GS) soils were higher than in the gold mine (GM) soils. The result from a modified Tessier sequential extraction procedure was that with the exception of Cu in soils near the smelter, the trace elements were predominantly associated with the residual fraction. After residual fraction, most Hg was mainly humic acid and strong organic fraction, while most As was the humic acid. Cd was associated with the water soluble, ion exchange, and carbonate fractions compared with the other trace elements. Furthermore, Cu, Pb, and Zn were more concentrated in the humic acid and Fe/Mn oxide fraction. The fractions of trace elements were affected by soil pH and Ec (Electrical conductivity). The humic acid fraction of Hg as well as the ion exchange fraction of Cd and Zn displayed negative correlations with soil pH. The strong organic fraction of Hg, the Fe/Mn oxide fraction of Cd, and the carbonate fraction of Zn were positively related to the soil Ec. The strong organic fraction and ion exchange fraction of Zn were negatively related to soil Responsible editor: Stuart Simpson * Liyuan Yang [email protected] 1

School of Resources and Environment, University of Jinan, Jinan 250022, China

2

Department of Environment, Beijing Normal University, Beijing 100875, China

Ec. However, the ion exchange and carbonate fractions of As showed significant positive correlations with soil pH. A calculated individual availability factor (Afi) is used; the values of each trace element in the soils are in the following order: Cu > Cd > Pb > Zn > As > Hg. When combined with a risk assessment code, data suggest that Hg, As, Pb, and Zn levels showed low risk for the environment, whereas Cd levels in soils adjacent to the GM and Cu levels in soils adjacent to the GS showed medium risk to the environment, and Cd levels in soils adjacent to the GS exhibited higher environment risk. Keywords Mining soils . Trace elements . Geochemical fraction . Risk assessment

Introduction Heavy metals are regarded as a dangerous group of anthropogenic pollutants due to their persistence and toxicity in the environment (Huang et al. 2013). There are many sources of heavy metals, mining and smelting activities are among the most significant in terms of both the severity of contamination produced and the total area contaminated (Wei et al. 2009). In general, a variety of heavy metals such as Pb, Cr, Cu, Cd, and Zn are contained in mining and smelting wastes and can be transported offsite where they can accumulate in adjacent soils (Shao et al. 2008). Once in soil, various metals and metalloids may contaminate surface and ground water or be absorbed by plants and other biota, negatively affecting both ecosystem and human health. Thus, the analysis of trace elements in soils is a useful method to prevent the element pollution in the ecosystem. Trace elements in sediments and soils are associated with a wide range of organic and mineral constituents and bound to particulate matter in a variety of ways. In some instances, the

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metals are tightly bound to the material or incorporated into the mineral lattice. Such elements cannot be mobile or bioaccumulate as they are unlikely to be released to pore water in the soil. However, under certain conditions, the metals may be easily removed from the particles and readily accumulated by biota (Basta and McGowen 2004). As a result of total trace metal concentration, it can lead to a potential overestimation of exposure risk, so these differences in total trace element concentration in soils is not the best indicator for assessing the environmental impact of heavy metal contaminants (Alvarenga et al. 2012). For environmental purposes, the amount of bioavailable pollutants in soils is of prime interest (Kartal et al. 2006), since this fraction (which usually represents only a small fraction of the total content) greatly influences plant growth and element uptake, the quality of ground waters, and the pollution status of waterways. Thus, the evaluation of trace element fraction distribution may be more useful for the prediction of trace element behavior, including solubility, mobility, bioavailability, and toxicity (Dhal et al. 2013). The geochemical fractions were commonly determined using an approach referred to as sequential extraction (Anju and Banerjee 2010), which includes the stepwise treatment of soil particles by different types of reagents, and each step is intended to release elements from a specific phase. The heavy metals in the soils can be classified according to the various geochemical forms with which they are associated, such as water-soluble fraction, exchangeable fraction, carbonateassociated fraction, Fe-Mn oxide-associated fraction, organicassociated form, and residual fraction (Favas et al. 2011). In order to provide basic data and reference information for improving the ecological environment and agriculture of Jiaojia gold mine, the main objectives of this study are (1) to investigate the total concentration of Hg, As, Cd, Pb, Cu, and Zn in soils adjacent to a Jiaojia gold mine and a Laizhou gold smelter in China; (2) to determine the chemical fractionation of Hg, As, Cd, Pb, Cu, and Zn using a modified sequential extraction procedure from Tessier; and (3) to assess the environmental risk associated with trace element pollution in the soils near the Jiaojia gold mine.

Materials and methods Study area Jiaojia gold mine is located in the north of Laizhou, Shandong Province, China. The Jiaojia gold mine and Laizhou gold smelter are located at the intersection of road S304 and S217. They are surrounded by villages and fields (Fig. 1) and distributed about 3 km away from each other. Mining and smelting activities were initiated in 1980 and have been developed rapidly in 30 years. Several types of waste, including wastewater, solid waste, and others, are produced in the

gold mine. No investigations of soil trace metals and metalloids for this area have been reported to date. The gold mine and gold smelter are state-operated mining enterprises, and they differ from some small-scale gold mines which extract gold in amalgamation. The study area was located in the temperate zone with a Southeast Asia monsoon climate, an annual average temperature of 12 °C, and annual average rainfall of 610 mm. The land was relatively flat, with slightly hilly topography, the tectonic position of the study area in the eastern margin Jiaobei uplift of the north China platform, with ancient basement-deformed metamorphic rocks (Zhao et al. 2007).

Sample collection Soil samples were collected in June 2009 from 18 places adjacent to the gold mine (GM) and gold smelt (GS), and the weight of each sample was 1 kg. The distribution of sample points is indicated in Fig. 1. Soil samples from 0 to 20 cm below the ground surface were collected randomly using a bamboo spoon. And then, they were placed in labeled polyethylene bags for transport to the laboratory. The samples were air-dried at room temperature, crushed, homogenized, and passed through a 100-mesh sieve to measure pH, electrical conductivity (Ec), and the trace element concentrations and fractions.

Sample analysis The soil pH was measured by a Leici pH meter PHS-3C in a 1:2.5 (w/v) soil-deionized water suspension after a 1-h agitation. Ec was determined with a conductivity meter (Systronics India, Ltd., model 507). The total concentration of trace elements within the soil samples was determined by digesting the samples in a concentrated HNO3 and HClO4 (in a ratio of 4:1) solution which were taken to dryness on a heating block. The residue was leached with 5 mol L−1 HCl, and diluted to 10 mL. Then, Hg and As were measured by hydride generation-atomic fluorescence spectroscopy (HG-AFS, XGY-1011A, China), while using inductively coupled plasma-atomic emission spectrometry (ICP-AES, iCAP6300, America) to determine the concentration of Cd, Pb, Cu, and Zn. According to the relevant standard (DD2005-03), the improved Tessier sequential extraction procedure (Arunachalam et al. 1996), ICP-AES, and HG-AFS were used to determine the fraction of trace elements associated with different organic/mineral phases in soils. The extraction was carried out on an initial weight of 2.5 g of soil. The extractants and operationally defined geochemical fractions were as follows: 1. Water-soluble fraction

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Fig. 1 Location of the study area and the distribution of sampling sites near the Jiaojia gold mine and the Laizhou gold smelter in Shandong Province, China.

5. Fe/Mn oxide component

Metals were extracted from soil with 25 mL of distilled water; the process involved ultrasonic digestion for 30 min, followed by centrifugation. The supernatant was then filtered through a 0.45-μm membrane. Part of the filtered supernatant was analyzed, whereas the residue was washed by distilled water and used in the following analysis.

The residue from step 4 was leached for 60 min with 50 mL 0.25 mol·L−1 NH2OH·HCl. The supernatant was stored for testing, and the residue was washed by distilled water for the following test.

2. Ion exchange fraction

6. Strongly bound organic fraction

Metals were extracted from the residue produced by step 1 using 25 mL of 1 mol·L−1 MgCl2. After 30 min, ultrasonic extraction was completed and the supernatant was centrifuged and stored for analysis. The residue was washed by distilled water and used in the following test.

Three milliliter 0.02 mol·L−1 HNO3 and 5 mL 30 % H2O2 were added to the residue from step 5. The samples were then heated progressively to 83 °C and kept at this temperature for 1.5 h with occasional agitation. And then, 5 mL 1.6 mol·L−1 NH4Ac-1.6 mol·L−1 HNO3 was added. The final volume was brought to 25 mL by dilution. The tubes were then continuously agitated for 1 min. The supernatant was stored for testing, and the residue was washed by distilled water for the following test.

3. Carbonate fraction The residue from step 2 was leached for 60 min by ultrasonic extraction with 25 mL of 1 mol·L−1 sodium acetate (NaAc). After centrifugation, the supernatant was stored for testing, and the residue was washed by distilled water for the following test. 4. Humic acid fraction The residue from step 3 was leached for 40 min with 50 mL 0.1 mol·L−1 sodium pyrophosphate (Na4P2O7). The supernatant was stored for testing, and the residue was washed by distilled water and used in the following test.

7. Residual fraction The residue from step 6 was dried and digested with HCl2– HNO3–HClO4–HF. The tubes were then continuously agitated for 1 min. The supernatant was stored for analysis. As is shown in Table 1, the data quality was assured by the quality assurance and quality control (QA/QC) in the process of sample analysis. We did the system blank in order to control and check the possible pollution. Meanwhile, we used the standard materials for quality control and parallel samples to

Environ Sci Pollut Res Table 1 Data of recovery, detection limit, and certified materials of each metals

Elements

Recovery (%)

Detection limit (mg·kg−1)

GBW07442 (ng·g−1)

GBW07443 (ng·g−1)

Hg As Cd Pb Cu

84.1±0.3 87.6±3.5 94.0±7.1 95.9±1.3 93.5±0.5

1 0.05 0.005 0.1 0.005

774×10−9 10.1×10−6 0.206×10−6 50.6×10−6 51×10−6

105×10−9 15.5×10−6 0.31×10−6 33×10−6 41×10−6

Zn

95.0±1.8

0.1

117×10−6

115×10−6

control the precision of experimental data. To ensure that each procedure separated the fraction completely, we used the corresponding reagent extracted three times repeated. The accuracy and precision of the analytical methods were assessed by use of international reference materials (GBW07442 and GBW07443) and analysis of duplicate samples. Evaluation index The background values play an important part in assessing pollution of trace elements. The Jiaojia gold mine is located at the east of Shandong Province, for this reason, the soil background values of elements in east are selected as the background values of soil in the Jiaojia gold mine (Dai et al 2011). A number of indices were calculated to assess the mobility, bioavailability, and potential risks associated with trace elements in the analyzed soils.

where Ci and Ctotal represent the particular trace element fractionation concentrations and total trace element concentrations, respectively. And, the total trace element concentrations were measured separately.

Individual availability factor (Afi) and the global availability factor (Af) The individual availability factor (Afi) is used to assess the relative retention time of trace elements in soils. Higher Afi values indicate lower relative retention time and higher risk to the environment (Barona et al. 1999). The Afi was calculated by dividing the sum of concentration of each trace element in the mobile phase (nonresidue phase) by its concentration in the residual phase. The Af was equal to the sum of individual availability factors.

Pollution load index (PLI) The PLI is used to comprehensively determine the pollution effect of study metals and for each site is defined as follows (Sekabira et al 2010; Adokoh et al 2011): PLI ¼ ðC F 1 *C F 2 *……C F n Þ1=n where n is the number of elements (six elements in the present study), and CF is the contamination factor. It can be calculated from CFn =Csoil/Cbackground, where Csoil and Cbackground represent the trace element concentrations and background values in soils, respectively, with the unit of milligram kilogram. The PLI value greater than 1 is polluted, while less than 1 indicates no pollution. Fractionation distribution coefficient (FDC) The FDC was defined as the ratio of trace element fractionation content to total amount of the same trace element (Yang et al. 2011). FDC ¼ C i =C total

Risk assessment code (RAC) The RAC is defined as the ratio of the concentration of trace element exchangeable and carbonate fractions to the total trace element concentration. The RAC is an indicator that can quantify the lowest release of trace elements to the environment. When the RACs of the exchangeable and carbonate fractions are less than 1 %, the trace element has no risk to the soil and surrounding environment. RACs of 1–10 % reflect low risk, 11–30 % medium risk, and 31–50 % high risk. RACs more than 50 % are considered highly dangerous and can easily enter the food chain (Dalmacija et al. 2010).

Statistical analysis Statistical analyses were performed with SPSS 18.0 and Microsoft Office (Excel 2010). Logarithmic transformations were performed to reduce the skewness and kurtosis of the data. All the transformed data passed the test of normality.

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Results and discussion Soil properties and total trace element concentrations in soil A statistical summary of the geochemical data derived from the analyzed soil samples is presented in Table 2. The pH of samples ranged from 4.47 to 5.90 in soils adjacent to the GM and from 4.27 to 5.65 in soils near the GS, with a mean value of 5.21 and 4.67, respectively. Compared with the soils from GM, the soils from GS had the lower pH values. Wide ranges of soil Ec were observed. The Ec in the soils from GM ranged from 66.8 to 187.7 μm·cm−1 and from 39.8 to 145.9 μm·cm−1 in the soils from GS. The mean Ec values in soils from GM were higher than those in the soils from GS. Mean values of trace elements in soils sampled at the 18 sites around the Jiaojia GM and the Laizhou GS are presented in Table 2. A great range of soil trace element concentration was observed across GM and GS. In order to determine the level of contamination in this study, the concentration of trace elements was compared with the background values and the Soil Environmental Quality Standards set by the State Environmental Protection Administration (SEPA). The CF can obviously determine the level of contamination and the degree of enrichment of the trace elements in soils adjacent to the GM and GS, with the order of Hg > Cd > As > Pb > Zn > Cu. High concentrations of Hg were above 5.8 and 6.6 times higher than the background values in soils, and the mean concentrations of As, Cd, and Pb in GM and GS were also above the corresponding soil

background values in the eastern part of Shandong Province, China (Table 2). The percent of exceeding background value (EBV) of Cu and Zn was 44.4 and 11.1 % in GS, though their mean values were below the maximum background threshold for contaminated soils. Fortunately, those trace elements concentrations were below the permissible limits of the SEPA for all soil samples tested. The concentration of trace elements was strongly influenced by the location of soil samples. Soil samples close to the GM, GS, and tailings had relatively higher concentrations of trace elements and been affected by human activities. For example, the concentration of Hg in GM7 and GM8 was 0.29 and 0.22 mg·kg−1, while it was 0.16 and 0.19 mg·kg−1 in GM1 and GM9, respectively; this result is same to Bi et al (2006) in zinc mining of Guizhou, China. Compared to soils near the GM, soils adjacent to the GS had the higher concentrations of trace elements. A similar result can also be obtained by examining the spatial variations in the PLI, by calculating the values of soils in GS and GM that were 1.48 and 1.90. The process of smelting caused the pollution of trace elements more than the mining activities. Those activities produced a large amount of tailing, waste rock, and so on, which were very unstable and served as significant sources of trace elements. Therefore, mining and smelting activities impacted the concentration and distribution of trace elements. Some research had shown that trace elements could enter the soils by deposition of aerosol particulates, irrigation with wastewater, and leaching of tailings (Salomons 1995). As a mining area, long-time mining-related activities left large amounts of tailings, which will bring serious pollution of trace elements.

Basic properties and trace element concentrations in different soil samples (mg·kg−1)

Table 2

GM (n=9)

GS (n=9)

SEPA limitsb

Mean±SDa

Range

Mean±SDa

Range

Hg As Cd Pb Cu Zn pH

0.17±0.064 7.11±1.32 0.33±0.023 28.3±4.6 12.9±2.1 39.7±3.5 5.21±0.48

0.07–0.29 4.82–9.22 0.30–0.37 22.6–34.5 10.8–17.2 33.5–45.6 4.47–5.90

0.19±0.012 14.86±9.75 0.36±0.05 31.3±8.5 17.1±5.9 47.0±12.8 4.67±0.39

0.06–0.39 6.58–38.38 0.28–0.45 24.0–44.9 8.2–24.3 33.1–75.5 4.27–5.65

1.5 40 1.0 500 400 500 –

Ecf

102.7±39.4

66.8–187.7

70.6±32.4

39.8–145.9



Background valuec

CFd GM

GS

GM

GS

0.029 6.3 0.108 25.4 19.6 56.1 –

5.86 1.13 3.05 1.11 0.67 0.71 –

6.55 2.36 3.33 1.23 0.87 0.84 –

100 % 77.8 % 100 % 66.7 % 0% 0% –

100 % 100 % 100 % 77.8 % 44.4 % 11.1 % –











n the number of samples a

Standard deviation

b

Soil Environmental Quality Standards (GB15618-1995) set by the State Environmental Protection Administration

c

Background value of the eastern part of Shandong Province, China

d

Contamination factor

e

Percent of sample exceeding background value

f

μm cm−1

EBVe

54.7 22.2±3.10 9.52 4.03±2.36 16.8 7.27±3.62 12.2 5.19±2.40 2.72 1.18±0.610 3.43 1.60±1.52 0.230±0.140 GS

0.590

60.2

29.1 4.62±1.58

22.1±3.43 7.15

11.7 2.29±2.86

2.60±0.660 16.2

18.5 3.08±1.11

5.95±0.970 10.8

26.6 4.56±2.15

3.97±0.790 3.29

10.8 1.83±1.06

1.20±0.39 2.00

1.27 0.180±0.14

0.740±0.38 0.360

1.95 0.320±0.190

0.130±0.150

GS

GM Zn

38.2

42.6 11.3±1.67

4.91±2.51 4.81

1.84 0.520±0.300

0.580±0.240 20.3

34.7 9.84±4.21

2.45±0.520 27.2

12.8 3.48±1.69

3.32±0.450 4.76

6.04 1.84±1.51

0.560±0.32 2.52

1.65 0.537±0.757

0.290±0.190 2.17

0.360 0.0990±0.0860

0.266±0.110

GS

GM Cu

41.9

45.8

51.9 12.5±1.21 1.71 0.430±0.330 30.6 7.50±1.67 8.53 2.11±0.840 5.83 1.47±0.820 1.15 0.270±0.150 0.270 0.0630±0.0380 GM Pb

0.145±0.0370 8.00 0.0280±0.0160 4.62 0.0160±0.0100 10.3 0.0370±0.0170 6.39 0.0230±0.015 13.1 0.0460±0.0170 15.7 0.0570±0.0380 GS

62.6 7.60±4.19

0.140±0.0320 6.04

0.610 0.0700±0.0430

0.0180±0.00600 12.4

9.91 1.42±1.43

0.0360±0.0190 11.8

20.0 2.69±2.02

0.0360±0.0170 6.20

1.55 0.180±0.100

0.0190±0.0120 7.57

0.750 0.0840±0.0420

0.0230±0.0120 10.2

4.66 0.630±0.490

0.0310±0.0370

GS

GM Cd

58.3

75.6 132±70.7

3.72±0.970 0.860

7.19 13.2±12.4

0.0520±0.00600 11.3

1.05 1.40±0.330

0.700±0.180 20.9

12.8 23.0±15.4

1.33±0.440 2.45

0.680 1.00±0. 700

0.144±0.0410 1.23

1.29 1.74±0. 850

0.0720±0.0190 4.99

1.33 1.81±0. 940

0.310±0.100

GS

GM As

78.8 128±43.9 9.24 14.4±7.10 0.870 1.31±0.480 8.22 13.7±9.30 0.580 0. 940±0. 700 0.810 1.18±0. 610 1.49 2.15±0. 990 GM Hg (10−3)

FDC (%) Mean±SD Mean±SD FDC (%) Mean±SD

FDC (%)

Mean±SD

FDC (%)

Mean±SD

FDC (%)

Mean±SD

FDC (%)

Strong organic Fe/Mn oxide Humic acid Carbonate Ion exchange Water soluble Chemical speciation

Chemical fractionation (mg·kg−1) and FDC of trace elements in soils adjacent to the GM and GS Table 3

Some studies of soils have concluded the fraction of trace elements rather than the total concentrations to evaluate biotoxicity (Arenas-Lago et al. 2014). To determine the potential environmental risk of trace elements to organisms, it was necessary to evaluate the mobile or available fractions in soils. Table 3 and Fig. 2 show the chemical fractionation and FDC of different trace elements in the soils adjacent to GS and GM. Hg in the soils was mainly found in the residual fraction, with the proportion of 78.79 and 75.63 % in GM and GS, respectively. The residual fraction mainly contains primary and secondary minerals which may hold heavy metals within their crystal structure where it can only be leached out with great difficulty (Dang et al. 2002). The second largest proportion of Hg was in the humic acid and strong organic fractions (17.45 and 20.02 % for GM and GS, respectively). Some researchers indicated that Hg has a high affinity for soil organic matter (Sanei et al. 2014). Lower FDCs for Hg within the extractable fraction (the water soluble and ion exchange fraction) were observed in all soil samples (Fig. 2). This is consistent with what was found in a gold mining region in Venezuela (Santos-Francés et al. 2011). Although the FDC of extractable fraction was low, due to the higher total mercury concentration, it caused the concentration of Hg in this fraction to still be very high, suggesting that Hg could pose a potential risk to surrounding soils. The FDCs of As in each fraction followed the order residual > organic (humic acid and strong organic) > Fe/Mn oxide > water soluble > carbonate > ion exchange. Relatively higher water-soluble fractions (4.99 and 4.66 % for GM and GS, respectively) were observed in the soils. The ion exchange fractions were very low (1.23 and 0.75 % for GM and GS, respectively) in the investigated soils, which might be due to the low cation exchange capacities of these soils. The root soils generally contain a large amount of organic matter, which has a strong binding capacity that could be acting as a strong As scavenger (Karak et al. 2011). This might partially explain the high proportion of As associated with the organic fraction of the soils. The FDCs of the Fe/Mn oxide fraction were 11.33 and 9.91 % for GM and GS, respectively. The exchangeable fraction included weakly absorbed metals retained on the soil surface (such as organic matter, clay minerals, and hydrous oxides) by relatively weak electrostatic interactions. This fraction can be released in the process of ion exchange and precipitation with the carbonates in the soil (Filgueiras et al. 2004). Trace elements associated with this fraction have more labile bounds and can be easily released into the environment (Koukina and Vetrov 2013). The fraction is typically used to evaluate the mobility and bioavailability of trace elements. In comparison with other trace elements, though the residual fraction was the main form of Cd, it

Residual

Trace element fraction in soils

Mean±SD

FDC (%)

Environ Sci Pollut Res

Environ Sci Pollut Res Fig. 2 The mean FDC of trace elements in soils located near the GM and GS

possessed the highest extractable fraction in soils from GM and GS. Its mean FDCs for extractable fraction were 17.72 and 28.79 % for the GM and GS, respectively. The high values may be due to the effect of an electric field of an ion causing other ions nearby to be polarized, resulting in strong adsorption of Cd by the soil colloids (Breuer and Melzer 1990). The highest FDCs of the extractable fraction were observed at GS1 and GS2, where the values were more than 40 %. In addition, trace elements of surface runoff can enter the soils along with irrigation water and leaching of tailings. This can also be used as a major factor for the high levels of exchangeable Cd in the nearby soils of GM and GS. The high levels of exchangeable Cd in crop soils might facilitate the high uptake of Cd by plants, accumulating in the edible parts. Overall, the Cd in the soils from GS and GM exhibited high bioavailability and mobility and might pose a high ecological risk. In the soils sampled from GM and GS, higher FDCs of Pb were mainly residual fraction, ranging from 41.69 to 58.55 % for GM and from 30.92 to 59.91 % for GS. Moreover, Pb was largely bound by the Fe/Mn oxide fraction (30.62 and 34.71 % for GM and GS, respectively), which was significantly higher than other trace elements. This suggests that Fe/Mn oxides may play an important role in controlling the mobility of Pb in soil (Rodríguez et al. 2009). Very low FDCs for Pb in the exchangeable fraction were observed in soils. Similar findings were reported by Li et al. (2007), and it showed that lead had a little risk to the surrounding soils. The FDCs of Cu in each fraction followed the order organic (humic acid and strong organic) > residual > Fe/Mn oxide > carbonate > exchangeable. Cu is mostly bound to organic matter in soil. Therefore, it was reasonable that the extraction steps may destroy organic matter and extract more Cu from the soils (Kim and McBride 2006). In the results of Fig. 2, the FDC of Cu in the organic fraction clearly followed this prediction. The exchangeable Cu in the soil was the lowest compared with the amount of Cu in the other fractions. However,

this small but active fraction is readily available for plant uptake (Zhang et al. 2014). The Fe/Mn oxide fraction is the second most important of non-residual fraction. Furthermore, the FDCs of the residual fraction of Cu in this study were relatively low. Some researchers (Wang et al. 2007) have also reported that highly contaminated soils contained very little residual copper near smelters. The FDCs of Zn in each fraction followed the order residual > organic (humic acid and strong organic) > Fe/Mn oxide > carbonate > exchangeable. The FDCs of residual fraction were 60.14 and 57.57 % for GM and GS, respectively. The organic fraction was the most important non-residual fraction for Zn. The FDCs of this fraction were 17.97 and 21.72 % for GM and GS, respectively. This might be due to organic matter dissolution during the extraction procedure since Zn, like Cu, had an affinity for organic complexes (Yan and Lo 2011). In addition, a large part of Zn was associated with the Fe/Mn oxide fraction, with the FDC of Zn being 16.24 and16.80 % for GM and GS, respectively. Correlation analysis of soil properties and FDCs of trace element The physical and chemical properties of soil could affect the bioavailability and mobility of trace elements. Pearson correlation coefficients were calculated for the relationships between FDCs of trace elements and both soil pH and Ec, and they are shown in Table 4. The wide ranges of soil pH and Ec in the study area likely influence the FDC of trace elements, which were confirmed by the correlation analysis. Soil pH was considered to be one of the most important parameters to control the availability of trace elements in soil. The humic acid fraction of Hg as well as the ion exchange fraction of Cd and Zn displayed negative correlations with soil pH. Availability of all the metals present in soils usually increased greatly under low pH conditions (Jan et al. 2010). Ec is the

Environ Sci Pollut Res Table 4

Hg As Cd Pb Cu Zn

Pearson correlation coefficients calculated for the relationships between FDCs of trace element and both soil pH and Ec Water soluble

Ion exchange

Carbonate

Humic acid

Fe/Mn oxide

Strong organic

Residual

−0.178 0.285 −0.225 0.184 −0.394 −0.369 −0.152 −0.149 −0.244 0.041 −0.343 −0.406

−0.057 0.313 0.621** 0.442 −0.471* −0.464 −0.330 −0.474* −0.050 0.345 −0.756** −0.541*

0.104 0.355 0.674** 0.337 0.189 0.044 0.047 −0.262 −0.181 −0.200 0.403 0.503*

−0.639** −0.356 −0.076 −0.128 0.022 −0.012 −0.273 −0.455 0.073 0.293 −0.177 −0.175

−0.096 0.460 0.360 −0.046 0.343 0.486* 0.023 −0.091 −0.002 0.121 0.039 0.160

0.178 0.589* 0.364 −0.591** −0.465 −0.319 0.192 −0.052 −0.296 −0.483* −0.474* −0.655**

0.401 −0.287 −0.412 −0.515* 0.218 0.385 0.253 0.562* 0.358 0.371 0.438 0.416

pH Ec pH Ec pH Ec pH Ec pH Ec pH Ec

*Significant at the 0.05 level **Significant at the 0.01 level

most common measure of soil salinity, and the redox potential can affect the migration and enrichment of elements. The strong organic fraction of Hg, the Fe/Mn oxide fraction of Cd, and the carbonate fraction of Zn were positively related to the soil Ec. The strong organic fraction and ion exchange fraction of Zn were negatively related to soil Ec. Compared with other trace elements, As displayed different properties. The ion exchange and carbonate fractions of As showed significant positive correlations with soil pH, suggesting that pH had positive effects on the ion exchange and carbonate fractions. Previous studies indicated that the mobility of As increases with increasing pH (Susaya et al. 2010). Besides that, the strong organic and residual fractions of As were negatively related to the soil Ec.

The mobility and bioavailability of trace elements Availability factor

organic fractions might be potentially bioavailable. However, the residual fraction is not available to either plants or microorganisms (He et al. 2005). The availability factor of trace elements is an important parameter, indicating the degree and retention time of environment risk. Table 5 shows the availability factor of each of the trace elements in the sampled soils. The availability factor was used to assess the retention time of trace elements retained in soils. The relative retention of the trace elements was in the following order: Hg > As > Zn > Pb > Cd > Cu. The results indicate that Cu and Cd might be released from soils faster than other trace elements, while Hg and As were slowest. Moreover, the high value of the availability factors for Cu and Cd showed a higher possible risk to the environment. The global availability factor (Af) indicates the different mobility and bioavailability conditions for all the trace elements in soils near the GM and GS. The soil near the GS had the higher Af values, which mean that smelter caused by trace element pollution was heavier than mining. The conclusion was consistent with the PLI.

The mobility of trace elements in soil depends on the mineral and organic phases within which they are associated. The exchangeable fraction was considered to be bioavailable, and the carbonate, humic acid, Fe/Mn oxide, and strong Table 5 Availability factor of trace elements in soils adjacent to the GM and GS Site

GM GS

Availability factor Hg

As

Cd

Pb

Cu

Zn

∑Afi =Af

0.27 0.33

0.75 0.62

1.28 1.63

0.95 1.44

1.80 2.86

0.68 0.86

5.73 7.74 Fig. 3 The RAC of trace elements from GM and GS

Environ Sci Pollut Res

Risk assessment code It is evident from the results of the above fractionation that different fractions of the elements are with different bioavailability and the risk associated with their presence in soils. The FDCs of exchangeable and carbonate fractions are determined to the RAC. These fractions are considered weakly bound to the soil and easy to migrate, and it will pose a greater risk to the soil environment (Jain 2004). The soils near both GM and GS showed low risk for Hg, As, Pb, and Zn, with RAC values less than 10 % (Fig. 3). These RAC values indicate that these trace elements did not exhibit any significant mobility. The RACs of Cd in GM and Cu in GS were between 10 and 30 %, indicating medium risk for the soil and surrounding environment. It was notable that Cd in soils near the GS showed high risk for our soil samples, and which might easily enter the food chain. Therefore, a significant remediation should be applied for Cd mobilization as soon as possible. Similar to the contamination factor, the higher values of RAC were observed in soil samples from GS. This indicated that the GS had a higher environment risk and that special attention should be paid.

Conclusion The soil samples collected near the gold mine and gold smelter showed relatively high concentrations of Hg, As, Cd, and Pb, which may lead to serious environmental hazards. The contamination level of GM and GS was in the order Hg > Cd > As > Pb. The mean concentration of Cu and Zn was indistinguishable from background values. Moreover, compared with soils near the GM, soils adjacent to the GS had the higher concentrations of trace elements. All the trace elements except Cu near the GS were mainly associated with the residual fraction, and it was mainly the humic acid fraction. In addition, Cd had the higher potential mobility and bioavailability. The humic acid fraction of Hg as well as the ion exchange fraction of Cd and Zn displayed negative correlations with soil pH. The strong organic fraction of Hg, the Fe/Mn oxide fraction of Cd, and the carbonate fraction of Zn were positively related to soil Ec. The strong organic fraction and ion exchange fraction of Zn were negatively related to soil Ec. The ion exchange and carbonate fractions of As showed significant positive correlations with soil pH. Compared with soils near the GM, the soil near the GS had the higher Af, which indicates a relatively higher capacity of trace elements to be released from the soil. This elements of Hg, As, Pb, and Zn had low risk for the environment; Cd in GM and Cu in GS showed medium risk for the environment. Furthermore, Cd indicated high risk for the environment in GS. In a word, the higher values of RAC were observed in

soil samples from GS, which indicates that the soils contaminated by smelting operations are more likely to cause environmental problems than those in the mining area. Acknowledgments This research was financially supported by the Natural Science Foundation of Shandong Province (No.ZR2012DL09).

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Geochemical fractions and risk assessment of trace elements in soils around Jiaojia gold mine in Shandong Province, China.

Soils located adjacent to the Jiaojia gold mine were sampled and analyzed to determine the degree of which they were contaminated by trace elements (H...
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