Geochemical Baseline Concentrations Research Articles

Geochemical characteristics and ecotoxicological risk of arsenic in water-level-fluctuation zone soils of the Three Gorges Reservoir, China

The Three Gorges Reservoir (TGR) has formed the water-level-fluctuation zone (WLFZ) due to reservoir regulation. However, as a sensitive zone in reservoir, little is known about the geochemical process and ecotoxicological risk of arsenic (As) in WLFZ soils under the anti-seasonal flow regulation. Hence, the anthropogenic contamination, mobility and ecotoxicological risks of As in WLFZ soils of the TGR were comprehensively assessed using the geochemical baseline concentration (GBC), chemical fractions, diffusive gradients in thin films (DGT) and toxicity data. The As concentrations in WLFZ soils showed a trend of increasing at the early stage of water impoundment and then stabilizing in recent years, which presented a low ecological risk of As according to the assessment by pollution indices. Based on GBC calculations, the average anthropogenic contribution of As was 13.95 %, indicating a slight influence of human activities. The distribution of labile As measured by DGT in WLFZ soils was mainly controlled by the Fe/Mn oxides, pH and organic matter. The DGT-induced fluxes in soils (DIFS) model further implied that resupply of As to soil solution was partially sustained by the soil solid phase, in which the resupply capacity was low and limited by the adsorption and desorption kinetics. In addition, the DGT was combined with toxicity data to obtain the risk quotient (RQ) and probabilistic risk assessment. The RQ value was lower than 1, indicating a low toxicity risk in WLFZ soils. Furthermore, the As in WLFZ soils had a low probability (5.97E-3 % and 7.77E-2 % in the mainstream and tributary, respectively) of toxic effects toward the aquatic biota. This study provides a comprehensive evaluation for the mobility and toxicity risk of As in WLFZ soils, which is beneficial to the prevention and control of heavy metals pollution in the riparian soils of lakes and reservoirs.

Pollution Risk Analysis of Heavy Metals at Illegal Mining Sites at Atiwa East District, Ghana

This study aims at determining the level of pollution of heavy metals (Cr, Cu and Hg) in the soils of illegal mining sites in Atiwa East District of Ghana. The concentrations of Copper (Cu), Chromium (Cr), and Mercury (Hg) in the soils were determined using Atomic Absorption Spectrometry (AAS). The extent of heavy metal pollution and pollution risk assessment was analyzed at the study site. Thirty (30) soil samples were collected from three (3) illegal mining sites within the district. The average levels of Cu, Cr, and Hg in the soil were 8.8, 6.75, and 3.19 mgkg-1 respectively, and were all above the WHO threshold. The geo accumulation indices (Igeo) of Cu, Cr, and Hg obtained were 1.92, 3.8, and 6.5 respectively, indicating moderately to extremely polluted soil at the study sites. The research has helped to establish the local Geochemical Baseline Concentrations (GBCs) of heavy metals in the study area so that an appropriate remediation method could be employed.

Estimation of baseline levels of bacterial community tolerance to Cr, Ni, Pb, and Zn in unpolluted soils, a background for PICT (pollution-induced community tolerance) determination

The PICT method (pollution-induced community tolerance) can be used to assess whether changes in soil microbial response are due to heavy metal toxicity or not. Microbial community tolerance baseline levels can, however, also change due to variations in soil physicochemical properties. Thirty soil samples (0–20 cm), with geochemical baseline concentrations (GBCs) of heavy metals and from five different parent materials (granite, limestone, schist, amphibolite, and serpentine), were used to estimate baseline levels of bacterial community tolerance to Cr, Ni, Pb, and Zn using the leucine incorporation method. General equations (n = 30) were determined by multiple linear regression using general soil properties and parent material as binary variables, explaining 38% of the variance in log IC50 (concentration that inhibits 50% of bacterial growth) values for Zn, with 36% for Pb, 44% for Cr, and 68% for Ni. The use of individual equations for each parent material increased the explained variance for all heavy metals, but the presence of a low number of samples (n = 6) lead to low robustness. Generally, clay content and dissolved organic C (DOC) were the main variables explaining bacterial community tolerance for the tested heavy metals. Our results suggest that these equations may permit applying the PICT method with Zn and Pb when there are no reference soils, while more data are needed before using this concept for Ni and Cr.

Geochemical Baseline and Contamination Level Assessment of Antimony (Sb) in Sediment around Agbaou Gold Mine, Côte d’Ivoire

Agbaou is one of the most recent gold mine exploitation sites in Côte d’Ivoire. Little studies are discussed on the geochemical baseline concentration of trace metals in the wetland sediments around Agbaou gold mine. The main objectives of this study were to establish geochemical baseline values and to assess the pollution status of antimony (Sb). The geochemical baseline concentration of Sb (GBCSb) was estimated using linear regression method. In this study, total Sb concentration was analysed in sediment (10 sediment samples) collected around Agbaou gold mine site. The average Sb concentration was 5.63 ± 2.50 µg.g-1 ranging from 2.50 to 11.3 µg.g-1. The spatial distribution of Sb showed a tendency to accumulate near gold mine site. Moreover, the GBCSb (5.72 µg.g-1) was slightly higher than the average concentration found in sediments. GBC of Sb was used to calculate the anthropogenic contribution rate (R) which exhibited a positive value (R > 0) for all samples, indicating that the sediments were influenced by gold mining activities. Due to lack of local baseline value in the study area, the GBCSb obtained could be used as reference value for Sb contamination level assessment in the sediments.

Bacterial community tolerance to Cu in soils with geochemical baseline concentrations (GBCs) of heavy metals: Importance for pollution induced community tolerance (PICT) determinations using the leucine incorporation method

PICT (Pollution Induced Community Tolerance) to Cu is a useful and sensitive tool to assess the effects of Cu pollution in soils under laboratory conditions. However, in field situations, the absence of reference values, i.e. bacterial community tolerance to Cu baseline from non-polluted soils, make the method uncertain when we want to know if a soil is or is not polluted from a microbiological point of view. In order to shed some light on this topic, the PICT (Pollution Induced Community Tolerance) concept was used to determine the bacterial community tolerance to Cu in uncontaminated soils developed on five different parent materials, using log IC50 as a tolerance index. IC50 was calculated as the amount of Cu that inhibit 50% of bacterial growth (estimated via the leucine incorporation method) in a bacterial suspension extracted from soil. With physico-chemical soil characteristics and type of parent material, a linear multiple regression equation was fitted explaining 80% of the variance in log IC50 values. This equation provides a useful tool to estimate the bacterial community tolerance to Cu baseline in a soil using the general soil characteristics, allowing for the more general use of PICT without the need of reference soils.

Pollution risk assessment of heavy metals in the sediments of upstream Hanjiang River, China

In China, the upstream Hangjing River (HJR) is an important surface water source for the South-to-North Water Transfer Project (SNWTP) because it has abundant water and better quality, which plays a crucial part in national drinking water safety and ecological sustainable development in China. This work was aimed at comprehensively studying the pollution status of heavy metals in sediments upstream of the HJR and apportioning sources. A total of 33 superficial sediment samples were collected from the main upstream of the HJR, which is located in Shaanxi and Hubei Provinces in China. The total concentrations of Zn, Cr, Ni, Cu, Cd, Pb, and As were analysed by using inductively coupled plasma mass spectrometry (ICP-MS). A standardized method was used to establish the environmental geochemical baseline concentrations (EGBCs) of the selected HMs as an alternative for local geochemical background values (LGBVs) to use for HM pollution assessment of sediment. The pollution status and potential ecological risk were assessed with the geochemical baseline factor pollution index (Ki), potential ecological risk index (RI), and sediment quality baseline evaluation (SQBEs). The source apportionment of heavy metals was performed by correlation analysis and principal component analysis (PCA). This study showed that the EGBCs of Zn, Cr, Ni, Cu, Cd, Pb, and As were 63.81 mg/kg, 23.47 mg/kg, 46.52 mg/kg, 35.26 mg/kg, 0.26 mg/kg, 6.97 mg/kg, and 6.76 mg/kg, respectively. The results indicated that Cd was the most common heavy metal pollutant. Mineral mining and smelting activities were the main sources of heavy metals in the sediments of the upstream HJR. Special attention should be paid to Cd, while Ni pollution cannot be ignored, especially in biotoxic effects. The high total Cd content affected individual and overall ecological risk indicators, indicating that Cd could represent a considerable ecological risk for upstream HJR.

An integrated exploration on health risk assessment quantification of potentially hazardous elements in soils from the perspective of sources

To make pollution evaluation of potentially hazardous elements in the soil more accurately, the regional geochemical baseline concentrations of eight potentially hazardous elements (Cr, Ni, Cu, Zn, As, Cd, Hg, and Pb) were established in Huilai County using cumulative frequency distribution curves. Then, the pollution load index and enrichment factor were applied to estimate the contamination levels, based on these geochemical baseline concentrations. The results suggested that topsoil was moderately polluted by potentially hazardous elements, while Cd pollution in the construction land and As pollution in the farmland was relatively severe. The possible sources of eight potentially hazardous elements were analyzed by correlation analysis, geostatistics and positive matrix factorization. Four sources have been determined and apportioned, namely industrial activities, natural sources, agricultural practices, and traffic emissions. Combining the health risk assessment with the source profiles, the health risks quantified from four sources were estimated under farmland, construction land, and woodland. The results showed that agricultural practices were the most main source of non-cancer and cancer risks under woodland and farmland for adults; industrial activities were the most main source of non-cancer and cancer risks under construction land for adults. Children's health risks, both carcinogenic risk and non-carcinogenic risk, were greater than adults, and the health risk trends of adults and children showed similarities. Therefore, agricultural practices under woodland and farmland should be controlled and managed as a priority, while industrial activities should be given priority to control and management under construction land.

Geochemical pollution of trace metals in permafrost-affected soil in the Russian Arctic marginal environment.

The Arctic marginal environment has been considered as far from industrial areas and low population. During June-July of 2016 "Russian High Latitude" expedition, 93 samples of soil genetic horizon from 25 soil profiles dug till frozen ground were sampled from 8 islands and 2 capes of the Russian Arctic without direct anthropogenic influences. Nine trace metals (Pb, Cd, Cu, Ni, Co, Zn, Fe, Mn and Hg) were measured and quantified by energy-dispersive X-ray analysis for elemental concentrations. Through analysis of divided soil groups (Haplothels, Turbels, Historthels), the factors of organic matter and cryoturbation had a significant influence on metals' distribution except for Fe and Mn. From summarized soil master horizons (O, A, B, C), Fe and Mn are abundant in all horizons suggesting as geochemical background values. Cu, Pb, Co and Ni are distributed specifically in different horizons with leaching and accumulation process, whereas Hg is evenly disturbed in all horizons. The correlation analysis reveals that distribution of most metals in present soils is highly depended on soil properties (pH, TOC, clay and silt). Li was selected as normalizing element for metals' concentrations from mineral layers to establish geochemical baseline concentrations. The concentrations of trace metals have been assessed by geoaccumulation index (Igeo) and enrichment factor, showing only Co and Zn are moderately polluted and slightly polluted, and Co, Cu, Zn and Pb are enriched in topsoil. Other indices as modified degree of contamination (mCdegree) and pollution load index (PLI), mCdegree show moderate degree of pollution and PLI shows unpolluted to moderate pollution load. The ecological risk indices, e.g., ecological risk factor (Er) and potential ecological risk index, show low ecological risk potential.

Characterizing pollution and source identification of heavy metals in soils using geochemical baseline and PMF approach

It is necessary to establish local geochemical baseline concentrations (GBCs) due to the lack or the inapplicability of regional background values in the study area. The establishment of GBCs of heavy metal (HM) in soil helps in making the accurate assessment of pollution, and then provides a basis for pollution control. Based on this, a case study was undertaken to study the GBCs of the Jiedong District, Guangdong Province, China. In this research, cumulative frequency distribution curves were utilized to determine the local GBCs in the subsoils. The determined GBCs of Cr, Hg, As, Pb, Ni, Cd, Cu, Zn, Co and V were 39.91, 0.072, 11.48, 47.62, 12.70, 0.17, 14.22, 64.54, 6.31, and 68.14 mg/kg, respectively. The average concentrations of Hg, As, Pb, Cd, Cu and Zn in the topsoils exceeded the corresponding baseline concentrations. In particular, the contents of Cd and Hg were 1.53 and 2.22 times higher than GBCs. According to this baseline criterion, enrichment factor (EF), pollution load index (PLI) and ecological risk index (RI) were applied to assessing HM pollution. EF and PLI suggested that most areas were under moderate contamination, while Hg and Cd pollution was more serious. And the RI values presented that the potential ecological risks were low in most parts of the study area. The possible origins of HMs were identified by combining positive matrix factorization with EF and geostatistics. Comprehensive analysis indicated that Hg and Cd were related to industrial activities, such as textile and garment processing, plastic and rubber production and metal manufacturing. Arsenic and part of Cu mainly came from agricultural activities, namely the use of pesticides, fertilizers and livestock manures. Lead and Zn were mainly attributed to traffic emissions. Chromium, Ni, V, Co, and part of Cu were originated from natural source controlled by parent materials. The corresponding contributions of these sources were 20.61%, 24.20%, 19.22% and 35.97%, respectively. This work provides information to prevent and control the soil HM pollution by proposing the efficient management of anthropogenic sources.

Geochemical and health risk assessments of antimony (Sb) in sediments of the Three Gorges Reservoir in China

Toxic metals in the sediments of the Three Gorges Reservoir (TGR) in China are a conspicuous scientific issue. However, compared with the commonly monitored metals, the geochemical behavior and potential risk of antimony (Sb) in TGR sediments remains unclear. Here, sediment samples were collected from the entire TGR. Multiple assessment approaches (i.e., geochemical baseline concentration of Sb (GBCSb), grain size normalization, potential ecological risk, and health risk assessment) were used to evaluate the Sb status in sediments. The average Sb concentration was 1.14 ± 0.20 mg/kg, ranging from 1.10 to 1.19 mg/kg. The spatial distribution of Sb exhibited a tendency to accumulate from upstream to downstream. Normalization by fine grain size revealed that fine grain particles mainly influenced the Sb spatial distribution in TGR sediments. The temporal variation of Sb revealed that the mean content of Sb was higher in the dry season than in the wet season. Moreover, GBCSb (1.10 mg/kg) was higher than the background value of Sb in Yangtze River sediments. Determination of the anthropogenic contribution rate gave a mean value of 11.43% using the GBC model, indicating that the main contribution of Sb in TGR sediments originated from natural sources. According to sediment loads during 2015 and 2016, the anthropogenic input deposited 2.74 and 3.32 t of sediments in 2015 and 2016, respectively. In addition, the assessment results of the potential ecological risk index based on GBCSb suggested that Sb presented a low ecological risk in TGR sediments. Sb accumulation in fish caused by the sediment resuspension was calculated by the environmental impact assessment model. Further assessment of target hazard quotients demonstrated that Sb was at a safe level for fish consumption.

Anthropogenic Impact and Ecological Risk Assessment of Thallium and Cobalt in Poyang Lake Using the Geochemical Baseline

As the largest freshwater lake in China, water environmental pollution in Poyang Lake is increasingly attracting attention. However, to date, the occurrence of seldom-monitored trace elements (SMTEs) (such as thallium (Tl) and cobalt (Co)) and their potential ecological influences in the Poyang Lake area remain unclear. Here, geochemical baseline concentrations (GBCs) were employed to investigate anthropogenic inputs of these two metals (Tl and Co) and were used to assess the potential ecological risk in surface sediments of Poyang Lake. The results showed that the mean concentrations of Tl and Co were 1.11 mg/kg and 15.42 mg/kg, respectively, slightly higher than background values (BVs) in local soil. Spatially, the Co concentrations in surface sediments of Poyang Lake varied; Co concentrations in the west of the study area were significantly lower than in the middle of the lake. In contrast, no significant spatial variation of Tl was found in studied areas of Poyang Lake. Average GBCs were similar to the mean measured concentrations of Tl and Co in the lake, and both were higher than the BVs in local soil. In anthropogenic source analysis based on the GBCs, 47.22% samples and 41.67% samples were influenced by human activity for Tl and Co, respectively; the mean anthropogenic contribution rate was 5.90% for Tl (0.43 to 16.22%), and 13.01% for Co (0.82 to 31.59%). These results indicated that Tl and Co mainly originate from natural processes. However, the anthropogenic contribution should not be ignored. Moreover, the geo-accumulation index (Igeo) and potential ecological parameter (Er) generally indicated no contamination and a low potential risk for Tl and Co in Poyang Lake sediments, which used the GBCs as BVs. The results of this study suggest that GBCs are more scientifically robust and practical as a reference than BVs. They can also be used when BVs are lacking.

Characterization of contamination levels of heavy metals in agricultural soils using geochemical baseline concentrations

It is currently very difficult to accurately evaluate the soil contamination by heavy metals (HMs) attributed to the unavailability of local geochemical background values (LGBVs). This study was performed to establish the geochemical baseline concentrations (GBCs), as an alternative for LGBVs to use for HM pollution assessment of agricultural soil. GBCs of the HMs selected were determined using the cumulative frequency distribution curves (CFDCs). GBCs were then used to pursue the HM soil pollution and associated ecological risks, via calculation of geo-accumulation indices (Igeo), pollution load indices (PLI), as well as potential ecological risk indices (RI). As to the soil investigated, the GBCs of Ni, Zn, Pb, and Cr were 29.34 mg/kg, 45.54 mg/kg, 21.81 mg/kg, and 33.65 mg/kg, respectively. Igeo values ranged from − 4.58 to 0.33 (Ni), from − 2.46 to 2.14 (Zn), from − 5.32 to 0.77 (Pb), and from − 3.83 to 0.96 (Cr), suggesting that the region was not polluted by these HMs. PLI values ranged from 0.08 to 2.45 with an average of 1.02. 49.6% of soil samples had the PLI values > 1.0, indicating that some of the soil may be moderately contaminated by HMs. The RI values of selected HMs were < 150, indicating a low potential ecological risk. Principal component analysis (PCA) implied Zn, Pb, and Cr were mainly sourced from parent (geological) materials, as well as agricultural activities, atmospheric deposition, etc., depending on the element. The present study illustrates the necessity of the characterization of GBCs at a regional scale, allowing for more accurate assessment of soil contamination by HMs. We hope that this will eventually lead to further development of better environmental management practices for agricultural soil polluted by HMs.

Application of DGT/DIFS and geochemical baseline to assess Cd release risk in reservoir riparian soils, China

As the sole drinking water source for Beijing City, Cd has been previously assessed as the major contaminant in Miyun Reservoir (MYR) riparian soils. However, the potential release risk of Cd in such soils, and the labile-Cd release–resupply process from the soil solid phase to solution after water impoundment remain poorly understood. We established a geochemical baseline concentration (GBC) of Cd in MYR riparian soils, combined with the diffusive gradient in thin films (DGT) technique and DGT-induced fluxes in soil (DIFS) model, to reveal a dynamic release–resupply process and influencing factors of labile Cd in riparian soils. The results showed that Cd GBC in riparian soils was 0.12 mg/kg, which was higher than the Cd background value (BV) for Beijing. Using Cd GBC as BV to assess the Cd contaminant level, the geo-accumulation index showed that Cd in riparian soils was at the uncontaminated level. In addition, Cd in the soils belonged to the non-residual fraction using the Community Bureau of Reference method. Cd mobility coefficients (F1/CTotal-Cd) of soils at low elevation had relatively high values, implying that Cd may be released during the initial impoundment of the MYR. Moreover, correlation analysis was used to found the major influencing factors between DGT-labile Cd and several parameters. The results showed that the DGT-labile Cd was positively correlated to the reducible and oxidizable fraction, CDGT-Fe, and total organic carbon, illustrating that the release of Cd from soils was controlled by Fe oxides and organic matter. The resupply ability (R values) and DIFS model parameters revealed that Cd in MYR soils belonged to the partially sustained case, and the slow desorption rate suggested that the release risk of Cd was low in the MYR riparian soils.

Thallium pollution in sediments response to consecutive water seasons in Three Gorges Reservoir using geochemical baseline concentrations

The Three Gorges Reservoir (TGR) is the world’s largest hydrological project. However, the response of thallium (Tl) in TGR sediments to reservoir operation remains highly uncertain. Here, we investigated the pollution characteristics of Tl in TGR sediments during five consecutive water seasons. Geochemical baseline concentrations (GBCs) were used to distinguish the anthropogenic input of Tl and to quantitatively estimate the Tl anthropogenic contribution in TGR sediments. The results showed that the average Tl concentration in TGR sediments was 0.72 ± 0.14 mg/kg (ranging from 0.26 to 1.07 mg/kg) during five consecutive water seasons. The average Tl content in tributary sediment was higher than that in mainstream sediment. In the mainstream, Tl in TGR sediments showed an accumulation tendency from the upstream to downstream. Additionally, the temporal variation revealed that the mean value of Tl in TGR sediments in the dry season was higher than that in the wet season during 2015–2016. Furthermore, the average GBCs of Tl (0.71 mg/kg) was higher than background values (BVs) in the Yangtze River sediments. Using the GBCs of different water seasons to calculate the anthropogenic input of Tl in the TGR, the average anthropogenic contribution was found to be approximately 6.43% (2.81%–9.12%). The assessment results by two different methods (geo-accumulation index and potential ecological risk index) used GBCs as the BVs, indicating that TGR sediments were at “uncontaminated” level and close to the “low ecological risk”, respectively. Comparing to the GBC of Tl, the assessment of Tl pollution in TGR using BVs in the Yangtze River sediments may be over-evaluated. This study is beneficial for assessing Tl pollution in TGR sediments response to consecutive water seasons and estimating the anthropogenic contribution of Tl.

Regional geochemical baseline concentration of potentially toxic trace metals in the mineralized Lom Basin, East Cameroon: a tool for contamination assessment

The distribution of trace metals in active stream sediments from the mineralized Lom Basin has been evaluated. Fifty-five bottom sediments were collected and the mineralogical composition of six pulverized samples determined by XRD. The fine fraction (< 150 µm) was subjected to total digestion (HClO4 + HF + HCl) and analyzed for trace metals using a combination of ICP-MS and AAS analytical methods. Results show that the mineralogy of stream sediments is dominated by quartz (39–86%), phyllosilicates (0–45%) and feldspars (0–27%). Mean concentrations of the analyzed metals are low (e.g. As = 99.40 µg/kg, Zn = 573.24 µg/kg, V = 963.14 µg/kg and Cr = 763.93 µg/kg). Iron and Mn have significant average concentrations of 28.325 and 442 mg/kg, respectively. Background and threshold values of the trace metals were computed statistically to determine geochemical anomalies of geologic or anthropogenic origin, particularly mining activity. Factor analysis, applied on normalized data, identified three associations: Ni–Cr–V–Co–As–Se–pH, Cu–Zn–Hg–Pb–Cd–Sc and Fe–Mn. The first association is controlled by source geology and the neutral pH, the second by sulphide mineralization and the last by chemical weathering of ferromagnesian minerals. Spatial analysis reveals similar distribution trends for Co–Cr–V–Ni and Cu–Zn–Pb–Sc reflecting the lithology and sulphide mineralization in the basin. Relatively high levels of As were concordant with reported gold occurrences in the area while Fe and Mn distribution are consistent with their source from the Fe-bearing metamorphic rocks. These findings provide baseline geochemical values for common and parallel geological domains in the eastern region of Cameroon. Although this study shows that the stream sediments are not polluted, the evaluation of metal composition in environmental samples from abandoned and active mine sites for comparison and environmental health risk assessment is highly recommended.

Background levels of some trace elements in calcareous soils of the Hamedan Province, Iran

Natural concentrations of trace elements are necessary for assessing trace elements contamination affected by anthropogenic activities in soils. This study was conducted to establish background concentrations of cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb) and zinc (Zn) in 50 unpolluted native soils with a total of 100 soil samples (surface and subsurface soil layers) in Hamedan province of Iran. Different methods have been used for the evaluation of background limits, and the relationships between soil properties and trace elements concentrations and among trace element concentrations have been analyzed. Values from Geometric Mean (GM) procedure had the lowest background limit, while the GM×GSD2 (geometric standard deviation) method produces the highest background limits. The percentage of outliers in Median+2MAD (median absolute deviation) ranged from 4.0 to 16.0% for natural data and from 0.0 to 12% for log-transformed data. The smallest outlier percentage was for Cd and Cr, and it was higher for Co, Cu, and Zn. The obtained geochemical baseline concentrations (mgkg−1) based on Median+2MAD were (log-transformed data) Cd 1.36, Co 15.42, Cr (natural data) 36.69, Cu 29.99, Fe 25.79 (gkg−1), Mn 368.68, Ni (natural data) 53.59, Pb 39.60, Zn 103.80. Carbonate calcium had significant negative correlations with Co, Cr, Cu, Fe, and Mn, indicating that trace elements are not included in the crystal structure of secondary carbonate minerals; consequently, accumulation of CaCO3 causes a dilution effect in the soils. The content of clay, silt and organic matter had significant role in the accumulation of Mn, Ni, and Pb in the soils of the studied area. Significant correlation was found among Co, Cr, Cu, Fe, Mn, and Ni and between Zn with Cd, Cr, Cu, Mn, and Ni. Factor analysis of trace elements explored six factors attributing 64.1% of the total variability. According to the results found by upper whisker method, correlation analysis and factor analysis, studied trace elements contaminated none of the soil samples, natural accumulation processes influenced their contents in soils and origin of trace elements may be lithogenic, but their sources may be different.

Comparison of four methods for bioavailability‐based risk assessment of mixtures of Cu, Zn, and Ni in freshwater

Although chemical risk assessment is still mainly conducted on a substance-by-substance basis, organisms in the environment are typically exposed to mixtures of substances. Risk assessment procedures should therefore be adapted to fit these situations. Four mixture risk assessment methodologies were compared for risk estimations of mixtures of copper (Cu), zinc (Zn), and nickel (Ni). The results showed that use of the log-normal species sensitivity distribution (SSD) instead of the best-fit distribution and sampling species sensitivities independently for each metal instead of using interspecies correlations in metal sensitivity had little impact on risk estimates. Across 4 different monitoring datasets, between 0% and 52% of the target water samples were estimated to be at risk, but only between 0% and 15% of the target water samples were at risk because of the mixture of metals and not any single metal individually. When a natural baseline database was examined, it was estimated that 10% of the target water samples were at risk because of single metals or their mixtures; when the most conservative method was used (concentration addition [CA] applied directly to the SSD, i.e., CASSD ). However, the issue of metal mixture risk at geochemical baseline concentrations became relatively small (2% of target water samples) when a theoretically more correct method was used (CA applied to individual dose response curves, i.e., CADRC ). Finally, across the 4 monitoring datasets, the following order of conservatism for the 4 methods was shown (from most to least conservative, with ranges of median margin of safety [MoS] relative to CASSD ): CASSD > CADRC (MoS = 1.17-1.25) > IADRC (independent action (IA) applied to individual dose-response curves; MoS = 1.38-1.60) > IASSD (MoS = 1.48-1.72). Therefore, it is suggested that these 4 methods can be used in a general tiered scheme for the risk assessment of metal mixtures in a regulatory context. In this scheme, the CASSD method could serve as a first (conservative) tier to identify situations with likely no potential risk at all, regardless of the method used (the sum toxic unit expressed relative to the 5% hazardous concentration [SumTUHC5 ] < 1) and the IASSD method to identify situations of potential risk, also regardless of the method used (the multisubstance potentially affected fraction of species using the IASSD method [msPAFIA,SSD ] > 0.05). The CADRC and IADRC methods could be used for site-specific assessment for situations that fall in between (SumTUHC5 > 1 and msPAFIA,SSD < 0.05). Environ Toxicol Chem 2017;36:2123-2138. © 2017 SETAC.

Geochemical baseline establishment and ecological risk evaluation of heavy metals in greenhouse soils from Dongtai, China

Currently, heavy metal (HM) contamination in greenhouse soils is a significant concern due to the rapid expansion of greenhouse agriculture. However, it is difficult to accurately assess HM pollution in greenhouse soils in China due to the lack of local geochemical baseline concentrations (GBCs) or corresponding background values. In the present study, the GBCs of HMs in Dongtai, a representative greenhouse area of China, were established from subsoils using cumulative frequency distribution (CFD) curves. The pollution levels of HMs and potential ecological risks were investigated using different quantitative indices, such as geo-accumulation index (Igeo), pollution index (PI), pollution load index (PLI) and ecological risk index (RI), based on these regional GBCs. The total concentrations of six metals (Cd, Cr, Cu, Ni, Pb and Zn) in surface soils were determined and shown to be lower than the concentrations reported in other greenhouse regions of China. The GBCs of Cd, Cr, Cu, Ni, Pb and Zn were 0.059–0.092, 39.20–54.50, 12.52–15.57, 20.63–23.26, 13.43–16.62 and 43.02–52.65mgkg−1, respectively. Based on this baseline criterion, Cd, Pb and Zn accumulated in the surface soils because they were present at concentrations higher than their baseline values. The soils were moderately polluted by Cd according to the Igeo values, and the PI results indicated that moderate Cd contamination was present in this area. The large variation of Igeo value of Cd revealed that Cd in this area was likely influenced by agricultural activities. The PLI showed that most of the study area was moderately polluted. However, an analysis of the RI showed that the investigated HMs had low ecological risks. Correlation analysis and principle component analysis suggested that the Cd, Pb and Zn in the greenhouse soils mainly originated from anthropogenic sources (agricultural activities, atmospheric deposition etc.), while Cr, Cu, and Ni originated from natural sources. The findings of this study illustrated the necessity of GBC establishment at the local scale to facilitate more accurate HM evaluation of greenhouse soils. It is advisable to pay more attention to Cd, which could cause environmental problems in the greenhouse system.

Baseline values of Cadmium and Zinc in three land uses in a selected mapping unit of the dry zone of Sri Lanka

Anthropogenic activities change the natural concentrations of soil trace metals in different land uses with varying magnitudes. Establishment of baseline concentration of metals is important in assessing human impact on metal concentrations in soils over time. A study was conducted to compare Cd and Zn concentrations in different land uses (lowland, upland and non-agricultural) to investigate relationships of Cd and Zn with soil properties and to establish geochemical baseline concentrations of the two metals for three land uses of Madawachchiya – Ranorawa – Elayapattuwam – Hurathgama - Nawagattegama soil association of the Dry Zone of Sri Lanka. Soils were analyzed for organic carbon (OC), clay, pH, electrical conductivity (EC), and HNO 3 acid-soluble Cd and Zn. Land use had a significant effect (p Tropical Agricultural Research Vol. 25 (1): 84-95 (2013)

Baseline concentrations of some trace elements in Alfisols of Sri Lanka

A study was conducted to establish the geochemical baseline concentrations of Cu, Pb, Ni, Zn and Cd to assess the possible trace metal contamination in a mapping unit in Sri Lanka consisting of Alfisols. Soils were analyzed for organic carbon (OC), clay %, pH, electrical conductivity (EC), and HNO3 acid soluble metals. Standard reference material (SRM-2586) from National Institute of Standard and Technology was used for the quality assurance. Nitric acid soluble Cu, Pb, Ni, Zn and Cd concentrations of soils were ranged from 1.56–33.5, 2.19–19.2, 1.58–32.2, 7.44–71.3 and 0.13–1.22mgkg−1 respectively. Established upper limits of the baseline ranges of Cu, Pb, Ni, Zn and Cd were 26.5, 18.0, 33.9, 51.2 and 1.38mgkg−1 respectively. All the tested metals have not reached the contamination level compared with the derived upper baseline limits except very few samples for Cu, Zn and Pb. According to the results of correlation analysis of metal–soil properties and metal–metal, the sources of Cd in studied soils can be different from the sources of other measured elements. Principal component analysis of trace metals identified two principal components (PCs) attributing 67.1% of the total variability. Accordingly, Cu, Pb, Ni and Zn were associated with PC 1 and Cd was associated with PC 2. Based on the correlation analysis and principal component analysis, source of origin for Cu, Pb, Ni and Zn could be suggested as lithogenic while an anthropogenic origin was evident for Cd in studied soils.