Three-step Sequential Extraction Procedure Research Articles

Geochemical Characteristics and Environmental Risks of Cu in the Soil of A Sloping Vineyard (Phu Tho Province, Vietnam)

In the vineyards, the intensive use of cupric fungicides and fertilizers has resulted in Cu enrichment in the soils. Specifically, in sloping vineyards, the mobility of Cu can contribute to intensify the environmental risks. The research on geochemical characteristics of Cu is a key solution to explore the distribution of Cu in different geochemical fractions and understand the mobility and toxicity of this element in the environment. In this study, we aim to investigate the geochemical properties of Cu in the vineyard topsoil (0-20 cm) and subsoil (20-40-60 cm), using the improved three-step sequential extraction procedure developed by the Commission of the European Communities Bureau of Reference (BCR). In addition, the environmental risk is calculated by the environmental risk code (RAC) based on the percentage of Cu in the acid-soluble fraction. The results reveal that the mobility of Cu in the acid-soluble fraction (F1) and reducible fraction (Cu associated with the iron and manganese oxyhydroxides) (F2) tends to decrease with increasing soil depth. The major portion of Cu mostly exists in the strong bond with silicate clays (F4), accounting for 84% of total Cu content on average. Contrarily, the minor propotion of Cu associates with soil organic matter (F3) (3% on average). On the other hand, the content and proportion of Cu in the soil fractions are largerly influenced by basic soil properties (organic matter contents and fine soil particles). In addition, under the impact of soil erosion, higher percentages of F1 and F2 fractions of Cu are observed in the surface soil layers at the top of the hill compared to those at the backslope of the hill. The mean calculated RAC of 10.66%, 5.76%, and 5.38% for the 0-20 cm, 20-40 cm, and 40-60 cm soil layers, respectively, demonstrate a low risk to medium environmental risk level in the studied vineyard. Although an overall low risk level is observed for Cu in the studied vineyard soil, the deposition of Cu originating from repeated Cu-based pesticides and erosion is of particular concern in the vineyard soils.

The significance of applying different factors for the evaluation of sediment contamination by toxic elements and estimation of the ecological risk.

The optimized three-step sequential extraction procedure for the fractionation of micro- and macroelements, was conducted to determine fractional characteristics of PTEs (potentially toxic elements) in surface sediments of rivers in the Vlasina watershed. The sequential extraction results, which enable the evaluation of mobility of the studied elements, have indicated that Zn, Ni, Cu, Cr, and As can be considered slightly mobile, whereas Pb, Mn, Cd, and Co were regarded as possibly mobile elements. Lead was dominantly bounded (specifically adsorbed or co-precipitated) to iron and manganese oxides (up to 80%) and may be released by reduction. Since the content of the exchangeable fraction (F1) is an indicator for anthropogenic impact on the aquatic environment, a low percentage (0-8%) of studied toxic elements in this fraction indicated that these elements have lithogenic origin in most sampling locations in the area of study. Except for Pb, the substantial positive correlations between Al and other elements showed that studied elements came primarily from terrigenous sources. Although the values obtained for the risk assessment code (RAC) indicated a slightly increased mobility of some elements (up to 22.44%), the values of the modified risk assessment code (mRAC), which include toxic effects on the environment, showed there is no danger of pollution by studied elements (all values were < 1%). Our recommendation is to use mRAC instead of RAC in ecochemical studies and assessment of the degree of sediment and soil pollution, because mRAC includes toxic effects of elements. Based on ATI values, river sediments show no toxic to a low toxic degree. Even though obtained results indicate that there was no considerable risk for river water contamination, the ecological risk for Fe and Pb should be monitored in the future.

Comparative studies on the effects of biochar and cow dung amendments on the mobility, bioavailability and toxicity of heavy metals in lead-acid contaminated soil

This study compared the heavy metals remediation potency of biochar and cow dung in soils contaminated by lead-acid batteries. Soil samples were gathered from three different battery charging shops in Benin City at the depth of 0-15cm using systematic grid sampling method. Hardwood was pyrolyzed at 350°C for 80minutes and cow dung was air dried and pound into powder. The soil was characterized using standard methods, and was fractionated using modified European Community Bureau of Reference (BCR) three-step sequential extraction procedure while the concentration of heavy metals was determined using Atomic Absorption Spectrophotometer (AAS). The total metal concentration in the lead-acid contaminated soil was 127.50mg/kg Pb, 0.32mg/kg Cr, 0.03mg/kg Cd, 0.18mg/kg Ni and 135.00mg/kg Fe. The contaminated soil was remediated with biochar and as well with cow dung at 5%, 10%, 15% and 20%. The soil was also amended using biochar-cow dung mixture (1:1, 2:1 and 1:2). The outcome revealed that the metal content in lead-acid contaminated soil remediated with biochar and cow dung were found to generally decrease as the percentage of amenders increases, with biochar being further efficient in lowering the levels of heavy metals in the contaminated soil. However, biochar when mixed with cow dung at 2:1 ratio at 20% amendment gives a better result than when used separately. Pot experiment was designed and the amounts of heavy metals bioavailable to plant were determined. The mobility factors and bioavailability indices of the metals reduced as the percentage of amenders’ increases. The result obtained from this study revealed that although biochar and cow dung were effective amenders, biochar was more potent in lowering the mobility, bioavailability and toxicity of heavy metals in lead-acid contaminated soil. Biochar when mixed with cow dung at 2:1 ratio gave the best result in remediation of lead-acid contaminated soil.

Investigation of metal mobility in gold and silver mine tailings by single-step and sequential extractions

Metal leachate from mine tailings has the potential to release toxic metals into the surrounding environment. A single-step extraction procedure mimicking rainwater and a three-step BCR sequential extraction procedure (acid, reducing and oxidizing conditions) were applied to gold (GMT) and silver (SMT) mine tailings. Major (Al, Ca, Fe, Mg, and Mn) and trace metals were monitored to better understand the mobility and geochemistry of these metals when exposed to various environmental leaching conditions. Rainwater extraction released only small quantities of metals, while the three-step BCR extraction was more effective in mobilizing metals from the tailings. Under the acidic conditions of BCR step 1, Ca, Mg, Cd, Cu, and Mn were released in high concentrations. The dissolution of Fe, Ca, and Mg were dominant along with Pb in step 2 (reducing conditions). In step 3 (oxidizing conditions), Fe was the most dominant species together with Co, Cu, Ni, and Se. A high fraction of Al, Be, Cr, Li, Mo, Sb, Tl, and V remained in the residue. From SMT, larger quantities of As, Ca, Cd, and Zn were released compared to GMT. The BCR extraction could be applied to tailings to predict the potential release of toxic metals from mine wastes; however, excessive amounts of Ca and Fe in the tailings could cause carry-overs and incomplete extraction and carry-overs, resulting in a misinterpretation of results.

Impacts of wet thermal treatment on heavy metals speciation in contaminated waste activated sludge using a modified sequential extraction scheme

The mobility and the bioavailability of heavy metals in waste activated sludge were determined according to their total content and chemical speciation. A modified three-step sequential extraction procedure was used to determine the total content and metal speciation distribution pattern of various heavy metals (As, Cd, Cr, Cu, Ni, Pb, and Zn) pretreated at a temperature of 100 °C to 200 °C. It was found that the organics solubilization was enhanced at higher temperature, increased by 1.75, 183 and 3.03 folds over the soluble chemical oxygen demand (SCOD) at 100 °C. The total contents of Cd, Pb and Zn exceeded the threshold value established in GB/T standard 23486 (2009), as a function of pH, due to the pollution from the local nonferrous metals industry. For most cases, the impacts of thermal pretreatment on the species distribution were limited and obscure. Cr was the only element showing a potential risk of metal mobilization, such that its residual fraction shifted towards oxidizable fraction at higher treatment temperature. The speciation distribution pattern of Ni, Cr, Cu, and Zn showed potential risks of contamination due to their bioavailability, mobility, or toxicity.

Effect of multi-walled carbon nanotubes on extractability of Sb and Cd in contaminated soil

The interaction between multi-walled carbon nanotubes (MWCNTs) and soil heavy metals was rarely studied. With the convenience of detecting multiple metal elements by ICP-AES, this paper examined the potential effectiveness of MWCNTs on extractability of antimony (Sb) and cadmium (Cd) in contaminated soil. Three-step sequential extraction procedure, toxicity characteristic leaching procedure, bioaccessibility and CaCl2 single extraction were employed to evaluate Sb and Cd speciations and their extractabilities. According to our results, only at low Sb content level of 100 mg/kg, antimony bioavailability reduced with MWCNTs addition of 0.3% and 0.9% by 22.97% and 20.74%, respectively, which might due to the increase of adsorption point, nevertheless, the excess Sb(OH)6- was not adsorbed more efficiently. Secondly, due to the difference in effective specific surface area, only under the condition of high content level and MWCNTs addition of 0.1%, the mild acid-soluble fraction increased at most by 15.40% for Sb and 9.40% for Cd, respectively. However, in terms of TCLP-extractable Sb and Cd and CaCl2-extractable Sb and Cd, no significant, continuous, regular extractability pattern were found. Overall, MWCNTs were selective on extractability of soil heavy metals due to mechanisms of physical adsorption. This paper provides data reference for the interaction between MWCNTs and soil heavy metals extractability.

Toxicity of soil antimony to earthworm Eisenia fetida (Savingy) before and after the aging process

Information on soil antimony (Sb) toxicity to earthworm Eisenia fetida (Savingy) is limited. This ecotoxicology study was designed to quantify the soil Sb toxicity to earthworm E. fetida before and after aging process, establishing dose-effect relationship between Sb content and mortality. Results of the avoidance test and acute test showed that the values of net avoidance response, escape rate and mortality were generally decreased in aged treatment compared to that in fresh treatment, respectively from 93.33% to 66.67%, 36.67% to 13.33% and 100% to 53.33% (15 d) taking TL800 (treatment level of 800 mg/kg) for example, meanwhile the values of median lethal content (LC50) at 72 h, 7 d and 15 d were respectively increased from 355.27 mg/kg to 2324.55 mg/kg, 322.19 mg/kg and 1743.19 mg/kg and 282.74 mg/kg to 745.94 mg/kg, indicating that aging process could reduce the Sb acute toxicity to earthworm. According to a three-step sequential extraction procedure, the bioavailable Sb ranged from 24.45% to 43.24% and 16.97% to 27.70% in fresh treatment and aged treatment, respectively, and the mortality of earthworm for 24 h decreased with the decrease of the content of mild acid-soluble antimony (which decreased averagely from 23.09% to 14.00%), which was more suited to assess Sb toxicity. This is the first report that confirms the toxicity of soil Sb to earthworm E. fetida as well as the considering of aging process and speciation.

Evaluation of mobility, fractionation, and potential environmental risk of trace metals present in soils from Struibult gold mine dumps

This study reports the fractionation of trace metals such as As, Bi, Cd, Co, Cr, Cu, Mo, Ni, Pb, Sb, Se, Tl and Zn in soils collected from Struibult gold mine dump, Gauteng, South Africa using a modified three-step BCR sequential extraction procedure. The extractable fractions such as exchangeable, easily reducible and oxidizable fractions were used assessed to the mobility and potential bioavailability of each investigated metal. Fractionation results revealed that As (55.4–80.6%), Bi (16.8–42.2%), Cr (83.3–94.8%), Cu (0–51.5%), Mo (0–80.4%), Ni (13.2–100%), Pb (55.6–79.6%), Sb (61.9–93.3%), Se (47.3–77.9%), Tl (58.8–100%) and Zn (8.7–100%) predominant metals in the residual fraction (F4) of soil samples. Individual contamination factors (ICF), geo-accumulation index (Igeo), contamination factor (CF), risk assessment code (RAC) and enrichment factor (EF) were used for assessment of the environmental impacts of trace metals in soil samples. The RAC and ICF values showed that Co, Ni and Zn have high environmental risk. The bioaccumulation of trace metals in the plants (Chrysopogon zizanioides) growing at the foot of the mine dump was assessed. Chrysopogon zizanioides was found to accumulate most of the studied metals that were available for uptake, with bioaccumulation factor (BAF>1). These results suggested that this plant species is a good accumulator for toxic metals in mining areas.

Environmental Activity and Ecological Assessment of Heavy Metals in the Reductive Leaching Residue from Zinc Hydrometallurgy Industry

Zinc hydrometallurgy residue is one of the main sources of heavy metals in the environment. The chemical components and mineralogical characteristics of the reductive leaching residue was obtained by ICP-AES, XRD and SEM + EDS analysis. The results showed that the main heavy metals in the residue were Pb, Zn, Cd and As. Pb, Zn and Cd in the residue existed as PbSO4, ZnS and CdS, respectively. The three-step sequential extraction procedure study showed that Zn and Cd mainly existed as oxidizable form; Pb and As mainly existed as the residue form. The leaching toxicity results using sulfuric acid and nitric acid method showed that the leaching toxicity of Zn and Cd exceeded the reference values. The potential ecological risk assessment results of heavy metals of the residue showed that the sequence of the environmental activity and ecological risk was Cd > Zn > As > Pb. Cadmium contributed to the potential risk index more greatly than any other heavy metal in the residue and the contribution rate reached 98.9%, which showed that the cadmium in the reductive leaching residue threw the greatest threat to the ecological environment.

Influence of pyrolysis temperature on chemical speciation, leaching ability, and environmental risk of heavy metals in biochar derived from cow manure

This study analyzed the chemical speciation, leaching ability, and environmental risk of heavy metals (Cd, Cr, Cu, Ni, Pb, and Zn) in cow manure biochar (CMBC) pyrolyzed at various temperatures. The total content, chemical speciation, and leaching ability of the heavy metals were determined through microwave digestion, modified BCR three-step sequential extraction procedure, and leaching solution systems (TCLP, distilled water, and SPLP). The risk assessment code, Muller geo-accumulation index, potential ecological risk index, and germination index were used to evaluate the environmental safety and ecotoxicity of heavy metals. Significant differences were observed in the physicochemical properties of CMBCs. The heavy metal contents in CMBCs were higher than those in CM. The bioavailable fraction of heavy metals was transformed into a relatively stable fraction with increasing pyrolysis temperature. Furthermore, the potential risks and ecotoxicity of biochar were reduced, thus improving environmental safety. The study results provide important data for biochar applications.

Study on heavy metals’ influence on buried cultural relics in soil of an archaeological site

ABSTRACT The protection of cultural relics in a chariot pit in the ancient ruins has become an important issue. In order to study the spatial distribution, speciation of heavy metals in soil at a cemetery where an ancient chariot was buried and the influence heavy metals have had on the cultural relics. Heavy metals in soil samples surrounding the cultural relic were analyzed via atomic absorption spectrometry (AAS) using a wet digestion method combined with a three-step sequential extraction procedure. Results for seven heavy metals (Cu, Pb, Zn, Cr, Fe, Mn and Sn) and the speciation of six heavy metals (Cu, Pb, Zn, Cr, Fe and Mn) indicated that their contents exceeded local soil background values, indicating that the soil around the site had been contaminated to a certain degree. Analysis of their speciation showed that Mn mainly existed in the form of a reducible fraction in the soil, while the other elements were mainly in the form of a residual fraction. Correlation analysis showed that, except for the HOAc soluble fraction, a significant positive correlation existed between the content of the different forms and their total amounts. Heavy metals present in the soil surrounding the ancient relic predominantly influence the relic due to their related chemical reactions. In particular, copper and iron have a significant influence on corrosion of the cultural relics in this chariot pit.

Geochemical Fractions of the Agricultural Soils of Southern Poland and the Assessment of the Potentially Harmful Element Mobility

Surface samples (0–25 cm each) of agricultural soils were investigated in five Regions (voivodeships) of southern Poland. The mean Potentially Harmful Element (PHE) pseudototal content ranges were as follows (mg/kg): As 5.19–10.9, Cd 0.34–1.56, Co 1.92–6.70, Cr 9.05–25.7, Cu 8.74–69.4, Hg 0.001–0.08, Ni 3.93–19.9, Pb 20.3–183, Sb 0.80–1.42, Tl 0.04–0.17, and Zn 61.3–422. The PHE availability depended on pH, the organic carbon (Corg) content, and the pseudototal PHE content in soils. Exchangeable and acid soluble PHE contents (BCRF1) determined in the Community Bureau of Reference (BCR) three-step sequential extraction procedure decreased in this order: Cd &gt; Zn &gt; Co &gt; Ni = Sb &gt; Cu &gt; Tl &gt; As &gt; Cr = Pb. Actually available PHE contents in pore water (0.01 mol/dm3 CaCl2) ranged as follows: Cd 0.81–17%, Cr 0–0.25%, Cu 0.01–2.31%, Ni 0.16–2%, Pb 0.2–0.49%, and Zn 0.25–2.12%. The potential soluble total content of PHEs in pore water (0.05 mol/dm3 Na2EDTA) ranged as follows: Cd 27–91%, Cr 0.7–7.1%, Cu 6.7–98%, Ni 3.6–41%, Pb 15–41%, and Zn 3–34%. The mobility factor (MF) values indicated Cd (31.6%) and Zn (21.0%) as the most mobile elements in soil. Other PHEs followed the order of Co &gt; Ni &gt; Tl &gt; As &gt; Sb &gt; Cu &gt; Cr &gt; Pb, with the MF values &lt;10%. The risk assessment code (RAC) values revealed a very high ecological risk of Cd and Zn in the Podkarpackie Region and a high ecological risk of Cd in the Regions of Opolskie, Śląskie, Małopolskie, and Podkarpackie, and the same of Zn in the Opolskie and Śląskie. The modified risk assessment code (mRAC) index pointed a very high potential of adverse effects in soils in the Podkarpackie and a medium potential in the Opolskie, Śląskie, Małopolskie, and Świętokrzyskie. The potential adverse effect risk, described by the individual contamination factor (ICF) factor, was the following in the Regions, in the decreasing order: Cd &gt; Pb &gt; Sb &gt; Zn &gt; Co &gt; Cu &gt; Ni &gt; Tl &gt; As &gt; Cr, and the same as described by the global contamination factor (GCF) values: Opolskie &gt; Podkarpackie &gt; Świętokrzyskie &gt; Śląskie &gt; Małopolskie.

Evolution of Cr, Cu, Mn, and Zn during the composting process of chicken manure and their integrated potential ecological risk assessment

The aim of this study was to ascertain the evolution of Cr, Cu, Mn, and Zn during the composting process of chicken manure and their integrated potential ecological risk. This study detected the total amounts of Cr, Cu, Mn, and Zn in 4 samples collected at four different stages in the composting workshop of an intensive chicken farm in Chengdu, China. Furthermore, the chemical fractionation of the four heavy metals was analyzed by the BCR (European Community Bureau of Reference) three-step sequential extraction procedure for each sample. At last, the integrated potential ecological risk of Cr, Cu, Mn, and Zn in the compost at four different stages was evaluated by the procedure of potential ecological risk assessment based on its results of chemical fractionation of Cr, Cu, Zn, and Mn. During the composting process, the total amounts of Cr, Cu, Zn and Mn presented an increasing trend, significantly. Nevertheless, the residual fraction (Res-F) percentage of Cr, Zn, and Cu increased, and the acid extractable fraction (Aci-F) percentage of Mn decreased. The value of integrated potential ecological risk of the four heavy metals in the final product was 9.91. These results indicated the integrated potential ecological risk of the four heavy metals is low. This study provided a support on the promotion and utilization of compost for the intensive chicken farms in China.

Analysis of 129I and 127I in soils of the Chernobyl Exclusion Zone, 29 years after the deposition of 129I.

The Chernobyl Exclusion Zone (CEZ) represents a unique natural laboratory that received significant 129I contamination across a range of soils and land-use types in a short time period in 1986. Data are presented on 129I and 127I in soil samples collected from highly contaminated areas in the CEZ in 2015. The geometric mean (GM) total concentration of stable iodine (127I) was 6.7 × 10-7 g g-1 and the (GM) total concentration of 129I was 2.39 × 10-13 g g-1, equivalent to 1.56 mBq kg-1. GM total 127I concentration is below the European average soil concentration of 3.94 × 10-6 g g-1, while 129I is significantly higher than the pre-Chernobyl activity concentration for 129I of 0.094 mBq kg-1. Significant differences were found in the extractability of native, stable 127I and 129I almost 30 years after the introduction of 129I to the soils. Both 127I and 129I were predominantly associated with alkaline-extractable soil organic matter, established using a three-step sequential extraction procedure. Whereas 127I was significantly correlated with gross soil organic matter (measured by loss on ignition), however, 129I was not. The ratio of 129I/127I was significantly lower in extracts of soil organic matter than in more labile (soluble and adsorbed) fractions, indicating incomplete equilibration of 129I with native 127I in soil humic substances after 29 years residence time in the CEZ soils. The initial physico-chemical form of 129I in the CEZ soils is unknown, but the widespread presence of uranium oxide fuel particles is unlikely to have influenced the environmental behaviour of 129I. Our findings have implications for long-term radiation dose from 129I in contaminated soils and the use of native, stable 127I as a proxy for the long-term fate of 129I.

Assessment of Heavy Metal Pollution and Potential Ecological Risk in Sewage Sludge from Municipal Wastewater Treatment Plant Located in the Most Industrialized Region in Poland-Case Study.

This study aimed to assess the pollution and potential ecological risk of seven heavy metals (Cd, Cr, Cu, Hg, Ni, Pb, and Zn) in the sewage sludge collected from a wastewater treatment plant (WWTP), located in the most industrialized region of Poland (Silesian Voivodeship). The concentrations of heavy metals were determined using inductively coupled plasma optical spectrometry (ICP-OES) and cold vapor atomic absorption spectrometry (CVAAS). The chemical forms (chemical speciation) of heavy metals were determined using the three-step chemical sequential extraction procedure, developed by the Community Bureau of Reference (BCR). To assess the pollution level and potential ecological risk, the following indices were used: Geoaccumulation Index (Igeo), Potential Ecological Risk Factor (ER), Individual Contamination Factor (ICF), Risk Assessment Code (RAC), and Ecological Risk Factor (ERF)—the author’s index. Sludge samples were collected at successive stages of processing. The results revealed that the activated sludge process and sludge thickening have a significant impact on heavy metal distribution, while anaerobic digestion and dehydration decrease their mobility. The most dominant metals in the sludge samples were Zn and Cu. However, the content of heavy metals in sewage sludge did not exceed the permissible standards for agricultural purposes. The concentrations of heavy metals bound to the immobile fractions exhibited higher concentrations, compared to those bound to mobile fractions (except Zn). The values of the total indices indicated that sludge samples were moderately to highly contaminated with Zn, Hg, Cd, Cu, and Pb, of which only Hg, Cd, and Cu posed a potential ecological risk, while according to the speciation indices, sludge samples were moderately to very highly polluted with Zn, Cu, Cd, Cr, and Ni, of which Zn, Ni, and Cd were environmentally hazardous. The obtained results proved that assessment of the pollution level and potential ecological risk of heavy metals in sewage sludge requires knowledge on both their total concentrations and their chemical forms. Such an approach will help prevent secondary pollution of soils with heavy metals, which may influence the reduction of health risks associated with the consumption of plants characterized by a high metal content.

Vanadium and chromium-contaminated soil remediation using VFAs derived from food waste as soil washing agents: A case study

Food waste (FW) is environmentally unfriendly and decays easily under ambient conditions. Vanadium (V) and chromium (Cr) contamination in soils has become an increasing concern due to risks to human health and environmental conservation. Volatile fatty acids (VFAs) derived from FW was applied as soil washing agent to treat V and Cr-contaminated soil collected from a former V smelter site in this work. The Community Bureau of Reference (BCR) three-step sequential extraction procedure was used to identify geochemical fractions of V and Cr influencing their mobility and biological toxicity. Optimal parameters of a single washing procedure were determined to be a 4 h contact time, liquid–solid ratio of 10:1, VFAs concentration of 30 g/L, and reaction temperature of 25 °C, considering for typical soil remediation projects and complete anaerobic fermentation of FW. Under the optimal conditions, butyric acid fermentation VFAs attained removal rates of 57.09 and 23.55% for extractable fractions of V and Cr, respectively. Simultaneously, a multi-washing process under a constant liquid–solid ratio using fresh and recycled VFAs was conducted, which led to an improvement on the total removal efficiency of toxic metals. The washing procedure could reach the pollution thresholds for several plants, such as of S. viridis, K. scoparia, M. sativa, and E. indica. This strategy enhances the utilization of VFAs derived from food waste, has a positive effect on V and Cr-contaminated soil remediation, wastewater control of soil washing and FW disposal.

Effect of dissolved oxygen and nutrient levels on heavy metal contents and fractions in river surface sediments

In aquatic systems worldwide, heavy metal pollution has been increasing alongside rapidly growing anthropogenic activities, and most heavy metals are stored in sediments. Overlying water conditions may influence whether sediments act as heavy metal sinks or sources. In this study, we investigated the effects of the dissolved oxygen (DO) and nutrient levels of overlying water on the total contents and fractions of Pb, Zn, Ni, Cu, Mo, and Fe in river surface sediments. Sediments and overlying water were collected from a tributary of the Hai River in Tianjin, China, and then incubated for 61 days under laboratory conditions. The chemical speciation of heavy metals was determined following the modified Community Bureau of Reference (BCR) three-step sequential extraction procedure. The results showed that Pb, Zn, and Fe were released from the sediments in an anoxic environment and adsorbed from the overlying water in an aerobic environment. High nutrient levels facilitated the adsorption of Pb, Zn, Cu, and Fe in the sediments, while the total content of Mo was higher under low nutrient level conditions. The DO and nutrient levels appeared to have no influence on the total content of Ni. According to the risk assessment code classification (RAC), anoxic conditions decrease the potential bioavailability risks of Pb, Zn, Ni, Cu, Mo, and Fe. Anoxic conditions can also reduce the percentage of the potentially mobile fractions of Pb, Zn, Cu, and Fe. The low nutrient level contributed, to some extent, to reducing the potential bioavailability risk of Pb, but increasing the risk of Cu. The high nutrient level increased the potentially mobile fractions of Pb, Zn, Cu, and Fe. The information obtained in this study improves our scientific understanding of the effects of overlying water conditions on the total heavy metal contents and fractions.

Sequential extraction of nickel and zinc in sewage sludge- or biochar/sewage sludge-amended soil

Fractionation of nickel (Ni) and zinc (Zn) in sewage sludge-amended soil and in sewage sludge/biochar-amended soil was investigated. The results were compared with ecotoxicological tests in order to determine the contribution of metals to the toxicity of amended soils. The study was conducted as a long-term field experiment. Sewage sludge (SL) or sewage sludge with a 2.5, 5 or 10% addition of biochar (BC) was added to the soil. Samples for analysis were taken immediately after experiment establishment as well as after 12 and 18 months from the beginning of the study. The fractionation analysis of Ni and Zn was performed using the BCR (Community Bureau of Reference) three-step sequential extraction procedure. The following forms were determined: mobile (F1); bound to FeMn oxides (F2); bound to organic matter (F3) and residual (F4). The soil, SL and BC differed in the contribution of individual forms of the metals. The application of SL into the soil resulted in an increased soil content of mobile forms of Ni and Zn by 180 and 103%, respectively. The mobility index (MI) significantly increased, which evidences the risk related to the presence of these metals. Biochar in the sewage sludge significantly reduced the content of Ni and Zn in F1 fraction. The study also demonstrated that biochar amendment promotes the transition over time of available forms of Ni and Zn into their residual forms (F4), which leads to a further reduction in the environmental risk related to their presence in the environment. The conducted statistical analysis revealed only intermittent relationships between the individual forms of the metals and soil physicochemical properties and toxicity, which may indicate more complex mechanisms that occur in the experimental systems investigated. Therefore, the use of SL in combination with BC can be an effective method for reducing the environmental risk related to the presence of metals in SL.

Distribution and risk assessment of heavy metals in overlying water, porewater, and sediments of Yongding River in a coal mine brownfield

Heavy metals from coal mines migrate into rivers and cause a severe impact on the health of local residents utilizing these rivers as a water source. However, current studies on coal mine brownfields have yet to thoroughly investigate river-associated heavy metals produced by coal mining. Therefore, this study aims to explore the distribution and risk assessment of heavy metals, namely Cr, Cu, Mn, Ni, Pb, and Zn, in overlying water, porewater, and sediments of the Yongding River, China. Overlying water, porewater, and sediments were sampled at 11 sites along the Yongding River. Heavy metal concentrations were determined through ICP-MS, and sediments were subjected to a three-step sequential extraction procedure to verify the behavior of heavy metals through principal component analysis (PCA). Sediments were separated into seven size fractions (< 4, 4–8, 8–16, 16–75, 75–150, 150–250, and 250–840 μm) with sedimentation method based on Stokes’ law. The characteristics of heavy metal distribution in different particle sizes were also explored using the Tucker 3 method. Interstitial water criteria toxic units (IWCTUs) were used to assess porewater heavy metal pollution. Risk assessment code (RAC), sediment quality guidelines (SQGs), and pollution load index (PLI) were applied to evaluate the ecological risk of heavy metals in sediments. Heavy metal concentrations increase in the following sequence: overlying water < porewater < sediment. Lead and Zn in porewater are higher than the criteria maximum concentrations (CMCs). The IWCTUs of Pb and Zn indicate their possible risk of toxicity. Principal component analysis reveals that Mn in sediments is preferentially associated with the exchangeable fraction, Cu and Zn are mainly associated with the reducible fraction, and Cr, Ni, and Pb are strongly related to the residual fractions. Heavy metals in sediments mainly accumulate in the fine fractions (< 4, 4–8, and 8–16 μm). Nickel, Pb, and Zn in sediments occasionally cause adverse biological effects. Overall, PLIs of sediments at sites 1, 4, and 10 in the Yongding River show moderate pollution due to Cr, Cu, Mn, Ni, Pb, and Zn. Different heavy metals possess unique partition coefficients between overlying water and sediments because these metals exhibit various properties and mobility. The chemical fractions of heavy metals also confirm the partition coefficients. Heavy metals in fine sediment fractions also enhance their migration and occasionally cause severe biological effects. Therefore, drinking water security in these areas should be ensured.

A field screening test for the assessment of concentrations and mobility of potentially toxic elements in soils: a case study on urban soils from Rome and Novi Sad.

The increasing demand for environmental pollution control results in the development and use of new procedures for the determination of dangerous chemicals. Simple screening methods, which can be used directly in the field for a preliminary assessment of soil contamination, seem to be extremely advantageous. In our laboratory, we developed and optimized a rapid test for a preliminary evaluation of both the concentration and the mobility of some potentially toxic metals in soils. This screening test consists of a single extraction of the soil sample with a buffer solution, followed by the titration of the extracted solution with dithizone to determine the contents of bi-valent heavy metals (such as Pb, Cu, Zn, and Cd). This screening method was then directly applied in the field during the sampling campaign in the framework of an Italian-Serbian collaborative project, finalized in the study of metal availability in soils. The results obtained in the field with the rapid test were compared with those obtained in the laboratory following the conventional procedure commonly used to evaluate metal bioavailability (diethylenetriaminepentaacetic extraction). Moreover, selected samples were analyzed sequentially in the laboratory using the standardized BCR three-step sequential extraction procedure. The screening test gave results conceptually in good agreement with those obtained via the BCR procedure. These preliminary data show that the proposed screening test is a reliable method for the preliminary rapid evaluation of metal total concentrations and of potential metal mobility in soils, supporting sampling activities directly in the field.