Chemical Speciation Of Heavy Metals Research Articles

Chemical speciation and mobility of heavy metals in soils of refuse dumpsites in some urban towns in the Niger Delta of Nigeria

Abstract Refuse dumpsites often contain materials which are capable of polluting surrounding soils especially if the dumpsites are not adequately shielded from the surrounding area. This study examined chemical speciation and mobility of heavy metals in three urban towns in the Niger Delta. Soil samples were collected from three dumpsites in each of the three selected urban towns at 0-15 cm, 15-30 cm and 30-45 cm depths. The chemical speciation of the heavy metals in the soils was determined using the Tessier’s sequential extraction procedure. The results showed that on the average, the residual fraction was the predominant fraction of all the metals except Pb which was dominant in the organic fraction. The mobility factor followed the order Zn > Fe > Pb > Cr > Ni > Cd > Cu. The study indicates that the metals studied do not pose environmental risk considering their relatively low concentrations and the chemical forms they are associated with. It is however recommended that the sites be continuously monitored because of the deleterious health effects of exposure to heavy metal pollution in the events of reclaim.

Distribution and chemical speciation of heavy metals in various size fractions of aggregates from zonal soils

ABSTRACT Aggregates are the basic structural units of soil; therefore, understanding the distribution and speciation of heavy metals (HMs) in soil aggregates is crucial for the clarification of the environmental behaviour of HMs. In this paper, seven soil profiles from different climatic type regions were sampled and grouped into six size aggregates (>2, 2–1, 1–0.6, 0.6–0.25, 0.25–0.053, <0.053 mm) to determine the distribution and chemical speciation of Cd, Cu, Mn and Pb. The results showed that the vertical distribution of Cd, Cu, Mn and Pb was differed, and the content of total Cd and Pb was ranked in the same order at both subsoil and parent material layer. Although the proportion of <0.053 mm size aggregate was lowest in bulk soil, fine particles showed higher content of total HMs and higher per cent of labile form distribution. However, the contents of total HMs were not always positively correlated with the content of acid soluble or potentially labile fractions of HMs. Total contents of Cu and Mn in aggregates from acidic soils were high, but these two HMs only posed light ecological risk according to the risk assessment code values. Soil organic matter (SOM) and soil pH were involved in the speciation of HMs. Acid exchangeable fraction of Mn in aggregates showed a decreasing trend from alkaline to acidic soils, and SOM positively correlated with the content of oxidisable fraction. For Cd, Cu and Pb, the content of potentially labile fraction of Cu positively associated with the content of Pb potentially labile fraction, and the content of residual fraction of Cd were negatively correlated with the content of Cu residual fraction.

Effect of Metal Oxide Nanoparticles on the Chemical Speciation of Heavy Metals and Micronutrient Bioavailability in Paddy Soil.

The effects of engineered nanoparticles (ENPs) on heavy metal fate and biotoxicity in farmland soil are mostly unknown. A flooding–drying simulation experiment was conducted to study the effects of three typical metal oxide nanoparticles (TiO2-NPs, ZnO-NPs and CuO-NPs) on the chemical speciation of heavy metals and micronutrient bioavailability in paddy soil. The results showed that the addition of ZnO-NPs and CuO-NPs caused significant increases in soil pH, Eh and EC after a 90-d flooding–drying process. ZnO-NPs and CuO-NPs addition caused clearly increase in the Zn and Cu concentrations in the acid-soluble fraction, Fe/Mn oxides-bound fraction and organic-bound fraction, leading to higher bioavailability in the soil. DTPA-extractable Zn and Cu increased to 184.6 mg kg−1 and 145.3 mg kg−1 in the maximum ZnO-NPs and CuO-NPs concentration treatments (500 mg kg−1). TiO2-NPs promoted the transformation of Mn from a Fe/Mn oxides-bound fraction to an acid-soluble fraction. Soil Cd bioavailability obviously decreased in the TiO2-NPs treatment but increased in the ZnO-NPs and CuO-NPs treatments.

Effect of co-combusted sludge in waste incinerator on heavy metals chemical speciation and environmental risk of horizontal flue ash

Incineration of sludge in waste incinerators is a trend of sludge disposal, and the problem of heavy metal in horizontal flue ash is a concern. Horizontal flue ash in waste incinerator was collected before and after the sludge was co-combusted. XRF, SEM-DES, and ICP were used to characterize the effect of sludge on the distribution of heavy metals on different heated surfaces. Potential ecological risk index of all horizontal flue ash was higher than 600, indicating the high ecological risk. After adding sludge for co-combustion, heavy metals content in all ash sample increased. As for chemical speciation of heavy metals, the addition of sludge increased the content of mild acid-soluble fraction, reducible fraction and oxidizable fraction of heavy metals, while decreased that of the residual fraction. Environmental pollution and potential ecological risks of heavy metals were increased when sludge was co-combusted. The fitting relation between the heavy metals content of each speciation and the gas temperature and the sludge mixing amount was given, which could be used to predict the heavy metal content in horizontal flue ash.

Insight into a new two-step approach of ozonation and chitosan conditioning for sludge deep-dewatering

Sludge deep-dewatering, capable of reducing water content (Wc) of sludge cake under 60%, is one of the current hot topics in sludge treatment. In this study, a new environmentally friendly two-step approach of ozonation and chitosan (CT) conditioning was proposed and examined to be practicable for sludge deep-dewatering. With 60 mg/gTS ozone and 20 mg/gTS CT conditioning, sludge capillary suction time (CST) and Wc of the dewatered sludge cake decreased from 196.3 s and 84.7% of raw sludge to 15.8 s and 57.5%, respectively. Ozonation treatment could efficiently crack sludge flocs and cells, and release biopolymers, causing the decreases in viscosity, zeta potential and particle size. Subsequently, CT ameliorated the sludge dewaterability successfully by neutralizing negative charges and flocculating colloids to promote the spread of interstitial water. Furthermore, the contents of heavy metals (As, Cd, Cr, Ni, Pb and Zn) in conditioned sludge cake decreased obviously except Cu, but all detected heavy metals contents satisfied the A level of agricultural land (GB4284-2018). For chemical speciation of heavy metals, the proportions of the acid soluble/exchangeable state and the reductive state increased apparently, implying higher toxicity and bioavailability, except Pb. Hence, pretreatments were required to reduce the environmental risk of heavy metals in conditioned sludge cake prior to a further utilization.

Chemical Speciation of heavy metals in Cd-polluted soil with different particle-sizes

In this paper, the Cd-contaminated soils in the eastern suburbs of Tianjin were divided into seven grain classes(I-VII). The distribution characteristics of soil grain size were analyzed. The soil content of 40-60 mesh and less than 160 mesh was the highest. The two grain size soils were about 50% in total, and the soil of 140-160 mesh rank had the lowest content, with the maximum content not exceeding 1%. The distribution characteristics of chemical forms of Cd in soils with different grain sizes were analyzed, which were divided into weak acid extractable, reducible, oxidizable and residual forms. The results showed that Cd mainly existed in the weak acid extractable form and the reducible form. The highest Cd concentration was found in 120-140 mesh, followed by 40-60 mesh.

Comparison of long-term stability under natural ageing between cement solidified and chelator-stabilised MSWI fly ash

Cement-solidification and chelator-stabilisation of municipal solid waste incineration fly ash (MSWI-FA) are two main treatment techniques to immobilise heavy metals. Differences in the long-term stabilities of those two methods of heavy-metal immobilisation were explored to aid in determining the better MSWI-FA treatment. However, few comparative studies have been conducted on 6-year-old cement-solidified FA (Ce-6-FA) and chelator-stabilised FA (Ch-6-FA). In this study, we compared the physicochemical and heavy metal leaching characteristics of Ce-6-FA and Ch-6-FA. The chemical speciation of heavy metals was modelled using geochemical software to assess long-term stability. The results showed weaker long-term stability in Pb immobilisation under the chelating system. The leaching concentrations of target heavy metals, acetic acid leaching tests, acid neutralising capacity, and pH-dependent leaching results indicated that Ce-6-FA had higher long-term stability than Ch-6-FA. A column experiment indicated that the cumulative release rates of Pb in Ce-6-FA and Ch-6-FA were 2.49% and 4.72%, respectively. The phase-controlled leaching of Pb in Ce-6-FA mainly occurred through Pb2(OH)3Cl and chloropyromorphite (Pb5(PO4)3Cl), whereas that in Ch-6-FA mainly occurred through Pb5(PO4)3Cl. The decomposition of heavy metal chelates in Ch-6-FA and salt generation in this process led to the release of Pb via the inorganic complex.

Metal Speciation in Sediment from Muara Angke, Jakarta Bay Using of BCR Sequential Extraction Procedure

The assessment of the biological availability of metals is rarely used only by knowing the total concentration of the metal. Therefore, six sediment samples from Muara Angke, Teluk Jakarta were assessed the chemical speciation of heavy metals. This study aims to determine metal speciation using the BCR sequential extraction procedure and to determine metal speciation to evaluate bioavailability in the sediments of Muara Angke, Jakarta Bay. In sediment from Muara Angke, the ability to move sequence of heavy metals studied was Pb&gt;Zn&gt;Cu&gt;Ni. The mostly accumulated in the non-residual fraction of the total concentrations are Cu, Ni, Pb and Zn which indicated that the mobility and anthropogenic inputs of these metals in Muara Angke were quite high. The Risk Assessment Code (RAC) reveal that Zn and Ni at almost station exist in exchangeable and a fraction of carbonate-bound and therefore high-risk category. Most of the Cu at most of the station is in the oxidizable fraction, except a small portion found at all station is in the exchangeable fraction and fraction of carbonate-bound thus posing a low risk for the waters environment. The patterns of Pb speciation show no to low risk to the waters environment. However, metal observations in the waters are necessary because they are persistent and can accumulate which threatening the water environment.

In-situ solidification/stabilization of heavy metals contaminated site soil using a dry jet mixing method and new hydroxyapatite based binder.

In this study, in-situ treatment using dry jet mixing construction method and SPC (single superphosphate and calcium oxide) new binder are used to solidify/stabilize a heavy metal contaminated site soil with relatively high content of organic matters. Time-dependent field performance of the soils at 41 and 326 days after treatment is evaluated, which includes electrical conductivity (EC), leachability of heavy metals and chemical oxygen demand (COD), soil penetration resistance, acid neutralization capacity (ANC), and chemical speciation of heavy metals. The results indicate that the stabilized soils exhibit satisfactory performance which is comparable with the laboratory study. In-situ SPC treatment significantly decreases EC values and increases penetration resistance values of the soils. Leachability of lead, zinc, cadmium and COD decreases with increasing SPC content or curing time. Large percentages of heave metals in the soils are transformed from exchangeable fractions to residual fractions after treatment. These, coupled with the improved ANC, result in low heavy metal leachability in stabilized soils.

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.

Rice husk and sewage sludge co-combustion ash: Leaching behavior analysis and cementitious property

The co-combustion of sewage sludge with rice husk is expected to become a trend because of its economic and environmental benefits. In this work, the ashes and its cementitious forms were investigated. The leachability characteristic of heavy metals and mechanical properties in cementitious forms was evaluated. The stabilization/solidification (S/S) mechanism of cementitious forms was also studied. Results showed that the leachability of heavy metals in co-combustion ashes decreased by an average of 30% after the hydration process. Non-crystal hydrates gradually formed and the compact structure hydrates became apparent in RSCA30 after 28 d (relative to SSMA30 and OPC1). The chemical speciation of heavy metals is transformed into immobilization state after hydration. In general, ashes from the co-combustion of rice husk and sewage sludge are beneficial to the development of cementitious materials.

Chemical speciation, vertical profile and human health risk assessment of heavy metals in soils from coal-mine brownfield, Beijing, China

The characterization of the concentration and chemical speciation of heavy metals in surface and vertical profile soils is a necessary for pollution monitoring and the potential risk assessment of the heavy metals (HMs) to animal and human health. Surface soil samples (n=14) and vertical profile soil samples (n=36) from selected sites (n=6) were collected from coal-mine brownfield in the Qingshui River Basin, in which the concentrations and chemical speciation of HMs (Cd, Cr, Cu, Mn, Ni, Pb, Zn) in surface soils and HM concentrations in vertical profile soils were determined by ICP-OES and analyzed using methods of geo-accumulation index (Igeo), Tucker 3 model and health risk assessment. The chemical fractions of HMs were extracted by BCR-sequential extraction procedure. Results show that HMs in surface soils accumulate in descending order of Cd>Pb>Cu>Ni>Mn>Zn>Cr. All HMs are associated with residue fraction to different degrees. Manganese and Ni are closely related to extractable BCR fractions and turn to be the severer pollutants in some sites. The Igeo values of HMs in vertical profile soils indicate ‘uncontaminated’. Whereas coal mining activities with long history increase HM concentrations in subsurface soils at the coal mine former site. The non-carcinogenic risk posed by HM extractable fractions to children and adults fall below the safe level of 1. Lead extractable fraction exhibits the highest risk value in the case of children. The levels of carcinogenic risk posed by Cr and Ni extractable fractions are above that of the United States Environmental Protection Agency (USEPA) acceptable level (1×10−6). Nickel extractable fraction exhibits the highest carcinogenic risk values for children with exceeding that of the maximum USEPA acceptable level (1×10−4).

Chemical Speciation of Heavy Metals in Soils of Jeju Island, Korea

Chemical Speciation of Heavy Metals in Soils of Jeju Island, Korea

Grain-Size Distribution and Chemical Speciation of Heavy Metals in Chinese Street Dust

Grain-Size Distribution and Chemical Speciation of Heavy Metals in Chinese Street Dust

Performance of Raphidocelis subcapitata exposed to heavy metal mixtures

Microalgae growth inhibition assays are candidates for referent ecotoxicological assays, and are a fundamental part in the strategy to reduce the use of fish and other animal models in aquatic toxicology. In the present work, the performance of Raphidocelis subcapitata exposed to heavy metals following standardized growth inhibition assays has been assessed in three different scenarios: 1) dilutions of single heavy metals, 2) artificial mixture of heavy metals at similar levels than those found in natural rivers and, 3) natural samples containing known mixtures of contaminants (heavy metals). Chemical speciation of heavy metals has been estimated with Eh-pH diagram and Visual MINTEQ software; heavy metal and free heavy metal ion concentrations were used as input data, together with microalgae growth inhibition, for Dr. Fit software. The final goal was to assess the suitability of the ecotoxicological test based on the growth inhibition of microalgae cultures, and the mathematic models based on these results, for regulatory and decision-making purposes.The toxicity of a given heavy metal is not only determined by its chemical speciation; other chemical and biological interaction play an important role in the final toxicity. Raphidocelis subcapitata 48h-h-EC50 for tested heavy metals (especially Cu and Zn) were in agreement with previous studies, when ion metal bioavailability was assumed to be 100%. Nevertheless, the calculated growth inhibition was not in agreement with the obtained inhibition when exposed to the artificial mixture of heavy metals or the natural sample. Interactions between heavy metal ions and the compounds of the culture media and/or the natural sample determine heavy metal bioavailability, and eventually their toxicity.More research is needed for facing the challenge posed by pollutant mixtures as they are present in natural environments, and make microalgae-based assays suitable for pollution management and regulatory purposes.

When soils become sediments: Large-scale storage of soils in sandpits and lakes and the impact of reduction kinetics on heavy metals and arsenic release to groundwater

Simulating the storage of aerobic soils under water, the chemical speciation of heavy metals and arsenic was studied over a long-term reduction period. Time-dynamic and redox-discrete measurements in reactors were used to study geochemical changes. Large kinetic differences in the net-complexation quantities of heavy metals with sulfides was observed, and elevated pore water concentrations remained for a prolonged period (>1 year) specifically for As, B, Ba, Co, Mo, and Ni. Arsenic is associated to the iron phases as a co-precipitate or sorbed fraction to Fe-(hydr)oxides, and it is being released into solution as a consequence of the reduction of iron. The composition of dissolved organic matter (DOM) in reducing pore water was monitored, and relative contributions of fulvic, humic and hydrophylic compounds were measured via analytical batch procedures. Quantitative and qualitative shifts in organic compounds occur during reduction; DOM increased up to a factor 10, while fulvic acids become dominant over humic acids which disappear altogether as reduction progresses. Both the hydrophobic and hydrophilic fractions increase and may even become the dominant fraction.Reactive amorphous and crystalline iron phases, as well as dissolved FeII/FeIII speciation, were measured and used as input for the geochemical model to improve predictions for risk assessment to suboxic and anaerobic environments. The release of arsenic is related to readily reducible iron fractions that may be identified by 1 mM CaCl2 extraction procedure. Including DOM concentration shifts and compositional changes during reduction significantly improved model simulations, enabling the prediction of peak concentrations and identification of soils with increased emission risk. Practical methods are suggested to facilitate the practice of environmentally acceptable soil storage under water.

Seasonal variability of heavy metal content and its chemical speciation in excess sludge by vermi-stabilization

Vermifiltration system has been reported to enhance sludge degradation and relieve the potential risks of heavy metals, whereas few studies focus on the seasonal variability of heavy metal content and its chemical speciation in excess sludge by vermi-stabilization. The results of this study showed that total contents of Zn, Pb, Cr and the treatment efficiency of vermifilter were higher in summer and lower in winter due to the temperature effect. While Cu was observed to not be dependent on season. Further investigation using a five-step fractionation procedure to evaluate the main chemical speciations of metals in the sludge showed that there were similar variations in the five fractions (F1-F5) between each season, which indicated that the chemical speciation of heavy metals were most affected by vermifiltration technique than seasonal factor. The transformations among the five fractions suggested that the vermifiltration significantly reduced the mobility and bioavailability of Zn and Pb due to their increased stable fractions and decreased unstable fractions. The higher stable fraction of Cu led to the stable morphology in sludge, which favoured the insignificant variations with seasons.

Potential ecological risk and speciation analysis of heavy metals in sediments from the Jialu River, China

To evaluate ecological risks and existing forms of heavy metals in the Jialu River of China, sediments samples were collected from 22 sites along this river. A BCR-sequential extraction procedure was applied to analyse the chemical speciation of heavy metals (i.e., Cr, Mn, Co, Ni, Zn, Cu and Cd) in sediment samples, including acid extractable, reducible, oxidisable and residual fractions. The geo-accumulation index, risk assessment code and enrichment factor were used to evaluate the pollution situation of these heavy metals. The results showed that the speciation of Cr was mainly associated with the exchangeable fraction with a mean percentage of 54.23%. Mn and Zn mainly occurred in the reducible fraction, accounting for 42.72% and 37.71% of the total contents, respectively. Co, Ni, Cu and Cd were mainly associated with the residual fraction with mean percentages of 58.75%, 59.02% and 48.21%, respectively. The sediment samples in the lower reach had higher heavy metals levels, and Cd showed a considerable risk relative to other metals.

Chemical speciation of heavy metals in the sediments of Longjiang River: after a cadmium spill

Chemical speciation of heavy metals in the sediments of Longjiang River: after a cadmium spill

Chemical Speciation and Quantitative Evaluation of Heavy Metal Pollution Hazards in Two Army Shooting Range Backstop Soils.

The chemical speciation and ecological risk assessment of heavy metals in two shooting range backstop soils in Korea were studied. Both soils were highly contaminated with Cd, Cu, Pb, and Sb. The chemical speciation of heavy metals reflected the present status of contamination, which could help in promoting management practices. We-rye soil had a higher proportion of exchangeable and carbonate bound metals and water-extractable Cd and Sb than the Cho-do soil. Bioavailable Pb represented 42 % of the total Pb content in both soils. A significant amount of Sb was found in the two most bioavailable fractions, amounting to ~32 % in the soil samples, in good agreement with the batch leaching test using water. Based on the values of ecological risk indices, both soils showed extremely high potential risk and may represent serious environmental problems.