Five-step Sequential Extraction Procedure Research Articles

Ecotoxicological risks of heavy metals in floodplain sediments: Linking current conditions to future threats

Given increasing concerns about the environmental impact of heavy metal pollution, assessing the level of contamination in floodplain suspended sediments is an important task. Effective environmental management and the preservation of an ecosystem depend on understanding existing pollution levels and potential concerns in the future. For this reason, floodplain-suspended sediments from major industrialized cities in Southeast Nigeria were sampled and analyzed for heavy metal contents. The investigation was conducted to evaluate the immediate and long-term bioavailability and pollution status of heavy metals in receptor organisms. A five-step sequential extraction procedure was adopted to fractionate iron, manganese, copper, zinc, nickel, lead, cadmium, and chromium to determine the geochemical phases in which they were distributed. Generally, the heavy metals were partitioned in the following order: residual >> oxidizable > carbonate > reducible > exchangeable. This indicates that a significant portion of the metals were tightly bound to the soil matrix, rendering them not readily bioavailable to the biota, except over an extended period. The levels of heavy metals, except for lead and cadmium in specific areas, were below the saturation point in terms of their bioavailability. Furthermore, the pollution assessment indices, such as the geo-accumulation index, reflected high levels of cadmium, copper, and lead contamination. This suggests a potential ecotoxicological risk to organisms near the sampling sites. The sites were classified as moderate and high risk in terms of immediate and future risk assessment, respectively. This research has established connections between current conditions and future threats and contributed valuable insights for understanding and mitigating potential environmental hazards. Proper cleaning methods and potential site reclamation are imperative to minimize or contain these heavy metals in stable forms within urban areas to prevent bioaccumulation.

Sequential extraction procedure of municipal solid waste incineration (MSWI) bottom ash targeting grain size and the amorphous fraction

Introduction: Bottom ash (BA) constitutes a significant by-product obtained during the incineration of municipal solid waste in waste-to-energy (WtE) plants. BA is a heterogeneous material made of different fractions, glass, minerals, metals, and unburned residual organic matter. Due to the non-hazardous nature of the unburned material, BA can be effectively recycled, becoming a valuable resource. However, BA displays a high content of potentially toxic elements (PTEs) within its finer grain size. The presence of these elements raises concerns regarding the potential toxicity associated with BA.Materials and methods: The release of PTEs in the smaller fraction (0.063–0.2 mm; 0.3–0.5 mm; 2–4 mm; bulk <4 mm) of BA collected from the Parma WtE plant was investigated using a new five-step sequential extraction procedure (SEP). Through this method, both leached solutions and solid residues were analyzed by inductively coupled plasma-mass spectroscopy (ICP-MS), X-ray powder diffraction (XRPD), and X-ray fluorescence (XRF) analysis. This integrated approach provided valuable insights into the mineralogy, chemical composition, and PTEs leachability of BA.Results and discussion: The novelty of this work is the development of a new SEP protocol specifically designed and planned for an anthropogenic material such as BA. The weight reduction recorded after each step is linked to the progressive disappearance of both crystalline and amorphous phases. Water-soluble phases, such as salts, are the first to react, followed by the carbonate fraction in the second step. At the end of the procedure, only quartz, corundum, and Ti-oxide are identified. Among the PTEs, Pb exhibits the highest release, particularly during the acid attack, followed by Zn. The significant release of Ni during the oxidizing and reducing steps can potentially be linked to hydroxides and metallic alloys, respectively. The integration of XRF and Rietveld refinement results on solid residues enabled the identification of several types of amorphous materials and their chemical evolution during the sequential extraction.

Ecological assessment of soil contamination by heavy metals affected in the past by the lead–zinc mining and processing complex in Kentau, Kazakhstan

Polymetallic ore processing plants are serious sources of heavy metal pollution. The present study examined the degree of pollution of surface soils with the metals zinc, cadmium, lead, and copper in the single-industry town of Kentau, Kazakhstan, where an enterprise for the processing of lead-zinc ore has been operating for a long time. This enterprise ceased operations in 1994, and this study may be of interest in terms of assessing the current ecological state of urban soils after a 27-year period of possible soil self-cleaning processes. The study showed that the surface soils of Kentau retain fairly high concentrations of metals. The maximum detected concentrations of zinc, cadmium, lead, and copper were 592mg/kg, 1.651mg/kg, 462mg/kg, and 82.5mg/kg, respectively. According to the classification of the geoaccumulation index, the soils of the town belong to pollution classes II, III, and IV with moderate and strong pollution. The calculated potential ecological risk factor indicates that cadmium poses a considerable potential ecological risk, while lead showed a moderate ecological risk. In general, according to the obtained values of potential ecological risk factors, metals can be arranged in the following order: Cd > Pb > Zn > Cu. In this study, a five-step sequential extraction procedure by the method of A. Tessier was used, and the mobility factors of metals were calculated. Based on the data obtained, it was found that cadmium and lead have the highest mobility and, consequently, availability for biota in modern conditions, which may pose a potential risk to public health in the town.

RISK ASSESSMENT, LEVELS, SPECIATION AND SEASONAL VARIATION OF HEAVY METALS (Cd and Cu) IN WATER AND PARTICLE SIZES OF SEDIMENTS FROM HUNKI OX-BOW LAKE, AWE LGA, NASARAWA STATE-NIGERIA

This research aimed at assessment of the levels, speciation, risk assessment indices and seasonal variation of heavy metals (Cd and Cu) in water and sediments from Hunki Ox-bow Lake in Awe L.G.A of Nasarawa State, using Atomic Absorption Spectrophotometer (AAS), during the dry and wet seasons. The mean concentration of Cd in water samples of both dry and wet seasons was higher than that of Cu, but Cu was higher than Cd on the whole (raw) sediment samples. The baseline levels of Cd and Cu in water samples (mg/L) were as follows: Cd (0.354) and Cu (0.014), which revealed that Cd level in water was higher than the WHO Guidelines for Drinking Water Quality. The baseline levels of Cd and Cu in sediment samples (mg/kg) were as follows: Cd (7.149) and Cu (8.363) which showed that Cd and Cu were lower than Interim Sediment Quality Guidelines – High of (Cd: 10 and Cu: 270 mg/kg). However, Cd level from sediment was higher than Interim Sediment Quality Guidelines – Low of 1.5 mg/kg but that of Cu was lower (65 mg/kg). Results of the Tessier five-step sequential extraction procedure indicated that Cd was more in the first four steps of the sequential extraction (non-residual) which accounted for 84.64 - 94.52 % in both seasons. Copper dominated more of the organic matter fraction of the sediments (48.17 – 85.54 %) for both dry and wet seasons. The mean of Bioavailability Index (BI) for wet season was relatively higher than that of dry season. The mean values of Mobility Factor (MF) revealed that Cd had higher values than Cu irrespective of seasons. This indicated that Cd was more mobilizable and bioavailable to this aquatic ecosystem compared to Cu. The geo-accumulation Index (I-geo) values of Cd showed practically unpolluted (sites 1, 2 and 5 of dry season), moderately polluted (sites 3 and 4 of dry season), heavily polluted (sites 1, 2, 4 and 5 of wet season) to very heavily polluted (site 3of wet season). The I-geo values of Cu indicated practically unpolluted. In dry season generally, Contamination Factor (Cf) values for Cd were all moderate in dry season. The Cf values of Cd indicated very high contamination factor for wet season, while that of Cu was low in both seasons. In both seasons, the ecological risk index (Er) of Cd in dry season had low to moderate ecological risk, and high to serious ecological risk in wet season. The Er values of Cu were low. This study revealed that: sediments and water samples of the dry season had lower concentration of Cd and Cu than in wet season; concentrations of Cd and Cu from sediments were more of manmade sources rather than natural sources and most ecological risk indices evaluated revealed that Cd had greater ecological risk.

Large extent of mercury stable isotope fractionation in contaminated stream sediments induced by changes of mercury binding forms

Mercury (Hg) release from contaminated legacy sites is a large contributor to riverine ecosystems and can represent a significant local and regional environmental issue even long after the initial site contamination. Understanding processes of in-stream species transformation is therefore important to assess the fate and bioavailability of the released Hg. In this study, we investigated in-stream Hg transformation processes with analyses of Hg binding forms and Hg stable isotopes. Stream sediments were collected downstream of a former kyanization facility (Black Forest, SW Germany), where highly soluble Hg(II)-chloride (HgCl2) was used as an anti-fouling agent to treat timber. Exfiltration of partly anoxic, contaminated groundwater with Hg concentrations of up to 700 μg L−1 into the adjacent Gutach stream is the main source of Hg to sediments. Total Hg concentrations in the stream bottom sediments (<2 mm) ranged from background values of 6.3 µg kg−1 upstream of the contaminated site to 77 mg kg−1 near the location of exfiltration of contaminated groundwater. A five-step sequential extraction procedure and Hg pyrolytic thermal desorption (PTD) analyses indicated changes in Hg binding forms in the sediments along the flow path towards a higher proportion of organically bound Hg. A large shift towards negative δ202Hg values was observed downstream of the contaminated site (change of ≈2‰) along with a minor offset in mass-independent fractionation. Binary mixing models based on Hg isotope ratios using one industrial and different natural background endmembers were tested to estimate their respective contribution of Hg to the sediments but failed to produce plausible allocations. Based on the observed changes in isotopic composition, total Hg concentrations and Hg binding forms, we propose that the large extent of fractionation observed in downstream sediments is the result of a combination of kinetic isotope effects during sorption, redistribution of Hg within the sediment and the preferential transport of Hg associated with the sediment fine fraction. These results highlight the importance of transformation processes when assessing the sources and fate of Hg in environmental systems and show limitations of using simple mixing models based on Hg stable isotopes.

Evaluation of Sequential Extraction Procedure (SEP) to Validate Binding Mechanisms in Soils and Soil-Nano-Calcium Silicate (SNCS) Mixtures

The soils in hazardous waste sites contain heavy metals which would leach into groundwater by various biotic and abiotic processes and eventually pose a threat to human health by contaminating the drinking water. In order to understand pattern of heavy metal leachability, the field conditions can be simulated by adopting various types of sequential extraction methods. In this study, an attempt was made to evaluate the effectiveness and selectivity of a sequential extraction process to determine heavy metal binding mechanisms in soils and soil treated with nano-calcium silicate (NCS). A five-step sequential extraction (SE) procedure was adopted on four soils obtained from a sanitary dumpsite, automobile and battery work units from different localities of Bangalore and a steel plant commissioned at Toranagallu, Bellary, India. The soils were mixed with NCS at varying range of 0.5 to 2% by dry weight of the soil. The NCS-amended soils were spiked with cadmium (Cd2+), nickel (Ni2+) and lead (Pb2+) in concentrations to the tune of 3000 mg/kg. It has been observed that there seems to be a gradual increase in binding ability for the targeted heavy metals when soils were amended with NCS compared to untreated soils. This binding phenomenon was attributed to the presence of exchangeable ions, carbonates, oxides of iron and manganese, organic matter and residual fractions. It was noticed that the residual fractions in soils amended with NCS attenuated maximum quantity of metal ions with Pb2+ at 21.46%, followed by 18.8% for Cd2+ and 9.25% for Ni2+ compared to untreated case. Further, this work highlights the role of residual fraction in enhancing the retention capacity of soils by encapsulation of higher concentrations of contaminants. The current study corroborated the fact that the addition of NCS aids in the better encapsulation of selected heavy metal ions.

Environmental Assessment of Trace Metals in San Simon Bay Sediments (NW Iberian Peninsula)

A gravity core (220 cm depth) was collected to investigate the geochemistry, enrichment, and pollution of trace metals in anoxic sediments from San Simon Bay, an ecosystem of high biological productivity in the northwest of Spain. A five-step sequential extraction procedure was used. The Cu, Pb, and Zn contents decreased with depth, with maximum values in the top layers. Ni and Zn were bound to pyrite fractions, while Cd and Pb were associated with the most mobile fractions. The analyzed metals were associated with the fractions bound to organic matter, mainly with the strongly bound to organic matter fraction. High Cd and Cu values were observed. The fractionation showed a high mobility for Cd (28.3–100%) and Pb (54.0–70.2%). Moreover, the pollution factor and the geoaccumulation index reflected a high contamination for Pb and a moderate contamination for Cu and Zn in the superficial layers, pointing to a possible ecotoxicological risk to organisms in San Simon Bay.

Changes in the total content and speciation patterns of metals in the dredged sediments after ocean dumping: Taiwan continental slope

The aim of this study was to understand the changes in heavy metals and speciation patterns in the dredged sediments after ocean dumping by a five-step sequential extraction procedure. The potential mobility and bioavailability of heavy metals in the sediments were also assessed. The results showed that the average contents of heavy metals, Cu, Zn, Ni, Cd, Cr, and Pb, in the dredged sediment of Kaohsiung Harbor are 120, 403, 33, 0.46, 112, and 40 mg/kg dw, respectively. The Cd and Zn basically bound in the carbonate fractions of the dredged sediments, which accounts for 36% and 45% of their total content on average. The highest level of Cu was present in the organic-matter fraction (92%), Cr and Pb were present in the Fe–Mn oxides fraction (59% and 52%) of the dredged sediments, and the most of Ni (52%) was found in the residual fraction of sediments. Except for Ni, the total amount of all heavy metals in the dredged sediments of Kaohsiung Harbor was about 1.5–4 times higher than the surface sediment of the ocean disposal site. The speciation patterns of heavy metals in the surface sediments of disposal site were similar to those of the reference site, whereas were distinctly different with the dredged sediments. The observation implies that the dredged sediments after dumping in the ocean disposal site, their heavy metals could be diluted by the physical and chemical effects in the marine environment and eventually to the stable state.

Evaluation of Acid Leaching on the Removal of Heavy Metals and Soil Fertility in Contaminated Soil

Heavy metal-contaminated soils were leached with various acid reagents, and a series of treatments was assessed to understand soil fertility after acid leaching. Aqua regia digestion and a five-step sequential extraction procedure were applied to determine heavy metal distribution. The average total concentrations of Zn, Cd, Cu, and Pb for contaminated soil were 1334, 25, 263, and 525 mg·kg−1 based on the ICP/AES quantitative analysis. Other than Pb extracted by H2SO4, over 50% removal efficiency of other heavy metals was achieved. A five-step sequential extraction revealed that the bound-to-carbonate and bound-to-Fe-Mn oxides were the major forms of the heavy metals in the soil. The addition of organic manure considerably promoted soil fertility and increased soil pH after acid leaching. Seed germination experiments demonstrated that after acid leaching, the soil distinctly inhibited plant growth and the addition of manure enhanced seed germination rate from 35% to 84%. Furthermore, the procedure of soil turnover after acid leaching and manure addition greatly increased seed germination rate by 61% and shortened the initial germination time. Seed germination in untreated soil was superior to that in acid-leached soil, illustrating that the phytotoxic effect of acid leaching is more serious than that of heavy metals.

Pollution potential leaching index as a tool to assess water leaching risk of arsenic in excavated urban soils

Leaching of hazardous trace elements from excavated urban soils during construction of cities has received considerable attention in recent years in Japan. A new concept, the pollution potential leaching index (PPLI), was applied to assess the risk of arsenic (As) leaching from excavated soils. Sequential leaching tests (SLT) with two liquid-to-solid (L/S) ratios (10 and 20Lkg−1) were conducted to determine the PPLI values, which represent the critical cumulative L/S ratios at which the average As concentrations in the cumulative leachates are reduced to critical values (10 or 5µgL−1). Two models (a logarithmic function model and an empirical two-site first-order leaching model) were compared to estimate the PPLI values. The fractionations of As before and after SLT were extracted according to a five-step sequential extraction procedure. Ten alkaline excavated soils were obtained from different construction projects in Japan. Although their total As contents were low (from 6.75 to 79.4mgkg−1), the As leaching was not negligible. Different L/S ratios at each step of the SLT had little influence on the cumulative As release or PPLI values. Experimentally determined PPLI values were in agreement with those from model estimations. A five-step SLT with an L/S of 10Lkg−1 at each step, combined with a logarithmic function fitting was suggested for the easy estimation of PPLI. Results of the sequential extraction procedure showed that large portions of more labile As fractions (non-specifically and specifically sorbed fractions) were removed during long-term leaching and so were small, but non-negligible, portions of strongly bound As fractions.

Metal contamination of bed sediments in the Irwell and Upper Mersey catchments, northwest England: exploring the legacy of industry and urban growth

PurposeManchester is often heralded as the first industrial city. Large volumes of physical and liquid contaminants were released into its river network throughout the industrial period up to the latter part of the twentieth century. Water quality has improved dramatically in recent decades, but, given their environmental significance, it is important to ascertain the extent to which a legacy of contamination persists in the modern bed sediments.Materials and methodsFine-grained bed sediments were sampled at 40 sites in the Mersey and Irwell catchments. Sediments were wet sieved to isolate the <63-μm grain size fraction. Metal concentrations were determined using XRF. Particle size characteristics were also measured. Sediments were subjected to a five-step sequential extraction procedure to ascertain the environmental significance of metal concentrations. Alongside archival research of past industry, enrichment factors, multivariate statistical techniques and conditional inferences trees were used to identify sources of heavy metals.Results and discussionBed sediment-associated heavy metal(loid) concentrations were as follows: As (9.89–110 mg kg−1), Cr (76.5–413 mg kg−1), Cu (53.1–383 mg kg−1), Pb (80.4–442 mg kg−1) and Zn (282–1020 mg kg−1). Enrichment factors ranged from moderate to extremely severe, with Pb showing the greatest enrichment across the catchments. Chemical mobility was generally low, but metal(loid) partitioning identified the influence of anthropogenic sources. Statistical analysis highlighted a number of point sources associated with former industrial sites that operated during the industrial period. Conditional inference trees highlighted the role of the textile industry on Cu concentrations in addition to indicating the complexity of sources, fluxes and stores of sediment-associated contamination throughout the system.ConclusionsFine-grained sediment-associated metal(loid)s in the Mersey and Irwell catchments are anthropogenically enriched. Concentrations also exceed sediment quality guidelines. A lack of distinct spatial patterning points to a complex network of contaminant inputs across the catchments, even in the headwaters. Whilst potential modern urban sources are likely to be important, spatial patterns and multivariate/data mining techniques also highlighted the importance of releases from former industrial sites as well as the reworking of historically contaminated floodplains and soils.

Interactions between Cd, Cu, Pb, and Zn and four different mine soils

The chemical associations of Cd, Cu, Pb, and Zn in four mine soil samples from the Amizour-Bejaia Pb/Zn mine (Algeria) have been investigated by a five-step sequential extraction procedure. Although Cd preferentially binds to carbonates, Cu, Pb, and Zn are mainly associated with the organic and reducible fractions. Batch adsorption experiments with either mono- or multi-metallic solutions are described with the Freundlich isotherm model. Whatever the nature of the soil sample, the sorption behavior for each given metal except Pb is very similar, indicating that the binding sites at the soil surface are progressively occupied by the metal from the solution. On each soil sample, the decreasing order of sorption can be established as Pb >> Cu > Cd > Zn. When the four metals are simultaneously applied to each soil sample, their specific behavior is strongly affected by their interactions and/or competition for the available surface sites: we generally observed isotherm curves with a slight maximum before the plateau at higher solution concentration. Although Cu is only slightly affected by the other metals, in the case of Pb, Cd, and Zn, the sorbed amounts strongly decreased.

Chemical speciation of some heavy metals and human health risk assessment in soil around two municipal dumpsites in Sagamu, Ogun state, Nigeria

Environmental and health risk posed by heavy metals from municipal landfill cannot be over emphasized. However, the toxicity and fate of metal in the soil is dependent on its chemical form and therefore quantification of the different forms of metal is more meaningful than the estimation of its total concentration. This study investigated the chemical form and potential hazards of heavy metal pollution at two municipal landfills in Sagamu, Ogun state, Nigeria. Soil samples were collected around the landfills and chemical form of Cu, Zn, Cd, Pb, and Fe were studied, using the Tessier Five-step sequential chemical extraction procedure. The results showed that Cu and Fe were speciated into residual fractions with averages of 23.9 and 31.3% respectively, while Cd and Zn were associated with Carbonate fractions with respective averages of 20.3 and 20.6%. The order of mobility and bioavailability of these metals are: Cd > Pb > Cu > Zn > Fe. A comparison of the result of total extractible metals with standard set by USEPA reveals that Cd and Cu level in the dumpsite soils are far above the critical permissible limit of 3.0 and 250 mg kg−1, respectively which potent a health risk. Assessment of soil pollution level using geoaccumulation index (Igeo) revealed that the landfill was extremely polluted by Cd (Igeo > 5). Pearson correlation and principal component analysis showed that there were no significant correlations (p < 0.05) among all the metals, suggesting that they are all from different anthropogenic sources. The cancer risk ranged from 1.36E−01 to 2.18E−04 and 5.82E−01 to 9.35E−04 for Children and Adult respectively. The level of cancer risk falls above the threshold values (10−4–10−6) which US Environmental Protection Agency considered as unacceptable risk. Based on the above findings, it was suggested that environmental management policy should be implemented to decrease the environmental risks.

Application of ecological risk indicators for the assessment of Greek surficial sediments contaminated by toxic metals.

Τhe present research investigates the partitioning of six selected toxic metals (Ni, Cr, Pb, Zn, Cu, and As) in eight sediment samples; half of them were collected from Elefsis Gulf, and the other half were taken from Koumoundourou Lake, Athens, Greece. Each one of them was treated by applying Tessier's five-step sequential extraction procedure. Regarding gulf sediments, the results indicated that Cu exhibits a strong affinity to the organic matter with percentages ranging from 65 to 78 %. Considerable amount of Zn (32-40 %) is bound to the Fe-Mn fraction and the non-residual fraction, while Cr and Ni are bound to the organic fraction, an observation that suits all toxic metals examined. Regarding lake sediments, Pb is the predominant metal bound to Fe-Mn (48-51 %). It is also noteworthy that the percentage of Zn bound to carbonated fraction (5-15 %), indicating biological availability. In conclusion, the application of several ecological risk indicators demonstrated that Elefsis Gulf sediments correspond to a moderate pollution level, with Pb and Ni being less bioavailable than in the lake's samples, in contrast to Zn which is more bioavailable. Finally, Koumoundourou Lakes' basin is characterized of "low risk."

Distribution and Fractionation of Heavy Metals in Sediments of Karra River, Hetauda, Nepal

A five-step sequential extraction procedure was applied for the determination of the distribution of four elements (Cr, Mn, Fe, and Ni) in sediment of the Karra River. Sediment samples were collected from 16 different sites in the Karra River (upstream, industrial belt, downstream). The distribution of trace metals among exchangeable, carbonate, reducible, oxidizable and residual fractions were determined. The total concentration of metals varies in the range of Cr 72–4339.54 mg kg?1, Mn 22–411.93 mg kg?1, Fe 2967.23-32423.0 mg kg?1 and Ni 31.70-180.74 mg kg?1. The accuracy evaluated by comparing total trace metal concentrations with the sum of the five individual fractions proved to be satisfactory. The chemical speciation of Cr, Mn, Fe, and Ni in most sampling stations were in the order of residual &gt; reducible &gt; oxidazable &gt; carbonate&gt; exchangeable. Fractionation analysis showed that dominant metals are in residual fraction. The highest metal concentrations were observed at the most polluted sites of the industrial belt. High concentration of chromium was found in the Fe-Mn oxide and organic fraction in some of the sites of industrial belt.Journal of Institute of Science and Technology, 2014, 19(2): 123-128

Study of metal mobility and phytotoxicity in bottom sediments that have been influenced by former mining activities in Eastern Slovakia

The aim of this study was to determine the mobility of metals in contaminated sediments in the water reservoir Ružin No.I, which is situated on the Hornad and Hnilec Rivers (Eastern Slovakia). Bottom sediments are contaminated above all by heavy metals, namely As, Cu, Cd, Cr, Hg, Mn and Zn, which were alluvial into the reservoir from localities of former mining activities, and thus they represent ecological load mainly at the inputs into reservoir. The mobilities and solid-state distributions of As, Cd, Cr, Cu, Hg, Ni, Pb, Sb, and Zn ions in impoundment materials were investigated using a five-step sequential extraction procedure. The greatest quantity of Hg was released in the organic–sulfide fraction (F4), in the range of 75.2–87.6 % in both samples. The highest percentage of the total metal content for As, Cr, and Sb was between 82.0 and 94.6 % in the fifth step for both samples also. Cu and Pb were released in the greatest quantities in the third step in the reducible fraction, from 45 to 65.7 % in sample HN and up to 68–50 % in sample HR. High bioavailability was observed for copper, zinc, lead, and cadmium. Nickel, arsenic, antimony, and chromium were only extracted in the residue fraction and displayed low bioavailability. The bioavailability of the metals in the sediments followed the sequence: Cu > Hg > Pb > Cd > Zn > Ni > As > Cr > Sb. The sediment phytotoxicity was evaluated based on the germination of seeds and decreases in the root growth of the plant Sinapis alba. The percentage inhibition of seed germination was 8.9–41.1 % in the 2010–2011 HR samples and 9.1–45.1 % in the 2010–2011 HN samples, which was higher than the inhibition of root growth. In the majority of tested Sinapis alba seeds, the metals displayed no phytotoxic effect. This indicates that the Sinapis alba test still exhibited a strong tolerance to contaminated sediment as this plant species has developed distinct detoxification mechanisms.

Heavy metals fractionation and risk assessment in surface sediments of Qarun and Wadi El-Rayan Lakes, Egypt.

This study establishes a baseline for trace metal speciation in Qarun and Wadi El-Rayan lakes. A five-step sequential extraction procedure was applied for the speciation of the Fe, Mn, Zn, and Cu in sediment samples collected at Qarun and Wadi El-Rayan lakes. Mn and Cu were the most mobile metals, whereas the residue fraction maintained the highest concentrations of Zn and Fe (≈ 60 %). No significant differences in metal concentrations were detected in the sediments of each lake sites, despite of the large distance between them (P > 0.05). Hazardous discharge sources are responsible for the high accumulation of metals in the nonresidual fractions. Qarun Lake showed high mobility factor for all studied metals than Wadi El-Rayan lakes; as such, all the humans, plants, animals and the general biota within the vicinity of this aquatic system are quite vulnerable to the trace metal exposure. According to geoaccumulation index (I-geo), the studied sediments were practically uncontaminated by Fe and Mn and classified as uncontaminated to moderately contaminated with Cu in Qarun and Zn in Wadi El-Rayan lakes. The low values of load pollution index (<1), confirmed the unpolluted condition of the lakes' superficial sediments.

Mineralogy and Mobility Pattern of Trace Metals in Brine Irrigated Dry Disposed Weathered Coal Fly Ash

This study determines mineralogical association of trace elements in the ash core samples and provides insight into various factors that promote their mobility and eventual release into surface and groundwater systems. Fly ash from a power station ash dump in Mpumalanga Province (South Africa) was characterized using X-ray diffraction and X-ray fluorescence. A five-step sequential extraction procedure was used to determined mineralogical association of elements as a function of depth in the ash dump. The dry disposed ash cores are sialic in chemical composition. The mineral peak height as revealed by X-ray diffraction analysis showed variations due to heterogeneity in the ash dump and in homogenous continuous brine irrigation. The sequential extraction results showed that some trace elements are moving in a leaching pathway through the fly ash in the water soluble fraction. Toxic analytes are present in water soluble, exchangeable, and carbonate fractions. Observed Pb concentration maxima in the carbonate fraction of ash cores suggests mobility due to reduction in the pore water pH. A relatively high concentration of As and Se in the exchangeable fraction indicates their possible release when fly ash comes in contact with slightly acidic rain water. This is of major environmental concern for possible contamination of surface and groundwater systems. The relative enrichment of As and Se in the residual fraction suggests that the dust from 8-year-old brine irrigated ash dump would be toxic to human health. This investigative study demonstrates that reduction in pore water pH, inhomogeneity in the ash dump, continuous brine irrigation, leachate from topsoil, moisture content level, ingressed CO2 from atmosphere, and percolating rain water are factors that promote trace metal mobility and leaching in the brine irrigated dry disposed ash dump.

Speciation and bioavailability of mercury in sediments impacted by gold mining in Colombia

Mercury (Hg) speciation and bioavailability were studied in surface sediments affected by artisanal and small-scale gold mining (ASGM) in the Mojana region of Colombia. The results demonstrated higher levels in sampling stations that receive water streams carrying Hg from mining areas. The T-Hg concentrations were slightly elevated with values between 196.2 and 1187.6ngg−1 dry weight (dw) (mean 524.2±256.8ngg−1dw). The MeHg concentrations were significantly correlated with the T-Hg and organic matter (OM) and represent between 1.7% and 3.6% (mean: 2.6%) of the T-Hg. A five-step sequential extraction procedure shown that most of T-Hg in sediments occur primarily as organically bound Hg (Hg-o), which constitutes 48.4% of the T-Hg, followed by elemental Hg fraction (Hg-e) bound to amorphous compounds, such as Fe/Mn oxides with 26.5%, and the fraction bound to sulfur (Hg-s), which constitutes 18.7%. Exchangeable Hg (Hg-w; water-soluble Hg and stomach acid soluble mercury; Hg-h) represents between 1.7% and 4.7%. These fractions constitute a low percentage but exhibit a high level of risk when entering the water column, and they can bioaccumulate in organisms. The significant relationship between OM, T-Hg and MeHg suggests an important role in the control of the distribution, mobility and bioavailability of the Hg in the sediments.

Research on Influences of "A Test of Different Initial pH from the Reaction" with Properties of Environment Materials on Distribution of Arsenic Speciation Arsenic-Ferric Precipitation

The distribution of arsenic speciation can be applied to elucidate the mechanism of removal arsenic during treatment the water containing arsenic with molysite. In this study, the effect of initial pH on the distribution of arsenic speciation in arsenic-ferric precipitation was determined by a five-step sequential extraction procedure. And then further explore the mechanism of arsenic removal with molysite. This experimental results showed that the main mechanisms governing the arsenic removal with ferric chloride were specific adsorption and coprecipitation. Besides, as pH increased from 5 to 9, the arsenic-ferric coprecipitation played a more and more important role in mechanism of arsenic removal with molysite. At the same time, the water soluble state As and the non-specific adsorption As were barely detectable, which suggested that physical absorption had almost no effect on arsenic removal.