Assessment of trace metals contamination in estuarine sediments using a sequential extraction technique and principal component analysis

Equilibrium partitioning approach for metal toxicity assessment in tropical estuarine sediment of Bandon Bay, Thailand

An equilibrium partitioning approach (EqPA) was employed to evaluate the metal toxicity and define sediment quality guidelines (SQGs) for arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), zinc (Zn), and mercury (Hg) in the cockle cultivated areas located in Bandon Bay, Thailand. An assessment of metal toxicity using the [∑SEM]-[AVS] and [∑SEM]-[AVS]/foc models indicated no adverse effect on benthic organisms. The normalized total metal concentrations in this area were below the established SQG values for As, Cd, Cu, Ni, Pb, Zn, and Hg, namely respectively 21.3, 0.8, 84.6, 36.0, 34.6, 440.9 mg/kg dry weight, and 49.3 μg/kg dry weight on sand and calcium carbonate free with 1 % total organic carbon basis, suggesting low metal toxicity. This study provides locality adapted SQG values for supporting sediment quality management specifically in Bandon Bay, potentially serving as a model for other coastal areas.

Bioaccumulation of Potentially Toxic Elements in Commercially Important Food Fish Species from Lower Gangetic Stretch: Food Security and Human Health Risk Assessment

Ganga river is the inhabitant of more than 190 fish species and important river system of India. Potentially toxic elements (PTEs) in the Gangetic riverine ecosystem are a hot environmental issue. A detailed evaluation of PTEs bioaccumulation in Gangetic fishes is required to safeguard human health. The present study investigated the bioaccumulation of PTEs (Cd, Co, Cr, Cu, Li, Ni, Pb, Se, Zn, and Mn) within 12 economic fish species (n = 72) collected from the lower Gangetic stretch. The mean concentrations of PTEs followed the order Zn > Cu > Mn > Ni > Se > Cr > Pb > Co ~ Li > Cd. Li and Se bioaccumulation were studied first time from Gangetic fishes. Results demonstrated that all the selected PTEs were below the maximum permissible limit recommended by reference standards except for Zn in L. catla and L. rohita. For all PTEs, the metal pollution index (MPI), hazard quotient (THQ), and hazard index (HI) were < 1, indicating that these PTEs do not pose a health risk to the public through the dietary intake of fish in this study area. All studied fish were acceptable in terms of carcinogenic risk (CR) from exposure to Cd, Cr, and Pb. Multivariate statistical analysis suggests that inter-correlated metals have similar dispersion properties and bioaccumulation homology within the body. This study provides a scientific basis for food safety assessment and continuous monitoring of PTEs in Gangetic fishes is suggested in the future to safeguard human health.

Source apportionment and source-specific risk assessment of bioavailable metals in river sediments of an anthropogenically influenced watershed in China

Integrated source analysis and risk assessment of metals facilitate the development of targeted risk management strategies. However, previous studies usually addressed total concentration rather than bioavailability, and consequently overestimated metal risk, especially natural source-related risk. In this study, a source-specific risk assessment was conducted by integrating the source analysis of bioavailable metals in surface sediments. Moreover, risk assessment was performed using two bioavailability-based indices: the total availability risk index (TARI) and a modified index of mean probable effect concentration quotients (mPEC-Q). A representative river watershed in eastern China was selected as the study area. Findings revealed that the total concentrations of Pb, Cu, Zn, Cr, and Ni in the sediments were 1.4-2.2 times higher than the local soil background values. Using a modified community bureau of reference (BCR) sequential extraction procedure, the dominant fraction for Pb, Cu, Zn, and Cr in the studied area was found to be the residual fraction, constituting 53.63-62.44% of the total concentrations. This suggested that a significant portion of the metals potentially originated from natural sources. Nevertheless, the concentration enrichment ratio (CER) indicated that anthropogenic sources contributed significantly, accounting for 67.84-87.68% of bioavailable metals. The positive matrix factorization (PMF) model further identified three different sources of bioavailable metals, with a descending concentration contribution sequence of industrial sources (37.61%), mixed traffic and natural sources (33.17%), and agricultural sources (29.22%). Both the TARI and mPEC-Q index values indicated that the bioavailable metals generally posed a moderate risk, and Ni was the priority pollutant. Industrial sources contributed the most to the total risk, although the contribution from TARI-based assessment (37.27%) was lower than that from the mPEC-Q assessment (46.43%). This study provides an example of the consideration of metal bioavailability in the context of source-specific risk assessments to develop more reasonable management strategies.

High resolution dissolved heavy metals in sediment porewater of a small estuary: Distribution, mobilization and migration

Identifying the distribution features, mobilization mechanisms and migration processes of heavy metals (HMs) in estuarine sediments is essential to predict their potential toxicity risk and for following contamination remediation. In this study, high-resolution dialysis (HR-Peeper) and a sequential extraction procedure were employed to determine the porewater dissolved iron (Fe), manganese (Mn), arsenic (As), chromium (Cr), vanadium (V), selenium (Se), molybdenum (Mo), nickel (Ni), zinc (Zn) and their geochemical species fractions in sediments of the Xixi River Estuary, Xiamen, China. The results showed that at estuarine sites with high TOC and TS content, sulfate reduction is the main diagenetic pathway of OC degradation and directly inhibits the reduction of Fe/Mn oxides. The mobility of most HMs in porewater profiles was influenced by multiple factors, such as the adsorption-desorption by Fe/Mn oxides, HM-sulfide co-precipitation, and the degradation of OM under different redox conditions. However, no environmental correlation and control factors of Ni and Zn have been found. In addition, the profile-averaged distribution of most HMs showed a seaward increasing trend, probably due to the severe industrial wastewater discharge and increasing salinity responsible for the competitive adsorption of HM ions. The overall positive fluxes of all HMs, together with the higher positive diffusion fluxes of some HMs such as Mn, Cr, V and Zn, suggest that the HMs mobility in small estuarine sediments should be seriously reconsidered due to its high contamination potential.

Characterization of Heavy Metal Fractions in the Soil Developed on Volcanic Rocks of Karadağ Mountain, Turkey by Sequential Extraction

In this work, soil samples were taken from 15 different sites and the contents of Cd, Cr, Cu, Ni, Pb, and Zn in the mobile and residual fractions of the soils formed from the volcanic materials were determined by the sequential extraction procedure. The mobility of each metal was revealed by analysing fractions. The order of heavy metals in each fraction of Karadağ samples was:Cd: Acid and Water Soluble > Reducible > Oxidizable > Residual; Cr: Residual > Oxidizable > Reducible > Acid and Water Soluble; Cu: Residual > Oxidizable > Reducible > Acid and Water Soluble; Ni: Residual > Reducible > Oxidizable > Acid and Water Soluble; Pb: Reducible > Residual > Oxidizable > Acid and Water Soluble; Zn: Residual > Reducible > Oxidizable > Acid and Water Soluble.According to the results, while the concentrations of Cd and Pb in the mobile fraction were higher than those in the residual fraction, Cr, Cu, Ni and Zn were higher in the immobile fraction. When the higher mobility levels of Cd and Pb are evaluated in terms of environmental pollution and toxicity in soil, these metals have been found to have a higher potential risk than other metals.Cd and Pb are likely to be in close contact with plant roots and thus could potentially affect soil fertility. To avoid threats to productivity and food security in the long term, further trace metal inputs to soils in these areas should be avoided by agricultural management or other means.

Receptor model-based source apportionment and ecological risk assessment of metals in sediment of river Ganga, India

Ganga river surface sediment was sampled from 11 locations, which revealed average concentrations (mg/kg) of metals in the order Mn (296.93) > Zn (61.94) > Cr (54.82) > Cu (30.19) > Pb (24.42) > Cd (0.36). Sediment quality guidelines showed metals rarely to occasionally exhibit adverse biological effects. Indices like potential ecological risk, contamination security index, hazard quotients, multiple probable effect concentrations quality, mean probable effects level quotients, mean effects range median quotient suggest nil to a very low level of pollution with low ecological risk. Contamination factor, geo accumulation index, enrichment factor, quantification of contamination revealed that Pb and Cd originated from anthropogenic activities. APCS-MLR model revealed that metals contributed from natural sources (Zn, Mn, Cr; 20.18 %), industrial-agricultural (Cd; 21.35 %); and discharge of paints, Pb batteries, fossil fuel (Pb; 8.49 %). Present findings will serve as an effective guideline for managing and ameliorating pollution in the river system.

Metal speciation in sediments and bioaccumulation in edible bivalves to assess metal toxicity in a sand mining impacted tropical (Aghanashini) estuary, southern India

The study aims to understand the metal toxicity through the relationship between bioavailability in sediments and bioaccumulation in edible bivalves in an estuary subjected to extensive sand mining. The higher deposition of total Fe, Mn, Ni and Zn in the middle region (core M) was ascribed to estuarine processes and proximity to anthropogenic sources. EF revealed moderate to severe enrichment of Ni and Cu in sediments. Igeo showed moderate degree of pollution from Co, moderate to strong pollution from Ni and strong to extreme level of pollution from Cu. In core N, the average bioavailable concentration of Fe, Mn, Zn, Cu, Co and Ni was 1.76 %, 43.18 %, 59.14 %, 62.11 %, 60.42 % and 27.33 % respectively. The average bioavailable concentration of Fe (61.23 %), Mn (56.87 %), Cu (67.98 %), Co (69.77 %) and Ni (40.99 %) was higher in the core M as compared to core N except for Zn (56.98 %). The significant (>25.00 %) proportion of metals in bioavailable fractions in cores N and M construed their non-natural sources. Metal speciation study indicated bioavailability to fauna that likely to enhance by extensive sand mining. The level of Fe, Mn, Zn, Cu and Ni in Saccostrea cucullate, Meretrix casta and Villorita cyprinoides revealed toxicity to bivalves and probably to humans.

Distribution, bioavailability, and ecological risk assessment of potentially toxic heavy metals in El-Burullus Lake sediments, Egypt

El-Burullus Lake is the second largest coastal lagoon in Egypt in addition to its connection to the Mediterranean Sea. In this study, geochemical fractionations of heavy metals (Fe, Pb, Cd, Cu, Cr and Zn) were investigated after the great efforts made to rehabilitate and restore the lake by the Egyptian Government. The results indicated that F4 (residual fraction) was the dominant fraction for all studied metals followed by F3 (oxidizable fraction). That means the majority of studied metals source in the lake is lithogenic. Contamination by each individual heavy metal or multi elements was low according to individual contamination factor (ICF) and global contamination factor (GCF). Risk assessment code (RAC) classification showed that Cd and Cu exhibited low risk, Zn was of moderate risk, whereas, other metals are safe. The toxicity calculated by toxic risk index (TRI) indicating that no toxic risk was expected in the Lake.

Sequential extraction of selected metals to assess their mobility, pollution status and health risk in roadside soil

Assessment of the mobility and contamination of trace metals in the roadside soil is important to explore the environmental quality and potential risks to the public health. The contents of selected metals (Ca, Mg, Sr, K, Na, Li, Fe, Mn, Zn, Cu, Ag, Co, Ni, Cr, Cd and Pb) in the roadside soil collected from major highways/roadsides of Lahore, Pakistan were quantified employing mBCR sequential extraction. Among the metals, Ca, Sr and Na showed highest contribution in exchangeable fraction, Pb in the reducible fraction and K, Li, Fe, Ag, Ni, Cu and Cr in the residual fraction. However, Mg and Mn exhibited relatively higher contents in exchangeable and residual fractions while Cd, Co and Zn showed relatively higher concentration in all four fractions. Comparatively higher mobility and availability in the soil was shown by Ca followed by Sr, Pb, Na, Cd, Zn, Co, Mn, Cu, Ag and Ni. Principal component analysis demonstrated considerable anthropogenic contributions of the trace metals in the roadside soil. The pollution indices showed that the soil was heavily to extremely polluted by Cd and Ag, followed by significant to very high contamination for Co, Ni and Pb. The modified degree of contamination (4.60 and 3.99 in summer and winter, respectively) revealed an overall high degree of contamination. The health risk assessment revealed that the calculated risks were within the safe limit thereby indicating insignificant non-carcinogenic and carcinogenic heath risk to the populace.

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.

Pollution status and risk assessment of heavy metals in the sediment of a historically contaminated lake treated by oxidation pond in China

Sediment plays an important role in controlling biogeochemical cycling of heavy metals in aquatic environment. The Ya-Er Lake is a typical lake which was historically contaminated by heavy metals in Hubei province, China. After industries surrounding the Ya-Er Lake being shut down, oxidation pond treatment and dredging program were conducted for pollution management since 1970s. To date, the Ya-Er Lake has been used for aquaculture for several decades. However, the status of heavy metal levels and ecological risks in this lake remains unclear. Herein, concentrations, chemical fractions, and risk assessment of heavy metals were investigated in the Ya-Er Lake sediment. Results showed that concentrations of heavy metals in the Ya-Er Lake sediment were higher than other reported lake systems, suggesting that heavy metal pollution in the Ya-Er Lake is still serious. Relatively higher proportions of carbonates bound form of Cd and Ni indicated high-risk potential of these two heavy metals, and Cd and Ni should be listed as the primary heavy metal pollutants in the Ya-Er Lake according to the results of potential ecological risk index (PERI) and sediment quality guidelines (SQGs). The risk assessment code (RAC) analysis showed that Ni and Cd poses higher bioavailability and mitigation potential, and may affect the Ya-Er Lake ecosystem and downstream aquatic environment. These findings reflected that oxidation pond treatment and dredging sediment to near place are not effective to control heavy metal pollution, and a long-term ecological risk is still posed to surrounding aquatic environment. Our study provides scientific basis on pollution control and management in aquatic system contaminated by heavy metals.

Geochemistry of trace metals in surface sediments from the continental slope of the states of Sergipe and Alagoas, Northeastern Brazil

Geochemical analyses were used to determine the origin and identify the main factors that lead to the metal trace distribution on the surface sediments from the continental slope of Sergipe in Brazil. Sediment samples were collected during the dry and rainy periods, from 36 sampling points distributed at water depths from 400 to 3000 m. In general, no effect of seasonality was observed on the metal concentrations and no significant differences were observed between the depth ranges. The correlation analysis indicated the continental origin as the most predominant, followed by authigenic deposition. Anthropogenic enrichment was not noted, nor was the possibility of adverse aquatic biota effects. The results made it possible to understand the contribution of rivers in the transport and transfer of particulate matter to the coastal region, in addition to providing new information on the content of trace metals in tropical Atlantic sediments.

Submerged zone and vegetation drive distribution of heavy metal fractions and microbial community structure: Insights into stormwater biofiltration system

Biofiltration system is a widely used stormwater treatment option that is effective in removing heavy metals. The concentration and distribution of heavy metal fractions in biofiltration filter media, as well as the microbiota composition affected by the design parameters, are relatively novel concepts that require further research. A laboratory-scale column study was conducted to investigate the microbial community and the fractionation of heavy metals (Pb, Cu, Cr, and Cd) extracted from filter media samples, subjected to the presence of vegetation, submerged zone (SZ), and major environmental parameters (pH, water content). Sequential extractions revealed that, compared to the three other fractions (exchangeable fraction, reducible fraction, and oxidizable fraction), the residual fraction was the most represented for each metal (41 - 82 %). As a result, vegetation was found to reduce pH value, and significantly decrease the concentration of the exchangeable fraction of Pb in the middle layer, and the oxidizable fraction of Pb, Cu, Cd, and Cr in the middle and bottom layers (p < 0.05). The formation of an anoxic environment by submerged zone settlements resulted in a significant decrease in the concentration of reducible fractions and a significant increase in the concentration of oxidizable fractions for four heavy metals (p < 0.05). In addition, the analysis of the microbiota showed that the diversity and richness of microorganisms increased in the presence of SZ and plants. The dominant phylum in biofiltration was Proteobacteria, followed by Firmicutes, Bacteroidetes, Acidobacteria, and Actinobacteria as major phyla. Heavy metal fractions could regulate the structure of microbial communities in biofiltration. The findings of this study would enrich our understanding of the improvement of multi-metal-contaminated runoff treatment and highlight the impact of design parameters and heavy metal fractionation on microbial community structure in the biofiltration system.

Speciation and risk assessment of Zn, Pb, and Cd in bottom sediments of two small upland dam reservoirs, Poland

Sediments of two small dam reservoirs in Poland, Zalew Zemborzycki (ZZ) and Brody Iłżeckie (BI), were studied. Sediments from both reservoirs were sampled at 17 sites in the transects perpendicular to the shoreline, at the river inflow and the frontal dam and analysed using the BCR procedure for speciation of zinc (Zn), lead (Pb) and cadmium (Cd). The risk assessment code (RAC) and the individual contamination factor (ICF) were determined. In BI, the sediments were removed from the considerable part of the reservoir, creating an opportunity to study the effect of dredging on the speciation of trace metals. Trace metals partitioning was differentiated according to the transect/site and in the case of BI sediments also on the transect location in the dredged or undredged part of the reservoir. Considering ZZ sediments, the order of fractions for Zn, Pb and Cd according to a decreasing overall mean percentage contribution to total metal content was the same: F4 (residual) >F3 (oxidisable) >F2 (reducible) >F1 (acid soluble). In sediments of ZZ at most sites, the RAC for Zn, Pb and Cd revealed low or medium risk and ICF low or moderate contamination. For BI sediments, the order of fractions for Pb was similar while for Zn and Cd quite the opposite compared to the sediments of ZZ and it was: Pb-F4>F3>F1>F2, Zn-F1>F3>F2>F4, Cd-F1>F2>F3>F4. For BI sediments, RAC values for Zn, on average, indicated high and very high ecological risk; for Pb low and moderate risk and for Cd - high risk in the initial part and dredged part and according to the average value in the reservoir, while a medium risk in undredged part sediments. The ICF index showed high contamination with Cd for all BI sediments. The sequential analysis showed that Pb is poorly mobile as in sediments of both reservoirs residual fractions accounted, on average, for about 60% of the total content.

Contamination and ecological risk assessment of heavy metals, and relationship with organic matter sources in surface sediments of the Cross River Estuary and nearshore areas

Chemical speciation of heavy metals (Zn, Pb, Cu, and Cd) was studied to evaluate the contamination status and associated risks and to constrain the sources of heavy metals in relation to sedimentary organic matter (OM) sources in surface sediments of the Cross River Estuary (CRE) and nearshore areas surrounded by a degrading mangrove ecosystem (typical C₃ plants). The contamination factor (CF) and geo-accumulation (I_geo) indicated that Cd and Zn were the most polluted heavy metals. High percentages of Zn (63.78%), Pb (64.48%), Cd (76.72%) and the considerable amount of Cu (48.57%) in non-residual fractions indicated that these heavy metals are bioavailable. Cd showed moderate to high ecological and bioavailability risk based on the ecological risk (E_r) and risk assessment code (RAC). Significant positive correlations occurred among the heavy metals, fine-grained sediments, and sedimentary OM from terrestrial C₃ sources. These correlations, together with high percentages of heavy metals in the oxidizable fraction (~33-50%), indicated that the erosive washout of OM and fine sediments ladened with heavy metals from the adjoining degraded mangrove ecosystem contributed significantly to the increased contents of heavy metals in surface sediments of the study area.

Bioavailability of chromium, nickel, iron and manganese in relation to their speciation in coastal sediments downstream of ultramafic catchments: A case study in New Caledonia

Coastal sediments downstream of ultramafic catchments can show Ni and Cr concentration well above sediment quality guidelines. Despite their potential ecological impact, the bioavailability of these trace metals in such sedimentary settings has been poorly investigated. In this study, we tried to fill this gap by performing kinetic EDTA-extractions across a shore-to-reef gradient in lagoon sediments downstream of an ultramafic catchment in New Caledonia and interpreting the results in regard of synchrotron-derived speciation. Measured bioavailability ranged from very low for Cr (below 1% of total Cr) to medium for Ni (below 5% of total Ni). Both trace metals showed a decreasing shore-to-reef bioavailability gradient reflecting the larger deposition of ultramafic sediments close to the shore. According to synchrotron-derived speciation data, the very low bioavailability of Cr is attributed to its major occurrence as Cr(III)-bearing Fe-(oxyhydr)oxides and phyllosilicates, with no evidence of Cr(VI). Considering the low occurrence of Fe-sulfides, the medium bioavailability of Ni is considered to arise mainly from the reductive dissolution of Ni-bearing Fe-(oxyhydr)oxides during early diagenesis. This reaction also explains the medium bioavailability of Fe (up to 15% of total Fe) and the positive correlation observed with Total Organic Carbon (TOC). In this regard, this latter parameter appears as a major driver of Ni and Fe bioavailability in coastal sediments downstream of ultramafic catchments. On the opposite, in the absence of Mn-oxides, TOC has no influence on Mn bioavailability (up to 30% of total Mn) that appears more likely driven by sediment sources. From an ecological point of view, considering the Australian and New-Zealand High Interim Sediment Quality Guidelines (ANZ-ISQG-H), Cr should not represent a significant risk towards benthic communities in coastal sediments downstream of ultramafic catchments. On the opposite, Ni, Fe and Mn might represent an ecological risk that should be further investigated in such sedimentary settings.

Combining single and complex indices of pollution with grain size trend analysis of surficial sediments in Edremit Gulf, western Turkey

Pollution risk assessment of heavy metals (Pb, Cr, Cu, Ni, Zn, As) in sediment samples from 68 locations in the Gulf of Edremit, western Turkey, was performed using single and complex indices of pollution assessment approaches. The pollution indices used in the sediment analyses included pollution load index, contamination factor, contamination degree for individual metals, geoaccumulation index (Igeo), enrichment factors, toxic risk index, modified pollution index, frequency of adverse biological effects (TEL-PEL), percent incidence of biological effects (ERL-ERM), and total risk quotients. Results indicated a low degree of contamination for the entire surveyed area except moderate contamination factor for arsenic using single indices. Enrichment factors and geoaccumulation indices indicated moderate to significant enrichment and uncontaminated to moderately contaminated both for arsenic (As) and lead (Pb), respectively. According to the results of ecological risk assessment based on TELs and PELs, the adverse biological effects of heavy metals on aquatic organisms; are for As, Cr, Ni frequently, Cu and Pb occasionally, and Zn rare. The toxic risk index values displayed low to considerably toxic risk for the entire Gulf and calculated toxic risk index results showed that arsenic accounted for most of the entire sediment toxicity. Transport patterns of sediment grain size trend analyses were correlated with the results of pollution assessment models. Transport trends are compatible with the sources of lithogenic, anthropogenic, mining activities and wastewater treatment/geothermal originated arsenic.

Metal enrichment in sediments and bioaccumulation in edible bivalve Saccostrea cucullata from mudflats of a tropical estuary, India: a study to investigate toxicity and consumption suitability

Mudflat sediment cores from lower (C-1), middle (C-2), and lower regions of upper (C-3) Chapora Estuary were investigated for grain size composition, total organic carbon, total and bioavailable Fe, Mn, Cu, Co, Ni, and Zn to assess metal contamination. Accumulation of metals by Saccostrea cucullata was studied to understand metal toxicity. In core C-1, Fe, Mn, Cu, Co, Ni, and Zn showed an average concentration of 1.73%, 648 ppm, 12 ppm, 12 ppm, 16 ppm, and 25 ppm, respectively, while core C-2 revealed their average concentration as 1.34%, 709 ppm, 10 ppm, 11 ppm, 13 ppm, and 28 ppm respectively. In core C-3, an average concentration of Fe, Mn, Cu, Co, Ni, and Zn was 1.72%, 907 ppm, 14 ppm, 13 ppm, 18 ppm, and 31 ppm respectively. Metals in sediments varied within the estuary due to hydrodynamics, discrepancies in metal sources and sand mining-induced remobilization of metals. Correlation and principal component analysis revealed Fe oxides as the key regulator of trace metal distribution in sediments along with clay and total organic carbon. Enrichment factor (EF) and geo-accumulation index (I_geo) showed more or less moderate contamination of Mn in core C-3. Also, the potential contamination index (PCI) indicated moderate contamination of Mn in core C-3 using the shale value as background concentration, whereas the application of upper crustal value revealed moderate contamination of Fe, Mn, Cu, Co, and Ni in core C-1, Mn, Co, and Ni in core C-2 and of Cu, Co, and Ni in core C-3. Mn was severely to very severely contaminated in core C-3. The mean probable effect level quotient and mean effect range median quotient showed medium to low-level contamination of Cu, Ni, and Zn. Metals were considerably allied to Fe-Mn oxide and organic/sulphide fractions which revealed their bioavailability. Mn was 36% in labile form (lower estuary) and indicated a high risk to biota. Mn, Ni, and Zn in Saccostrea cucullata exceeded the permissible limit and suggested toxicity and non-suitability for human consumption.

Characteristics, source apportionment and health risk assessment of heavy metals in urban road dust of the Pearl River Delta, South China

To investigate the characteristics of heavy metals (As, Cd, Cr, Cu, Pb, Hg, Ni and Zn) in urban road dust from different cities and functional areas in the Pearl River Delta (PRD), South China, a total of 294 dust samples were analyzed. The contamination characteristics and health risk of heavy metals in the dust were assessed, their chemical speciation were distinguished, and their sources were identified by the correlations, cluster and principal component analysis (PCA). The mean concentrations of As (15.89 mg/kg), Cd (1.59 mg/kg), Cr (143.75 mg/kg), Cu (184.42 mg/kg), Pb (114.82 mg/kg), Hg (0.11 mg/kg), Ni (41.53 mg/kg) and Zn (645.94 mg/kg) in urban road dust were in high or moderate levels compare with other previous researches. In this case, the contamination of Cr, Cu, Ni and Zn in the industrial area (IA) and the contamination of Cd and Hg in the commercial area (CA) were significantly higher relative to other functional areas (P < 0.05), and the contamination of heavy metals in Foshan City was significantly higher than other cities (P < 0.01). The order of mobility of the heavy metals with higher concentration in urban road dust of the Pearl River Delta declined in the following order: Zn, Ni, Cu, Pb and Cr. Statistical analysis result showed the contaminated heavy metals in urban road dust were mainly contributed by industrial activities, traffic activities and building pollution. There were no significant carcinogenic and noncarcinogenic risks for adults, children however showed significant noncarcinogenic effect caused by As and Cr in partial points, albeit with low contamination level of the two metals. The ingestion was a principal pathway for heavy metals via urban road dust to exposure population. More protection measures should be considered to reduce children's exposure to the dust, especially in the CA and IA.

Assessing long-term performance of stabilized Zn-contaminated dredged sediment slurry treated with the PHDVPSS method

Solidification/stabilization (S/S) has been widely used for effective treatment of dredged sediment (DS) for many years, with the objective of improving the mechanical properties of DS through the addition of inorganic cementitious materials. Most previous studies have reported the short-term performance of S/S. However, long-term effectiveness is critical, as contaminants remain underground and are subjected to a variety of environmental stresses that can degrade S/S materials. In this regard, this experimental work investigated the long-term efficacy of solidification/stabilization of dredged contaminated sediments (DCS) treated with a new integrated method, namely PHDVPSS, which uses a prefabricated horizontal drain (PHD) assisted by vacuum pressure (VP) as well as solidification/stabilization. The DCS were treated with Portland cement (PC) as binder in the PHDVPSS method (abbreviated as VP-PC) at different zinc (Zn) concentration levels and compared with the traditional cement-based solidification/stabilization method (abbreviated as SS-PC). A series of experimental tests such as unconfined compressive strength (UCS), toxicity characteristics leaching procedure (TCLP), X-ray diffraction (XRD) and scanning electron microscopy in conjunction with energy-dispersive spectroscopy (SEM-EDS) were performed to assess the long-term strength, leaching and microstructural characteristics of high-water-content DCS, respectively. The UCS test results indicated that the strength of VP-PC mixes increased significantly with curing time compared to the limited strength development of SS-PC mixes. After 180-day curing, VP-PC mixes exhibited 3.5-5.5 times higher UCS values than the SS-PC mixes. Furthermore, when compared to the SS-PC mixes, the VP-PC mixes had 14.7-36.4% lower leached Zn concentrations at different Zn levels. This is attributed to an increase in the least reactive F4 (residual) fraction and a decrease in the most mobile F1 (acid-soluble) fraction as confirmed by the BCR method. Microstructural tests including XRD and SEM-EDS revealed that calcium silicate hydrate-like compounds were identified as the main hydration products of both the VP-PC and SS-PC mixes. However, portlandite, a major hydration product of PC, was not detected in either case, which is attributed to the retardant effect of Zn on cement hydration. Overall, the experimental results showed that the PHDVPSS method, when compared to the conventional solidification/stabilization method, is a viable choice for treating high-water-content DCS at different Zn concentration levels with low cement content.

Assessment of role of rhizosphere process in bioaccumulation of heavy metals in fine nutritive roots of riparian mangrove species in river Hooghly: Implications to global anthropogenic environmental changes

Biota of coastal estuarine habitats of tropics and subtropics are extremely vulnerable. In the study, we have investigated the role of rhizosphere process in bio-accumulation of heavy metals in fine nutritive roots of riparian mangroves at eleven sampling locations of river Hooghly. The rhizospheric sediment of river Hooghly was accumulating HMs due to the presence of organic content and anthropogenic inputs. The mean EF (2.03-8.3), Igeo (-2.27-0.71), and CF (0.62-2.53) values signifies the enrichment of HMs in sediment fine fraction (<62.5 μm) whereas, the mean PLI (0.83 to 1.18) indicates gradual environmental degradation of river Hooghly. Low BCF observed in the river Hooghly might be due to barrier to hypodermal structures and/or any prevailing mechanism of saturation of HMs. However, BCF > 1 for Al, Cu, Cr, Mn, and Zn, signifies the phyto-remediation potential of riparian mangroves to mitigate amplified global anthropogenic environmental changes.

Occurrence, spatial distribution and ecological risk assessment of trace elements in surface sediments of rivers and coastal areas of the East Coast of Bangladesh, North-East Bay of Bengal

Coastal and estuarine ecosystems provide habitats for many organisms. Recently, the estuaries and coastal areas of the East Coast of Bangladesh have become heavily contaminated due to dumping of untreated wastewater into the rivers from a number of different industries. The current study analyzes potentially toxic elements contamination in surface sediments of the Karnaphuli, Sangu, Bakkhali and Naf Rivers, Kutubdia and Moheshkhali Channel, and St. Martin's Island, and assesses the consequent ecological risks. The pollution load index (PLI), geoaccumulation index (I_geo) and potential ecological risk (PER) indices show that the contaminated sediments have negative effects on the aquatic environments. The PLI values ranged between 0.45 and 1.67, which suggests the severity of trace-element contamination. The mean I_geo values showed the sediments range from uncontaminated to heavily contaminated state. The Enrichment Factor (EF) values suggested that the sediments were contaminated by anthropogenic sources, and PER values demonstrate that sites at Sangu, Naf and St Martin's Island are less contaminated compared to sites at Karnaphuli, Bakkhali, Kutubdia and Moheshkhali. Overall, results showed that Karnaphuli river is the most contaminated and St Martin's Island is the least based on the spatial distribution of PLI, C_d, PER and ∑TUs of trace metals in surface sediments. Comparing with the neighboring countries, the concentrations of Cd and Pb were found to be higher while Cr is lower in the East Coast of Bangladesh than the estuarine and coastal waters of the Bay of Bengal rim countries. The present study reveals that the lack of water quality guidelines in Bangladesh for the coastal, estuarine and marine water escalated the dumping of untreated wastewater. Immediate measures need to be taken to address the ecological risks so that an effective management program can be undertaken. A systematic approach for collecting pollutant data and use of isotopes to trace anthropogenic sources of contamination is recommended for pollutants like toxic metals, pesticides and other contaminants in sediment and aquatic products in the entire coastal waters of the Bay of Bengal.

Assessing heavy metals in surface sediments of the Seomjin River Basin, South Korea, by statistical and geochemical analysis

We investigated particle size distribution and heavy metal concentrations in surface sediments of streams and lakes in the Seomjin River Basin by comparison with Sediment Quality Guidelines (SQGs). Origins were identified using statistical and geochemical approaches. Sand was prevalent in mean particle size of surface sediments (except lakes). Mean concentrations of Pb, Zn, Cd, and Hg were similar for the Seomjin and Boseong rivers, while those of Cu, As, Cr, and Ni were approximately 1.5-2.0 times higher in the Boseong. SQGs revealed no serious pollution in the basin's site concentrations, although As and Ni levels in the Boseong had some potential for benthos toxicity. Correlation and principal component/factor analysis showed that concentrations of Cu, As, Cr, and Ni were dominant from geological origins rather than anthropogenic. The reducible fraction bound to Fe and Mn-oxides was prevalent in Pb, while the water- and acid-soluble fractions were easily exchangeable or bound to high Cd carbonates. The fraction bound to the highest lattice in residual prevailed in Zn, Cu, Cr, and Ni, accounting for 64%, 65%, 87%, and 86%, respectively. Similarly, results indicated geological origins. Risk assessment to benthos based on labile fractions (F1 + F2 + F3) were Cd (72%) < Pb (66%) < Zn (36%) ≈ Cu (35%) < Ni (14%) ≈ Cr (13%). While Cd and Pb showed the highest risk, their concentrations were relatively lower. However, Cr and Ni showed the highest concentrations but low risk levels, suggesting their pollution is unlikely to have adverse effects on benthos.

Metallic contamination of global river sediments and latest developments for their remediation

This review article represents the comparative study of heavy metal concentration in water and sediments of 43 important global rivers. The review is a solitary effort in the area of heavy metal contamination of river-sediments during last ten years. The interpretation of heavy metal contamination in sediments has been verified with different indices, factors, codes and reference guidelines, which is based on geochemical data linked to background value of metals. It is observed that health hazards arise due to dynamics of movement of metals between water and sediments, which is primarily influenced by several factors such as physical, chemical, biological, hydrological and environmental. Also, the reason behind accumulation and assimilation of heavy metals on river water system is explained with appropriate mechanisms. Several factors e.g. pH, ORP, organic matter etc. are mainly involved in the distribution, accumulation and assimilation of metals in the sediment phase to water phase. Remediation technologies such as in-situ and ex-situ have been discussed for the removal of heavy metals from contaminated sediments. We have also compared the performance efficiencies of the technologies adopted by different researchers during the period 2003 to 2019 for the removal of metal bound sediments. Many researchers have preferred in-situ over ex-situ remediation due to low cost and time saving remediation effects. In this work we have also incorporated the safety measures and strategies which can prevent the metal accumulation in sediments of river system.

Assessment of bottom sediment quality in Niterói harbor (Brazil, South America) through ecological indexes concerning nutrients and trace metals

Bottom sediment quality from the Niterói harbor at Guanabara Bay (Rio de Janeiro, Brazil) was evaluated based on concentrations of organic phosphorus (OP) and inorganic phosphorus (IP) and bioavailability of trace metals through BCR fractionation analysis (Zn, Cu, Pb, Cr, Ni, Cd). The study area revealed elevated concentrations of fine sediments and organic matter (TOC: 2.26-7.31%). OP presented extremely elevated concentrations between 0.57 and 47.04 μmol/g, whereas IP reached a maximum concentration of 4.99 μmol/g. The anoxic bottom at the study area was confirmed by high TOC/OP values in most stations. Phosphorus enrichment index (PEI) varied between 0.07 and 2.57, pointing to ecological risk at some stations. Trace metals were mostly bonded to the bioavailable fractions (exchangeable, reducible, oxidizable), and decreasing order of mobility was Zn > Cu > Pb > Cr > Ni > Cd. The Risk Assessment Code (RAC) suggested a high risk of bioavailability for Zinc and a medium risk for the other metals. Overall, the Niterói harbor revealed poor sediment quality suggesting a strong anthropogenic pressure in the area.

Occurrence, distribution, and pollution indices of potentially toxic elements within the bed sediments of the riverine system in Pakistan

Potentially toxic elements (PTEs) are a major source of pollution due to their toxicity, persistence, and bio-accumulating nature in riverine bed sediments. The sediment, as the largest storage and source of PTEs, plays an important role in transformation of mercury (Hg), lead (Pb), nickel (Ni), chromium (Cr), copper (Cu), zinc (Zn), and other toxic PTEs. Several important industrial hubs that contain a large population along the banks of different rivers, such as Kabul, Sutlej, Ravi, Jhelum, and Chenab in Pakistan, are acting as major sources of PTEs. In this study, 150 bed sediment samples (n=30 from each river) were collected from different sites. Total (acid extracted) PTE (Hg, Cu, Cr, Ni, Zn, and Pb) concentrations in bed sediments were determined using inductively coupled plasma mass spectrometry (ICP-MS). Sediment pollution indices were calculated in the major rivers of Pakistan. The results demonstrated high levels of Hg and Ni concentrations which exceeded the guideline standards of river authorities in the world. The contamination factor (CF) and contamination degree (CD) indices for Hg, Ni, and Pb showed a moderate to high (CF≥6 and CD≥24) contamination level in all the selected rivers. The values of geo-accumulation index (I_geo) were also high (I_geo≥5) for Hg and Pb and heavily polluted for Ni, while Cr, Cu, and Zn showed low to unpolluted (I_geo) values. Similarly, the enrichment factor (EF) values were moderately severe (5≤EF≤10) for Hg, Pb, and Ni in Sutlej, Ravi, and Jhelum, and severe (10≤EF≤25) in Kabul and Jhelum. Moreover, Hg and Ni showed severe to very severe enrichment in all the sampling sites. The ecological risk index (ERI) values represented considerable, moderate, and low risks, respectively, for Hg (The ERI value should not be bold. Please unbold the  ERI in the whole paper. It should be same like RI, CD and EF. [Formula: see text]≥160), Pb and Ni (40≤[Formula: see text]≤80), and Cr, Cu, and Zn ([Formula: see text]≤40). Similarly, potential ecological risk index (PERI) values posed considerable (300≤RI≤600) risk in Ravi and moderate (150≤RI≤300) in Kabul and Jhelum, but low (RI≤150) risk in Ravi and Chenab. On the basis of the abovementioned results, it is concluded that bed sediment pollution can be dangerous for both ecological resources and human beings. Therefore, PTE contamination should be regularly monitored and a cost-effective and environmentally friendly wastewater treatment plant should be installed to ensure removal of PTEs before the discharge of effluents into the freshwater ecosystems.

Chemical Fractionation, Environmental, and Human Health Risk Assessment of Potentially Toxic Elements in Soil of Industrialised Urban Areas in Serbia

The primary focus of this research was the chemical fractionation of potentially toxic elements (PTEs) and their presence in several industrialised cities in Serbia. Furthermore, their origin, contamination levels, and environmental and human health risks were assessed. The results indicated that the examined soils were characterised by slightly higher Cu, Ni, Pb, and Zn levels than those set by European and national regulations. These elevated Cu, Pb, and Zn concentrations were caused by intensive traffic and proximity to industry, whereas the higher Ni levels were a result of the specific geological substrate of the soil in the study area. The environmental risk was found to be low and there was no enrichment/contamination of the soil with these elements, except in the case of Pb, for which moderate to significant enrichment was found. Lead also poses a potential non-carcinogenic risk to children through ingestion and requires special attention due to the fact that a significant proportion of this element was present in the tested soil samples in a potentially available form. Analysis of the health risks showed that children are more at risk than adults from contaminants and that ingestion is the riskiest exposure route. The carcinogenic risk was within the acceptable limits.

Spatial distribution, contamination assessment and potential ecological risk of some trace metals in the surface sediments of the Gulf of Tunis, North Tunisia

To evaluate the trace metals contamination status in the Gulf of Tunis, forty one sediment samples were analyzed using different approaches. According to certain contamination and ecological risk indices (Contamination Factor, Geoaccumulation index and Ecological risk index), Hg has the highest contamination level while pollution by Ni, Pb, Cd and Cr was absent. The highest concentrations of trace metals were found in sediments collected from the offshore and coastal areas located opposite the main exchange points with the gulf particularly, the Mejerda and Meliane Rivers, the Khalij Channel, Ghar El Melh and El Malah lagoons, Tunis Lake and Sebkhat Ariana. However, further ecological indices (Potential ecological risk index, Toxic unit and Mean effect-range median quotient) and comparison with sediment quality guidelines suggest that in addition to Mercury, Cr, Pb and Ni concentrations are detrimental to biota in both the offshore and areas near to the exchange points with the gulf. Moreover, in these areas the results from sequential extraction and individual contamination factor calculation pointed to the mobility and bioavailability of Cr, Pb and Ni.

Integrated Assessment of Affinity to Chemical Fractions and Environmental Pollution with Heavy Metals: A New Approach Based on Sequential Extraction Results

To assess the affinity degree of heavy metals (HMs) to geochemical phases, many indices with several limitations are used. Thus, this study aims to develop a new complex index for assessing contamination level and affinity to chemical fractions in various solid environmental media. For this, a new integrated approach using the chemical affinity index (CAF) is proposed. Comparison of CAF with %F on the literature examples on fractionation of HMs from soils, bottom sediments, atmospheric PM₁₀, and various particle size fractions of road dust proved a less significant role of the residual HMs fraction and a greater contribution of the rest of the chemical fractions in the pollution of all studied environments. This fact is due to the normalization relative to the global geochemical reference standard, calculations of contribution of an individual element to the total pollution by all studied HMs, and contribution of the particular chemical fraction to the total HMs content taken into account in CAF. The CAF index also shows a more significant role in pollution and chemical affinity of mobile and potentially mobile forms of HMs. The strong point of CAF is the stability of the obtained HM series according to the degree of chemical affinity and contamination. Future empirical studies are necessary for the more precise assessment of CAF taking into account the spatial distribution of HMs content, geographic conditions, geochemical factors, the intensity of anthropogenic impact, environmental parameters (temperature, humidity, precipitation, pH value, the content of organic matter, electrical conductivity, particle size distribution, etc.). The combined use of CAF along with other indices allows a more detailed assessment of the strength of HMs binding to chemical phases, which is crucial for understanding the HMs’ fate in the environment.

Element Content in Volcano Ash, Soil and River Sediments of the Watershed in the Volcanic Area of South Iceland and Assessment of Their Mobility Potential

In this work, we present the results of element content in river sediments and soil of the Rangárvellir river in southern Iceland as well as in the volcano ash from the Eyjafjallajökull eruption in 2010. Severe natural catastrophes have devastating impact on the environment. We selected the Rangárvellir area located in the vicinity of Mt Hekla, Iceland’s most active volcano, for our study. This study site is ideal to investigate wind and water erosion and sediment transport processes of two main glaciers rivers: the Eystri-Rangá and the Ytri-Rangá and the Hroarslækur River. Sediments of these rivers consist of volcano materials, ash and lava. In order to assess the sediment dynamics, we collected sediment, soil and volcanic ash. The fractioning of the elements was carried out using sequential extractions. The distribution of Si indicates that the sediments originate from the same geochemical basis. Li and partly B exist in the first phase of volcanic ash and river sediments but not in the mobile phases of soils. In the mobile phase of volcanic ash, P was found but it did not exist in the first phase of soil and sediments. These results suggest the different chemical fingerprints in the water sediments and surrounding soil.

Soil metal pollution assessment in Sarcocornia salt marshes in a South American estuary

Soil metal pollution in two Sarcocornia salt marshes within the Bahía Blanca estuary (Argentina, South America) was evaluated through pseudo-total and bioavailable metal levels and pollution indexes. Soil conditions were also studied. The pseudo-total metal concentrations were similar in both salt marshes and followed the same decreasing order: Fe > Zn > Cu > Cr > Ni > Pb > Cd. Bioavailable metals presented different patterns between salt marshes. The percentages of the bioavailable fraction varied between 28 and 80%, being higher than 60% for Cu, Zn and Pb. Organic matter ruled the distribution of all metals, except Pb. Using shale average concentration as background level, indexes did not show pollution nor enrichment, whereas using as background levels local values, anthropogenic enrichment was found for all metals and most metals showed moderate metal pollution. Our results showed that bioavailable metals levels and indexes using local background values provide an adequate assessment of metal pollution in salt marsh soils.

Fast and easily obtained information about mobilizable metals from sediment samples. Extraction assisted by benzothiophene-based ionic liquids

A fast and easy method for trace metal extraction on sediments was developed in our laboratories. Three new stable S-metylbenzothiophenium salts were employed along with microwaves to modify the BCR protocol to obtain the concentration of metals of the first two fractions in only one step. The optimum conditions were obtained with 0.125 g of sediment irradiated at 250 W for 30 s at 120 °C, in 5 ml of an aqueous mixture of 10 mM of 1,2-dimethylbenzothiophenium tetrafluoroborate and 0.5 M of hydroxylamine chlorhydrate at pH 2. The method validation was carried out employing BCR 701. The extracted metals were determined by ICP OES. A student's paired t-test was applied with the reference method, giving satisfactory results.

Geochemical fractionation study in combination with equilibrium based chemical speciation modelling of Cd in finer sediments provide a better description of Cd bioavailability in tropical estuarine systems

Geochemical fractionation study of cadmium (Cd) in combination with equilibrium based chemical speciation modelling (visual MINTEQ) in finer sediment samples (silt and clay portion), provided a better description of Cd bioavailability for sessile organisms (like oysters) in the Zuari estuary, west coast of India. A substantial fraction of total Cd in the finer sediment samples was present as water soluble, exchangeable and carbonate/bicarbonate forms and showed a strong positive relationship with Cd-bioaccumulation in oysters (Magallana sp.) from the study area. Cadmium bioaccumulation (ranged from 2.4-7.9 mg·kg^-1) in soft tissues of the edible oyster was high (higher than the maximum permissible limit for human consumption) throughout the study period of one year. Equilibrium based speciation modelling suggest that sedimentary CdCl₂, CdCl⁺ and Cd²⁺ were responsible for Cd bioaccumulation in the oysters. This study describes that combination of geochemical fractionation study of metals in finer sediments and equilibrium based speciation modelling can be very useful in comprehending link between sedimentary metal speciation and its bioaccumulation in sessile organisms.

Variability factors of heavy metals in soils and transfer to pasture plants of Mayabeque in Cuba

Studies to assess variability factors of heavy metals in soils are essential to understand their behavior in the environment and for the assessment of contaminated areas. In this context, this research aimed to study the factors that influence the variability of heavy metal levels and their bioavailability in pasture areas in the Alturas de Nazareno region, Mayabeque, Cuba, as well as the transfer to plants. Forty-five points were distributed in a natural pasture and at two depths (0-20 and 20-40 cm) as a function of relief and soil type. Pseudo-total heavy metal contents were determined according to method 3051A of USEPA, geochemical fractionation according to the Community Bureau of Reference method, and plant digestion according to method 3052 of USEPA. Soil samples were separated into two groups, according to cluster analysis. The type of soil associated with the pH and Ca attributes were the factors that most influenced the variability of the total and bioavailable levels of metals in natural pasture soils in the region of Alturas de Nazareno. Group 1 showed the lowest heavy metal contents and the highest pH and calcium values, which were predominantly associated with carbonate soils. Group 2 had the highest contents of heavy metals and Fe, corresponding mainly to the soil Ferralítico Rojo. The concentration of metals in plants was directly related to their bioavailable content in the soil, where G2 represents the group with the highest risk of transferring metals to the food chain.

Bioavailability and risk assessment of trace metals in sediments of a high-altitude eutrophic lake, Ooty, Tamil Nadu, India

Ooty lake, in the southern part of India, has raised huge concern about the role of metals in a lake due to increasing anthropogenic activities. Present study is aimed at understanding fate of trace metals in a lake's sediment. Sixteen sediment samples collected from bottom of the lake at various locations during March 2017 were analysed for trace metals cobalt, chromium, copper, iron, lead, manganese, nickel and zinc. Fe and Mn dominate total metal concentration followed by Ni and Cr. A high concentration of Cr, Cu, Ni and Zn in residual fraction indicates weathering as the source for these metals. A significant concentration of metals in exchangeable, reducible and oxidisable fraction indicates adsorbtion/chelation of these metals with oxides and organic matter due to change in oxic state. Geo-accumulation index for metals show unpolluted to moderate nature of sediments at all sampling locations. Moderate to significant enrichment factor of Cr, Ni and Zn indicates influence of anthropogenic sources. Co, Pb and Zn show a high amount of bioavailability for aquatic life. Other metals (Cr, Ni, Fe and Mn) show scarce to moderate bioavailability. On the other hand, a global contamination factor denotes moderate to high metal contamination of sediments in the entire lake. Statistical analysis of metals shows good inter-element correlation among metals Fe, Cr, Ni, Co, Cu and Zn indicating natural source. Influence of domestic sewage and recreational activities as the main/additional source is revealed by negative loading of Pb and Zn in principal component analysis. The present study, in essence, has identified rock weathering, as a major source of trace meals in the sediments of Ooty lake entering through stream and surface runoff from an adjacent forest area. The study has also identified high bioavailability of Pb and Zn, which is derived through the recreational activities (boating) causing permanent adverse impact.

A cost effective method for immobilization of Cu and Ni polluted river sediment with nZVI synthesized from leaf extract

This study investigates the performance of oak (OL) and mulberry (ML) leaves for synthesized of nanoscale zero-valent iron (nZVI), in immobilizing Cu and Ni in contaminated sediment. Characterization of synthesized Fe nanoparticles from oak and mulberry leaf extracts demonstrated that they are nontoxic and stabile nanomaterials for application in the sediment remediation. Effectiveness of stabilization process was performed by microwave-assisted sequential extraction procedure (MWSE) and single-step leaching tests which have been applied to evaluate the metal extraction potential. This research showed that OL-nZVI and ML-nZVI were effective in transforming available Cu and Ni to stable fraction. The maximum residual percentage of Cu increased by 76% and 73%, and for Ni 81% and 80%, respectively, with addition of 5% OL-nZVI and 5% ML-nZVI. Used single-step leaching tests (Toxicity Characteristic Leaching Procedure-TCLP and German standard test- DIN) indicated that all stabilized samples can be considered as non-hazardous waste, as all leached metal concentrations met the appropriate set criteria. Cost analysis showed that the operating cost for contaminated sediment treatment with green synthesized nZVI are 50.37 €/m3/per year. This work provides a new insight into the immobilization mechanism and environmental impact of Cu and Ni in contaminated sediment and potential way of treatment with OL-nZVI and ML-nZVI. Generally, nZVI can be an effective and versatile tool for stabilization of sediment polluted with toxic metals.

Comprehensive characterization and environmental risk assessment of end-of-life automotive catalytic converters to arrange a sustainable roadmap for future recycling practices

Environmentally appropriate economic recycling of spent automotive catalytic converters (SACCs) is difficult due to their complexity. The prominent reason is the lack of knowledge and comprehensive characterization of SACCs. This study focused on the characterization of SACCs in terms of their structural, morphological, physiochemical, surface, and thermal properties. The accurate determination of metals content, including 4975 mg/kg platinum group metals, 42,119 mg/kg rare earth elements, and other base metals, showed a great potential wealth in SACCs. Besides, the sequential extraction method was applied for metals fractionation, which represents a unique harsh recycling approach needed due to the stable structure of SACCs, metals embedded in silicate phases, and the presence of barely soluble metal phosphates. This waste was also examined for environmental criteria and leaching tests, including Toxicity Characteristic Leaching Procedure, Waste Extraction Test, and Synthetic Precipitation Leaching Procedure. The findings declare that Waste Extraction Test was the most aggressive procedure to assess mobility. The contamination indexes, such as risk assessment code, contamination factor, and global contamination factor, were also investigated, which show SACCs must be regarded as hazardous waste. As an example, the global contamination factor of 11.87 depicts SACCs have a moderate contamination degree.

Geochemical Fractionation and Risk Assessment of Potentially Toxic Elements in Sediments from Kupa River, Croatia

This study investigated the quality of Kupa River sediment using sequential extraction, ecological risk, and contamination indexes (Risk assessment code, Index of geoaccumulation, Enrichment factor, Ecological risk factor, Ecological risk index), determination of magnetic susceptibility of sediments, and statistical methods. The BCR sequential extraction technique was used for evaluating various element-binding forms. Most of the elements were considered to be immobile due to the high availability in the residual fraction. Lead was present mainly in the reducible fraction, while more easily mobile and bioavailable forms were predominant for cadmium and barium. Sediment samples from the river catchment exhibited low ecological risk. The most toxic element, Cd, is the main contributor to the total potentially ecological risk. Increased values of contamination factors have been observed for Zn, Cr, and Ba in some localities. Results of the comparison of element contents in sediments in a 15-year period (2018 vs. 2003) indicated that the situation with toxic element content in sediments along Kupa River improved formost of its course. Unfortunately, on the lower course of the river, the situation has worsened. Using the example of Kupa River sediments, it was shown that the magnetic susceptibility method is excellent indetecting increased values of Cr.

Speciation and migration of heavy metals in sediment cores of urban wetland: bioavailability and risks

To examine the status and risk of heavy metal pollution in an urban wetland in China, the distribution and speciation of chromium (Cr) and other metals (Cd, Cu, Pb, and Zn) were examined. We investigated the impact of three major land uses (residential and industrial (RI), orange plantation (OP), and mixed OP and RI (OPRI)) on the heavy metal characteristics using sediment cores (0-60 cm below water/sediment interface) collected in Sanyang Wetland, China. It was found that all the metals (Cr, Cd, Cu, Pb, and Zn) had lower concentrations in the top layers but higher contents in the bottom layers of sediments. Species of metals in sediments were dominated by their secondary phase (i.e., exchangeable and carbonate bound, Fe-Mn bound and organic bound) with relatively low contents of primary phase (i.e., residual form), except for Cr in RI affected river sediments that had a relatively high content of primary phase (20.97-36.07%). The ratio of secondary phase to primary phase (RSP) and risk assessment code (RAC) methods were applied to assess environmental risk. The results implied that the metal mobility and bioavailability could significantly cause urban wetland environmental quality decline, and thus enhanced strategies should be required to target the capture and removal of metals.

Terrestrial organic matter input drives sedimentary trace metal sequestration in a human-impacted boreal estuary

Coastal sediments play a fundamental role in processing anthropogenic trace metal inputs. Previous studies have shown that terrestrial organic matter (OM) is a significant vector for trace metal transport across the land-to-sea continuum, but little is known about the fate of land-derived metal-OM complexes in coastal sediments. Here, we use a comprehensive set of sediment pore water and solid-phase analyses to investigate how variations in terrestrial OM delivery since the 1950s have influenced trace metal accumulation and diagenesis in a human-impacted boreal estuary in the northern Baltic Sea. A key feature of our dataset is a strong correlation between terrestrial OM deposition and accumulation of metal-OM complexes in the sediments. Based on this strong coupling, we infer that the riverine input of terrestrial metal-OM complexes from the hinterland, followed by flocculation-induced settling in the estuary, effectively modulates sedimentary trace metal sequestration. While part of the trace metal pool associated with these complexes is efficiently recycled in the surface sediments during diagenesis, a substantial fraction is permanently buried as refractory metal-OM complexes or through incorporation into insoluble sulfides, thereby escaping further biological processing. These findings suggest that terrestrial OM input could play a more pivotal role in trace metal processing in coastal environments than hitherto acknowledged.

Benthic hypoxia in anthropogenically-impacted rivers provides positive feedback enhancing the level of bioavailable metals at sediment-water interface

We investigated the effect of hypoxic-anoxic range of dissolved oxygen (DO) on metal release/bioavailability at sediment-water interface (SWI) in the Ganga River. Here, we consider eight sites in the main river stem along 518 km; sixty sites downstream two point sources and two tributary confluences covering 630 km; and an incubation experiment to verify these results. We found higher concentrations of metals and bioavailable fractions at SWI at two locations of main stem and up to 700 m, 1000 m, 400 m and 500 m downstream Assi drain, Wazidpur drain, Ramganga confluence and Varuna confluence respectively where DO at SWI (DO_sw) was <2.0 mgL^-1. The incubation experiment did show higher levels of metal- and P-release and bioavailability under anoxic-hypoxic range of DO. The risk assessment code and eutrophication index indicated high to very high risks of contaminated river sediment and water to aquatic environment at sites with hypoxic-anoxic range of DO_sw. Further, the principal component analyses separated metals and bioavailable fractions opposite to FDAase indicating greater risk at these locations. The study, which forms the first report on benthic hypoxia/anoxia-driven metal release, potential bioavailability and risk to the Ganga River ecosystem will help understanding how human-driven perturbations influence geochemical cycling of metals and ecosystem responses in large rivers.

Assessment of Heavy Metal Concentrations with Fractionation Method in Sediments and Waters of the Badovci Lake (Kosovo)

The concentrations of thirteen metals (Al, As, Ba, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, V, and Zn) were analyzed in waters and sediments of the Badovci Lake. The total metal concentrations in the water followed the descending order: Fe > Al > Mn > Cu > Ba > Zn > As > Ni > Pb > V > Co > Cd > Cr, and the total metal content in the sediments also followed the descending order: Fe > Al > Mn > Ni > Cr > Pb > Ba > Zn > V > Cu > As > Co > Cd. According to EC 98/83, Al, Fe, and Mn at some sampling sites exceeded safety limits for drinking water, whereas other elements were at acceptable levels. The total content of Cr, Cu, Ni, Pb, and V in the sediments exceeded the target values of the New Dutch List. Using pollution indicators such as the contamination factor (CF) and geoaccumulation index (I_geo), most of the samples were unpolluted to moderately polluted by Cu, Cr, Pb, V, and Ni. The values of the pollution load index (PLI) were more than one (>1), indicating progressive deterioration of the sediment quality. The enrichment factor (EF) for all the studied metals suggests their enrichments in sediments of the Badovci Lake. Most of the elements were found in the residual fraction strongly bonded to the crystalline component. Pb, Mn, and Cu were bound in the organic and exchangeable components. The extent of pollution by heavy metals in sediments of the Badovci Lake implies that the environmental condition is relatively stable, and attention should be paid to metals bonded in the extractable and organic phases. It is recommended to periodically monitor water and sediment quality.

Probabilistic hazard assessment of contaminated sediment in rivers

We propose a probabilistic framework rooted in multivariate and copula theory to assess heavy metal hazard associated with contaminated sediment in freshwater rivers that provide crucial ecosystem services such as municipal water source, eco-tourism, and agricultural irrigation. Exploiting the dependence structure between suspended sediment concentration (SSC) and different heavy metals, we estimate the hazard probability associated with each heavy metal at different SSC levels. We derive these relationships for warm (spring-summer) and cold (fall-winter) seasons, as well as stormflow condition, to unpack their nonlinear associations under different environmental conditions. To demonstrate its efficacy, we apply our proposed generic framework to Fountain Creek, CO, and show heavy metal concentration in warm season and under stormflow condition bears a higher hazard likelihood compared to the cold season. Under both warm season and stormflow conditions, probability of exceeding maximum allowable threshold for all studied heavy metals (Cu, Zn, and Pb, in recoverable form) at a standard hardness of 100 mg/lCaCo₃ and at a high level of SSC (95th percentile) is consistently more than 80% in our study site. Moreover, a longitudinal study along the Fountain Creek demonstrates that urban and agricultural land use considerably increase likelihoods of violating water quality standards compared to natural land cover. The novelty of this study lies in introducing a probabilistic hazard assessment framework that enables robust risk assessment with important policy implications about the likelihood of different heavy metals violating water quality standards under various SSC levels.

Trace metal mobility in sub-seabed sediments by CO2 seepage under high-pressure conditions

Carbon capture and storage (CCS) is the third contributor to cumulative carbon emission reductions required by the second half of this century. Although this is a promising technology for reducing atmospheric CO₂, it is only affordable if the confinement of the gas is guaranteed for hundreds of years. Hence, it is of paramount importance to figure out and predict the chemical and biological effects associated with potential CO₂ leakage, to provide decision makers with a good basis for choosing technology and potential storage sites. To this end, a titanium reactor (1.4 m³) was used to study CO₂ seepage under realistic sub-seabed conditions (30 bar pressure and 7 °C). The injection of CO₂ was calibrated to decrease the pH value from 8.1 to 7.3, which may be the pH found near a leakage point. This pH value also coincides with predictions for near-future ocean pH under current CO₂ emissions worldwide. The results from this study demonstrate that there are some elements, i.e., Fe, Co, Pb, Ce, Zn and Cu, present in deep marine sediments, that are strongly affected by the reduced pH levels related to CO₂ addition. The dissolved concentrations of Fe, Pb and, to a lesser extent, Cr increased, due probably to weakening of the Fe/Mn shuttle by increased dissolved concentrations of CO₂. Desorption processes from oxyhydroxide surfaces due to acidification may explain the release of Co, Ni and Ce observed during the experiment. The increased CO₂ concentration also led to increased metal bioavailability, suggested by higher values for labile metal species. Conversely, Cd mobility seems not to be affected by CO₂-associated acidification. It is concluded that the determination of those elements most affected by CO₂-related acidification in a sub-seabed CO₂ storage perimeter (i.e., sediment, sediment-water interface and water column) would be a simple and effective technique to verify suspected leakage.

The distributions, contamination status, and health risk assessments of mercury and arsenic in the soils from the Yellow River Delta of China

The surface soils were collected from four areas in the Yellow River Delta (YRD), including three functional areas in the natural reserve of the YRD (the core area, buffer area, and experimental area) and a neighboring area of the natural reserve. The total concentrations, speciations, contamination status, and health risk assessments of the mercury (Hg) and arsenic (As) in surface soils of the YRD were investigated. The average Hg concentration was about three times that of the background value, while As was just slightly higher than the background. Hg levels in the sites of experimental area were significantly higher than those in the core area and buffer area, which was consistent with the human activity intensities of the three functional areas. However, no significant differences of As levels were observed across different areas. According to the sequential extraction experiments, only less than 5% of Hg and As were associated with the exchangeable fraction, while over 80% of them were found in the residual fraction, indicating low mobility and bioavailability of both Hg and As. The soil contamination status assessments suggested a "good state," and the health risk assessments indicated a "low risk" of Hg and As in the soils of YRD.

Quantitative evaluation of n-alkanes, PAHs, and petroleum biomarker accumulation in beach-stranded tar balls and coastal surface sediments in the Bushehr Province, Persian Gulf (Iran)

Coastal areas within the Bushehr Province (BP), Persian Gulf, Iran, face great challenges due to the heavy organic contamination caused by rapid industrialization, and the presence of numerous oil fields. In addition, in 2014, a significant number of tar balls are found along the coasts of BP. A total of 96 samples (48 coastal sediments and 48 tar balls) were taken from eight sampling points at the BP coast during the summer of 2014. These samples were analyzed to identify the sources and characteristics of their organic matter using diagnostic ratios and fingerprint analysis based on the distribution of the source-specific biomarkers of n-alkanes, PAHs,¹ hopanes and steranes. Mean concentration of n-alkanes (μg g^-1 dw) and PAHs (ng g^-1 dw) varied respectively from 405 to 220,626, and 267 to 23,568 in coastal sediments, while ranged respectively from 664 to 145,285 and 390 to 46,426 in tar balls. In addition, mean concentration of hopanes and steranes (ng g^-1 dw) were between 18.17 and 3349 and 184.66 to 1578 in coastal sediments, whereas in tar balls were 235-1899 and 520-1504, respectively. Pri/Phy² ratio was 0.25 to 1.51 (0.65) and 0.36 to 1 (0.63) in coastal sediment and tar ball samples, respectively, and the occurrence of UCM³ in both matrices, reflecting the petrogenic OM⁴ inputs and chronic oil contamination, respectively. The C₃₀ and C₂₉ homologues followed Gammacerane were detected in both matrices, in particular those collected from intensive industrial activities, suggesting petrogenic sources of OM. The coastal sediment PAHs profiles were significantly dominated by HMW⁵-PAHs in the Bahregan Beach (BAB) (78% of total PAHs), Bandare-Genaveh (GP) (66%), and Bandare-Bushehr (BUB) (61%) stations, while the Bashi Beach (BSB) (40%), Bandare-Kangan (KP) (57%), and Bandare-Asaluyeh (AP) (51%) stations exhibited higher proportion of LMW⁶-PAHs. PCA⁷ indicated that the tar ball and coastal sediment samples deposited along the Southwest of the BP beaches are most likely originated from the Abuzar oil. Based on the intensity of the anthropogenic activities, NPMDS⁸ analysis revealed that the GP, BAB, NNP, AP, and KP sampling sites had a high concentration of detected organic pollutants. To the best of our knowledge, this is the first study that investigates oil pollution in costal sediments and tar balls in the BP, providing insights in to the fate of oil in the coastal areas of the Persian Gulf, Iran.

An insight into fractionation, toxicity, mobility and source apportionment of metals in sediments from El Temsah Lake, Suez Canal

El Temsah Lake is one of the most important wetlands in the Suez Canal area and the major source of fish for the area. In this study, the relative role of sediments' geochemical properties and metals geochemical fractionation in determining Cd, Cr, Fe, Mn, Ni, and Pb mobility and toxicity was especially concerned. The results reflected that the increasing order of contamination for the investigated metals according to individual contamination factor (ICF) was: Cr > Mn > Ni > Pb > Cd > Fe. Risk assessment code (RAC) classification showed that the relative amounts of easily dissolved phases of metals in the sediments followed the order of Ni > Cr > Cd > Pb > Fe > Mn. The toxicity as indicated by toxic unit (TU) due to an individual metal followed a descending order of Ni > Cr > Pb > Cd, indicating that Ni and Cr accounted for the majority of the overall sediment toxicity while, Cd contributed the least to the ΣTU. This work constitutes a good basis for further studies about metal fractionation in El Temsah Lake which might help policy makers to take effective decisions for proper management of the lake.

Fractionation and risk assessment of metals in sediments of an ocean dumping site

Sediments of Yellow Sea dumping sites (YSDS) collected in 2015 were analyzed using the European Community Bureau of Reference (BCR) sequential extraction method to assess the contamination and potential risk to the environment. Cr, Ni, Cu, and Zn exhibited the most dominant residual fraction, whereas Cd was mostly in the exchangeable fraction and Pb in the reducible fraction. Cr contains a significant amount of oxidizable fraction in the dumping area due to the dumping of tannery sludge with high concentrations of Cr, mainly in the organic matter-bound form. The global contamination factor (GCF) showed that high non-residual fractions of Cd and Pb contributed considerably to contamination. Nevertheless, modified potential ecological risk index (MRI) suggested low ecological risk for metals in YSDS because of the low total content of Cd and the small mobile fraction of other metals.

Metals geochemistry and ecological risk assessment in a tropical mangrove (Can Gio, Vietnam)

Mangrove sediments act as natural biogeochemical reactors, modifying metals partitioning after their deposition. The objectives of the present study were: to determine distribution and partitioning of metals (Fe, Mn, Ni, Cr, Cu, Co and As) in sediments and pore-waters of Can Gio Mangrove; and to assess their ecological risks based on Risk Assessment Code. Three cores were collected within a mudflat, beneath Avicennia alba and Rhizophora apiculata stands. We suggest that most metals had a natural origin, being deposited in the mangrove mainly as oxyhydroxides derived from the upstream lateritic soils. This hypothesis could be supported by the high proportion of metals in the residual fraction (mean values (%): 71.9, 30.7, 80.7, 80.9, 67.9, 53.4 and 66.5 for Fe, Mn, Ni, Cr, Cu, Co, and As respectively, in the mudflat). The enrichment of mangrove-derived organic matter from the mudflat to the Rhizophora stand (i.e. up to 4.6% of TOC) played a key role in controlling metals partitioning. We suggest that dissolution of Fe and Mn oxyhydroxides in reducing condition during decomposition of organic matter may be a major source of dissolved metals in pore-waters. Only Mn exhibited a potential high risk to the ecosystem. Most metals stocks in the sediments were higher in the Avicennia stand than the Rhizophora stand, possibly because of enhanced dissolution of metal bearing phases beneath later one. In a context of enhanced mangrove forests destruction, this study provides insights on the effects of perturbation and oxidation of sediments on metal release to the environment.