Impact of sediment characteristics on the heavy metal concentration and their ecological risk level of surface sediments of Vaigai river, Tamilnadu, India

Unveiling the Rising Threat of Cadmium Pollution and Alarming Health Risks Associated with the Consumption of 15 Commercially Important Fish Species in the Middle Stretch of River Ganga, at Patna, India

Among environmental contaminants, the rising level of cadmium in freshwater ecosystems is one of the most significant global concerns. The study addresses the current pollution status of cadmium in the middle stretch of River Ganga and explores the potential hazard associated with the consumption of 15 commercially important fish species by the inhabitants. Together 72 water and sediment samples were analyzed from the four representative sampling sites of River Ganga after the surveillance of major anthropogenic stressors. The concentration of cadmium ranges from 0.003 to 0.011 mg/l and 0.2 to 3.48 mg/kg in water and sediment respectively in 2022. The average concentration of cadmium was recorded to be the highest in Channa punctatus (1.35 mg/kg), followed by Rita rita = Johnius coitor (1.15 mg/kg), and the lowest in Labeo bata (0.2 mg/kg). The finding highlights greater exposure duration and feeding preferences of fish species have played a significant role in the bioaccumulation of the metal in the riverine system. Notably, the domestic effluents, agricultural runoffs, and pollutants brought along by the tributaries of River Ganga are identified as the main anthropogenic stressors for the moderate to considerably polluted status of the River Ganga. The target hazard quotient (THQ) and target carcinogenic risk (TCR) have revealed a higher susceptibility to cadmium contamination in children followed by females, and males. In addition, hierarchical cluster analysis (HCA) has noted intake of Rita rita, Channa punctata, Puntius sophore, and Johnius coitor could be more detrimental to children's health than adults.

Potentially toxic elements (PTEs) in coastal sediments of Bandar Abbas city, North of Persian Gulf: An ecological risk assessment

The concentration of potentially toxic elements (PTEs; Lead (Pb), Nickel (Ni), and Cadmium (Cd) Pb, Ni, and Cd), using flame atomic absorption spectrometry (FAAS) was measured in fifty surface coastal sediment samples collected from 5 points coastal sediment of Bandar Abbas city, Iran besides the potential ecological risk index (RI) estimated the environmental health risk. The rank order of PTEs was Pb (52.090 ± 4.113 mg/kg dry weight) > Ni (34.940 ± 8.344 mg/kg dry weight) > Cd (2.944 ± 0.013 mg/kg dry weight). RI due to PTEs in sediments for A, B, C, D, and E points were 187.655, 190.542, 191.079, 189.496, and 192.053, respectively. RI for sampling points A to E was at moderate risk (150 ≤ RI < 300). Therefore, it is recommended to carry out control programs to reduce the amount of PTEs in the coastal sediment of the Persian Gulf.

Spatial distribution of heavy metals in the sediments of River Ganges, India: Occurrence, contamination, source identification, seasonal variations, mapping, and ecological risk evaluation

Present study analyzed the seasonal and spatial distribution patterns, sources, and ecological risks of seven heavy metals (Cr, Fe, Ni, Cu, Zn, Cd and Pb) in the sediments of River Ganges, finding that the majority of concentrations were lithologic, except for Cd, which was significantly higher than background standards. Elevated values of geochemical indices viz. Igeo, CF, RI, Cd, mCd, HQ, mHQ, and PN suggest moderate to high ecological risk in the benthic environment and its organisms due to the synergistic effect of heavy metals. The PEC-Qmetals revealed 8-10 % toxicity in the upstream and downstream sites, due to the influence of agricultural activities. Multivariate statistical techniques (PCM and PCA) indicated that Cd and Pb predominantly originated from anthropogenic sources, while other metals primarily derived from geological background. These geochemical findings may help to understand the potential risks and recommend strategies to mitigate the effects of metallic contamination in river sediments.

Magnetic susceptibility and heavy metal contents in sediments of Riam Kiwa, Riam Kanan and Martapura rivers, Kalimantan Selatan province, Indonesia

Kalimantan Selatan is proud of the Martapura River's natural and cultural history. Martapura tributaries include Riam Kanan and Kiwa. The Martapura River is essential because it provides clean water and a livelihood for riverside residents. Human-caused river pollution grows with population density (also known as anthropogenic pollutants). This study characterizes surface sediment magnetic characteristics and heavy metal contents along the Riam Kanan, Riam Kiwa, and Martapura rivers. The purpose of this research is to evaluate the magnetic signal with respect to heavy metal contents found in surface sediments taken from rivers and to confirm the use of the rock magnetism method in environmental studies in the study area. Surface sediment samples were gathered and tested for magnetic, heavy metal, and mineralogical content. According to the findings, the pseudo-single domain (PSD) magnetite mineral predominates among the magnetic minerals that can be found in the surface sediments of the rivers Riam Kanan, Riam Kiwa, and Martapura. This substantially greater grain size may be due to magnetic particles produced by erosion along the river banks. The mass-specific magnetic susceptibility of surface sediments ranges from 103.11 to 1403.64 × 10^-8 m³/kg, with an average value of 355.67 × 10^-8 m³/kg due to the peatland environment. Magnetic susceptibility strongly negatively correlates with heavy contents like Cu, Zn, and Hg, according to Pearson correlation analysis. Due to this correlation, magnetic susceptibility may indicate heavy metal pollution in certain rivers. This current study demonstrates the novelty of the relationship between magnetic susceptibility and the contents of heavy metals in surface sediments from rivers in peatland and tropical environments by illustrating how the relationship affects the magnetic susceptibility of the sediments.

Brief status of contamination in surface water of rivers of India by heavy metals: a review with pollution indices and health risk assessment

Water is polluted via various means; among these, heavy metal (HM) contamination is of great concern because of the involvement of metal toxicity and its effect on aquatic environment. The significance and novelty of this study is that it focuses on assessment of HMs in the surface water of Indian rivers only from 1991 to 2021. For this, multivariate studies were used to find multiple sources of HMs. The average concentrations of Fe, Cr, Pb, Ni, Cd, Mn, Hg, Co, and As in surface water of rivers were found to far exceed the permitted limits established by both World Health Organisation and Bureau of Indian Standards. The HM indices like HM pollution, degree of contamination, evaluation index, water pollution, and toxicity load data all indicated that the rivers under investigation are heavily polluted by HMs. In this study, health risk assessment indicated non-carcinogenic effects of Fe, Cr, Cu, Pb, Cd, Mn, Hg, Co, and As in children and those of Fe, Cr, Pb, Cd, Hg, Co, and As in adults. Values investigated for Cancer index were higher for Cr, Pb, Ni, Cd, and As indicating a high risk of cancer development in adults and children via the ingestion pathway than the cutaneous pathway. Moreover, children are more prone to be exposed to both non-carcinogenic and carcinogenic effects of HMs than adults. To reduce human dangers, remediation approaches, such as environment-friendly, cost-effective adsorbents, phytoremediation and bio-remediation, as well as tools like bio-sensors, should be included in river management plans.

Trace metal contamination status in soils of the abandoned gold mining district of Bindiba (East Cameroon): Pollution indices assessment, multivariate analysis and; geostatistical approach

In this study, contamination by trace metals (TMs) such as Cr, Ni, Cu, As, Pb and Sb in the soils of the Bindiba mining district was assessed. This study aims to reveal the current status of the soil quality of the abandoned gold mining district of Bindiba and provide a scientific basis for its future remediation and overall management. 89 soil samples were systematically collected and characterized in order to determine the concentration of TMs (Cr, Ni, Cu, As, Pb and Sb). To assess the degree of metallic contamination, pollution indices were employed. Both multivariate statistical analysis (MSA) and geostatistical modelling (GM) were used to identify the potential sources of TMs elements and to determine the values of the modified contamination degree (mCd), the Nemerow Pollution Index (NPI) and the potential ecological risk index (RI) at un-sampled points. The results of trace metals (TMEs) characterization showed that the concentration of Cr, Ni, Cu, As, Pb and Sb ranged from 22.15-442.44 mg/kg, 9.25-360.37 mg/kg, 1.28-320.86 mg/kg, 0-46.58 mg/kg, 0-53.27 mg/kg and 0-6.33 mg/kg, respectively. The mean concentration of Cr, Cu and Ni exceeds the continental geochemical background values. The Enrichment Factor (EF) assessment indicates two categories of enrichment: moderately to extremely enrichment for Cr, Ni, and Cu and deficiency to minimal enrichment of Pb, As and Sb. Multivariate statistical analysis shows weak linear correlations between the studied heavy metals and suggests that these metals could not come from the same origins. The geostatistical modelling based on the values of mCd, NI and RI suggests a potential high pollution risk existed in the study area. The mCd, NPI and RI interpolation maps showed that the Northern part of the gold mining district was characterized by a high degree of contamination, heavy pollution, and considerable ecological risk. The dispersion of TMs in soils could mainly be attributed to anthropogenic activities and natural phenomena (chemical weathering or erosion). Appropriate measures should be taken to manage and remediate the TMs pollution in this abandoned gold mining district in order to reduce its negative effects on the environment and health of the local population.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40201-023-00849-y.

Spatial distribution and sources of heavy metals in the sediment and soils of the Yancheng coastal ecosystem and associated ecological risks

Studies of heavy metal pollution are essential for the protection of coastal environments. In this study, positive matrix factorization (PMF) and a GeoDetector model were used to evaluate the sources of heavy metal contamination and associated ecological risks along the Yancheng Coastal Wetland. The distribution of heavy metals was shown to be greatly affected by clay content, except for Cr in shoal. Components from 6.5 to 9φ have the strongest ability to absorb heavy metals, where the effects of Cd and Zn sequestration in the wetlands were most apparent. The abilities of various wetland environments to sequester heavy metals were shown to be Spartina alterniflora wetland > woodland > Phragmites australis wetland > aquaculture pond > shoal > paddy > meadow > dry land. The sources of the heavy metals included parent soil material (59%), agriculture (15%), and industrial pollutants (26%). According to the single-factor pollution index, there was no evidence of pollution except Cr and Pb. In general, the heavy metal pollution was insignificant. The order of pollution loading index was shoal > paddy field > dry land > Spartina Alterniflora wetland > aquaculture ponds > woodland > meadow > Phragmites australis wetland. The ecological harm of heavy metal exposure was slight except for Cd and Hg, where vehicle emissions appeared to be the main cause of heavy metal pollution.

Analysis and potential ecological risk assessment of heavy metals in surface sediments of the freshwater ecosystem in Zhenjiang City, China

Heavy metals contamination in freshwater ecosystems has drawn attention worldwide. It is necessary to investigate heavy metals content and assess their ecological risk in order to protect the aquatic ecosystems. In this study, we collected surface sediment samples from the freshwater ecosystem of the city of Zhenjiang, in China, in both winter and summer. Then, we analyzed the seasonal and spatial distribution patterns of lead (Pb), chromium (Cr), cadmium (Cd), zinc (Zn), and copper (Cu). The contamination factor (CF), enrichment factor (EF), geo-accumulation index (Igeo), and potential ecological risk (Eri) were jointly used to assess the pollution degree and the ecological risk posed to the freshwater ecosystem by the aforementioned elements. Multivariate statistical analysis, including Pearson’s correlation and principal component analysis and cluster analysis, were used to identify potential sources of the investigated metals in this research area. Study results showed that: (1) the average concentrations values were 1.81 mg/kg and 1.15 mg/kg for Cd, 55.3 mg/kg and 62.2 mg/kg for Cu, 88.0 mg/kg and 52.5 mg/kg for Cr, 27.3 mg/kg and 22.8 mg/kg for Pb, 87.0 mg/kg and 271 mg/kg for Zn, in winter and summer, respectively. Amongst the investigated elements, the average concentrations of Cd, Cu, Cr, and Pb, were above the local background values in winter, whereas, Cd, Cu and Zn concentrations were higher than the background values in Zhenjiang; (2) The CF and EF indicated that Cd had a high contamination degree and a significant enrichment compare to others investigated metals in the surface sediment of in this research area. (3) Cd posed moderate, considerable, or very high ecological risks in different sites, while the other elements (i.e., Cu, Cr, Pb, and Zn) presented a low degree of ecological risk. (4) Multivariate statistical analyses results indicated Pb, Cu, and Zn had similar geochemical characteristics, while, Cd and Cr had significant differences with the above elements. Therefore, Pb, Cu, and Zn probably originate from the same sources, while Cd and Cr might have mixed sources, including both natural sources and human activities. Overall, more attention should be paid to Cd for risk assessment in the current study area. The findings of this study provide fundamental information for the evaluation and management of the heavy metals investigated in the freshwater ecosystem of Zhenjiang.

Spatial variation, sources, and potential ecological risk of metals in sediment in the northern South China Sea

Heavy metals are of great concern to humans because of their persistence, bioaccumulation, and toxicity. A study on the spatial variation, sources, and potential ecological risk of heavy metals in the coastal sedimentary environment are helpful to clarify the pollution history of aquatic systems and effectively manage and control heavy metal pollution. However, most studies are limited to the Pearl River Estuary region. To investigate the spatial distribution characteristics, sources, and potential ecological risks of heavy metals (Cr, Cu, Pb, Ni, Sn, Zn, As, Cd), a total of 41 sediment samples from the northern South China Sea (NSCS) region were analyzed. The results show that Cu, Ni, Pb, and Zn have similar distribution patterns and their migration path in the coastal area is mainly controlled by the coastal current in western Guangdong. Meanwhile, these metals also have similar sources, i.e. natural weathering products. The distribution patterns of Cr, Sn, Cd, and As are not affected by the coastal current, and the sources of these metals are not only natural weathering products but also human inputs such as electroplating and electronic industries and runoff from agricultural sites. Agricultural activities, coal-burning activities, and aerosol precipitation may be another important source of human activities for As. More than half (65.9 %) of the sampling sites were categorized as having low potential ecological risk, 24.4 % for moderate risk, 7.3 % for considerable risk, and 2.4 % for high potential ecological risk, and the potential ecological risk metals of Cr, Cd, and As in NSCS should be more attention.

Improvement of Ecological Risk Considering Heavy Metal in Soil and Groundwater Surrounding Electroplating Factories

Heavy metals in groundwater and soil are toxic to humans. An accurate risk assessment of heavy metal contamination can aid in environmental security decision making. In this study, the improved ecological risk index (RI) is used to comprehensively investigate the influence of heavy metals in soil and groundwater within electroplating factories and their surrounding regions. In the non-overlapping area, the RI of soil and groundwater is computed individually, and in the overlapping area, the greater RI of soil and groundwater is employed. Two typical electroplating factories are used to examine the heavy metal distribution pattern. The heavy metal concentrations are compared between Factory A, which is in operation, and Factory B, which is no longer in operation, in order to analyze the heavy metal concentrations and associated ecological risks. Heavy metals continue to spread horizontally and vertically after Factory B was closed. Heavy metal concentrations in groundwater surrounding Factory B are substantially greater, and the maximum concentration exists deeper than in Factory A. Because Cr, Cu, and Hg in soil contribute significantly to the RI, the primary high RI region is observed at Factory A and the region to the southwest. The RI of Factory B demonstrates a broad, moderate risk zone in the west and southwest.

Coastal reclamation mediates heavy metal fractions and ecological risk in saltmarsh sediments of northern Jiangsu Province, China

Coastal reclamation has created enormous extra land for the rapidly growing economy, but it has also caused serious environmental pollution problems and threatened the sustainable development of coastal areas. However, there are few studies focusing on the distribution patterns, geochemical speciation and ecological risks of heavy metals along the land-to-sea belt, as well as the differences between reclamation and non-reclamation. Here, we collected 69 sediment samples from four sediment types along the land-to-sea sampling belts in the reclaimed and non-reclaimed tidal flats of Jiangsu, China. Geochemical speciation and contents of heavy metals were determined to investigate their spatial distributions, ecological risks and effect factors. Results showed that As, Cd, Cr and Ni in the sediments posed considerable or moderate ecological risk according to the Ontario guidelines and sediment quality guidelines (SQGs) of USEPA, but they were lower than the SQGs of China. Higher geoaccumulation index and potential ecological risk index suggested that the sediments were moderately to heavily polluted by Cd and As. Generally, reclaimed sediments exhibited higher metal pollution levels. Additionally, reclaimed areas showed a unimodal pattern of metal content along the direction of land-to-sea, suggesting that Spartina alterniflora could accelerate the deposition and accumulation of metal pollutants caused by reclamation, and ultimately control the transfer of terrigenous metals to marine environment. We found that residual fraction was the dominant geochemical fraction for the metals determined. Reclamation processes have changed the composition of heavy metal fractions, especially Cd, Pb, Zn, and Ni. Approximately 20% of Cd existed in the acid extractable/exchangeable fraction and posed medium ecological risk according to the risk assessment code. The principal component analysis and correlation matrix further indicate that organic matter and particle size of sediment could be the major factors regulating the metal distribution, and Cd and Zn might be anthropogenic sources.

Distribution and ecological risk assessment of heavy metals using geochemical normalization factors in the aquatic sediments

Thamirabharani river acquires a noticeable quantity of sewage and agriculture waste from local inhabitants. The distribution of heavy metals in the surface sediments of the Thamirabharani river was analyzed using Inductively Coupled Plasma- Mass Spectrometry (ICP-MS) to study the ecological risks. The heavy metal concentrations in the sediments ranged from 0.098 ± 0.03(Cd) to 159.181 ± 13.36 mg kg^-1 (Fe). The Cd, Zn, Ni, Fe, and Mn concentrations in the sediments were above the US Environmental Protection Agency-Sediment Quality Guidelines. The fact that Cd, Co, and Cu concentrations at sites 4 and 5 exceeded the background values (BGVs) of 0.2, 13, and 32 mg kg^-1 suggests anthropogenic activity, notably in the downstream of the river. The sediment contaminated with Cd is more evident, particularly in the estuarine region. The potential ecological risk index (150<PERI≤300) and ecological risk co-efficient (40 < Er < 80) revealed moderate ecological risk at the estuarine region (S5). There was a moderate level of pollution in the downstream region (S4 and S5) based on a geo-accumulation index (Igeo), contamination factor (CF), pollution load index (PLI), and the moderate degree of contamination (mCd) values. According to the geochemical normalization factors, the downstream region (sites 4 and 5) was moderately polluted than the upstream region (S1 and S2), which may affect the estuarine/marine ecosystem. This information may facilitate the relevant regulatory authorities to implement the requisite stringent monitoring program in the aquatic ecosystem.

The spatial-temporal impact on dissolved and particulate metals in Brunei Bay, Malaysia: Spectrometric and chemometrics approach

The concentrations of metals in the waters of Brunei Bay, Malaysia were determined to define the current level and changes of its distribution. Discriminant analysis showed that metals distribution was spatially influenced by anthropogenic activities, whereas the distribution of cadmium (Cd) and zinc (Zn) was temporally influenced by the seasonal changes. High concentration of particulate metals in the coastal region during the wet season was presumably affected by freshwater intrusion and strong current disturbance. Generally, the enrichment factor of the aluminium (Al), Cd, copper (Cu), lead (Pb), and Zn proved enrichment by anthropogenic sources, except for iron (Fe). Furthermore, Cd has the highest enrichment factor value, signifying the potential risk of Cd on the Brunei Bay waters even at a low level. However, the Malaysia Marine Water Quality Criteria and Standard have classified the Brunei Bay waters as unpolluted.

Preliminary assessment of heavy metals in surface water and sediment in Nakuvadra-Rakiraki River, Fiji using indexical and chemometric approaches

River water and sediment embody environmental characteristics that give valuable environmental management information. However, indexical and chemometric appraisal of heavy metals (HMs) in river water and sediment is very scarce in Island countries including Fiji. In this research, forty-five sediment and fifteen water samples from the Nakuvadra-Rakiraki River, Fiji were analyzed for appraising spatial distribution, pollution, and source identification of selected heavy metals (HMs) using the coupling tools of self-organizing map (SOM), compositional data analysis (CDA), and sediment and water quality indices. The mean concentration of HMs increased in the order of Cd < Co < Pb < Cu < Zn < Ni < Cr < Mn < Fe for sediment and Cd < Pb < Cu < Ni < Zn < Co < Cr < Fe < Mn for water, respectively. The outcomes of the enrichment factor, geo-accumulation index and contamination factor index varied spatially and most of the sediment samples were polluted by Pb, Mn, and Cu. The potential ecological risk recognized Cd, and Pb as ecological and public health risks to the surrounding communities. Based on SOM and CDA, three potential sources (e.g., point, nonpoint and lithological sources) of HMs for sediment and two sources (e.g., geogenic and human-induced sources) of HMs for water were identified. The spatial patterns of EWQI values revealed that the northern and northeast zones of the studied area possess a high degree of water pollution. The entropy weight indicated Ni and Cd as the main pollutants degrading the water quality. This study gives a baseline dataset for combined eco-environmental measures for the river's water and sediment pollution as well as contributes to an inclusive appraisal of HMs contamination in global rivers.

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.

Influence of flocculation conditioning on environmental risk of heavy metals in dredged sediment

This study comprehensively analyzes the environmental risk of heavy metals (HMs) in the dewatering process of dredged sediment. First, the toxicity leaching capacity, total content, and chemical speciation of the HMs (As, Cd, Co, Cr, Cu, Hg, Mo, Pb, Sb, Sr, Tl, Zn) in dewatered sediment were determined using toxicity characteristic leaching procedure and modified Community Bureau of Reference sequential extraction procedure. The ecotoxicity and environmental risk of the HMs were then evaluated based on sediment quality guidelines, geo-accumulation index, enrichment factor, potential ecological risk, and risk assessment code. The results showed that flocculants reduced the ecological risk of Hg and Mo in sediment, and promoted the transformation of Mo, Sb, and Tl from the biologically active fraction to the more stable fraction. The transformation percentages of Mo, Sb, and Ti were 45.15%, 50.59% and 76.44%, respectively, after chitosan (CTS) treatment, and 64.55%, 31.75% and 99.90%, respectively, after cationic polyacrylamide (CPAM) treatment. CTS reduced the potential risks of bioavailable As, Cr, Cu, Mo, Sb, and Hg by (at most) 46.28%, 45.92%, 43.01%, 100.00%, 44.45%, and 39.69%, respectively, whereas CPAM decreased the ecotoxicity of bioavailable Cd, Co, and Zn by (at most) 27.49%, 16.10%, and 20.89%, respectively. According to the result of principal component analysis, the main factors affecting the environmental risk of HMs in sediment dewatering were nitrogenous organic compounds (mainly protein substances), fulvic acid substances, and minerals. The most essential factor was nitrogenous organic compounds, which accounted for 89.52% of the total variance. Chemical speciation was apparently more suitable for environmental risk assessment of sediment dewatering than total content. This study provides an important basis for controlling the environmental risk of HMs caused by sediment dewatering.

Distribution and Ecotoxicological Risk Assessment of Heavy Metals in Streams of Amanos Mountains from Southern Turkey

Assessing the potential ecological risks of chemical pollutants like heavy metals is a key tool of a sustainable environment. With this goal, ecotoxicological significant metal (Al, As, Cd, Cr, Cu, Fe, Hg, Ni, Pb, and Zn) levels of the water (n = 32) and sediment (n = 32) samples of streams [rural (8 points) and urban (8 points) sides] on Amanos Mountains were determined by inductively coupled plasma-optical emission spectrometry (ICP-OES) and ecotoxicological risk assessment was performed through the potential ecological risk index (RI). The study region with intense urban activities has also ecological importance with regards to wildlife. It is located on the migration route of birds, hosts loggerhead and green sea turtles, Mediterranean seals, and some terrestrial species like mountain gazelle and striped hyena. All calculated RI values were below the potential risk limits and the ecotoxicological risk was observed to be very low. Metal levels should be monitored periodically, and necessary measures should be taken before the reflection of the increase to be determined by the risk assessment on the ecosystem.

Occurrence, risk assessment, and source of heavy metals in Liaohe River Protected Area from the watershed of Bohai Sea, China

The occurrence, ecological risk, and source of heavy metals in the Liaohe River Protected Area from the watershed of the Bohai Sea were investigated. The maximum concentrations of Cu, Zn, Ni, Cd, Cr, Pb, and As in water were 8.50, 25.22, 3.80, 0.14, 1.76, 8.52, and 3.19 μg/L, respectively. The maximum concentrations of Cu, Zn, Ni, Cd, Cr, Pb, and As in sediment were 27.0, 109, 33.2, 0.56, 318, 43.7, and 29.3 mg/kg, respectively. The percentages of soil samples with observed concentrations above background values were 31.25%, 31.25%, 25%, 28.13%, 56.25%, 34.38%, and 37.5% for Cu, Cr, Zn, Ni, Cd, Pb, and As, respectively. I_geo suggested that sediments were polluted with Cd, Pb, As, Cr, and Zn, whereas soils were contaminated with all seven metals. Potential ecological risk index values exhibited that sites L25 and L12 were classified as moderately polluted in sediment and soil, respectively.

Bioavailability, distribution and health risk assessment of arsenic and heavy metals (HMs) in agricultural soils of Kermanshah Province, west of Iran

Kermanshah Province as an agricultural hub exports food crops to neighboring countries. In this study, contamination status, bioavailability, spatial distribution, and ecological and human health risk of arsenic and heavy metals (HMs) in soil were investigate. For this purpose, 121 agricultural soil samples were collected and analyzed using ICP-MS. The data were studied by calculating some geochemical indices, and using geographical information system and statistical analysis. Results showed that Cd has the highest bioavailability, following by Cu and As. Also, Cu was severely associated with organic matter. Enrichment factor (EF) followed the order of As > Cu > Pb > Se > Cd > Zn > Ni > Cr, and the soil pollution index (SPI) ranged from 0.82 to 2.65. Low potential ecological risk was measured for most of the samples. However, Kermanshah County and Eastern parts of the Province showed the highest HMs enrichment and ecological risk. Moreover, high carcinogenic risk of Cr and Ni threatens the children. Cr showed also high non-carcinogenic hazard index (HI) for children. Principal component analysis (PCA) indicated the anthropogenic origins for As, Cd, Cu, Pb, Se and Zn, while Cr and Ni originated mainly from a geogenic source. Furthermore, Kruskal-Wallis H test revealed that As, Cd, Cr, Cu, Ni, Pb, Se and Zn concentrations were significantly different (p < 0.05) between 16 Counties of the Kermanshah Province. Overall, the management of urban and industrial contamination sources is required to minimize the concentration of bioavailable portion of HMs and preventing residents of the area from being exposed to contaminants.

Assessment of trace element pollution and ecological risks in a river basin impacted by mining in Colombia

Trace element pollution in rivers by anthropogenic activities is an increasing problem worldwide. In this study, the contamination and ecological risk by several trace elements were evaluated along a 100-km stretch of the San Jorge River in Colombia, impacted by different mining activities. The increase of average concentration levels and range of trace elements in sediments (in μg/g) was as follows: Cu 6656 (454-69,702) > Cd 1159 (0.061-16,227) > Zn 1064 (102-13,483) > Ni 105 (31-686) > Pb 7.2 (5.1-11.7) > As 1.8 (1.0-3.2) > Hg 0.31 (0.12-1.37). Results showed that surface sediments could be classified as very high ecological risk index (RI > 600), associated with high contamination of Hg, Cd, and Cu, in stations close mining activities. Values for pollution load index indicate an environmental deterioration (PLI > 1), and sediment quality guidelines (SQGs) suggested that Cu, Ni, Zn, and Hg caused adverse biological effects. We further used pollution indices such as contamination factor (CF), enrichment factor (EF), and geoaccumulation index (Igeo) to assess the extent of contamination. According to these indices, discharges of hazardous chemicals over many years have resulted in a high degree of pollution for Cu, Pb, and Cd, with critical values in stations receiving wastes from mining activities. Multivariate statistical analysis suggested that Hg, Cd, Cu, and Zn derived from gold and coal mining, Ni and As were related from the mining of ferronickel and coal, respectively, whereas the high Pb load was attributed to diffuse source of pollution. In sum, our study provided the first detailed database on metal concentration and ecological risks to organisms in sediments of the San Jorge River Basin, and the current results also suggested future research for public health action.

Trends and Sources of Heavy Metal Pollution in Global River and Lake Sediments from 1970 to 2018

Heavy metal pollution is a global problem although its sources and trends differ by region and time. To data, no published research has reported heavy metal pollution in global rivers and lakes. This study reviewed past sampling data across six continents from 1970 to 2018 and analyzed the trends and sources of 10 heavy metal species in sediments from 289 rivers and 133 lakes. Collectively, river sediments showed increasing trends in Cd, Cr, Ni, Mn, and Co and decreasing trends in Hg, indicating that rivers acted as a sink for the former and a source for the latter. Lake sediments showed increasing trends in Pb, Hg, Cr, and Mn, and decreasing trends in Cd, Zn, and As, indicating that lakes acted as a sink for the former and a source for the latter. Due to difference in natural backgrounds and development stage in continents, mean metal concentrations were generally higher in Europe and North America than in Africa, Asia, and South America. Principal component analysis showed that main metal source was mining and manufacturing from the 1970s to 1990s and domestic waste discharge from the 2000s to 2010s. Metal sources in sediments differed greatly by continent, with rock weathering dominant in Africa, mining and manufacturing dominant in North America, and domestic waste discharge dominant in Asia and Europe. Global trends in sediment metal loads and pollution-control measures suggest that the implementation of rigorous standards on metal emissions, limitations on metal concentrations in manufactured products, and the pretreatment of metal-contaminated waste have been effective at controlling heavy metal pollution in rivers and lakes. Thus, these efforts should be extended globally.

Can climate change transform non-toxic sediments into toxic soils?

Our work addresses a neglected aspect of heavy metal (HM) pollution of sediments in small floodplain reservoirs. Very little is known about this type of water bodies, in contrast to oxbow lakes or old river beds. The study examines the spatial horizontal distribution of HM and the effect of texture, organic carbon (OC) content, morphometric and location features on HM concentrations. Moreover, the data from the assessment of sediment toxicity were analysed with respect to recent years' droughts to estimate the potential toxicity of sediments as soils. The statistical analyses showed that the texture and the OC content had a significant impact on the HM concentrations. Fine-grained and OC-rich sediments exhibited higher HM pollution. Only one morphometric/location factor was shown to affect HM levels in sediments - the angle between the reservoir axis and the riverbed. The angle value affected the texture and, consequently, the HM content: with a rising angle the share of the coarse-grained fraction increased leading to a decrease in the HM concentration. The spatial horizontal HM distribution did not show statistically significant results, nonetheless, HM content was found to rise along with the distance from the initial part of reservoir. The toxicity levels were not exceeded in sediments, however, the evaluation of the material as soil showed that, according to European Union guidelines, the content of at least one HM was toxic in 80% of the samples. Contaminated floodplain reservoirs should be regarded as a double threat to riverine ecosystems. On the one hand, they are one of the main non-point sources of river valley pollution; on the other hand, given the drying up of reservoirs, sediments become soils and the soil-bound heavy metals become more toxic to the environment.

Distribution, contamination and source identification of heavy metals in bed sediments from the lower reaches of the Xiangjiang River in Hunan province, China

Concentrations of heavy metals Ba, Sc, V, Cr, Mn, Co, Ni, Th, U, Cu, Pb, Zn, and Cd in sediments from the lower reaches of the Xiangjiang River were analyzed using inductively coupled plasma mass spectrometry. The results suggest that there are two metal distribution patterns in these sediments: (1) Ba, Sc, V, Cr, Mn, Th, and U are relatively homogeneously distributed and (2) Cd, Pb, Zn Cu, Co and Ni are heterogeneously distributed. The heterogeneously distributed metals are significantly enriched in these sediments and, thereby, contribute to contamination. Assessments of heavy metal contamination using the Geoaccumulation index, Pollution load index, and potential ecological risk index suggest that the levels of contamination from Cd and Mn are extremely high and moderately high, respectively, in all the sediments from the lower river. In comparison, the levels of contamination by Cu, Zn, and Pb varied spatially, decreasing progressively downriver. The level of contamination by Pb, Zn, and Cu in sediments from the Zhuzhou reach is extremely high, and is moderate to significant high for the Xiangtan, Changsha, and Xiangyin reaches. The ecological potential risks posed heavy metals are ranked, in descending order, as Cd > Pb > Cu > Zn > Cr > Ni > Co > Mn for sediments from the Zhuzhou reach and Cd > Pb > Cu > Ni > Cr > Co > Zn > Mn for sediments from the Xiangtan, Changsha, and Xiangyin reaches. Principal component analysis and enrichment factor calculations suggest that Ba, Sc, V, Cr, Th, and U mostly originate from natural processes. While, Cd, Pb, Zn, Cu, Co, Ni, and Mn are derived from both natural processes and anthropogenic activities. Therefore, strategies for environmental protection in this watershed should focus on contamination by Cd, Pb, Zn, and Cu, with Cd requiring particular attention.

Distribution and risk assessment of trace metals in multifarious matrices of Vembanad Lake system, Peninsular India

Trace metal contamination in aquatic ecosystems is of significant concern in countries like India having a recent industrial history. The present study mainly focuses on the spatial and temporal distribution, occurrence and toxicity of five trace metals (Hg, Cd, Zn, Cu and Pb) in water and sediment matrix of Vembanad Lake system (VLS), India. Mercury analysis was done by using Cold Vapor Atomic Fluorescence Spectrometer, and the other metals were analysed using Volta metric-Trace metal analyser. The spatial distribution of trace metals in the study area showed the following trends, Zn > Pb > Cu > Cd > Hg, Zn > Pb > Cu > Hg > Cd for surface water and bottom water respectively. Health risk assessment on human population associated with trace metals was also calculated to predict their health impacts on human through non-dietary exposure. The trace metals contamination in water and sediments of VLS are potential to cause cancer on human population associated with the system. Ecological risk indices showed that the northern portion of VLS is more contaminated with trace metal than the other part of the system.

Mineral and magnetic parameters as proxies for natural radioactivity level in Vaigai river sediment: Horizontal and vertical approach

The present study is aimed to show that the mineral and magnetic parameters are proxies for radioactivity level of Vaigai river sediment. In order to show the usefulness of above said parameters as proxies for radioactivity level of the river, elaborate analyses along with radioactivity level need to be analyzed in horizontal (different locations) and vertical (upper, first, second and third feet) views of the river. The radioactivity analysis shows that average concentrations of ²³⁸U, ²³²Th and calculated absorbed dose rate are within the recommended safety level in all depth samples. Eleven minerals have been identified and characterized by FTIR, and are confirmed by XRD techniques. Based on the calculated results of extinction co-efficient, the amount of major minerals are decreased in the order of quartz > microcline feldspar > orthoclase feldspar > kaolinite in all depth samples. The presence of ordered crystalline quartz in all depth samples have been assessed by the calculated crystallinity index values. These observations are matched with XRD results. Magnetic susceptibility measurement was carried out in horizontal and vertical views which show the presence of dia, ferri, antiferri and ferrihydrate magnetic minerals in present sediments. Studied characteristics and their distributions are almost similar in all the depths. Multivariate statistical analyses include cluster analysis (CA), Factor analysis (FA) and Principal component analysis (PCA) are effective tool to show the above said parameters as proxy and the analyses are carried out. Relevant justification is also given for explaining the parameters as proxy. In the clay mineral, high adsorption of radionuclides and magnetic minerals occurs in lattice defects or onto crystal and grain boundaries due to the high cation exchange capacity. Since, the parameters such as content of clay, magnetic susceptibility and amount of kaolinite (clay) in all depth samples are strongly associated with radioactivity variables, one can say that above said parameters may be proxies for determining the level of radioactivity in Vaigai river sediment.

The role of the estuarine zone on the river particulate toxicity

Annually, a great volume of sediment and suspended particulate matters (SPMs) enters into the seas through estuaries. In the estuarine zone, metals present in SPMs may undergo conservative or non-conservative changes. In the present study, oxidation-reduction potential (ORP) as the most complex chemical parameter of open sea water and its relationship with the behavior of t metals in the estuarine area were investigated. Dissolved oxygen was used as a strong oxidant to increase the ORP. According to the absorption and desorption experiment, Mn and Cu are desorbed from SPMs during estuarine mixing. However, Zn and Pb are absorbed into the SPMs. In addition, the analysis results were indicative of the conservative behavior of Ni. The results of the three-step chemical partitioning of the SPMs revealed that Mn and Cu are desorbed from the SPMs physically, whereas Zn is absorbed into the SPMs chemically. Also, results showed that Pb is physically desorbed from the SPMs, while it is absorbed into SPMs chemically. All metals, except for Ni and Zn, whose reactions with the SPMs are not affected by an increase in the ORP, are affected by the escalation of this parameter.

Effects of mangrove plant species on accumulation of heavy metals in sediment in a heavily polluted mangrove swamp in Pearl River Estuary, China

The present study compared accumulation of heavy metals in a mangrove swamp dominated by Kandelia obovata with that by Sonneratia apetala in Pearl River Estuary, China. The results showed that the concentrations of heavy metals at all sediment depths in the S. apetala site were significantly higher than that in K. obovata. The geo-accumulation index and potential ecological risk index also showed that S. apetala sediment had a higher contamination of heavy metals, especially Cd. S. apetala significantly altered the biogeochemical cycles of Cd, lead (Pb), nickel (Ni) and chromium (Cr). In S. apetala sediment, TOC played an important role in sequestering heavy metals as reflected by its positive correlations with Zn and Pb. This study demonstrated the importance of plant species in altering soil quality and heavy metal accumulation, and S. apetala is more efficiently working as a pollution barrier than K. obovata.

Evaluating the role of particle size on urban environmental geochemistry of metals in surface sediments

In this study, non-destructive techniques (X-ray Diffraction, Infrared and Scanning Electron Microscopy with Energy Dispersive spectroscopies) and invasive procedures (pseudo-total and sequential metal extraction methodologies) were used to highlight the significance of evaluating different particle sizes of sediments for assessing the potential environmental and health implications of metal geochemistry in an urban ecosystem. The variability in composition and properties between bulk (<2 mm) and fine (<63 μm) fractions influenced the availability, and by extension, the toxicity of metals. Indeed, the fine fraction presented not only higher metal pseudo-contents, but also greater available metal percentages. Besides the larger surface area per unit of mass and the high content of clay minerals, it was observed that it was principally Fe/Mn oxyhydroxides that favour adsorption of metals on the fine surface sediments. However, although we demonstrated that the origin of metals in the bulk surface sediments was predominantly lithogenic, use of the <2 mm fraction proved to be a useful tool for identifying different sources of available metals throughout the Deba River catchment. Specifically, discharges of untreated industrial and urban wastewaters, and even effluents from wastewater treatment plants were considered to greatly increase the health risk associated with metal availability. Finally, an evaluation of sediment dynamics in different hydrological conditions has highlighted the role played by each particle size as a vector of metal transport towards the coastal area. While resuspension of fine surface sediments notably induced significantly higher particulate metal concentrations in water during the dry season, resuspension of bulk surface sediments and, fundamentally, downstream transport of suspended particulate matter became more relevant and lowered the ecological risk during the wet season. Greater attention therefore needs to be paid to the new hydrological scenarios forecast to result from climate change, in which longer seasons with low river discharges are forecast.

Assessment of heavy metal contamination, distribution and source identification in the sediments from the Zijiang River, China

In this study, the contents of 10 heavy metals (Sb, Cd, Cr, Mn, Co, Ni, Cu, Zn, As, and Pb) in 49 sediment samples from the Zijiang River were determined by using inductively coupled plasma-optical emission spectrometry. Contamination indexes including geoaccumulation index, modified degree of contamination, sediment quality guidelines, potential ecological risk index, together with potential ecological risk factor were used to assess heavy metal contamination in the sediments of the Zijiang River. Pearson's correlation analysis and principal component analysis were used to identify the sources of heavy metals. The results indicated that the mean values of heavy metals in the Zijiang River's sediments were found to be significantly higher than the corresponding background values. But when comparing with that in other rivers in the world, they were at medium levels except for Sb. Furthermore, a comparison of the heavy metal concentrations and the consensus-based sediment quality guidelines showed that the heavy metal pollutions (Cd, Cr, Ni, Cu, Zn, As, and Pb) tended to occasionally pose harmful impacts on the ecosystem. The values of contamination indexes revealed that serious heavy metal contamination and relatively high potential ecological risks were mainly existed in the downstream of antimony mining and smelting factories (S23-S49). In addition, high potential ecological risks of Sb were observed in sampling sites that were close to those factories (S23, S24, S25, and S27), and high potential ecological risks of Cd were observed in the downstream (S37-S49). Basing on the Pearson's correlation analysis and principal component analysis, three main sources were identified. Co, Zn, Cd, and Cu contaminants were mainly derived from agricultural activities; As, Sb, Mn, and Pb mainly came from mining and smelting activities; Cr and Ni were mainly from natural sources.

Metallic characteristics of PM2.5 and PM2.5-10 for clustered Aeolian Dust Episodes occurred in an extensive fluvial basin during rainy season

Aeolian dust episodes (ADEs) have been an emergency disaster in the Kaoping River Valley during the rainy season (May-September), which can severely deteriorate ambient particulate air quality in the region surrounding the Kaoping River. Thus, this study aims to characterize the metallic fingerprint of Aeolian dust (AD) and investigate the effects of ADEs on ambient particulate air quality along the Kaoping River Valley. Four manual sampling sites adjacent to the riverside were selected to collect fine (PM2.5) and coarse (PM2.5-10) aerosol samples during and after the ADEs in the periods of six events. A total of 13 metallic elements were analyzed using an inductively coupled plasma-atomic emission spectrometer. With metallic elements analysis and nonparametric statistical methods of Wilcoxon rank-sum test and Kruskal-Wallis test, this study successfully derived the metallic indicators of ADEs. The mass ratios of crustal elements (Fe, Ca, or Al) to reference element (Cd) obtained during the ADEs were much higher than those obtained after the ADEs. High mass ratios of Fe/Cd, Ca/Cd, and Al/Cd in PM2.5-10 were observed on the influenced areas of ADEs. Among them, (Fe/Cd)2.5-10 was proven as the best indicator which can be applied to effectively validate the existence of ADEs and evaluate their influences on ambient air quality. Moreover, PM2.5 concentrations during the ADEs were 3-3.6 fold higher than those after the ADEs. PM2.5 should be a contributor to AD, even though the mass ratios of PM2.5/PM10 ranged from 0.05 to 0.20 during the ADEs. Our findings provide valuable information regarding the characteristics of the AD during the ADEs in the Kaoping River.

IMPLICATIONS

Indicators of (Fe/Cd)_2.5-10 are approximately applied to observe the effects of ADEs. Local governments could realize the mechanisms of S- and NW-type aeolian dust episodes (ADEs). They can cause deterioration in different ways for the regional air quality surrounding Kaoping River Valley. Residents who have been living in the influenced areas can take precautions to prevent damage from aeolian dust. Strategies for curbing ADEs must reduce the area of bare lands by artificial measures in the long period of the sunny days during the rainy season. Future research should examine physical conditions of topsoils and other chemical composition in aeolian dust.

Heavy metal contamination in river water and sediments of the Swarnamukhi River Basin, India: risk assessment and environmental implications

The concentration of heavy metals was analyzed each of 20 river water, suspended sediments and bed sediments along the stretch of Swarnamukhi River Basin. River water is not contaminated with heavy metals except Fe and Mn. Contamination factor in sediments shows considerable to very high degree contamination with Cr, Cu, Pb and Zn. The sources of these metals could be residential wastes, sewer outfall, fertilizers, pesticides (M-45 + carbondine) and traffic activities apart from natural weathering of granitic rocks present in the basin area. Principal component analyses indicate the interaction between metals in different media. The comparison of metals (Cu, Pb and Zn) in bed sediments of Swarnamukhi River with the Indian and world averages indicates that the values obtained in the basin are above the Indian averages and far below to the world averages. Average shale values and sediment quality guidelines point toward the enrichment and contamination of Cu, Cr, Pb and Zn to several fold leading to eco-toxicological risks in basin.

Seasonal variations and environmental risk assessment of trace elements in the sediments of Uppanar River estuary, southern India

Twenty four surface sediments were gathered from the Uppanar river estuary, southern India to evaluate the trace element contamination risk in the sediments. The circulation of organic matter and calcium carbonate were controlled by algal blooms and shell fragments. Moreover, the concentrations of iron and manganese in the estuarine sediments were possibly contributed by riverine sources and geogenic processes. The geoaccumulation index, enrichment factor and contamination factor reveals that the sediments were contaminated by copper and chromium. The pollution load index recommends that the estuarine sediments have the risk of pollution. The sediment pollution index highlights that the majority of the sediments are low polluted sediments. The potential ecological risk index discloses that the Uppanar river estuary is under moderate risk. The statistical analysis reveals that the organic matter content is managed by fine fractions and the majority of the trace elements are associated with each other having similar origin.

Bioavailability and toxicity of trace metals (Cd, Cr, Cu, Ni, and Zn) in sediment cores from the Shima River, South China

Five sediment cores (S1-S5) were collected from the Shima River to determine the bioavailability of trace metals (Cd, Cr, Cu, Ni, and Zn) using the modified European Community Bureau of Reference (BCR) procedure. The toxic effects of polluted sediment were assessed using the LUMISTox^® bioassay with Vibrio fischeri and chemical models such as the toxicity unit (TU) of each metal, sum of all TUs (∑TU), and toxic risk index (TRI). The results showed that Cd, Ni, and Zn were present mainly in the acid-soluble and residual fractions, and the residual fraction of Cr accounted for the majority of the metal content (44%), while Cu was present mainly in the reducible and residual fractions. Cd had a mean enrichment factor (EF) of 15.1 and was considered to be severely enriched, while there was a minor enrichment of Cr and moderately severe enrichment of Zn, Cu, and Ni. From the LUMISTox^® bioassay, an acute TU (TUa) value exceeding 0.4 was found at the upper and middle reach sites and was considered to represent slightly acute toxicity, whereas little acute toxicity was found at the lower reach site. The acid-soluble fraction of trace metals was the geochemical fraction mainly responsible for the acute toxicity of the sediment, and acid-soluble Zn and Ni were identified as important contributors to sediment toxicity.

Toxicity profile of organic extracts from Magdalena River sediments

The Magdalena River, the main river of Colombia, receives contaminated effluents from different anthropogenic activities along its path. However, the Magdalena River is used as drinking water source for approximately 30 million inhabitants, as well as a major source of fish for human consumption. Only a few studies have been conducted to evaluate the environmental and toxicological quality of the Magdalena River. To evaluate sediment toxicity, wild-type and GFP transgenic Caenorhabditis elegans were exposed to methanolic extracts, and effects on lethality, locomotion, growth, and gene expression were determined based on fluorescence spectroscopy. These biological and biochemical parameters were correlated with measured pollutant concentrations (PAHs and trace elements), identifying patterns of toxicity along the course of the river. Effects on lethality, growth, and locomotion were observed in areas influenced by industrial, gold mining, and petrochemical activities. Changes in gene expression were evident for cyp-34A9, especially in the sampling site located near an oil refinery, and at the seaport, in Barranquilla City. Body bend movements were moderately correlated with Cr and As concentrations. The expression of mtl-1, mtl-2, hsp-6, and hsp-70 were significantly associated with Pb/U, Pb, Sr, and As/Sr/Pb/U, respectively. Interestingly, toxicity of methanolic as well as aqueous extracts were more prone to be dependent on Cd, Zn, and Th. In general, ecological risk assessment showed sediments display low environmental impact in terms of evaluated metals and PAHs. Different types of waste disposal on the Magdalena River, as a result of mining, domestic, agricultural, and industrial activities, incorporate toxic pollutants in sediments, which are capable of generating a toxic response in C. elegans.

Variations in the Concentration of Magnetic Minerals and Heavy Metals in Suspended Sediments from Citarum River and Its Tributaries, West Java, Indonesia

The Citarum River has a volcanic catchment area in West Java Province, and is one of the nationally strategic rivers in tropical Indonesia due to its roles in water supply and in power generation. The river is economically important, but it is also polluted by industrial, agricultural, and residential wastes. Suspended sediment samples were collected along a certain section of the Citarum River, starting in Balekambang through the area of Bandung Regency to the downstream village of Nanjung, where the river is dammed. Similar samples were also collected from seven tributaries of the Citarum River. Magnetic and heavy metal analyses show that unlike river sediments from a non-volcanic catchment area in temperate climates, magnetic susceptibility values tend to decrease downstream, showing that the magnetic minerals in the upstream area are mostly lithogenic in origin, containing more Fe-bearing minerals compared to those in tributary samples which are anthropogenic in origin. Anthropogenic pollution is also represented by the increase of Zn content along the river. The results suggest that applying magnetic methods for monitoring river pollution in the tropics or in the volcanic areas should be carefully analyzed and interpreted.

Ecological risk assessment and source identification for heavy metals in surface sediment from the Liaohe River protected area, China

Surface sediment samples collected from 19 sites in the Liaohe River protected area were analysed for heavy metals to evaluate their potential ecological risk. The results demonstrated that the degree of pollution from seven heavy metals decreases in the following sequence: cadmium(Cd)>arsenic(As)>copper(Cu)>nickel(Ni)>lead(Pb)>chromium(Cr)>zinc(Zn). The metal speciation analysis indicated that Cd, Pb and Zn were dominated by non-residual fractions and have high mobility and bioavailability, indicating significant anthropogenic sources. Based on the potential ecological risk index (PERI), geo-accumulation index (I_geo) and risk assessment code (RAC), Cd made the most dominant contribution, with a high to very high potential ecological risk being determined in this studied area. Moreover, in reference to the results of multivariate statistical analyses, we deduced that Cd and Zn originated from agriculture sources within the Liaohe River protected area, whereas Cu, Cr and Ni primarily originated from natural sources.

Heavy metals in the riverbed surface sediment of the Yellow River, China

One hundred and eleven riverbed surface sediment (RSS) samples were collected to determine the heavy metal concentration throughout the Inner Mongolia reach of the Yellow River (IMYR), which has been subjected to rapid economic and industrial development over the past several decades. Comprehensive analysis of heavy metal contamination, including the enrichment factor, geo-accumulation index, contamination factor, pollution load index, risk index, principal component analysis (PCA), hierarchical cluster analysis (HCA), and Pearson correlation analysis, was performed. The results demonstrated that a low ecological risk with a moderate level of heavy metal contamination was present in the IMYR due to the risk index (RI) being less than 150 and the pollution load index (PLI) being above 1, and the averaged concentrations of Co, Cr, Cu, Mn, Ni, Ti, V, and Zn in the RSS, with standard deviations, were 144 ± 69, 77.91 ± 39.28, 22.95 ± 7.67, 596 ± 151, 28.50 ± 8.01, 3793 ± 487, 69.11 ± 18.44, and 50.19 ± 19.26 mg kg^-1, respectively. PCA, HCA, and Pearson correlation analysis revealed that most of the RSS was heavily contaminated with Zn, Ni, and Cu, due to the influence of anthropogenic activities; moderately contaminated with Ti, Mn, V and Cr because of the dual influence of anthropogenic activities and nature; and slightly to not contaminated with Co because it occurs mainly in the bordering desert areas. Graphic abstract ᅟ.

Ecological risk, source and preliminary assessment of metals in the surface sediments of Chabahar Bay, Oman Sea

In this study, concentrations of Aluminum (Al), Iron (Fe), Chromium (Cr), Copper (Cu), Nickel (Ni), Vanadium (V), Zinc (Zn), Arsenic (As), Cobalt (Co) and lead (Pb) in the surface sediments from Chabahar Bay were studied to assess the degree of heavy metal pollution as a consequence of natural and anthropogenic sources. Metal contents in the sediments were observed in the order of: Al>Fe>Cr>V>Ni>Zn>Cu>>As>Pb>Co. According to enrichment factor (EF), Arsenic was higher than 1.5 at some sites, indicating anthropogenic inputs. Contents of Ni, As and Cr in the some sampling sites were higher than sediment quality guideline implying adverse impacts of these metals. Based on potential ecological risk (PER), the Chabahar Bay had low ecological risk.

Ecological risk assessment of heavy metals in sediment in the upper reach of the Yangtze River

Heavy metal pollution in China's Yangtze River basin has been of high concern. The concentrations of heavy metals (Cr, Cd, Hg, Cu, Zn, Pb, and As) in the sediment were investigated in the upper reaches of the river, China. Sediment quality guidelines (SQGs), an enrichment factor (EF), an index of geo-accumulation (I geo), and potential ecological risk were used to evaluate the extent of contamination from the heavy metal concentrations in the sediment. Among the seven metals, a noticeable degree of pollution was seen only in the case of Cd and Cd posed a considerable ecological risk at some sample sites. The Pearson correlation analysis was implemented to determine the relationships among the heavy metals, and principal component analysis (PCA) was performed to determine the most common pollution sources. The elements As, Cd, Pb, and Zn were grouped together, and the anthropogenic sources of these heavy metals were closely related. The sites with higher Cd concentrations were mainly confined to the river's reach near industrial areas. Controlling the pollution sources will effectively reduce the pollutant concentrations in the sediment.

Assessment of the hazard posed by metal forms in water and sediments

This study aimed to describe the prevalence heavy metals (Zn, Cu, Pb, and Cd) forms in the ecosystem of the Utrata river in order to determine the mobile forms and bioavailability of metals. To extract the dissolved forms of metals in the water of the Utrata PHREEQC2 geochemical speciation model was used. The river waters show a high percentage of mobile and eco-toxic forms of Zn, Cu and Pb. The percentage of carbonate forms for all the studied metals was low (<1%). The content of carbonates in the water and the prevailing physical and chemical conditions (pH, hardness, alkalinity) reduce the share of toxic metal forms, which precipitate as hardly soluble carbonate salts of Zn, Cu, Cd and Pb. Cu in the water in 90% of cases appeared in the form of hydroxyl compounds. To identify the forms of metal occurrence in the sediments Tessier's sequential extraction was used, allowing to assay bound metals in five fractions (ion exchange, carbonate, adsorption, organic, residual), whose nature and bioavailability varies in aquatic environments. The study has shown a large share of metals in labile and bioavailable forms. The speciation analysis revealed an absolute dominance of the organic fraction in the binding of Cu and Pb. Potent affinity for this fraction was also exhibited by Cd. The rations of exchangeable Zn and Cu forms in the sediments were similar. Both these metals had the lowest share in the most mobile ion exchange fraction.

Distribution, speciation, environmental risk, and source identification of heavy metals in surface sediments from the karst aquatic environment of the Lijiang River, Southwest China

The distribution and speciation of several heavy metals, i.e., As, Cd, Cr, Cu, Hg, Pb, and Zn, in surface sediments from the karst aquatic environment of the Lijiang River, Southwest China, were studied comparatively. The mean contents of Cd, Cu, Hg, Pb, and Zn were 1.72, 38.07, 0.18, 51.54, and 142.16 mg/kg, respectively, which were about 1.5-6 times higher than their corresponding regional sediment background values. Metal speciation obtained by the optimized BCR protocol highlighted the bioavailable threats of Cd, Cu, and Zn, which were highly associated with the exchangeable fraction (the labile phase). Hierarchical cluster analysis indicated that in sediments, As and Cr were mainly derived from natural and industrial sources, whereas fertilizer application might lead to the elevated level of Cd. Besides, Cu, Hg, Pb, and Zn were related to traffic activities. The effects-based sediment quality guidelines (SQGs) showed that Hg, Pb, and Zn could pose occasional adverse effects on sediment-dwelling organisms. However, based on the potential ecological risk assessment (PER) and risk assessment code (RAC), Cd was the most outstanding pollutant and posed the highest ecological hazard and bioavailable risk among the selected metals. Moreover, the metal partitioning between water and sediments was quantified through the calculation of the pseudo-partitioning coefficient (K P), and result implied that the sediments in this karst aquatic environment cannot be used as stable repositories for the metal pollutants.

Behavior of suspended particles in the Changjiang Estuary: Size distribution and trace metal contamination

Suspended particulate matter (SPM) samples were collected along a salinity gradient in the Changjiang Estuary in June 2011. A custom-built water elutriation apparatus was used to separate the suspended sediments into five size fractions. The results indicated that Cr and Pb originated from natural weathering processes, whereas Cu, Zn, and Cd originated from other sources. The distribution of most trace metals in different particle sizes increased with decreasing particle size. The contents of Fe/Mn and organic matter were confirmed to play an important role in increasing the level of heavy metal contents. The Cu, Pb, Zn, and Cd contents varied significantly with increasing salinity in the medium-low salinity region, thus indicating the release of Cu, Pb, Zn, and Cd particles. Thus, the transfer of polluted fine particles into the open sea is probably accompanied by release of pollutants into the dissolved compartment, thereby amplifying the potential harmful effects to marine organisms.

Use of multi-objective dredging for remediation of contaminated sediments: a case study of a typical heavily polluted confluence area in China

Sediments in confluence areas are typically contaminated by various pollutants that have been transported there by inflowing rivers. In this study, we evaluated the pollution status of a confluence area in Lake Chaohu (China). Both the nutrients and hazardous pollutants were analysed. Most sediment cores showed large variations in nutrient concentrations at depths of 10 to 18 cm. Positive release rates of NH4(+)-N and PO4(3-)-P were detected in sediment cores. Hg and Cd were the most typical problematic metal contaminants encountered, and their contamination levels extended to depths of 20 and 25 cm, respectively. Polycyclic aromatic hydrocarbons (mostly acenaphthene and fluorine) were the primary persistent organic pollutants (POPs) present in sediments, and contamination levels frequently could be detected up to a depth of 16 cm. Simulated dredging operations were implemented in the laboratory, with a dredging depth of 15 cm found to be suitable for nutrient suppression. With the goal of suppressing nutrients release and removing high-risk metals and POPs, a multi-objective dredging plan was developed. This plan subdivides the confluence area into five parts that were treated with different dredging depths. A demonstration area was dredged in the most heavily polluted part, and the observed dredging effects were consistent with those expected on the basis of the plan. Such an approach to dredging might also be useful in other areas in the future.

Characterization of the Particle Size Fraction associated with Heavy Metals in Suspended Sediments of the Yellow River

Variations in the concentrations of particulate heavy metals and fluxes into the sea in the Yellow River were examined based on observational and measured data from January 2009 to December 2010. A custom-built water elutriation apparatus was used to separate suspended sediments into five size fractions. Clay and very fine silt is the dominant fraction in most of the suspended sediments, accounting for >40% of the samples. Cu, Pb, Zn, Cr, Fe and Mn are slightly affected by anthropogenic activities, while Cd is moderate affected. The concentrations of heavy metals increased with decrease in particle size. For suspended sediments in the Yellow River, on average 78%-82% of the total heavy metal loading accumulated in the <16 μm fraction. About 43% and 53% of heavy metal in 2009 and 2010 respectively, were readily transported to the Bohai Sea with "truly suspended" particles, which have potentially harmful effects on marine organisms.