Spatial variation, environmental assessment and source identification of heavy metals in sediments of the Yangtze River Estuary

Geochemical elements in suspended particulate matter of Ensenada de La Paz Lagoon, Baja California Peninsula, Mexico: Sources, distribution, mass balance and ecotoxicological risks

The present study aimed to evaluate multi-element concentrations (Al, As, Ca, Cd, Co, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Pb, Sr) in suspended particulate material (SPM) collected from Ensenada de La Paz (ELP) lagoon, Baja California Sur, Mexico in two different periods (September and May) to comprehend their origin, geochemical behavior, mass transfer and associated ecotoxicological risks. The 24 hr variation coefficient of volumetric SPM levels were found to be 51.7% in September and 40.5% in May, signifying the effects of oceanic waters. The calculated enrichment factor (EF) values for all the studied elements were of higher magnitude because of the high surface area and oxide nature of SPM, and in this study, Mo had the highest EF of 46.77 probably due to its origin from continental weathering. From the ecotoxicological perspective, the integrated toxic risk index revealed low toxic risk to the benthic community. However, the mean-ERM-Quotient calculated using the particulate concentrations of As, Cd, Cr, Cu, Ni, Pb indicated 9% probability of toxicity to biota. The comprehensive geochemical and ecotoxicological assessment of particulate metal concentrations in the ELP lagoon signify low to moderate contamination.

Magnetic signature and X-ray fluorescence for mapping trace elements in soils originating from basalt and sandstone

The knowledge of the lithological context is necessary to interpret trace elements concentrations in the soil. Soil magnetic signature (χ) and soil X-ray fluorescence (XRF) are promising approaches in the study of the spatial variability of trace elements and the environmental monitoring of soil quality. This research aimed to assess the efficiency of measurements of χ and XRF sensors for spatial characterization of zinc (Zn), manganese (Mn), and copper (Cu) contents in soils of a sandstone-basalt transitional environment, using machine learning modeling. The studied area consisted of the Western Plateau of São Paulo (WPSP), with soils originating from sandstone and basalt. A total of 253 soil samples were collected at a depth of 0.0-0.2 m. The soils were characterized by particle size and chemical analysis: organic matter (OM), cation exchange capacity (CEC), ammonium oxalate-extracted iron (Feo), sodium dithionite-citrate-bicarbonate-extracted iron (Fed), and sulfuric acid-extracted iron (Fet). Hematite (Hm), goethite (Gt), kaolinite (Kt), and gibbsite (Gb) contents were obtained by X-ray diffraction (XRD). Magnetite (Mt) and maghemite (Mh) contents were obtained by soil χ, while trace elements contents were obtained by XRF and predicted by χ. Descriptive analysis, the test of means, and correlation were performed between attributes. Zn, Mn, and Cu contents were predicted using the machine learning algorithm random forest, and the spatial variability was obtained using the ordinary kriging interpolation technique. Landscape dissections influenced iron oxides, which had the highest contents in slightly dissected environments. Trace elements contents were not influenced by landscape dissections, demonstrating that lithological knowledge is necessary to characterize trace elements in soils. The prediction models developed through the machine learning algorithm random forest showed that χ can be used to characterize trace elements. The similar spatial pattern of trace elements obtained by XRF and χ measurements confirm the applicability of these sensors for mapping it under lithological and landscape transition, aiming for sustainable strategic planning of land use and occupation.

Exploring the Spatial Pattern of Urban Forest Ecosystem Services based on i-Tree Eco and Spatial Interpolation: A Case Study of Kyoto City, Japan

Urban forest, as an essential urban green infrastructure, is critical in providing ecosystem services to cities. To enhance the mainstreaming of ecosystem services in urban planning, it is necessary to explore the spatial pattern of urban forest ecosystem services in cities. This study provides a workflow for urban forest planning based on field investigation, i-Tree Eco, and geostatistical interpolation. Firstly, trees across an array of land use types were investigated using a sampling method. Then i-Tree Eco was applied to quantify ecosystem services and ecosystem service value in each plot. Based on the ecosystem services estimates for plots, four interpolation methods were applied and compared by cross-validation. The Empirical Bayesian Kriging was determined as the best interpolation method with higher prediction accuracy. With the results of Empirical Bayesian Kriging, this study compared urban forest ecosystem services and ecosystem service value across land use types. The spatial correlations between ecosystem service value and four types of point of interest in urban places were explored using the bivariate Moran's I statistic and the bivariate local indicators of spatial association. Our results show that the residential area in the built-up area of Kyoto city had higher species richness, tree density, ecosystem services, and total ecosystem service value. Positive spatial correlations were found between ecosystem service value and the distribution of urban space types including the tourist attraction distribution, urban park distribution, and school distribution. This study provides a specific ecosystem service-oriented reference for urban forest planning based on land use and urban space types.

Three gorges dam shifts estuarine heavy metal risk through suspended sediment gradation

Damming alters downstream sediment supply relationships and erosion in the estuarine delta. Given that sediment grainsize serves as a key parameter for the ability to adsorb heavy metals from water, the assessment of estuarine heavy metal risk needs to get connected initially. Hence, fine suspended sediment (<63 μm) in the Yangtze River estuary (YRE) was divided into four grainsize fractions to simulate the surface suspended sediment concentration (SSC) and grainsize composition before and after the completion of the Three Gorges Dam (TGD). Representative months were selected for flood peak reduction (October) and runoff compensation in the dry season (March) to maximize the scheduling impact of the TGD on runoff and riverine sediment input to the YRE. An improved Water Quality Index (WQI) approach was proposed to assess the combined risk alteration of five heavy metals in six estuarine sensitive targets due to TGD-induced sediment characteristics. The results demonstrated that TGD significantly but tardily reduced the SSC and the proportion of fine sediment in the YRE, decreasing the risk of heavy metals resuspension. Seasonally, the total SSC became higher in the flood season than in the dry season during post-TGD period. However, the fine SSC in the flood season was averaged only 59.7% of that in the dry season due to the pronounced grainsize coarsening effect. As the significant reduction in fine SSC overcomes the increase in heavy metal content per unit of SS, the integrated resuspension risk declined significantly, particularly for Pb and Cr. Spatially, the risk reduction for sensitive targets near the turbidity maximum zone (TMZ) is 8.4 times greater than for inner river channel. However, undiminished anthropogenic metal inputs to the YRE signified greater pressures on the depositional environment.

Geochemical controls on the distribution and bioavailability of heavy metals in sediments from Yangtze River to the East China Sea: Assessed by sequential extraction versus diffusive gradients in thin-films (DGT) technique

This study conducted a comprehensive investigation on the distribution and bioavailability of heavy metals (Cr, Co, Ni, Cu, Zn, Cd and Pb) in sediments along two typical transects from Yangtze River to the East China Sea continental shelf that spanning large physicochemical gradients. Heavy metals were mainly associated with the fine-grained sediments (enriched with organic matter), exhibiting decreasing trends from nearshore to offshore sites. The turbidity maximum zone showed the highest metal concentrations, which evaluated as polluted for some tested metals (especially Cd) using the geo-accumulation index. Based on the modified BCR procedure, the non-residual fractions of Cu, Zn and Pb were higher within the turbidity maximum zone, and significantly negatively correlated with bottom water salinity. The DGT-labile metals all positively correlated with the acid-soluble metal fraction (especially for Cd, Zn and Cr), and negatively correlated with salinity (except Co). Therefore, our results suggest salinity as the key factor controlling metal bioavailability, which could further modulate metal diffusive fluxes at the sediment-water interface. Considering that DGT probes could readily capture the bioavailable metal fractions, and reflect the impacts of salinity, we suggest DGT technique can be used as a robust predictor for metal bioavailability and mobility in estuary sediments.

Long-Term Changes in the Pollution of Warta River Bottom Sediments with Heavy Metals, Poland-Case Study

Variability in the heavy metal concentrations in aquatic environments may be influenced by a number of factors that may occur naturally or due to anthropopressure. This article presents the risk of contaminating Warta River bottom sediments with heavy metals such as As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, and Zn. Samples collected from 35 sites located along the river course were analysed over the period of 2010-2021. The calculated pollution indices are characterised by significant spatial variability that was additionally subject to changes in subsequent years. The analysis may have also been influenced by individual measurement results that, in extreme cases, may strongly deviate from the concentration values determined in the same site during the remaining years. The highest median concentrations of Cd, Cr, Cu, Hg, and Pb were in samples collected from sites that are surrounded by areas of anthropogenic land use. Samples from adjacent sites to agricultural areas showed the highest median concentrations of Co, Mn, and Ni, and Zn for those adjacent to forest areas. The research results indicate that, when analysing the degree of the risk of contaminating river bottom sediments with heavy metals, it is necessary to take into account long-term variability in metal concentrations. Taking into consideration data from only one year may lead to inappropriate conclusions and hinder planning protective measures.

Dietary Chlorella vulgaris effectively alleviates oxidative stress, immunosuppression, and enhances the resistance to Streptococcus agalactiae infection in cadmium-intoxicated Nile tilapia fingerlings

Aquatic pollutants, including cadmium (Cd), cause oxidative stress on aquatic animals. The use of probiotics, including microalgae as a feed additive to alleviate the toxic impacts of heavy metals, is a much more interesting point. Hence, the current study investigated the oxidative stress and immunosuppression in Nile tilapia (Oreochromis niloticus) fingerlings caused by Cd toxicity as well as the preventive function of dietary Chlorella vulgaris against Cd toxicity. Accordingly, fish were fed on 0.0 (control), 5, and 15 g/kg diet of Chlorella up to satiation thrice a day, along with being exposed to 0.0 or 2.5 mg Cd/L for 60 days. Following the experimental procedure, fish from each group were intraperitoneally injected with Streptococcus agalactiae, and their survivability was observed for further ten days. Chlorella-supplemented diets meaningfully (P < 0.05) boosted the antioxidative capability of fish, which was evidenced by higher activities of hepatic superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and glutathione-S-transferase (GST) as well as higher levels of reduced glutathione (GSH) along with significant reductions in hepatic malondialdehyde levels. Moreover, the innate immunity indices [phagocytic activity (PA), respiratory burst activity (RBA), and alternative complement activity (ACH50)] were significantly higher in Chlorella-fed fish, particularly in the group of 15 g/kg diet. Additionally, serum of Chlorella-fed fish showed potent bactericidal activities against S. agalactiae, particularly at the treatment of a 15 g/kg diet. Feeding Chlorella diets to Nile tilapia fingerlings upregulated SOD, CAT, and GPx genes expression alongside the down-regulation of IL-1β, IL-8, IL-10, TNF-α, and HSP70 genes expression. Conversely, Cd toxicity caused oxidative stress and suppressed the fish's innate immunity with upregulation of the expression of IL-1β, IL-8, IL-10, TNF-α, and HSP70 genes. Feeding Cd-exposed fish on Chlorella-containing diets attenuated these adverse effects. The current research revealed that supplementing feeds with the treatment of 15 g/kg diet of C. vulgaris supports the antioxidant-immune responses and alleviates the Cd toxicity effects on Nile tilapia fingerlings.

Potential arsenic-chromium-lead Co-contamination in the hilly terrain of Arunachal Pradesh, north-eastern India: Genesis and health perspective

In the recent times, multi-metal co-contamination in the groundwater of various parts of the globe has emerged as a challenging environmental health problems. While arsenic (As) has been reported with high fluoride and at times with uranium; and Cr & Pb are also found in aquifers under high anthropogenic impacts. The present work probably for the first time traces the As-Cr-Pb co-contamination in the pristine aquifers of a hilly terrain that are under relatively less stress from the anthropogenic activities. Based on the analyses of twenty-two (n = 22) groundwater (GW) samples and six (n = 6) sediment samples, it was found that Cr being leached from the natural sources as evident from 100% of samples with dissolve Cr exceeding the prescribed drinking water limit. Generic plots suggests rock-water interaction as the major hydrogeological processes with mixed Ca²⁺-Na⁺-HCO₃^- type water. Wide range of pH suggests localized human interferences, as well as indicative of both calcite and silicate weathering processes. In general water samples were found high only with Cr and Fe, however all sediment samples were found to contain As-Cr-Pb. This implies that the groundwater is under-risk of co-contamination of highly toxic trio of As-Cr-Pb. Multivariate analyses indicate that the changing pH as the causative factor for Cr leaching into the groundwater. This is a new finding for a pristine hilly aquifers, and we suspect such condition may also be present in other parts of globe, and thus precautionary investigations are needed to prevent this catastrophic situation to arise, and to alert the community in advance.

Vertical distribution, contamination status and ecological risk assessment of heavy metals in core sediments from a mangrove-dominated tropical river

Understanding the vertical distribution of heavy metals aids in tracing the contamination history, however, it is limited for mangrove-dominated river. Thus, this study aimed to assess the vertical distribution of nine heavy metals and their possible ecological risk in several layers of core sediments from a mangrove-dominated river inside the Sundarban mangrove forest (World heritage and Ramsar site), Bangladesh. 45 core samples from five stations were analyzed using Flame Atomic Absorption Spectrophotometer (FAAS). The findings showed that, with the exception of Fe, Ni, and Cu, which suggested increased metal release in recent times, higher metal levels were recorded in the surface layer (0-10 cm), followed by the middle layer (10-20 cm), and inner layer (20-30 cm) of sediment cores. When compared to non-industrial forest sediment, core sediment from industrial sites contained noticeably more metals (p < 0.05). Overall, the mean metal concentration (mg/kg) followed the increasing order of Cd < As < Pb < Cu < Cr < Zn < Ni < Mn < Fe. Among the studied metals, the levels of Cd and Ni exceeded the average shale value. Contamination indices such as enrichment factor (EF), contamination factor (CF), and geo-accumulation index (I_geo) showed that the studied sediments were only contaminated by Cd. Ecological risk assessed by ecological risk factor (E_rⁱ) and risk index (RI) suggested that the analyzed heavy metals, with the exception of Cd, posed no significant ecological threats. All of the heavy metals analyzed might have originated from similar anthropogenic sources, according to the correlation matrix, cluster analysis (CA), and principal component analysis (PCA).

Significance of the great protection of the Yangtze River: Riverine input contributes primarily to the presence of PAHs and HMs in its estuary and the adjacent sea

The Yangtze River protection strategies are expected to improve the water quality and ecological function of the Yangtze River Estuary (YRE). The concentrations of 16 polycyclic aromatic hydrocarbons (PAHs) and 6 heavy metals (HMs) in the YRE were measured and the riverine fluxes were calculated subsequently. In particular, the concentrations of low molecular weight PAHs (LMW-PAHs), arsenic (As) and mercury (Hg) in seawater decreased over time, while those of other studied pollutants did not change a lot. In sediments, the concentration changes for all the pollutants were insignificant. For the present pollutants, the river input is the dominant source, and the flux decreased after the protection. The contribution of the discharge from wastewater treatment plants (WWTPs) was quantified. Its influence cannot be ignored. The seafood quality remained stable and the risk via diet was insignificant. Long-term monitoring is necessary, and the positive impact of the Protection Strategy is gradually emerging.

Characteristic regional differences in trace element pattern of 2014 German North Sea surface Wadden sediments - A judge and assessment

The European Marine Strategy Framework Directive (MSFD) requires good ecological status of the marine environment. This also includes the Wadden Sea located in the southeastern part of the North Sea and its chemical status of sediments. Based on results from campaigns conducted in the 1980s, 32 surface sediment samples were taken in 2014 to check whether the sampling strategy required for characterizing the trace element content in sediments is representative and to determine the degree of pollution and potential changes over the last decades. For this purpose the elemental mass fractions of 42 elements were assessed in the ≤20 μm grain size fraction of the surface sediments. Based on cluster analysis a clear correlation between the element distribution and the geographical location of the sampling locations of the German Wadden Sea could be found. As a result of the principal component analysis, three sub-catchments were significantly separated from each other by the characteristic element distributions in the sediments (Norderney and Weser, Elbe and offshore areas, and North Friesland). With the help of discriminant analysis, the classification was confirmed unambiguously. Small anomalies, such as potentially contaminated sites from WWII, could be identified. This proved that the sampling strategy for sediment characterization with reference to trace elements in the Wadden Sea of the German Bight is representative. The impact of regulation and changes on the overall sediment quality is most evident when looking at the environmentally critical elements such as As, Cd, Hg, and Cr. For these elements the mean mass fractions show a significant reduction over the last three decades. Current sediments feature only slightly elevated mass fractions of Ag, Cd, Ce, Cs, Nd, Pb and Se at some sampling locations.

Spatiotemporal patterns and influencing factors of dissolved heavy metals off the Yangtze River Estuary, East China Sea

Dissolved heavy metal pollution in the ocean is becoming an environmental concern. Their distribution patterns are complex and influenced by multiple factors in the coastal ocean. Therefore, more investigations are needed to understand their behavior in the seawater. This study systematically investigated the distribution of Cu, Pb, Cd, As, Zn and seawater properties in the surface and bottom water off the Yangtze River Estuary, East China Sea in spring, summer and autumn, 2019. The results showed significant spatiotemporal distribution that three-zone-pattern of estuary, nearshore, and offshore can be divided. While sources, hydrodynamics, biological uptake and sediment resuspension affected the overall distribution, dissolved oxygen and pH dominantly influenced the estuary and offshore respectively, with more complex factors in the nearshore. Low ecological risks were assessed during the study, but global warming, ocean acidification and hypoxia are essential concerns to understand the biogeochemistry of dissolved heavy metals in the ocean.

Evaluation of ecotoxicological effects associated with coastal sediments of the Yellow Sea large marine ecosystem using the marine copepod Tigriopus japonicus

A copepod bioassay with Tigriopus japonicus was applied to evaluate the relative ecotoxicity of sediments in the Yellow and Bohai seas, and contributions of individual PAHs to copepod toxicity were evaluated. Mean toxicity was greatest in the Yellow Sea of China, followed by the Bohai Sea and Yellow Sea of Korea. Elevated concentrations of sedimentary PAHs, alkylphenols, and styrene oligomers back-supported the significant toxicities observed in bioassay. Copepod toxicity in relation to PAHs indicated the greatest contribution by indeno[1,2,3-c,d]pyrene. However, lacked contribution by PAHs, viz., 2.4 and 3.0 % for the total immobilization and mortality, respectively, indicated a large proportion of unknown toxicants being widely distributed along the Yellow Sea Large Marine Ecosystem (YSLME) coastline. Overall, the present study provides useful baseline information for evaluating the potential sedimentary toxicants, with emphasizing further investigation to identify the unknown toxicants at an LME scale, and elsewhere.

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.

Environmental Geochemistry and Fractionation of Cadmium Metal in Surficial Bottom Sediments and Water of the Nile River, Egypt

Heavy metals such as cadmium (Cd) pollute the environment. Heavy metal pollution endangers the Nile River since it serves as an irrigation and freshwater source for the cities and farms that line its banks. Water and sediment samples from the Nile River were tested for Cd content. In addition, a sequential experiment analytical method was performed to determine the metal's relative mobility. According to the data, there is an average of 0.16 mg kg-1 of Cd in sediments. The BeniSuef water treatment plant and brick factory, the iron and steel factory of Helwan, the oil and detergent factory of Sohag, and the discharge of the cement factory in Samalut had the greatest concentration of Cd in their vicinity. According to the risk assessment code, there are four categories of Cd: residual (57.91%), acid-soluble (27.11%), reducible (11.84%), and oxidizable (3.14%). Bioavailable and mobile Cd levels in sediment and water were found in Beni Suef, Aswan; Helwan; Samalut; Sohag; and Helwan. Because the other metal is highly bioavailable, its concentration is not a risk factor at the Samalut station. Cd's toxicity and bioaccumulation make it an extra hazard to aquatic animals and human life. There should be a deterministic approach to monitoring Cd near industrial sources.

Interactions of Co, Cu, and non-metal phthalocyanines with external structures of SARS-CoV-2 using docking and molecular dynamics

The new coronavirus, SARS-CoV-2, caused the COVID-19 pandemic, characterized by its high rate of contamination, propagation capacity, and lethality rate. In this work, we approach the use of phthalocyanines as an inhibitor of SARS-CoV-2, as they present several interactive properties of the phthalocyanines (Pc) of Cobalt (CoPc), Copper (CuPc) and without a metal group (NoPc) can interact with SARS-CoV-2, showing potential be used as filtering by adsorption on paints on walls, masks, clothes, and air conditioning filters. Molecular modeling techniques through Molecular Docking and Molecular Dynamics were used, where the target was the external structures of the virus, but specifically the envelope protein, main protease, and Spike glycoprotein proteases. Using the g_MM-GBSA module and with it, the molecular docking studies show that the ligands have interaction characteristics capable of adsorbing the structures. Molecular dynamics provided information on the root-mean-square deviation of the atomic positions provided values between 1 and 2.5. The generalized Born implicit solvation model, Gibbs free energy, and solvent accessible surface area approach were used. Among the results obtained through molecular dynamics, it was noticed that interactions occur since Pc could bind to residues of the active site of macromolecules, demonstrating good interactions; in particular with CoPc. Molecular couplings and free energy showed that S-gly active site residues interacted strongly with phthalocyanines with values ​​of - 182.443 kJ/mol (CoPc), 158.954 kJ/mol (CuPc), and - 129.963 kJ/mol (NoPc). The interactions of Pc's with SARS-CoV-2 may predict some promising candidates for antagonists to the virus, which if confirmed through experimental approaches, may contribute to resolving the global crisis of the COVID-19 pandemic.

Behaviour and distribution of arsenic in seawater and suspended particulate matter in the adjacent area of the Changjiang Estuary during summer and autumn

Water and suspended particulate matter (SPM) were collected from the Changjiang Estuary and its adjacent areas during summer (July) and autumn (October) to study the distributions and partitioning of arsenic. The dissolved arsenic (DAs) and particulate arsenic (PAs) concentration distributions were strongly affected by inputs from riverine discharge and water masses in the East China Sea, generally exhibiting a decreasing trend from inshore to offshore. The DAs concentration was higher in the surface water due to the influence of seawater stratification in summer, but it was not obvious in autumn. DAs and PAs concentrations in the estuary were significantly higher in autumn than in summer. Seasonal variations in arsenic were due to seasonal differences in riverine input (mainly the Changjiang River) and the intrusion of water masses. PAs showed a positive correlation with both SPM and turbidity. The highest PAs concentration was observed in the northern Changjiang Estuary affected by the YSCC, with higher turbidity during autumn. The higher concentration of PAs in autumn was affected by the high SPM input and resuspension of sediment. The water-particulate distribution coefficient of As in summer showed an increasing tendency with salinity, which might be caused by the decrease in the diameter of suspended particles in the open sea.

Assessment of metal enrichment and contamination in surface sediment of Mandovi estuary, Goa, West coast of India

Metal concentration in the sediments was determined to assess the metal enrichment and level of contamination in the Mandovi estuary. The metal distribution in the Mandovi estuary revealed preferential input through open-cast iron-ore mining, industrial, fishing, and agricultural activities. The heavy riverine runoff associated with high rainfall influenced the distribution of Mn, Zn, and Pb during monsoon season. In addition, sediment grain size and associated organic matter governed metal distribution in surface sediments. The role of grain size and organic matter along with Fe-Mn oxides in the distribution of metals was construed through correlation and factor analysis. Geo-accumulation index, contamination factor, and potential contamination index indicated contamination of surficial sediments of the Mandovi estuary with Cr and Pb.

Mitigation of petroleum-hydrocarbon-contaminated hazardous soils using organic amendments: A review

The term "Total petroleum hydrocarbons" (TPH) is used to describe a complex mixture of petroleum-based hydrocarbons primarily derived from crude oil. Those compounds are considered as persistent organic pollutants in the terrestrial environment. A wide array of organic amendments is increasingly used for the remediation of TPH-contaminated soils. Organic amendments not only supply a source of carbon and nutrients but also add exogenous beneficial microorganisms to enhance the TPH degradation rate, thereby improving the soil health. Two fundamental approaches can be contemplated within the context of remediation of TPH-contaminated soils using organic amendments: (i) enhanced TPH sorption to the exogenous organic matter (immobilization) as it reduces the bioavailability of the contaminants, and (ii) increasing the solubility of the contaminants by supplying desorbing agents (mobilization) for enhancing the subsequent biodegradation. Net immobilization and mobilization of TPH have both been observed following the application of organic amendments to contaminated soils. This review examines the mechanisms for the enhanced remediation of TPH-contaminated soils by organic amendments and discusses the influencing factors in relation to sequestration, bioavailability, and subsequent biodegradation of TPH in soils. The uncertainty of mechanisms for various organic amendments in TPH remediation processes remains a critical area of future research.

Heavy metal pollution and toxicity assessment in Mallorquin swamp: A natural protected heritage in the Caribbean Sea, Colombia

This work reports the level and ecotoxicity impact of metals in the sediments of the Mallorquín swamp, a protected coastal lagoon in the Caribbean coast of Colombia. The distribution of metals was in the following decreasing order: Zn > Cu > Pb > Cd > Hg, showing statistically significant differences among sites. The average Pb and Cd concentrations in sediments were about 17 and 5 times higher, respectively, compared to those in background values. Several contamination indices suggested moderate contamination of Hg, Cu, and Zn, and strong pollution due to Cd and Pb. Multivariate analysis revealed spatial variations for metals and its anthropogenic origin, such as municipal and industrial wastewater discharges (Pb, Zn, and Hg) and agricultural activities (Cd and Cu). These findings showed the negative impact of human activities and the need to apply protective management strategies.

Distribution profile of heavy metals and associated contamination trend with the sedimentary environment of Pakistan coast bordering the Northern Arabian Sea

Spatiotemporal distributions of heavy metals (HMs) and their contamination status linked with the sedimentary environment were investigated in 2 monitoring years (MY-I and MY-II) along the Pakistan coast. The concentrations of HMs in sediments were analyzed through an atomic absorption spectrometer and presented the following order: Fe > Zn > Cu > Pb ≈ Cr > Ni > Co > Cd in MY-I and Fe > Cr > Zn > Ni > Cu > Pb > Co > Cd in MY-II. In the coastal sediments, all HMs surpassed the edges of shale values and sediment quality guidelines, excluding Fe. The burial flux (F_B), mass inventory (M_I), and deposition flux (F_D) of HMs were evaluated and compared to explore the potential of sediments to adsorb and desorb the metals into the marine environment during the last decade. Metal-specific pollution indices (I_geo, EF, C_f, and E_r) presented moderate contamination of Cu, Zn, Cr, Ni, and Co but considerable contamination of Pb and Cd in sediments. However, site-specific geoindicators (CD, RI, and PLI) signified the Sandspit as the highest polluted site along the coastal vicinity. Multivariate analyses via principal component analysis (PCA) and cluster analysis (CA) also highlighted the significant interactions between geochemical properties. The current study concluded the high pollution state toward the HMs and rendered the knowledge for policymaking and conserving the coastal and estuarine environment of Pakistan bordering the Northern Arabian Sea.

Occurrence of microplastics and heavy metals accumulation in native oysters Crassostrea Gasar in the Paranaguá estuarine system, Brazil

The ubiquitous presence of contaminants in the marine environment is considered a global threat to marine organisms. Heavy metals and microplastics are two distinct classes of pollutants but there are interactions between these two stressors that are still poorly understood. We examined the potential relationship between heavy metals (Al, Cr, Mn, Fe, Ni, Cu, Zn, As, Cd, Ba, Hg, Pb) and microplastic particles in oysters sampled along the Paranaguá Estuarine System. The results suggested high levels of As and Zn in the bivalves, which are destined for human consumption. Microplastic particles were found in oysters from all sampled locations, demonstrating the spread of this pollutant in the marine environment and its ability to bioaccumulate in oysters. However, our data did not demonstrate a direct relationship between microplastics and heavy metals, suggesting that these particles are not the main route for heavy metal contamination of oysters in the Paranaguá Estuarine System.

Assessment of trace metal contamination in the core sediment of Ramsar wetland (Kabar Tal), Begusarai, Bihar (India)

The concentration of trace metals Mn, Pb, Ni, Zn, and Cu in the core sediment from Kabar Tal wetland was analyzed to understand the level of contamination in the vertical profile. Additionally, total organic carbon (TOC) and available phosphorus (AP) were also analyzed to infer the biogeochemistry of trace metals and the correlation that exists among them. Five core sediments were collected at the end of the monsoon season from different locations in the study area, representing diverse anthropogenic and agricultural activities. The average concentration of trace metals in sediments followed the order Mn > Pb > Ni > Zn > Cu. The trace metal concentration in the surface sediments was higher and decreased with depth in the vertical profile. Contamination factor (CF), geoaccumulation index (Igeo), enrichment factor (EF), and pollution load index (PLI) were used to evaluate sediment quality and the pollution status of the lake sediments. Cu, Zn, and Ni showed minor to moderate enrichment, and Pb showed a severe level of enrichment in all the core sediment samples. However, the sediment quality guidelines' index indicates that the sediments are moderately polluted with copper, zinc, and nickel and severely polluted with lead. There exists a strong positive correlation among Pb-Ni, Ni-AP, and AP-Pb, and a strong negative correlation among TOC-Ni, TOC-Pb, and TOC-AP for all the sediment samples. Additionally, the principal component analysis (PCA) and cluster analysis (CA) suggest that a good similarity exists among Pb, Ni, and Zn. The study indicates that trace metals in wetland sediments have originated from multiple anthropogenic sources like agricultural runoff (fertilizers), direct addition of solid wastes, discharge of untreated wastewater, and long-range transport from the oil refinery in the wetland.

Identification and uncertainty analysis of high-risk areas of heavy metals in sediments of the Yangtze River estuary, China

In this study, ordinary kriging (OK) and indicator kriging (IK) were used to analyze the uncertainty associated with high-risk areas of seven heavy metals (As, Cd, Cr, Cu, Hg, Pb, and Zn) in sediments of the Yangtze River estuary during four seasons. The OK results showed that the high-risk areas of Cd, Cr, Cu, Hg, and Pb had a high proportion, with the highest corresponding to Cr pollution (up to 60%). Predictions based on IK revealed that the proportion of high-risk areas of Cr, Cd, and Hg pollution were high, especially that of Cr was higher than 90%. However, there were uncertainties between the OK and IK results. The uncertainty results revealed that the uncertainty areas of Cr pollution were relatively large, accounting for about 30%, while those of Cd, Cu, and Hg pollution were lower than 10%.

Titanium and zinc-containing nanoparticles in estuarine sediments: Occurrence and their environmental implications

Understanding the behavior and risk of nanoparticles (NPs) in the aquatic environment is currently limited by the lack of quantitative characterization of NPs in the environmental matrices, such as sediments. In this study, based on the single particle (SP)-ICP-MS technique, metal-containing NPs, including Ti- and Zn-containing NPs, were analyzed in sediments taken along the Yangtze Estuary. Combined with the traditional sequential extraction method that has been widely used for metal risk assessment, different single extraction methods were used to understand the association of NPs with different chemical fractions in sediments and their potential environmental implications. Ti-containing NPs, with an average size of 81 nm, ranged from 3.02 × 10⁷ parts/mg to 9.61 × 10⁷ parts/mg, and Zn-containing NPs, with an average size of 41 nm, ranged from 2.47 × 10⁶ parts/mg to 1.21 × 10⁷ parts/mg. Both correlation and redundancy analyses showed that particle concentrations of Ti-containing NPs in sediment were significantly correlated to the Ti-containing NPs in the residual fraction and salinity, indicating that Ti-containing NPs in sediments may be dominated by Ti-containing NPs in the residue fractions of sediments. Large amounts of these NPs may be released from the residual fraction that has been considered to be not bioavailable and "environmentally safe" in the traditional environmental risk assessment of metals in sediments. Zn-containing NPs, mostly associated with carbonates, were positively correlated to all the bioavailable fractions of Zn in sediments, suggesting that these NPs may be largely presented in the bioavailable fraction. This study showed that, vast numbers of NPs with minute sizes were present in estuarine sediments, and that they were associated with different chemical fractions with different potential environmental risks. The study findings call for further research to update the traditional risk assessment method.

Heavy metal pollution in the East China Sea: A review

Due to rapid urbanization and industrialization, heavy metal (HM) pollution in coastal areas of the East China Sea (ECS) has attracted extensive attention. This article attempts to review recent studies on the temporal and spatial distributions, ecological risks, and possible sources of HMs in typical bays and estuaries of ECS. The levels of HMs are closely related to local economic development and local characteristics. The anthropogenic activities and the particle size of sediments are important factors affecting the distribution of HMs. During the late 1970s to the 1990s, HMs levels in the Yangtze Estuary (YRE) sediments showed an upward tendency due to the increased emissions. However, HMs levels in the early 2000s were lower than that in the late 1970s to the mid-1990s. Cd caused serious pollution and brought potential ecological risks in the Yangtze Estuary, Hangzhou Bay (HZB), Sanmen Bay (SMB), and Quanzhou Bay (QZB). In Fujian province of China, the Quanzhou Bay was heavily polluted by HMs and high contents of HMs were found in biota. Among different species, molluscs in the coastal areas of ECS have the highest levels of HMs exceeding safety limits.

Assessing the remobilization and fraction of cadmium and lead in sediment of the Jialing River by sequential extraction and diffusive gradients in films (DGT) technique

Cadmium (Cd) and lead (Pb) are two typical heavy metals of the Jialing River, and their threat to the river has been considered by the government in recent years. In this study, the diffusive gradient in thin films (DGT) technique and sequential extraction were employed together to analyse the remobilization and fraction of Cd and Pb in the sediments. The total concentration of Cd and Pb in four sampling sites both followed the order S3>S4>S2>S1. The sequential extraction results indicated that large amounts of Cd and Pb (over 50% of the total concentration) were bound to the exchangeable and reducible fraction. The DGT results showed that both Cd and Pb presented a significant increasing trend at the bottom of the DGT probe (-10 cm to -12 cm) and that the two metals had a significant positive correlation (r = 0.831, p < 0.01). The apparent diffusive flux result indicated that Cd and Pb had a potential risk of release from surface sediments. A significant correlation was observed between the DGT-labile fraction and sequential extraction at the surface sediments. A further correlation analysis found that the concentration of labile Cd/Pb measured by DGT (C_DGT-Cd and C_DGT-Pb) had a strong negative correlation with C_DGT-Fe, and this process was mainly mitigated by the iron oxides in the sediments. In addition, the correspondence of a "dark area" of AgI gel with corresponding "hotspots" of Chelex gel also proved that the release of Cd and Pb may regulate the dissolved sulfide in the sediments.

Antibiotic resistance genes (ARGs) and their associated environmental factors in the Yangtze Estuary, China: From inlet to outlet

The occurrence of antibiotic resistance genes (ARGs) and their associated environmental factors in estuaries are poorly understood. In this study, we comprehensively analyzed ARGs in both water and sediments from inlet to outlet of the Yangtze Estuary, China. The relative abundances of ARGs were higher in the turbidity maximum zone (TMZ) than other sites, implying that suspended particulate matter (SPM) was the major reservoir for ARGs in water. ARGs showed an increasing trend from inlet to outlet in sediments. Positively correlation between intI1 and sul1 in both water and sediments indicated that sul1 may be regulated by intI1. Correlation analysis and redundancy analysis showed that the spatial variations of estuarine ARGs were positively correlated with sample properties (e.g., temperature, SPM, pH) and chemical pollutants (e.g., heavy metals and antibiotic residues), among which chemical pollutants were the major drivers for the ARG distribution in both water and sediments.

Elemental Contaminants in Surface Sediments from Jiulong River Estuary, China: Pollution Level and Ecotoxicological Risk Assessment

Estuaries, being the transitional zones between freshwater and marine environments, are important for protecting and rehabilitating the aquatic environments. Sediments from freshwater and marine environments were studied in Jiulong River Estuary (JRE) in different years for rare earth elements (REEs) and some environmentally important metal and metalloid elements (MMEs). The concentration of REEs ranged from 0.11 (Tm) to 296.20 mg kg−1 (Ce), while that of MMEs ranged from 0.40 (Cd) to 86,000 mg kg−1 (Al). The temporal analysis indicated an increase of both REEs and MMEs contaminants from 2012 to 2018. Fractionation of REEs and Ce and Eu anomalies indicated natural weathering, erosion processes and changes in redox chemistry at the sampling sites. Spatial structure analysis showed relatively higher levels of both REEs and MMEs in the freshwater sediments. These variations among the sampling sites indicated different land use and anthropogenic activities. The values of enrichment factor (EF) and geoaccumulation index (Igeo) indicated anthropogenic sources of accumulation, while, ecological risk assessment (Eix) and potential ecological risk index (PERI) indicated potential hazards for biota due to the accumulation of Pb, Zn and As elements.

Spatial and seasonal distribution of multi-elements in suspended particulate matter (SPM) in tidally dominated Hooghly river estuary and their ecotoxicological relevance

The present work represented first study of the spatio-seasonal distribution of the multi-elements in the suspended particulate matter (SPM) of the tropical Hooghly river estuary (HRE), eastern part of India. The high load of SPM (20-3460 mg/l) might have induced negative impact on the phytoplankton density. The relative abundance of the studied elements exhibited the following decreasing trend (concentration in μg/g and %): Si(26.44 ± 3.75%) > Al(7.94 ± 1.52%) > Fe(6.17 ± 1.9%) > K(3.05 ± 1.5%) > Ca(1.97 ± 1.11%) > Mg(1.57 ± 1.71%) > Na(1.45 ± 8.40%) > Mn(1273 ± 2003) > Zn(178.43 ± 130.95) > V(151.54 ± 27.13) > Cr(147.08 ± 32.21) > Cu(62.06 ± 14.03) > Ni(49.64 ± 12.09) > Pb(21.5 ± 10.45). The accumulation of Ni, Cr, Pb, and Cu is mainly controlled by the formation of Fe hydroxides along with particulate organic carbon (POC) and salinity. The average geo-accumulation index (I_geo) and enrichment factor (EF) endorsed the substantial input of Cr (I_geo = 0.037; EF = 1.61) and Zn (I_geo = 0.123; EF = 2.07) from diffused pollution sources. From ecotoxicological point of view, the quality guidelines (QGs) suggested that Cr and Ni might possess frequent adverse biological effects. However, the mean probable effect level (PEL) quotient values revealed 49% probability of toxicity to the aquatic biota for five toxic elements (Cr, Ni, Cu, Zn, and Pb). The geochemical approaches, pollution indices, and statistical evaluation together revealed low to moderate contamination in the estuary. This baseline data would be beneficial in adopting proper management strategies for sustainable utilization and restoration of the water resources. The authors strongly recommend continuous systematic monitoring and installation of treatment plants for management of this stressed estuary.

Organic soil additives for the remediation of cadmium contaminated soils and their impact on the soil-plant system: A review

Immobilization is among the most-suitable strategies to remediate cadmium (Cd) contaminated sites. Organic additives (OAs) have emerged as highly efficient and environment-friendly immobilizers to eradicate Cd contamination in a wide range of environments. This review article is intended to critically illustrate the role of different OAs in Cd immobilization and to highlight the key findings in this context. Owing to the unique structural features (high surface area, cation exchange capacity (CEC), presence of many functional groups), OAs have shown strong capability to remediate Cd polluted soils by adsorption, electrostatic interaction, complexation and precipitation. Research data is compiled about the efficiency of different OAs (bio-waste, biochar, activated carbon, composts, manure, and plant residues) applied alone or in combination with other amendments in stabilization and renovation of contaminated sites. In addition to their role in remediation, OAs are widely advocated for being classical sources of essential plant nutrients and as agents to improve the soil health and quality which has also been focused in this review. OAs may contain considerable amounts of metals and therefore it becomes essential to assess their final contribution. Elimination of Cd contamination is essential to attenuate the contaminant effect and to produce the safe food. Therefore, deployment of environment-friendly remediation strategies (alone or in combination with other suitable technologies) should be adopted especially at early stages of contamination.

Mini review of trace metal contamination status in East China Sea sediment

This study reviewed the published papers and employed the guideline values of USEPA (ERL and ERM) and China (MSQ, Class I, II, III) to assess the contamination status of potential toxic metals in East China Sea sediment (ECS). The percentages of metal concentrations exceeding the ERL value follow the sequences: Ni (96%) > As(71%) > Cr(53%) > Cu (19%) > Zn (2.4%) > Hg (0.5%) > Pb (0.4%) > Cd (0%). The similar ranking is also seen for MSQ class I. All metal concentrations were less than the ERM value, except Ni of which value 10.3% exceeded the ERM value. The potentially ecological risk from these sedimentary metals could be reduced because they were mainly present in the residual fraction, which is not available for marine organisms. It seems that the Ni ERL value is too low (20.8. mg kg^-1), close to the value (18.6 mg kg^-1) of the upper continental crust, to obey.

Occurrence, migration, and allocation of arsenic in multiple media of a typical semi-enclosed bay

Under the gradients of salinity and redox, the transportation and distribution of dissolved, particulate, and sedimentary arsenic present differences from estuary to bay. Samples of water, suspended particulate sediment (SPS), and sediment from the Jiaozhou Bay were analyzed. The concentrations of arsenic decreased significantly from the estuaries toward the bay. The sedimentary arsenic mostly existed as hydrous oxide-bound and residual fractions and tended to be attached to smaller particles. Sedimentary particles were more capable of absorbing arsenic than SPS and the capacity increased from the estuaries toward the bay. The spatial distribution of arsenic was impacted by the residual currents, resulting in higher contents of dissolved arsenic in the eastern coastal zone and higher concentrations of sedimentary arsenic in the inner bay. In water, total phosphorus (TP), dissolved organic carbon (DOC), and alkalinity had significant positive correlations with the dissolved arsenic. In sediments, Fe oxides and sediment organic matter (SOM) would promote adsorption of arsenic. The significant correlation between non-residual fractions and enrichment factors of arsenic indicated that the sedimentary arsenic was more likely to originate from anthropogenic sources, mainly impacted by riverine transport from the eastern urban regions and agricultural production in the western farmland.

Assessment of heavy metals in water, sediment and shellfish organisms in typical areas of the Yangtze River Estuary, China

Identifying the transformations of heavy metal in different media is a scientific issue, and geographical detector is applied to evaluate the spatiotemporal stratified heterogeneity mechanisms for heavy metals in the Yangtze River Estuary. Heavy metal concentrations in water and sediment were consistent with lognormal distributions. Their concentrations were organized into four classes. Class 1 included concentrations that were less than or equal to 25%, Class 2 included those between 25%-50%, Class 3 concentrations were between 50%-75% and Class 4 were >75%, which were based on their lognormal distributions. In water and sediment, the mean heavy metal concentrations yearly decreased from 2012 to 2016. The Chongming area was significantly lower than those found in the other areas, which is the least affected area by anthropogenic activities. The explanatory power of sediment to spatiotemporal stratified heterogeneity of heavy metals in shellfish organisms was much greater than that of water.

Environmental magnetic parameter characteristics as indicators of heavy metal pollution in the surface sediments off the Zhoushan Islands in the East China Sea

The pollution of continental shelf sea sediments has always been an important issue for scientists because it can directly affect marine life and marine ecology. Thus, we carried out detailed studies of environmental magnetism and heavy metals in 145 surface sediment samples from the area southeast of the Zhoushan Islands in the East China Sea. The magnetic minerals in the sediments are mainly magnetite with a small amount of goethite and hematite. The magnetic mineral particles are mainly pseudosingle domain and contain a certain amount of superparamagnetic particles. The distribution of the magnetic mineral content shows a gradual decreasing trend from land to sea, which is closely related to the sediment transport pattern. The anhysteretic remanent magnetization (χ_ARM) and χ_ARM ratio to magnetic susceptibilities (χ_ARM/χ) were more sensitive than other indexes to sediment pollution and could be used as indicators for environmental pollution in the nearshore area. Additionally, a correlation analysis with the major elements showed that the χ_ARM ratio to saturation isothermal remanence (χ_ARM/SIRM) can well explain the sources of terrigenous sediment. Therefore, the environmental magnetic parameters in the continental shelf area can be used as a precursor for geochemical research and provide data support for further research.

Distribution, Source Identification, and Assessment of Potentially Toxic Elements in the Sediment Core from the Estuarine Region of the Golmud River to the Qarhan Salt Lake, Qinghai, China

The Qarhan Salt Lake has attracted increasing attention due to its significant national economic status and increased human activity, especially mining. Therefore, a sediment core collected from the confluence of the Golmud River to the Qarhan Salt Lake was chosen to investigate the concentrations, pollution levels, and ecological assessment of nine targeted elements (Al, As, Cd, Cr, Cu, Ni, P, Pb, and Zn). The excess 210Pb activities were calculated and a sedimentation rate of approximately 0.041 cm/y was estimated. Elements sources were identified, and the results show that Al, As, Cu, Ni, Pb, and Zn were mainly from natural sources, Cd and P were mainly from human input, and Cr appeared to have both sources. For Cd and P there was an increasing trend from 1987 and 1975, respectively, coinciding with the Chinese economic reform, Qarhan Salt Lake development and utilization, and also with the gross domestic product of Haixi State, Qinghai Province. Though the pollution and ecological assessment showed that there was nil to very low contamination and ecological risk, which is different from previous assumptions, the obviously increasing trend of Cd and P in the surface is still a concern. More attention should be paid to Cd and P in the further development of the Qarhan Salt Lake and the Golmud City.

Contamination and ecological risk assessment of heavy metals pollution from the Shalateen coastal sediments, Red Sea, Egypt

To assess the contamination and ecological risk assessment of the Shalateen coastal sediments, Red Sea, Egypt, 35 samples were collected to analyze Cu, Sr, Zn, Cd, Pb, Fe, Co, Ni, Mn, and total organic matter with an atomic absorption spectrophotometer. Several indices were calculated to estimate the contamination levels. The results indicated the following order of metal concentrations: Fe > Sr > Mn > Zn > Ni > Pb > Cu > Co > Cd, and revealed that the investigated sediments are highly enriched and contaminated with Sr, Cd, Pb and Zn. Statistical analyses subdivided the elements into Fe and Mn from natural sources, Sr, Cd, Pb and Zn from anthropogenic sources, and Ni, Cu and Co from combined natural and anthropogenic sources. The average Pb and Cd concentrations are considerably higher compared to the Caspian Sea, Indian Ocean, northern Red Sea, background shale, and continental crust. Possible sources of pollutants are fishing operations, antifouling paints, runoff, desalination plants, industries and dissolution of carbonate sediments.

Arsenic pollution of sediments in China: An assessment by geochemical baseline

Arsenic (As) contamination in sediments has been reported worldwide. However, few studies have investigated As contamination on a national scale in China. This study aims to address this gap by analyzing the existing literature on As contamination and sediment samples collected from ten main river basins: the Songhua River Basin (SRB), Liao River Basin (LRB), Hai River Basin (HRB), Yellow River Basin (YRB), Huai River Basin (HuRB), Yangtze River Basin (YtRB), Pearl River Basin (PRB), Southeastern River Basin (SeRB), Southwestern River Basin (SwRB), and Northwestern River Basin (NwRB). Regional geochemical baseline (RGB) values of As in the sediments of river basins were calculated to estimate human contributions of As using normalization and cumulative frequency distribution curves. The established RGB values in the SRB, YtRB, and PRB were higher than the corresponding regional soil background (RSB), possibly because of the high intensity of human activities in the SRB, YtRB, and PRB. Taking RGB and RSB values as the background references, contamination assessment yielded important information on As contamination in China. With high As contributions from Yunnan province, the PRB suffered from the highest level of contamination, and the mean human contribution of As in the PRB was 64.4%. The contamination levels in the less developed southwestern regions were even higher than in some river basins in economically developed regions (e.g., YRB). In addition, As in the PRB and YtRB was found to be partially contributed by industrial wastewater discharge, and the response of As contamination in sediments to industrial wastewater discharge was analyzed. The temporal change (2004-2016) of As in sediments from the PRB, YtRB, and YRB corresponded well with that of As discharged in wastewater within the corresponding river basins. This study thus serves as a valuable foundation for policies focused on ameliorating As contamination in China.

Spatial-temporal variation of heavy metals' sources in the surface sediments of the Yangtze River Estuary

In this study, positive matrix factorization, multilinear engine 2, and geographic information systems were used to characterize the spatial-temporal patterns of sources for nine heavy metals in the surface sediments of the Yangtze River Estuary in different seasons. Results showed that six sources were identified: agricultural pesticide, marine transportation, chemical factory wastewater, metal smelter waste, atmospheric deposition, and agricultural fertilizer. The proportions of sources were similar during the entire year but varied among the seasons. The differences in the proportions of agricultural pesticide between winter and other seasons were greater than 12%. Over 40% of the Cd concentration in most seasons was attributed to atmospheric deposition, while less than 5% in autumn. The impact strength of most sources, except marine transportation and metal smelter waste, decreased from the inner regions to the adjacent sea. The difference in the impact strength of agricultural pesticide was the largest throughout the study area.

Distribution, pollution, bioaccumulation, and ecological risks of trace elements in soils of the northeastern Qinghai-Tibet Plateau

Environmental quality of the northeastern Qinghai-Tibet Plateau has attracted more attention due to increasing anthropogenic disturbance. Therefore, this study investigated the distribution, pollution, ecological risks, and bioaccumulation of 12 target heavy metals and 16 rare earth elements (REEs) in soils of this area. The average concentrations of target trace elements in soils ranged from 0.16 (Hg) to 500.46 (Cr) mg/kg. Pb caused more serious pollution than the other elements based on geo-accumulation index evaluation. Hg exhibited the strongest enrichment feature with the average enrichment factor of 8.41. Compare with modified contamination degree and pollution load index, Nemerow pollution index method obtained the most serious evaluation results that 45.67% and 16.54% of sampling sites possessed high and moderate pollution. Evaluation results of potential ecological risk index showed that trace elements in soils posed very high and considerable ecological risks in 34.65% and 7.09% of sampling sites, respectively. Mining area was the region with the most serious pollution and ecological risks. Average bioaccumulation factor (BCF) values of target trace elements ranged from 0.05 (REEs) to 2.67 (Cr). Cr was the element that was easier to bio-accumulate in plants of the study area than the other target elements. It is in urgent need to take effective measures for controlling current pollution and potential ecological risks of trace elements in soils of the northeastern Qinghai-Tibet Plateau.

Source identification, environmental risk assessment and human health risks associated with toxic elements present in a coastal industrial environment, India

This study investigated the source and contamination levels of toxic elements (Cd, Cr, As, Pb, Ni and Hg) present in a coastal environment, Paradip-an industrial hub of the east coast of India. The ecological risk assessment indices and human exposure models were used to evaluate the pollution status. Enrichment factor indicated that all the metal(loid)s found in the sediment are mostly derived from the anthropogenic source. According to the sediment quality quotient, 8.33% of sediments have crossed the ERM limit for Ni that can be fatal to biota. Meanwhile, 66.66, 41.66 and 8.33% of sediments have exceeded PEL range for Cr, Ni and As, respectively, that can register frequent lethal toxicity to benthic biota. As had the highest potential ecological harm coefficient (Er_f > 80), and Hg had moderate ecological harm coefficient (40 < Er_f < 80). Summarily, the sediment quality of this site is moderate to heavily toxic to benthic organisms. The concentration of toxic metals in seawater was below the permissible limit (CCC and CMC) set by USEPA indicating that water is relatively safer for free floating aquatic biota. The health risk index of toxic metal (loid)s present in soils of the residential sites has confirmed that there is a severe non-carcinogenic threat for children (HI child > 1) and a borderline carcinogenic risk for both adult and children. THQ_Cr possesses highest non-carcinogenic threat, which contributed approximately 50% to HI followed by THQ_As. The contribution of carcinogenic risk of chromium (CR_Cr) to TCR is approximately 60%. Cr is the significant contaminant of this site that has highest health effects. Highest exposure risks were associated with ingestion pathway accounting for about 85% of the total for most of the elements.

Lead contamination in sediments in the past 20 years: A challenge for China

Lead (Pb) contamination was recognized in China early in the 1920s. However, the response of Pb contamination in sediments to China's rapid economic and social development remains uncertain to date. We conducted a literature review of over 1000 articles from 1990 to 2016 and the first national-scale survey of Pb contamination in China. A literature review showed that available research in China focused on the economically highly developed river basins, including the Pearl River Basin (PRB), Yellow River Basin (YRB), and Yangtze River Basin (YtRB), whereas those in the less developed southeastern, southwestern, and northwestern river basins received limited attention. The YtRB and YRB had higher Pb contamination levels than other basins, corresponding with the rapid economic development in those regions. However, the less economically developed river basins in the southeastern and northwestern regions of China were also contaminated by Pb. Analysis of 146 studies in the PRB, YRB, and YtRB revealed that Pb contamination in PRB sediments showed a tendency to improve over time, whereas that from the YtRB exhibited a tendency to worsen. For the YRB, there was a slight increase from 1990 to 2006 and a decreasing trend from 2007 to 2014. The overall temporal trend in Pb levels in PRB and YRB sediments corresponded with that of the Pb discharged in wastewater in the surrounding cities, indicating that industrial wastewater discharge was possibly one of the main anthropogenic sources of Pb in those sediments. For the YtRB, the increasing trend in Pb concentrations was related to the considerably high atmospheric Pb emissions in the surrounding cities and its geographical characteristics. These findings suggested that China should develop systematic and consistent approaches for monitoring Pb contents in sediments and adopt a regional economic development policy focusing on pollution prevention.

Bioaccumulation, tissue distribution and joint toxicity of erythromycin and cadmium in Chinese mitten crab (Eriocheir sinensis)

The bioaccumulation of erythromycin (ETM) and cadmium (Cd) in Chinese mitten crab (Eriocheir sinensis) and subsequent toxicity on pathological changes and enzymatic activities were investigated during 21-day exposure to ETM, Cd, and Cd + ETM mixture. The bioaccumulation of Cd and ETM residues in crab tissues decreased as gill > hepatopancreas > muscle > ovary, with higher Cd bioaccumulation than ETM. The highest Cd bioaccumulation in crab reached 1.15 mg/g dry weight in gill and 461.29 μg/g in hepatopancreas, on the 14th day of Cd treatment. Cd exposure promoted the bioaccumulation of ETM in four tissues. ETM exposure caused tubular vacuolization in epithelial and edema and degeneration of hepatic ducts in hepatopancreas, and disconnected gill epithelial layer and indistinctly cellular structure in gill. During Cd exposure, mitochondria acted as a main biomarker to identify the damage, including reduced and swollen mitochondria, and broken mitochondrial structure. Moreover, Chinese mitten crab showed defence capability against ETM and Cd exposure by physiological adjustment of metabolic enzymes glutathione S-transferase activity.

Macrobenthic community characteristics and ecological health of a constructed intertidal oyster reef in the Yangtze Estuary, China

Development of substrate organisms (oysters, barnacles) and the health of a monitored oyster reef were investigated in the Yangtze Estuary. Very low salinity suppressed oyster survival. Nevertheless, middle- to high-salinity significantly increased the abundance and biomass of substrate organisms, and macrobenthos species and diversity. Long-term variation in substrate organisms was steady after a major fluctuation, yet the macrobenthic community structure lagged behind that of oysters. Overall, the oyster reef was in a healthy state. The M-AMBI results showed that its ecological status under high-salinity was better than medium-salinity conditions. Redundancy analysis indicated these results were associated with changes in water salinity and substrate factors. Taken together, our results suggest this constructed intertidal oyster reef has had a positive effect on the community and health status of macrobenthos in the Yangtze Estuary. Further, these ecological benefits increased going from medium- to high-salinity waters, but were generally absent under low salinity.

Comparison of the common spatial interpolation methods used to analyze potentially toxic elements surrounding mining regions

The appropriate spatial interpolation methods must be selected to analyze the spatial distributions of Potentially Toxic Elements (PTEs), which is a precondition for evaluating PTE pollution. The accuracy and effect of different spatial interpolation methods, which include inverse distance weighting interpolation (IDW) (power = 1, 2, 3), radial basis function interpolation (RBF) (basis function: thin-plate spline (TPS), spline with tension (ST), completely regularized spline (CRS), multiquadric (MQ) and inverse multiquadric (IMQ)) and ordinary kriging interpolation (OK) (semivariogram model: spherical, exponential, gaussian and linear), were compared using 166 unevenly distributed soil PTE samples (As, Pb, Cu and Zn) in the Suxian District, Chenzhou City, Hunan Province as the study subject. The reasons for the accuracy differences of the interpolation methods and the uncertainties of the interpolation results are discussed, then several suggestions for improving the interpolation accuracy are proposed, and the direction of pollution control is determined. The results of this study are as follows: (i) RBF-ST and OK (exponential) are the optimal interpolation methods for As and Cu, and the optimal interpolation method for Pb and Zn is RBF-IMQ. (ii) The interpolation uncertainty is positively correlated with the PTE concentration, and higher uncertainties are primarily distributed around mines, which is related to the strong spatial variability of PTE concentrations caused by human interference. (iii) The interpolation accuracy can be improved by increasing the sample size around the mines, introducing auxiliary variables in the case of incomplete sampling and adopting the partition prediction method. (iv) It is necessary to strengthen the prevention and control of As and Pb pollution, particularly in the central and northern areas. The results of this study can provide an effective reference for the optimization of interpolation methods and parameters for unevenly distributed soil PTE data in mining areas.

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.