Multistage remediation of heavy metal contaminated river sediments in a mining region based on particle size

Effects of water replenishment on lake water quality and trophic status: An 11-year study in cold and arid regions

Water replenishment is an important measure for maintaining and improving the aquatic environmental quality of lakes. The problems of water quality deterioration and water shortage can be alleviated by introducing water of higher quality. However, the mechanism of water replenishment in the improvement of the water quality and trophic status of lakes remains unclear. This study investigated water replenishment in Wuliangsuhai Lake (WLSHL) from 2011 to 2021 by collecting seasonal water samples and conducting laboratory analyses. Water replenishment was found to be capable of significantly improving lake water quality and alleviating eutrophication. It is worth noting that single long-term water replenishment measures have limitations in improving the water quality and trophic status. The whole process was divided into three stages according to the water quality and trophic status, namely the buffer period, decline period, and stable period. During the buffer period, the water quality and trophic status showed only slight improvement because of the small amount of water replenishment and the low proportion of higher-quality water from the Yellow River. In the decline period, with increasing water replenishment, the proportion of higher-quality water from the Yellow River gradually increased, leading to the most significant and stable degree of improvement. In the stable period, increases in the amount of water replenishment had little effect on improving the water quality and trophic status, which is attributable to the balance between internal pollutants (lake water-sediment), and the balance between internal-external pollutants (lake water-irrigation return flow + Yellow River water). On the premise of stable water quality, with eutrophication control as the management goal, the optimal water replenishment would be approximately 10.58 ×108 m3. Further necessary measures for solving aquatic environmental problems include the combination of sediment dredging, optimization of the water replenishment route, and implementation of quality management in water replenishment.

Use of selected amendments for reducing metal mobility and ecotoxicity in contaminated bottom sediments

The aims of the study were 1) to assess the suitability of selected amendments for reducing the mobility of metals in sediments by evaluating their effects on metal sorption capacity, and 2) to assess the ecotoxicity of sediment/amendment mixtures. Three different amendments were tested: cellulose waste, biochar, and dolomite. The efficiency of metal immobilization in mixtures was dependent on pH, which increased with concentrations of amendment. The higher negative charge observed for dolomite and cellulose waste corresponded with greater attraction of cations and enhanced metal sorption. For cellulose waste, the highest values of the Q parameter were attributed to the presence of OH groups, which corresponded with the highest immobilization of metals. Biochar reduced the negative surface charge, which highlights the importance of additional factors such as high specific surface area and volume of pores in metal immobilization. All amendments increased the SSA and VN2, indicating a higher number of sorption sites for metal immobilization. Most bioassays established a reduction of the ecotoxicity for amendments. Mixtures with dolomite (25%, 45% doses) and biochar (45% dose) were low toxic. Mixtures with cellulose waste were toxic or highly toxic. The mobility of metals from contaminated sediments can be limited by reused industry side products, which could contribute to further closing the circular economy loop.

Revealing the release and migration mechanism of heavy metals in typical carbonate tailings, East China

Refining the occurrence characteristics of tailings hazardous materials at source is of great importance for pollution management and ecological reclamation. However, the release and transport of heavy metals (HMs) from tailings under rainfall drenching in simulated real-world environments is less well portrayed, particularly highlighting the inherent neutralisation in tailings wastes under superimposed dynamic conditions. In this study, dynamic leaching columns simulating actual conditions were used to observe the release and transport of HMs from tailings under acid rainfall infiltration at spatial and temporal scales. The release rate of trace elements (e.g., As, Cr, Ni, Pb, Cd) is high. Neutralisation in the presence of carbonate rocks in the gangue reduces HMs release intensity from tailings with high heavy metal content, along with the precipitation of iron oxides and chromium-bearing minerals, etc. In addition, the vertical differentiation of HMs is more relevant to physical processes. In the absence of carbonate rocks in gangue, the lowest pH value is reached within 1.2 h after acid rain infiltrates the tailings. At the same time, Cu, Zn and Cd are released significantly from the minerals at the superficial level. The release of As(III) is mainly concentrated in the early and late stages of water-rock contact.

Removal of toxic metals using iron sulfide particles: A brief overview of modifications and mechanisms

Growing mechanization has released higher concentrations of toxic metals in water and sediment, which is a critical concern for the environment and human health. Recent studies show that naturally occurring and synthetic iron sulfide particles are efficient at removing these hazardous pollutants. This review seeks to provide a concise summary of the evolution in the production of iron sulfide particles, specifically nanoparticles, through the years. This review presents an outline of the synthesis process for the most dominant forms of iron sulfide: mackinawite (FeS), pyrite (FeS2), pyrrhotite (Fe1-x S), and greigite (Fe3S4). The review confirms that both natural forms of iron sulfide and modified forms of iron sulfide are highly effective at removing different heavy metals and metalloids from water. Concurrently, this review reveals the interaction mechanism between toxic metals and iron sulfide, along with the impact of conditions for remedy and rectification. None the less, modifications and future investigations into the synthesis of novel iron sulfides, their use to adsorb diverse environmental pollutants, and their fate after injection into polluted aquifers, remain crucial to maximizing pollution control.

Assessing the impacts of fine sediment removal on endogenous pollution release and microbial community structure in the shallow lakes

Resuspension is a crucial process for releasing endogenous pollution from shallow lakes into the overlying water. Fine particle sediment, which has a higher contamination risk and longer residence time, is the primary target for controlling endogenous pollution. To this end, a study coupling aqueous biogeochemistry, electrochemistry, and DNA sequencing was conducted to investigate the remediation effect and microbial mechanism of sediment elution in shallow eutrophic water. The results indicated that sediment elution can effectively remove some fine particles in situ. Furthermore, sediment elution can inhibit the release of ammonium nitrogen and total dissolved phosphorous into the overlying water from sediment resuspension in the early stage, resulting in reductions of 41.44 %-50.45 % and 67.81 %-72.41 %, respectively. Additionally, sediment elution greatly decreased the concentration of nitrogen and phosphorus pollutants in pore water. The microbial community structure was also substantially altered, with an increase in the relative abundance of aerobic and facultative aerobic microorganisms. Redundancy analysis, PICRUSt function prediction, and the correlation analysis revealed that loss on ignition was the primary factor responsible for driving changes in microbial community structure and function in sediment. Overall, the findings provide novel insights into treating endogenous pollution in shallow eutrophication water.

Pollution characteristics and source identification of farmland soils in Pb-Zn mining areas through an integrated approach

Long-term mining activities have caused serious heavy metals contamination of farmland soils. In this study, we investigated the concentrations, distributions, accumulations, potential ecological risk, and sources of eight heavy metals in farmland soils of Pb-Zn mining areas. According to the soil standard GB15618-2018, Cd was the most contaminated, followed by Pb and Zn. The geo-accumulation index showed that Pb, Zn, Cd, and Hg accumulated seriously. The potential risk index indicated that Cd, Hg, and Pb were the main environmental risk elements. An integrated approach combining multivariate statistical analysis, PMF, and GIS mapping was used to analyze the sources of heavy metals. Four main sources were identified and quantified: (1) mining activities source, the main source of Cd (71.09%) and Zn (61.88%); (2) agricultural activities source, dominated by Hg (73.01%); (3) atmospheric deposition sources, with Pb (85.11%) as the main contributor; (4) natural source, characterized by Cr (72.96%), Ni (66.04%), As (55.98%) and Cu (37.70%). This study would help us understand the pollution characteristics and sources of farmland soils in mining areas and provide basic information for the next step of pollution control and remediation.

Metal Oxides Nanoparticles: General Structural Description, Chemical, Physical, and Biological Synthesis Methods, Role in Pesticides and Heavy Metal Removal through Wastewater Treatment

Nanotechnology (NT) is now firmly established in both the private home and commercial markets. Due to its unique properties, NT has been fully applied within multiple sectors like pharmacy and medicine, as well as industries like chemical, electrical, food manufacturing, and military, besides other economic sectors. With the growing demand for environmental resources from an ever-growing world population, NT application is a very advanced new area in the environmental sector and offers several advantages. A novel template synthesis approach is being used for the promising metal oxide nanostructures preparation. Synthesis of template-assisted nanomaterials promotes a greener and more promising protocol compared to traditional synthesis methods such as sol-gel and hydrothermal synthesis, and endows products with desirable properties and applications. It provides a comprehensive general view of current developments in the areas of drinking water treatment, wastewater treatment, agriculture, and remediation. In the field of wastewater treatment, we focus on the adsorption of heavy metals and persistent substances and the improved photocatalytic decomposition of the most common wastewater pollutants. The drinking water treatment section covers enhanced pathogen disinfection and heavy metal removal, point-of-use treatment, and organic removal applications, including the latest advances in pesticide removal.

Feasibility of soil and sludge standards for freshwater sediment pollutant determination and quality judgment

The environmental standards of soil and sludge have been typically referenced for freshwater sediment determination and quality assessment, especially in some areas without sediment standards. The feasibility of determination method and quality standard of soils and sludge for freshwater sediment was investigated in this study. Fractions of heavy metals, nitrogen, phosphorus, and reduced inorganic sulfur (RIS) in different type of samples were determined, including freshwater sediments, dryland and paddy soils, and sludge with air-drying (AD) and freeze-drying (FD) treatment, respectively. Results showed fraction distributions of heavy metals, nitrogen, phosphorus, and RIS in sediments markedly differed from those of soils and sludge. Fraction redistributions of heavy metals, nitrogen, phosphorus, and RIS in sediments were observed with AD compared to those treated by FD. The proportions of heavy metals, nitrogen, and phosphorus associated with organic matter (or sulfide) in FD sediments decreased by 4.8-74.2%, 9.5-37.5%, and 16.1-76.3%, respectively, compared to those in AD sediments, while those associated with Fe/Mn oxides increased by 6.3-39.1%, 50.9-226.9%, and 6.1-31.0%, respectively. The fraction proportions of RIS in sediments with AD also sharply decreased. Determination of standard methods for sludge and soil caused the distortion of pollutant fraction analysis in sediment. Similarly, the quality standard of sludge and soil was inappropriate for sediment quality assessment due to the differences in pollutant fraction pattern between sediment and soils/sludge. Totally, soil and sludge standards are inapplicable for freshwater sediment pollutant determination and quality judgment. This study would greatly advance the establishment of freshwater sediment determination methods and quality standards.

Zero-Waste Approach for Heavy Metals' Removal from Water with an Enhanced Multi-Stage Hybrid Treatment System

The aim of the work was to develop a zero-waste technological solution for hybrid removal of heavy metals from river sediments. The proposed technological process consists of sample preparation, sediment washing (a physicochemical process for sediment purification), and purification of the wastewater produced as a by-product. A suitable solvent for heavy metal washing and the effectiveness of heavy metal removal were determined by testing EDTA and citric acid. The process for removing heavy metals from the samples worked best with citric acid when the 2% sample suspension was washed over a 5-h period. The method was chosen of the adsorption of heavy metals from the exhausting washing solution on natural clay. Analyses were performed of the three main heavy metals, Cu(II), Cr(VI), and Ni(II), in the washing solution. Based on the laboratory experiments, a technological plan was prepared for the purification of 100,000 tons of material per year.

Distribution and variation of metals in urban river sediments in response to microplastics presence, catchment characteristics and sediment properties

Despite well documented studies on metal pollutants in aquatic ecosystems, knowledge on the combined effects of catchment characteristics, sediment properties, and emerging pollutants, such as microplastics (MPs) on the presence of metals in urban river sediments is still limited. In this study, the synergistic influence of MPs type and hazard indices, catchment characteristics and sediment properties on the variability of metals present in sediments was investigated based on a typical urban river, Brisbane River, Australia. It was noted that the mean concentrations of metals in Brisbane River decreases in the order of Al (94,142 ± 12,194 μg/g) > Fe (62,970 ± 8104 μg/g) > Mn (746 ± 258 μg/g) > Zn (196 ± 29 μg/g) > Cu (50 ± 19 μg/g) > Pb (47 ± 25 μg/g) > Ni (25 ± 3 μg/g) while the variability of metals decreases in the order of Pb > Cu > Mn > Al > Ni > Zn > Fe along the river. According to enrichment factor (Ef) contamination categories, Mn, Cu and Zn exert a moderate level of contamination (Ef > 2), while Fe, Ni, and Zn show slight sediment pollution (1 <Ef < 2). In the case of Pb, extremely high enrichment (Ef > 3) was found at sampling locations having a high urbanisation level and traffic related activities. Crustal metal elements (namely, Al, Fe, Mn) were found to be statistically significantly correlated with sediment properties (P < 0.05). Anthropogenic source metals (namely, Cu, Ni, Pb, Zn) were observed to be highly correlated with catchment characteristics. Additionally, the presence of metals in sediments were positively correlated with MPs concentration, and negatively correlated with MPs hazard indices. The outcomes of this study provide new insights for understanding the relationships among metals and various influential factors in the context of urban river sediment pollution, which will benefit the formulation of risk assessment and regulatory measures for protecting urban waterways.

Contamination and Health Risk Assessment of Heavy Metals in Soil and Ditch Sediments in Long-Term Mine Wastes Area

The ecological and health risks posed by wastes discharged from mining areas to the environment and human health has aroused concern. 114 soil samples were collected from nine areas of long-term mine waste land in northwestern Yunnan to assess the pollution characteristics, ecological and health risks of heavy metals. The result revealed that the geo-accumulation indexes were Cd (4.00) > Pb (3.18) > Zn (1.87) > Cu (0.25). Semi-variance analysis revealed that Cd and Cu showed moderate spatial dependency, whereas Pb and Zn showed strong spatial dependency. Cd posed an extreme potential ecological risk. Slopes and ditches were extreme potential ecological risk areas. Non-carcinogenic risk to children from Pb and Carcinogenic risk to adult and children from Cd was non-negligible and direct ingestion was the major source. This study provided a scientific basis for policymakers in management and exposure reduction.

Effect of application mode (capping and amendment) on the control of cadmium release from sediment by apatite/calcite mixture and its phosphorus release risk

In this research, the influence of application mode (capping and amendment) on the control of cadmium (Cd) liberation from sediment by apatite/calcite mixture and its phosphorus release risk were investigated. The results showed that calcite addition had a limited effect on the speciation of Cd in sediment, but apatite addition had a significant impact on the fractionation of Cd in sediment. Apatite amendment could effectively immobilize the most readily mobilized Cd by transferring the acid-soluble fraction to the reducible and residual fractions. Apatite addition also could effectively reduce the concentration of toxicity characteristic leaching procedure (TCLP)-leachable Cd in sediment, and apatite had a much higher reduction efficiency of TCLP-leachable Cd than calcite. Apatite/calcite mixture capping could reduce the risk of Cd liberation from sediment into the overlying water, and the controlling efficiency of apatite/calcite mixture capping was higher than that of apatite/calcite mixture amendment. The effect of apatite/calcite mixture addition on the concentration of reactive soluble phosphorus (SRP) in the overlying water was limited. The introduction of calcite into the apatite capping layer could lower the risk of phosphorus release from apatite to the overlying water as compared to single apatite capping. However, the apatite/calcite mixture capping layer still had a relatively high risk of phosphorus liberation into the overlying water. Results of this work suggest that apatite/calcite mixture has a high potential to be used as a capping material to control Cd release from sediment from the perspective of controlling efficiency and application convenience.

Immobilization of lead, copper, cadmium, nickel, and zinc in sediment by red mud: adsorption characteristics, mechanism, and effect of dosage on immobilization efficiency

The objective of this work was to determine the effect of dosage on the immobilization of lead (Pb), copper (Cu), cadmium (Cd), nickel (Ni), and zinc (Zn) in sediment by red mud (RM). To achieve this aim, the adsorption characteristics and mechanism of Pb, Cu, Cd, Ni, and Zn from aqueous solution on RM were studied at first, and then the influence of the RM dosage on the fractionation and leaching potential of Pb, Cu, Cd, Ni, and Zn in sediment was investigated. The results showed that RM possessed high adsorption capacities for Pb(II), Cu(II), Cd(II), Ni(II), and Zn(II) in aqueous solution. The maximum monolayer Pb(II), Cu(II), Cd(II), Ni(II), and Zn(II) adsorption capacities for RM derived from the Langmuir isotherm model were found to be 296, 39.2, 70.2, 46.0, and 50.7 mg/g, respectively. The addition of RM into sediment could effectively reduce the toxicity characteristic leaching procedure (TCLP)-leachable concentrations of Pb, Cu, Cd, Ni, and Zn in the sediment. The added RM could effectively immobilize the mobile (exchangeable, reducible, and oxidizable fractions) Pb in sediment by the conversion of the exchangeable and reducible fractions into the residual fraction, and it could effectively immobilize the mobile Cu, Cd, Ni, and Zn in sediment by the conversion of the exchangeable fraction into the residual fraction. The quantities of mobile Pb, Cu, Cd, and Ni immobilized by RM had a good linear relationship with the added RM. The above results suggest that RM is a promising amendment for the immobilization of mobile Pb, Cu, Cd, Ni, and Zn in sediment, and the linear relationship between the RM dosage and the quantities of immobilized Pb, Cu, Cd, and Ni by RM can be employed to determine the RM dosage required for the immobilization of mobile Pb, Cu, Cd, and Ni in sediment.

Evaluation of Sediments from the River Drava and Their Potential for Further Use in the Building Sector

Sedimentation is a naturally occurring process of allowing particles in water bodies to settle out of the suspension under a gravity effect. In this study, the sediments of the Drava River were fully investigated to determine the heavy metal concentrations along the river and their potential reuse in the construction sector. Naturally dehydrated sediments from the Drava River were tested as an additive for the production of fired bricks. The dredged sediments were used as a substitute for natural brick clay in amounts up to 50% by weight, and it was confirmed that up to 20% by weight of the added sediment could be used directly in the process without critically affecting performance. Finally, the naturally dehydrated sediments were also evaluated for their use as a filling material in the construction of levees. The natural moisture content of the dehydrated sediment was too high for it to be used without additives, so quicklime was added as an inorganic binder. The test results showed an improvement in the geotechnical properties of the material to such an extent that it is suitable as a filling material for levees.

Tissue-specific distribution and bioaccumulation pattern of trace metals in fish species from the heavily sediment-laden Yellow River, China

The Yellow River is one of the largest contributors to the global riverine sediment flux from the land to the ocean. Tissue-specific bioaccumulation of trace metals in fish from heavily sediment-laden rivers remains unclear to date. The concentrations and distributions of trace metals in water, suspended matters, sediments, and various fish tissues were investigated in the mainstem of the Yellow River were investigated. The concentrations of most metals in abiotic media were high in the Gan-Ning-Meng of upstream and downstream segments, and were highest in fine-sized suspended matters. The highest concentrations of most metals were in the gill and liver, followed by the gonad, and lowest in the muscle, and there were a significant overall differences among the tissues. The concentrations of metals in some tissues (e.g., muscle and gill) significantly differed among regions and feeding habits. The highest values of the bioaccumulation factor for suspended matters (BF_SPM) were observed in the midstream region (e.g., reaching to 19.0 for Se in the liver). This was determined by metal type and tissue specificity, food composition, and concentration of metals in abiotic media. The results highlight the significance of suspended matters for the distribution of trace metals in abiotic and biotic media.

Release of sediment metals bound by glomalin related soil protein in waterfowls inhabiting mangrove patches

Glomalin-related soil protein (GRSP) has received extensive attention due to its ability to immobilize metals in the environment. However, whether it can enter the food chain through digestion is still unclear. Mangroves occupy the transition zone between the sea and land, have important ecological functions. Mangroves suffer from fragmentation due to human activities and urbanization. A variety of waterfowls inhabit near the mangroves and ingest sediment settled on their food inadvertently or for grit; therefore, they are ideal for revealing GRSP's role in metal enrichment. In this study, we investigated the release of metals from mangrove surface sediments and GRSP through a physiologically based extraction test. The investigated metals (As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Zn) in sediments and those bound to GRSP would be mainly released in the gizzard phase. GRSP appeared to be an efficient carrier of Cu, Zn, Pb, and As from sediments to the waterfowls via direct sediment ingestion. For instance, 3.21% and 3.34% of sediment Cu were released in the gizzard and intestinal phases, respectively, meanwhile GRSP-bound Cu contributed 5.04% and 5.42% to this flux. The continuum of GRSP enrichment - complexation of GRSP and metals - biological accessibility of GRSP-bound metals, influenced by both direct and indirect effects from major nutrients (e.g., C, N, P, and S) and metal contents (e.g., Cu, Cd, Ni), controlled the release of GRSP-bound metals during simulated digestion. Overall, this study provides new insights into the potential risk of GRSP acting as a metal delivery vehicle in the food chain.

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.

Low impact leaching agents as remediation media for organotin and metal contaminated sediments

All over the world, elevated levels of metals and the toxic compound tributyltin (TBT) and its degradation products are found in sediments, especially close to areas associated with shipping and anthropogenic activities. Ports require regular removal of sediments. As a result, large volumes of often contaminated sediments must be managed. The aim of this study was to investigate enhanced leaching as a treatment method for organotin (TBT) and metal (Cu and Zn) contaminated marine sediments. Thus, enabling the possibility to reuse these cleaner masses e.g. in construction. In addition to using acid and alkaline leaching agents that extract the OTs and metals but reduce the management options post treatment, innovative alternatives such as EDDS, hydroxypropyl cellulose, humic acid, iron colloids, ultra-pure Milli-Q water, saponified tall oil ("soap"), and NaCl were tested. Organotin removal ranged from 36 to 75%, where the most efficient leaching agent was Milli-Q water, which was also the leaching agent achieving the highest removal rate for TBT (46%), followed by soap (34%). The TBT reduction accomplished by Milli-Q water and soap leaching enabled a change in Swedish sediment classification from the highest class to the second highest class. The highest reduction of Zn was in HPC leached samples (39% removal) and Cu in EDDS leached samples (33% removal). Although high metal and OT leaching were achieved, none of the investigated leaching agents are sufficiently effective for the removal of both metals and OTs. The results of this study indicate that leaching with ultra-clean water, such as Milli-Q water, may be sufficient to treat TBT contaminated sediments and potentially allow mass reuse.

Underestimated heavy metal pollution of the Minjiang River, SE China: Evidence from spatial and seasonal monitoring of suspended-load sediments

Previous assessments on rivers in SE China with highly developed economy and enormous population indicate diverse and relatively low particulate heavy metal pollution levels. However, the controlling mechanisms for heavy metal enrichment and transport remain enigmatic. Here, we target a mesoscale mountainous river, the Minjiang River, and obtain grain size, mineralogical and heavy metal concentration (Pb, Cd, Cr, Mn, Mo, Zn, V, Co, Ni, Cu) data from seasonal suspended particulate matter (SPM) near the river mouth, riverbed sediments and SPM samples from mainstream and major tributaries of the river. The results indicate that SPM samples have higher particulate heavy metal concentrations than riverbed sediments collected in pairs. Heavy metal concentrations of Cd, Zn, Cr, V, Co, Ni and Cu are higher in upstream SPM samples than those in downstream regions, whereas Pb, Mn and Mo concentrations don't show this spatial variation. Most heavy metals (e.g., Pb and Zn) show high concentrations in flood seasons and relatively low concentrations in dry seasons, revealing a hydrologic control. However, Cr and Mn show high concentrations in some dry season samples, suggesting incidental anthropogenic input events. The SPM-based pollution assessments using enrichment factor, geoaccumulation index and potential ecological risk index demonstrate that the Minjiang River is moderately to strongly polluted by particulate Pb, Cd, Mo and Zn contaminations and most particulate heavy metals have moderate to considerable potential ecological risks. We contend that transport and discharge of particulate heavy metals by the Minjiang River are controlled by both natural and anthropogenic forcings and the pollution levels are worse than previously known. Our findings suggest that particulate heavy metal discharge by subtropical mountainous rivers is related to sediment types and hydrologic characteristics. Therefore, high-spatiotemporal-resolution investigations on river SPM samples are highly recommended to better evaluate particulate heavy metal pollution levels and aquatic environmental conditions.

Heavy metal distribution in particle size fractions of floodplain soils from Dongchuan, Yunnan Province, Southwest China

The heavy metal pollution level in soils is heavily affected by the soil particle size distribution. However, the heavy metal loss during particle size extraction and the effect of calcite on the heavy metals removal in terms of the particle size are unclear. In this study, the distribution of heavy metals (Cu, Cd, Cr, Co, Ni, Zn, Pb, U, and V) was determined in five particle fractions (> 2, 2-0.25, 0.25-0.02, 0.02-0.002, and < 0.002 mm) of two soil and one sediment samples collected from the floodplain of Dongchuan, Yunnan Province, Southwest China. The sampled floodplain soils were mainly composed of gravel and sand fractions (> 97%). The concentrations of all nine heavy metals in the sampled soils and sediment increase significantly with decreasing particle sizes. The maximal loss rate of Cd and Cu reaches 54% and 8.6%, respectively, which should be considered in the process of particle size fraction extraction in soils. The removal amount and removal rate of heavy metals in solution by pure calcite ranks in the order of Pb²⁺ > Cu²⁺ > Cr⁶⁺, while the removal rate of Pb (93.13%) is much higher than that of Cu (24.56%) and Cr (10.71%), which increase with the calcite particle size decreasing. The stabilization of carbonate minerals in soils is crucial for heavy metal pollution control in floodplain soils with high carbonate concentrations in Dongchuan, China.

Quantitative isotopic fingerprinting of thallium associated with potentially toxic elements (PTEs) in fluvial sediment cores with multiple anthropogenic sources

Thallium (Tl) is a dispersed trace metal showing remarkable toxicity. Various anthropogenic activities may generate Tl contamination in river sediments, posing tremendous risks to aquatic life and human health. This paper aimed to provide insight into the vertical distribution, risk assessment and source tracing of Tl and other potentially toxic elements (PTEs) (lead, cadmium, zinc and copper) in three representative sediment cores from a riverine catchment impacted by multiple anthropogenic activities (such as steel-making and Pb-Zn smelting). The results showed high accumulations of Tl combined with associated PTEs in the depth profiles. Calculations according to three risk assessment methods by enrichment factor (EF), geoaccumulation index (I_geo) and the potential ecological risk index (PERI) all indicated a significant contamination by Tl in all the sediments. Furthermore, lead isotopes were analyzed to fingerprint the contamination sources and to calculate their quantitative contributions to the sediments using the IsoSource software. The results indicated that a steel-making plant was the most important contamination source (∼56%), followed by a Pb-Zn smelter (∼20%). The natural parental bedrock was found to contribute ∼24%. The findings highlight the importance of including multiple anthropogenic sources for quantitative fingerprinting of Tl and related metals by the lead isotopic approach in complicated environmental systems.

Contaminated aquatic sediments

The remediation of contaminated aquatic sediments requires a range of expertise from assessment (investigation, risk evaluations, modeling, and remedy selection) to design and construction. Research in 2019 has added to knowledge on optimizing the use of passive samplers for assessing chemical concentrations in sediment porewater. The porewater and black carbon appear to be better predictors of contaminant bioaccumulation than total organic carbon alone. This has led to better characterization of potential risk at sediment sites. Tools to identify and model sources of chemicals have been developed and used particularly for some metals, polynuclear aromatic hydrocarbons and polychlorinated biphenyls. There is great emphasis on beneficially using dredged sediment, treating it as a resource rather than a waste. Amendments used in sediment caps continue to be refined including the use of activated carbon within the caps and by itself. A technique involving 16S rRNA has been established as a means of identifying microbiological composition that naturally degrade contaminants. © 2020 Water Environment Federation PRACTITIONER POINTS: Sediment capping technology continues to advance Sampling and testing methods continue to be refined Natural processes such as biodegradation are being better understood Beneficial use of dredged sediment continue to be emphasized.

Distribution of metals in sediments of the Guadiamar river basin 20 years after the Aznalcóllar mine spill: Bioavailability and risk assessment

In April 1998, 6 million m³ of acid water and sludge were accidently spilled on to the Guadiamar riverbed (South of Spain). In this study, the long term distribution of Al, Cd, Cu, Fe, Mn, Pb, and Zn in the sediments of the Guadiamar river basin is described using fractionation analysis. Changes in the availability of metals from 2002 to 2018, covering a period of 20 years after the dam collapse, have been evaluated and their potential environmental risks have been examined. A substantial decrease in the concentrations of all the metals studied was observed, except Pb. However, the concentrations of Cu, Zn, and Pb remained higher than the background concentrations, which indicates a high influence of the mining activity, even in 2018. An increase of the residual fraction was observed from 2002 (47%) to 2018 (67%), which was mainly due to the mobilisation of metals from their oxidisable fraction to their residual fraction. Environmental risk assessment revealed a significant decrease in the risk associated with metals from 2002 to 2018, mainly due to the decrease of the metals concentration in the sediments over the year and to the lower availability of these metals in 2018. In 2002, the most challenging metals were Pb and Zn, whereas in 2018, Zn and Cd were the most problematic due to their toxicity and availability.

Attempt of basin-scale sediment quality standard establishment for heavy metals in coastal rivers

Heavy metal sediment quality standards (SQSs) derived from sediment quality guidelines (SQGs) are crucial in risk evaluation and environmental management. However, the establishment of SQSs is quite complex, especially for heavy metals. This study attempted to establish basin-scale SQSs for Cd, Cu, Pb and Zn based on SQGs combined with water quality standards in two coastal rivers in North China, named Jiaolai River (JL) and Jiahe River (JR), respectively. The spatial distribution, fraction, partition coefficients and environmental risk of heavy metals in sediments-porewater were investigated. The results showed that most heavy metals in sediments in JH were higher than those in JL, however, in the porewater, it exhibited an opposite trend. The geochemical fraction showed that most heavy metals in sediments were dominated by residual fraction. The partition of heavy metals between sediment and porewater were mainly affected by both sediment and porewater properties, and exogenous input of heavy metals. Contamination factors showed that Cd in sediment posed high pollution degree; the interstitial water criteria toxicity units and Nemerow Indexes suggested that heavy metal toxicities in porewater were low. The basin-scale heavy metal SQGs were calculated based on porewater quality derived from surface water quality standards using the modified equilibrium partitioning approach. The basin-scale heavy metal SQGs was classified with different grades to deduce the SQSs. Evaluated results of heavy metals in sediments based on SQSs showed lower potential bio-toxic effects in two rivers. In total, basin-scale SQGs for heavy metals were feasible for basin-scale SQSs establishment in coastal rivers.

Distribution and Source Identification of Pu in River Basins in Southern China

The ^239+240Pu activities and ²⁴⁰Pu/²³⁹Pu atom ratios in surface sediments from the major river basins in southern China were analyzed to investigate the distribution and source of Pu. We clarified that the ^239+240Pu activities in these river basins were very similar, however, only the ^239+240Pu activities in the Jinjiang Basin were generally higher than other samples. Because of river transport function, the distribution of ^239+240Pu activities in these river basins presented an increasing trend from the upstream region to the estuary. According to the ²⁴⁰Pu/²³⁹Pu atom ratios, the Pu source in the inner river basins might be from global fallout, and the Pu in river estuaries might be from the global fallout and the Pacific Proving Grounds (PPG) in the Marshall Islands. Using a mass balance of the Pu model, we quantified in the Pearl River Estuary and the Pu contribution from the Pearl River Basin to Pu inventory was 13 ± 5%. These data not only filled in a knowledge gap of Pu in these river basins but also served as background data for Pu contamination from a nuclear reactor. Also, there are several planned and operating nuclear power plants in these river basins and these data could provide some indications for dealing with nuclear accidents in different parts of river basins in the future. In this study, we also analyzed some factors that would affect the distribution of ^239+240Pu activities; however, only total organic carbon (TOC) content and the heavy metal As had a positive correlation with the ^239+240Pu activity.

Quantitative identification of anthropogenic trace metal sources in surface river sediments from a hilly agricultural watershed, East China

Quantitative identification of anthropogenic trace metal sources in surface river sediments is vital for watershed pollution control and environmental safety. In this study, we developed a reliable approach by integrating enrichment factor (EF), multiple linear regression of absolute principal component scores (MLR-APCS), and Pb stable isotopes, and applied it to a typical hilly agricultural watershed in Eastern China. Results showed that trace metals have accumulated in the river sediments during long-term agricultural development, with special concern of Cu, Ni, Pb, and Cr that may pose adverse biological effects. Among them, Pb was the most anthropogenically impacted trace metal due to its high EF value, but its excessive concentration still did not exceed background concentration. Based on the excessive trace metal concentrations, atmospheric deposition, livestock manure, and chemical fertilizer were identified as the three major anthropogenic pollution sources, and their respective contributions were further estimated by using MLR-APCS model. Together with natural contributions, atmospheric deposition contributed on average 35.3%, 43.1%, and 30.4% of total Ni, Pb, and Cr concentrations in the sediments, respectively. Similarly, livestock manure contributed 41.0% of total Cu and 40.6% of total Zn concentrations, while chemical fertilizer was responsible for 44.3% of total Cd concentration. For Pb, the source contribution of atmospheric deposition to sediment pollution was also quantitatively assessed by isotopic analysis, which was generally close to the value of 43.1% and therefore verified the EF and MLR-APCS results.

Effects of drying pretreatments on the analysis of the mercury fraction in sediments

The geochemical fractions of heavy metals in sediments are crucial indexes for their mobility and bioavailability evaluations. However, different drying processes of sediment pretreatment could change metal geochemical fractions, especially for Hg, which is potentially volatile. In this study, the influence of pretreatment methods including oven-drying, air-drying, freeze-drying, and fresh sediments on the analysis of Hg fractions in sediments was investigated. Results showed that remarkable differences of Hg concentration were observed between fresh sediments and dried pretreatment sediments (P < 0.05). Briefly, the concentrations of the water-soluble and human stomach acid-soluble fractions in oven-dried and air-dried sediments generally showed significant increasing trends compared with those in the fresh sediments, while the organo-chelated fraction exhibited significant decreasing trends. The cause of this phenomenon was primarily the oxidation of organic matter, aging process, and the diffusion of Hg into micropores. The significant loss was also observed at elemental Hg fraction due to its volatilization effect. The freeze-drying posed minor influence on changes of Hg fraction analysis compared with oven-drying and air-drying. Moreover, the total Hg concentrations in pretreated sediments showed a decline of varying degrees compared with those in fresh sediments ascribing to the volatilization of elemental Hg. Finally, Pearson correlation analysis further confirmed that freeze-drying could minimize the errors of the Hg fraction analysis in sediments.