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

Size-dependent distribution of metal(loid)s in recent marine sediments of the Adriatic sea

This paper investigates occurrence of metal(loid)s, and size-dependent changes in their concentration in recent marine sediments from coastal and open-sea environments in the eastern Adriatic. Size fractionation of sediments was performed after removal of organic matter (OM), and the individual fractions, comprising particles below 8 μm, 4 μm, 2 μm, 1 μm and 0.45 μm, were analysed using HR ICP-MS. The concentrations of most elements increased with decreasing particle size, as a result of accumulation of clay minerals and Fe and Mn (oxyhydr)oxides. A decrease in concentrations was observed for Ba, Sr, Ti and U, due to lowering of the carbonate content and presence in the coarse-grained and heavy mineral fraction. The highest element concentrations were determined in the fraction comprising particles below 1 μm. Occasionally, depending on the sedimentological environment and/or the element in question, the peak concentrations occurred in the <2 μm or <0.45 μm fraction. The lowest size-dependent enrichment was observed for elements associated with aluminosilicates (Al, Be, Cs, Co, Fe, K, Li, Rb). A different size-dependent behaviour of the elements was observed between deep-sea areas and shallow environments under greater coastal influence, mainly due to differences in sediment sorting, and between the northern and central vs. southern Adriatic due to the different catchment geologies. The Fe and Mn (oxyhydr)oxides, abundant in the deep-sea sediments, played an important role in the geochemical cycle of As, Cd, Co, Mo, Sb and V.

Spatio-seasonal patterns of the impact of wastewater treatment plant effluents on antibiotic resistance in river sediments

There is a growing concern about the risk of antibiotic resistance emergence and dissemination in the environment. Here, we evaluated the spatio-seasonal patterns of the impact of wastewater treatment plant (WWTP) effluents on antibiotic resistance in river sediments. To this purpose, sediment samples were collected in three river basins affected by WWTP effluents in wet (high-water period) and dry (low-water period) hydrological conditions at three locations: (i) upstream the WWTPs; (ii) WWTP effluent discharge points (effluent outfall); and (iii) downstream the WWTPs (500 m downriver from the effluent outfall). The absolute and relative abundances of 9 antibiotic resistance genes (ARGs), 3 mobile genetic element (MGE) genes, and 4 metal resistance genes (MRGs) were quantified in sediment samples, as well as a variety of physicochemical parameters, metal contents, and antibiotic concentrations in both sediment and water samples. In sediments, significantly higher relative abundances of most genes were observed in downstream vs. upstream sampling points. Seasonal changes (higher values in low-water vs. high-water period) were observed for both ARG absolute and relative abundances in sediment samples. Chemical data revealed the contribution of effluents from WWTPs as a source of antibiotic and metal contamination in river ecosystems. The observed positive correlations between ARG and MGE genes relative abundances point out to the role of horizontal gene transfer in antibiotic resistance dissemination. Monitoring plans that take into consideration spatio-temporal patterns must be implemented to properly assess the environmental fate of WWTP-related emerging contaminants in river ecosystems.

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.

Heavy metal load and effects on biochemical properties in urban soils of a medium-sized city, Ancona, Italy

Urban soils are often mixed with extraneous materials and show a high spatial variability that determine great differences from their agricultural or natural counterparts. The soils of 18 localities of a medium-sized city (Ancona, Italy) were analysed for their main physicochemical and biological properties, and for chromium (Cr), copper (Cu), cobalt (Co), lead (Pb), nickel (Ni), zinc (Zn), and mercury (Hg) total content, distribution among particle-size fractions, and extractability. Because of the absence of thresholds defining a hot spot for heavy metal pollution in urban soils, we defined a "threshold of attention" (ToA) for each heavy metal aiming to bring out hot spot soils where it is more impellent to intervene to mitigate or avoid potential environmental concerns. In several city locations, the soil displayed sub-alkaline pH, large contents of clay-size particles, and higher TOC, total N, and available P with respect to the surrounding rural areas, joined with high contents of total heavy metals, but low availability. The C biomass, basal respiration, qCO₂, and enzyme activities were compared to that detected in the near rural soils, and results suggested that heavy metals content has not substantially compromised the soil ecological services. We conclude that ToA can be considered as a valuable tool to highlight soil hot spots especially for cities with a long material history and, for a proper risk assessment in urban soils, we suggest considering the content of available heavy metals (rather than the total content) and soil functions.

Geochemical characterization and the assessment of trace element retention in sediments of the Reconquista River, Argentina

The mineralogical and geochemical characterization of sediments of the Reconquista River allows analyzing the geochemical partition of trace elements in one of the most polluted water courses of Argentina. The low dissolved oxygen and high ammonia contents, together with the high chemical oxygen demand, attest to the poor water quality. Ammonia, Cd and Cu content in surficial water exceeds the maximum guidelines for freshwater in Argentina. The recent sediments of the uppermost bed are enriched in organic matter (OM), sulfur, Zn, Cu and Pb. The enrichment factor is moderate, and the geoaccumulation index (Igeo) for Cu and Pb indicates uncontaminated to moderately contaminated sediments. The positive and significant correlation between As, Cr, Pb and Zn with the iron content suggests that their retention is controlled by the amount of iron oxy (hydr)oxides in the sediments, probably combined with the silt + clay abundance. In comparison with its tributary, the Las Catonas Stream, the Reconquista River, has less OM and trace elements in the sediments and more dissolved trace elements in the interstitial water. We interpret that OM is the main sorbent of the trace element. In the absence of OM, the iron oxy (hydr)oxides and the silt + clay fraction are a less efficient substitute. Consequently, the interstitial waters of the Reconquista River are enriched in these elements. Therefore, minor changes in the environmental conditions may generate significant release of hazardous trace elements from the sediments to the interstitial water and, in turn, to the surficial water of the river. As most of the big cities and the agricultural activities of Argentina are developed on the loessic substrate, the understanding of its interaction with polluted waters is crucial.

Spatial Variability of Metals in Coastal Sediments of Ełckie Lake (Poland)

This study aimed to determine the content and spatial distribution of metals (Ca, Mg, Fe, Na, K, Mn, Zn, Cr, Cu, Pb, Co) in sediments in the coastal zone of Ełckie Lake located in the area of "Green Lungs of Poland" in the north-eastern part of the country, depending on the land use (urban area, agricultural and forest area, and beaches). The concentration of metals was determined using atomic absorption spectrometry. The average contents of major elements in 28 sediment samples occurred in the following order: Ca > Mg > Fe > Na > K > Mn. The order of these elements in the coastal sediments located within the different parts of the catchment was identical. These elements may originate from natural sources such as the Earth’s crust, soil, and wind-blown dust from unpaved roads. The average contents of potentially toxic elements (PTEs) in the sediments were as follows: Cr > Zn > Pb > Cu > Co in agricultural and forest areas and beaches (the exception was Cu for beach B, which occurred at the end of the series). A different pattern occurred in urbanized areas: Zn > Cr > Cu > Pb > Co. The spatial distribution of heavy metals in the sediments indicated the highest contents in the shoreline adjacent to the urbanized part of the catchment. The primary sources of metals in sediment are transportation, coal burning, sanitary sewage from unsewered developments on the lakeshore, and storm runoff from roads. This was confirmed by positive correlations of Zn with Cu (r = 0.58), Pb (r = 0.90), Fe (r = 0.40). No correlations between the studied metals and organic matter were found, which may indicate its insignificant influence on metal content in the sediments. Pearson correlation coefficients also showed no relationship between sediment pH and the presence of metals. Factor analysis (FA) indicated that lithogenic (geogenic) and anthropogenic factors have almost equal shares in the distribution of most of the metals studied. The analysis of variance (ANOVA) showed that the average contents of Zn, Cu, Co, and Na in the sediments from urbanized areas are statistically significantly higher than the sediments from other areas (rural/forest, beaches).

Trace metal fractions, sources, and risk assessment in sediments from Umurbey Stream (Çanakkale-Turkey)

Trace metal contamination has become a worldwide problem for aquatic systems, as sediments act as a sink for trace metals. This study was conducted to assess geochemical fractions, sources and potential risks of trace metals (Cd, Cr, Cu, Ni, Pb, and Zn) in sediments of Umurbey stream (Çanakkale-Turkey). Sediment samples were taken from seven different locations of Umurbey stream. Aqua regia wet digestion procedure was applied to determine total contents of trace metals and BCR sequential extraction procedure was applied to determine geochemical fractions of trace metals. Trace metal total values were ordered as Zn > Pb > Cr > Cu > Ni > Cd. Just because of topography, geology, and agricultural practices, S4, S5, S6, and S7 sampling points had greater total trace metal concentrations than the other locations. Potential mobility of trace metals in sediment samples was ordered as Cd (62.1%) > Zn (60.8%) > Pb (54.8%) > Cu (46.1%) > Cr (43.0%) > Ni (29.7%). Cd, Zn, Pb, and partially Cu were encountered mostly in mobile phases. Multivariate analyses revealed that pollution in sediment samples was originated from not only anthropogenic but also natural factors. Except for Zn, trace metal concentrations were found to be at tolerable levels of biota. When the contamination factor and risk assessment code results were assessed together, it was observed that Cd, Zn, and partially Pb were weakly adsorbed onto sediments, thus might pose risks on environment in the long run.

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.

The effects of urban vehicle traffic on heavy metal contamination in road sweeping waste and bottom sediments of retention tanks

Diffuse pollution formed during a surface runoff on paved surfaces is a source of heavy metals (HMs) of various origin. This research study indicates the connection between bottom sediments of retention tanks located on urban streams and road sweeping wastes (RSW) that migrate during surface runoff to the stormwater drainage systems with discharge to the retention tanks. Moreover, we test the primary sources of HMs in RSW by analysing the mechanical wastes (MW) produced by vehicles in order to track the relationship between car parts and HMs deposited in the retention tanks receiving the surface runoff from streets. To identify the origin of HMs diverse source tracking approaches were used: statistical methods, Pb isotope ratios, and the flag element ratio approach. MW presented a very high HMs content (max observed values in mg/kg d.w.: 10477-Zn, 3512-Cu, 412-Pb, 3.35-Cd, 226-Ni, and 633-Cr), while for RSW the HMs content was similar to the bottom sediments. The total carcinogenic risk raises concerns due to the Cr content. The source of Zn was tyre wear and traffic. Ni, Cr, Fe, and Cd were correlated to Zn and shared a common/similar origin. PCA suggested that Cu features quasi-independent behaviour. The Pb isotopic ratios of RSW indicated Pb enrichment originating from coal combustion, while the gasoline and diesel source of Pb was excluded. The Pb isotopic ratios characteristic for MW were in within the following ranges: 1.152-1.165 (²⁰⁶Pb/²⁰⁷Pb), 2.050-2.085 (²⁰⁸Pb/²⁰⁶Pb), and 2.350-2.418 (²⁰⁸Pb/²⁰⁷Pb). The complex analysis of HMs origin confirmed the motorization origin of HMs: Zn, Cr, Ni, and Cd, except Pb (coal combustion as the main source) and Cu (non-uniform origin). The results of various source tracking methods were coherent, but Pb isotope ratios alone brought important information allowing to link Pb in sediments to the atmospheric deposition of coal combustion products.

Correlation patterns between magnetic parameters and heavy metals of core sediments in the Yellow River Estuary and their environmental implications

The potential use of environmental magnetism to investigate heavy metal pollution was investigated by analyzing sediment samples from a short sediment core (Z07) from the Yellow River Estuary. The heavy metal concentrations and speciation, grain sizes, and magnetic properties were determined, and correlations between the parameters were identified. Strong exponential relationships were found between the Hg concentrations and χ_fd%, χ_ARM-20mT, and clay content. Linear correlations were found between the As, Cd, Co, Cr, Ni, Pb, and Zn concentrations and χ_fd%, χ_ARM-20mT, and clay content. This indicated that Hg was mainly sorbed to the surfaces of nano-sized magnetic and clay minerals and predominantly had anthropological sources but the other heavy metals had mineralogical and other natural sources. These conclusions were supported by the heavy metal fractionation results. Heavy metal concentrations in sediment at site Z07 have decreased markedly since 2003 in response to water and sediment regulations being implemented.

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.

Spatial Distribution and Ecological Risks of the Potentially-Toxic Elements in the Surface Sediments of Lake Bosten, China

Aiming at the pollution and ecological hazards of the lake sediments of Bosten Lake, once China's largest inland lake, the spatial distribution and influencing factors of the potentially-toxic elements in its surface sediments were studied with the methods of spatial autocorrelation, two-way cluster analysis, and redundancy analysis. Finally, based on the background value of potentially-toxic elements extracted from a sediment core, a comprehensive evaluation of the risk of these potentially-toxic elements was conducted with the potential-ecological-risk index and the pollution-load index. With data on the grain size, bulk-rock composition, and organic matter content, this comprehensive analysis suggested that with the enrichment of authigenic carbonate minerals, the content of potentially-toxic elements exhibited distinctive characteristics representative of arid regions with lower values than those in humid region. All potentially-toxic elements revealed a significant spatial autocorrelation, and high-value areas mainly occurred in the middle and southwest. The content of potentially-toxic elements is related to Al2O3, K2O, Fe2O3, TiO2, MgO, and MnO, and the storage medium of potentially-toxic elements mainly consists of small particles with a grain size <16 μm. The pollution load index (PLI) for the whole lake due to the potentially-toxic elements was 1.31, and the surface area with a PLI higher than 1 and a moderate pollution level accounted for 87.2% of the total lake area. The research conclusions have an important scientific value for future lake ecological quality assessment and lake environment governance.

Combining punctual and high frequency data for the spatiotemporal assessment of main geochemical processes and dissolved exports in an urban river catchment

The assessment of dissolved loadings and the sources of these elements in urban catchments' rivers is usually measured by punctual sampling or through high frequency sensors. Nevertheless, the combination of both methodologies has been less common even though the information they give is complementary. Major ion (Ca²⁺, Mg²⁺, Na⁺, K⁺, Cl^-, SO₄^2-, and alkalinity), organic matter (expressed as Dissolved Organic Carbon, DOC), and nutrients (NO₃^-, and PO₄^3-) are punctually measured in the Deba river urban catchment (538 km²), in the northern part of the Iberian Peninsula (draining to the Bay of Biscay). Discharge, precipitation, and Electrical Conductivity (EC) are registered with a high frequency (10 min) in three gauging stations. The combination of both methodologies has allowed the assessment of major geochemical processes and the extent of impact of anthropogenic input on major composition of riverine water, as well as its spatial and temporal evolution. Three methodologies for loading estimation have been assessed and the error committed in the temporal aggregation is quantified. Results have shown that, even though carbonates dominate the draining area, the water major ion chemistry is governed by an evaporitic spring in the upper part of the catchment, while anthropogenic input is specially noted downstream of three wastewater treatment plants, in all nutrients and organic matter. The results of the present work illustrate how the combination of two monitoring methodologies allows for a better assessment of the spatial and temporal evolution on the major water quality in an urban catchment.

Multivariate statistical analyses for water and sediment quality index development: A study of susceptibility in an urban river

In this study, multivariate statistical analyses were performed to develop water and sediment quality indexes, allowing us (i) to select with reliability the most appropriate chemical variables for the evaluation of river quality susceptibility; (ii) to weight the influence of each variable based on monitored data; (iii) to consider possible synergism or antagonism derived from the combined effect of several pollutants; and (iv) to express the quality as a deviation from selected site-specific reference conditions. For the establishment of these threshold/maximum values, combining two biological indicators related to denitrifying bacteria in sediments turned out to be applicable to ensure compliance with the European water quality standard. The joint implementation of water and sediment quality indexes assisted us in the rapid detection of the deleterious effect of different anthropogenic contamination sources, as well as the influence of hydrological regime seasonality on river quality. In addition, metal-dependent water quality appeared to be coupled to sediment dynamics, since they were preferentially adsorbed onto sediments during low flow seasons, whereas there was potential for metal mobilization to water during sediment resuspension in high flow seasons. Therefore, an annual determination of sediment quality index was also recommended as suitable tool for prospective monitoring water quality, identifying those sites which could deserve special attention during certain periods, and planning future strategies for river quality improvement. However, two limitations were found: (1) sediment was not appropriate for water physicochemical quality early monitoring due to organic matter and nutrient continuous transformation; and (2) a multimetric index did not provide a concise and definitive quality information, thus a new tool for combining with quality index was proposed for specifically evaluate the water and sediment quality by identifying pollutant/s of concern at each location.

Migration and Diffusion of Heavy Metal Cu from the Interior of Sediment during Wave-Induced Sediment Liquefaction Process

Sediments are an important sink for heavy metal pollutants on account of their strong adsorption capacity. Elevated content of Cu was observed in the Chengdao area of the Yellow River Delta, where the surface sediment is mainly silt and is prone to be liquefied under hydrodynamic forces. The vertical transport of fine particles, along with pore water seepage, during the liquefaction process could promote the migration and diffusion of Cu from the interior of sediment. The present study involved a series of wave flume experiments to simulate the migration and diffusion of Cu from the interior of sediment in the subaqueous Yellow River Delta area under wave actions. The results indicated that sediment liquefaction significantly promoted the release of Cu from internal sediment to overlying water. The variations of Cu concentrations in the overlying water were opposite to the suspended sediment concentrations (SSCs). The sediment liquefaction caused high initial rises of SSCs, but led to a rapid decline of dissolved Cu concentration at the initial period of sediment liquefaction due to the adsorption by fine particles. Afterwards, the SSCs slightly increased and then gradually decreased. Meanwhile, the dissolved Cu concentration generally kept increasing under combined effects of intensively mix of sediment and overlying water, pore water seepage, and desorption. The dissolved Cu concentration in the overlying water during sediment liquefaction phase was 1.5–2.2 times that during the consolidation phase. Sediment liquefaction also caused vertical diffusion of Cu in sediment and the diffusion depth was in accordance with the liquefaction depth. The results of the present study may provide reference for the environmental management in the study area.

Mercury and methylmercury concentrations, sources and distribution in submarine canyon sediments (Capbreton, SW France): Implications for the net methylmercury production

Submarine canyons are important stocks of commercial interest fish, whose consumption is one of the main monomethymercury (MeHg) exposure to humans. Currently, biogeochemistry of mercury in those biologically productive system is unknown. In this work, inorganic mercury (Hg(II)) and organic mercury (MeHg) distributions were measured in sedimentary accumulative zones (slopes and terraces) against adjacent continental shelf sediments. Hg compound concentrations in these sediments show a huge range of concentrations (Hg(II) ranging from 18 to 973 ng g^-1 and MeHg ranging from 0.07 to 2.03 ng g^-1) exhibiting factors 50 and 20 fold, respectively. Higher values of mercury compounds were observed in canyon locations suggesting a high accumulation of mercury associated with higher values of clay fraction and organic matter content. The reactivity of mercury was investigated in sediment of three locations along Capbreton submarine canyon axis using slurry incubations experiments and isotopic tracers. Specific methylation and demethylation rate constants (k_M and k_D) were calculated. Results clearly showed that MeHg concentrations in these sediments are controlled by competing and simultaneous methylation and demethylation reactions mainly mediated by biotic process. Mercury reactivity was found higher in coastal stations compared to the offshore station due to more labile organic matter which may stimulate microbial activities. However, higher net MeHg production was estimated for the offshore station due to high Hg(II) concentrations suggesting a potential MeHg source for such marine environments.

Combined use of diffusive gradients in thin film, high-resolution dialysis technique and traditional methods to assess pollution and bioavailability of sediment metals of lake wetlands in Taihu Lake Basin

The geochemical behavior of trace metals at the sediment/water interface in Taihu Lake, the third-largest fresh water lake in China, has been widely explored. However, information on metals in lake wetlands of the basin is lacking. Here, diffusive gradients in thin film (DGT), high-resolution dialysis technique (HR-Peeper) and traditional methods were jointly used to study the occurrence characteristics, pollution degree, bioavailability, and mobility of sediment metals in the northern lake wetlands of Jiaxing City in Taihu Lake Basin. The contents of Cr, Ni, Cu, Zn, As, Cd and Pb were 101, 52.8, 62.3, 184, 10.3, 0.4, and 39.8 mg/kg, respectively. The metals in the sediments were in an overall low enrichment level. The main form of Cd was acid-soluble (F1), and the other metals mainly existed in residual (F4) or oxidable (F3) forms. The mean DGT-labile contents (C_DGT) of Cr, Ni, Cu, Zn, As, Cd and Pb were 1.3, 1.2, 9.3, 6.7, 13.4, 0.7, and 0.8 μg/L, respectively. C_DGT-Cu and C_DGT-As were significantly and positively related to the Cu and As contents in pore water (C_sol). C_DGT-Cr, C_DGT-Cd, C_DGT-Pb, and C_DGT-Cu were significantly and positively related to C_F1-Cr, C_F1-Cd, C_F1-Pb, and C_F3-Cu, respectively. The stability of Cd was the worst with a mean risk assessment code of 40%, indicating a high risk of remobilization in the sediment. The remobilization risks of other metals were low or moderate. The C_DGT/C_sol ratio of Cd was also the largest, with a mean of 0.99, suggesting that the Cd resupplying ability from sediment solid to pore water was strong.

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

Sediment pollution is an important environmental problem, and the remediation of heavy metal contaminated sediments is crucial to river ecosystem protection, especially in mining regions. In this work, characteristics of heavy metals (Cu, Zn, Cd, As and Hg) were investigated, including contents and fractions based on particle size (PS) in river sediments. Chemical leaching and stabilization for sediment remediation were performed, and the technology feasibility was assessed. The results indicated that the heavy metals were primarily reserved within fine sediments (PS < 75 μm), comprising 79.8% of the total. For the sequentially extracted fractions, residual fraction dominated the total content in large PS sections (PS > 150 μm), while the oxidizable fraction, reducible fraction and weak acid extractable fraction dominated the total content in fine sediments, except for that of Hg. Chemical leaching can transform most metals in sediments from large-sized particles to fine particles because the metals are absorbed by fine particles in solution rather than complexation. The stabilization suggested that cement could be an effective agent for ecological risk control for heavy metals. In field engineering, a total of 145,000 m³ sediment was divided into various sections by PS and synchronously washed by eluting agents. Finally, clean sediments (PS > 150 μm) were used as building material and clean backfilling; meanwhile, heavily polluted sediments (PS < 150 μm) were buried as general industrial solid waste after stabilization treatment. Over 90% of the contaminated sediments were reused throughout multistep remediation. Furthermore, a reduction in waste and harm, along with resources, was obtained. This study provided a feasible technology for heavy metal contaminated sediment remediation.

A multivariate approach and sediment quality index evaluation applied to Baixada Santista, Southeastern Brazil

Current studies use indices and chemometric approaches to assess the health quality of estuarine systems to support estuarine management. This study aims to use a multivariate approach and a set of indices to evaluate sediment health quality. Levels of Al, As, Cd, Cr, Cu, Fe, Ni, Pb, Sc, V, and Zn were quantified by ICP-OES, and nine indices were applied and evaluated individually. Most of the indices presented high values of Cu, Pb, and Zn, and the aggregative indices differed from each other in magnitude; however, the spatial distribution demonstrated the same trends. From PCA results, it was possible to differentiate lithogenic from the anthropogenic contribution, especially by Cu, Pb, and Zn. Thus, the integration of geochemical approaches and chemometric tools supported the interpretation of elemental contribution in terms of sources and pathway of heavy metals, which was similar to the results of other studies conducted in the area.