Pollution and Ecological Risk Evaluation of Heavy Metals in the Soil and Sediment around the HTM Tailings Pond, Northeastern China

Experimental Study on Tailings Deposition Distribution Pattern and Sedimentation Characteristics

Tailings pond accidents frequently occur during an extended period, resulting in loss of life and property, wastage of resources, and environmental pollution. Relying on tailings pond engineering, this paper carried out sample particle fragmentation experiments and settling column experiments to explore the deposition distribution pattern of tailings in both horizontal and vertical directions as well as the impact of particle size distribution on the sedimentation stratification effect. The results show that the median particle size on the dry beach surface in the horizontal direction slowly decreased with the increase in the distance from the subdam. The particle size of tailings showed great fluctuations in the vertical direction, which gradually became finer with the increase in the depth overall. At the same time, saturated sedimentation experiments suggested the inconsistent variation rule with the field test, namely, coarse on the bottom and fine at the top, and the change in particle size greatly affected the tailing sedimentation stratification effect. With the increase in fine particle content in tailings, the appearance time of the water-sand interface was shortened to within 30 min, but the sedimentation and consolidation completion times were delayed to about 1400 min. The settling column results indicate that the increase in fine particle content gradually weakened the sedimentation stratification effect, and the sedimentation pattern transformed from independent sedimentation to floc-type average sedimentation, which led to the enhanced water-retaining property of the settled layer. This may lead to an increase in the saturation line and a decrease in the length of the dry beach, seriously affecting the safe operation of the tailings pond. The research results provide some theoretical guidance and basic data for analyzing the consolidation efficiency of tailings and the stability of the tailings pond.

Improvements in Hydrolytic Stability of Alkali-Activated Mine Tailings via Addition of Sodium Silicate Activator

Over 14 billion tons of mine tailings are produced throughout the world each year, and this type of waste is generally stored onsite indefinitely. Alkali activation is a promising strategy for the reuse of mine tailings to produce construction materials, converting this waste stream into a value-added product. One major problem with alkali-activated mine tailings is their low durability in water (i.e., low hydrolytic stability). In this article, the influence of a mixed sodium hydroxide/sodium silicate alkali activator on the compressive strength, hydrolytic stability, and microstructure of alkali-activated materials (AAMs) were systematically investigated. XRD, FTIR, NMR, and NAD were used to investigate microstructural changes, and a water immersion test was used to show improvements in hydrolytic stability. For gold mine tailings activated with pure sodium hydroxide, the compressive strength was 15 MPa and a seven-day water immersion test caused a strength loss of 70%. With an addition of 1 M sodium silicate in the activator, the AAMs achieved a compressive strength of over 30 MPa and strength loss of only 45%. This paper proposes a mechanism explaining why the strength and hydrolytic stability of AAMs are dependent on the dosage of soluble silicate. A high dosage of sodium silicate inhibits the depolymerization of the source material, which results in a sample with less amorphous aluminosilicate gel and, therefore, lower hydrolytic stability.

Isotopic insights and integrated analysis for heavy metal levels, ecological risks, and source apportionment in river sediments of the Qinghai-Tibet Plateau

The research was carried out to examine the pollution characteristics, ecological risk, and origins of seven heavy metals (Hg, As, Pb, Cu, Cd, Zn, and Ni) in 51 sediment samples gathered from 8 rivers located on the Qinghai-Tibet Plateau (QTP) in China. The contents of Hg and Cd were 5.0 and 1.1 times higher than their background values, respectively. The mean levels of other measured heavy metals were below those found naturally in the local soil. The enrichment factor showed that the study area exhibited significantly enriched Hg with 70.6% sampling sites. The Cd contents at 19.6% of sampling sites were moderately enriched. The other sampling sites were at a less enriched level. The sediments of all the rivers had a medium level of potential ecological risk. Hg was the major ecological risk factor in all sampling sites, followed by Cd. The findings from the positive matrix factorization (PMF) analysis shown agricultural activities, industrial activities, traffic emissions, and parent material were the major sources. The upper, middle, and low reaches of the Quanji river had different Hg isotope compositions, while sediments near the middle reaches were similar to the δ202Hg of the industrial source. At the upstream sampling sites, the Hg isotope content was very close to the background level. The results of this research can establish a strong scientific sound to improve the safety of the natural circumstances of rivers on the QTP.

Risk assessment and source identification of soil heavy metals: a case study of farmland soil along a river in the southeast of a mining area in Southwest China

To investigate the heavy metals (HMs) contamination of surface farmland soil along the river in the southeast of a mining area in southwest China and identify the contamination sources, 54 topsoil samples were collected and the concentrations of seven elements (Zn, Ni, Pb, Cu, Hg, Cr, and Co) were determined by inductively coupled plasma optical emission spectrometry (ICP-OES) and atomic fluorescence spectrometry (AFS). The geo-accumulation index ([Formula: see text]) and comprehensive potential ecological risk index ([Formula: see text]) were used for analysis to determine the pollution degree of HMs and the risk level of the study area. Meanwhile, the Positive Matrix Factorization (PMF) model was combined with a variety of statistical methods to determine the sources of HMs. To explore the influence of the river flowing through the mining area on the concentrations of HMs in the farmland soil, 15 water samples were collected and the concentrations of the above seven elements were determined. The results showed that the concentrations of Pb, Cu, and Zn in soil all exceeded the risk screening value, and Pb in soil of some sampling sites exceeded control value of "Agricultural Land Soil Pollution Risk Control Standard".[Formula: see text] showed that Pb was heavily contaminated, while Cu and Zn were moderately contaminated. RI showed that the study area was at moderate risk. PMF and various statistical methods showed that the main source of HMs was the industrial source. In the short term, the river flowing through the mine has no significant influence on the concentration of HMs in the soil. The results provide a reference for the local government to control contamination and identify the sources of HMs.

Speciation characteristics, ecological risk assessment, and source apportionment of heavy metals in the surface sediments of the Gomishan wetland

Metal contamination is one of the worldwide environmental issues. The main aim of this study was to evaluate the concentration, probable environmental risk, and source of investigated elements (Al, As, Co, Cr, Cu, Fe, Mn, Ni, and Zn) in sediments and water of the Gomishan wetland. Sediment contamination indices revealed sediments were solely polluted by As. The potential ecological risk index (RI), toxic risk index (TRI), and chemical speciation assessments indicated no major ecological hazards for investigated metals. Correlation analysis and principal component analysis (PCA) indicated that all studied metals in the Gomishan wetland sediments derived from natural sources. HPI, and HEI indices showed that the water quality in terms of hazardous components was inappropriate for aquatic life.

Assessment of heavy metal pollution and preschool children health risk in urban street dusts from different functional areas in a typical industrial and mining city, NW China

To assess the pollution characteristics and health risks associated with street dust exposure among preschool children in typical industrial and mining areas, we analyzed heavy metal concentrations of 20 urban street dusts in commercial area (CA), residential area (RA), scientific and educational area (SEA) and industrial and mining area (IMA) from Baiyin, NW China. The average concentrations of Cr, Mn, Ni, Cu, Zn, Cd, Pb, As and Hg were 614.96, 484.25, 1757.74, 6868.86, 893.19, 77.62, 1473.99, 15.01 and 0.59 mg·kg-1, respectively. The ecological risk indexes for Cd, Cu and Hg were found as 20,075.20, 1425.07 and 1174.86, respectively, and the ecological risk was extremely high. The pollution load indexes (PLI) were > 1 for all four functional areas. The total hazard index (THI) for different functional areas were more than 1, and the main exposure pathway for children was ingestion route. Heavy metals in street dust of the IMA had the highest THI for children (43.88), and HI of Pb was being most significant (17.38). In addition, the carcinogenic risk to children via the respiratory route was acceptable. Furthermore, factor analysis and cluster analysis classified heavy metals into two groups, indicating common anthropogenic sources for Cr, Ni, Cu, Zn, Cd, Pb, As and Hg. In conclusion, urban street dusts from industrial and mining area of Baiyin, NW China were found polluted by heavy metals and the pollution would pose an obvious non-carcinogenic risk to preschool children.

Effects of dissolved organic matter derived from cow manure on heavy metal(loid)s and bacterial community dynamics in mercury-thallium mining waste slag

Organic amendments in aided phytostabilization of waste slag containing high levels of heavy metal (loid)s (HMs) are an important way to control the release of HMs in situ. However, the effects of dissolved organic matter (DOM) derived from organic amendments on HMs and microbial community dynamics in waste slag are still unclear. Here, the effect of DOM derived from organic amendments (cow manure) on the geochemical behaviour of HMs and the bacterial community dynamics in mercury (Hg)-thallium (Tl) mining waste slag were investigated. The results showed that the Hg-Tl mining waste slag without the addition of DOM continuously decreased the pH and increased the EC, Eh, SO42-, Hg, and Tl levels in the leachate with increasing incubation time. The addition of DOM significantly increased the pH, EC, SO42-, and arsenic (As) levels but decreased the Eh, Hg, and Tl levels. The addition of DOM significantly increased the diversity and richness of the bacterial community. The dominant bacterial phyla (Proteobacteria, Firmicutes, Acidobacteriota, Actinobacteriota, and Bacteroidota) and genera (Bacillus, Acinetobacter, Delftia, Sphingomonas, and Enterobacter) were changed in association with increases in DOM content and incubation time. The DOM components in the leachate were humic-like substances (C1 and C2), and the DOC content and maximum fluorescence intensity (FMax) values of C1 and C2 in the leachate decreased and first increased and then decreased with increasing incubation time. The correlations between HMs and DOM and the bacterial community showed that the geochemical behaviours of HMs in Hg-Tl mining waste slag were directly influenced by DOM-mediated properties and indirectly influenced by DOM regulation of bacterial community changes. Overall, these results indicated that DOM properties associated with bacterial community changes increased As mobilization but decreased Hg and Tl mobilization from Hg-Tl mining waste slag.

Reclaiming abandoned mine tailings ponds for agricultural use: Opportunities and challenges

Tailings ponds, large man-made structures conceived during the mining process for waste storage, often become deserted post-mining, leaving behind a stark, contaminated landscape. This paper posits that these forsaken tailings ponds can be rejuvenated into fertile agricultural land through adept reclamation efforts. Serving as a discussion paper, it engages in a stimulating exploration of the environmental and health risks linked to tailings ponds. It sheds light on the potential and impediments in the transformation of these ponds into agricultural land. The discussion concludes that despite the substantial hurdles in repurposing tailings ponds for agriculture, there are encouraging prospects with the application of multifaceted efforts.

Statistical and spatial analysis for soil heavy metals over the Murray-Darling river basin in Australia

Heavy metals (HMs) are a vital elements for investigating the pollutant level of sediments and water bodies. The Murray-Darling river basin area located in Australia is experiencing severe damage to increased crop productivity, loss of soil fertility, and pollution levels within the vicinity of the river system. This basin is the most effective primary production area in Australia where agricultural productivity is increased the gross domastic product in the entire mainland. In this study, HMs contaminations are examined for eight study sites selected for the Murray-Darling river basin where the inverse Distance Weighting interpolation method is used to identify the distribution of HMs. To pursue this, four different pollution indices namely the Geo-accumulation index (I_geo), Contamination factor (CF), Pollution load index (PLI), single-factor pollution index (SPLI), and the heavy metal pollution index (HPI) are computed. Following this, the Pearson correlation matrix is used to identify the relationships among the two HM parameters. The results indicate that the conductivity and N (%) are relatively high in respect to using I_geo and PLI indexes for study sites 4, 6, and 7 with 2.93, 3.20, and 1.38, respectively. The average HPI is 216.9071 that also indicates higher level pollution in the Murray-Darling river basin and the highest HPI value is noted in sample site 1 (353.5817). The study also shows that the levels of Co, P, Conductivity, Al, and Mn are mostly affected by HMs and that these indices indicate the maximum HM pollution level in the Murray-Darling river basin. Finally, the results show that the high HM contamination level appears to influence human health and local environmental conditions.

Contamination, Source Apportionment, and Health Risk Assessment of Heavy Metals in Farmland Soils Surrounding a Typical Copper Tailings Pond

Tailings resulting from mining and smelting activities may cause soil heavy-metal pollution and harm human health. To evaluate the environmental impact of heavy metals from tailings on farmland soils in the surrounding area, heavy metals (As, Cd, Cr, Cu, Ni, Pb, and Zn) in tailings and farmland soils in the vicinity of a typical copper tailings pond were analyzed. Contamination status, potential sources, and health risks for farmland soils were investigated. The results showed that the tailings contained a high concentration of Cu (1136.23 mg/kg). The concentrations of Cd and Cu in the farmland soils exceeded the soil quality standard. The geoaccumulation index (I_geo) indicated that the soils were moderately polluted by Cu and Cd, and slightly polluted by Ni, Cr, and Zn. The absolute principal component scores-multiple linear regression (APCS-MLR) model was applied for source apportionment. The results showed that tailings release is the main source of soil heavy-metals contamination, accounting for 35.81%, followed by agricultural activities (19.41%) and traffic emission (16.31%). The health risk assessment suggested that the children in the study region were exposed to non-carcinogenic risks caused by As, while the non-carcinogenic risk to adults and the carcinogenic risk to both adults and children were at acceptable levels. It is necessary to take effective measures to control heavy-metal contamination from tailings releases to protect humans, especially children, from adverse health risks.

Heavy Metals Enrichment Associated with Water-Level Fluctuations in the Riparian Soils of the Xiaowan Reservoir, Lancang River

The cascade hydropower development in the Lancang River has significantly modified the hydrologic regime and is consequently responsible for many local environmental changes. The influence of the altered hydrological regime on heavy metals accumulation in the soils of the riparian zone was evaluated for the Xiaowan Reservoir (XWR). Specifically, this study focused on investigating the trace metals As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn and their concentrations in the riparian soils. Furthermore, this research aimed to examine the contamination levels of heavy metals by employing the geoaccumulation index (I_geo) and the ecological risk index (RI), respectively. Additionally, the relationship between heavy metals and water level fluctuations as caused by the dam operation was explored. The results showed that heavy metals deposits occurred in relatively low levels in the riparian soils of XWR, even though several of these metals were revealed to occur in higher concentrations than the local background value. The I_geo assessment indicated that the riparian soils exhibited slight pollution by Hg at the Zhujie wharf (ZJW) and Cr at the transect of the Heihui River (HHR), and moderate contamination by As at ZJW. Moreover, the RI revealed that As in riparian soils is moderately hazardous while Hg poses a high risk at ZJW. The polluted water and sediments from upstream and upland of the riparian zone may be contributing to the changed concentrations of heavy metal in the riparian soils. The present study inferred that the WLFs due to reservoir impoundment play a vital role in the accumulation of trace metals in the riparian zone. However, more exhaustive investigations are necessary for verification.

The regulatory role of abscisic acid on cadmium uptake, accumulation and translocation in plants

To date, Cd contamination of cropland and crops is receiving more and more attention around the world. As a plant hormone, abscisic acid (ABA) plays an important role in Cd stress response, but its effect on plant Cd uptake and translocation varies among plant species. In some species, such as Arabidopsis thaliana, Oryza sativa, Brassica chinensis, Populus euphratica, Lactuca sativa, and Solanum lycopersicum, ABA inhibits Cd uptake and translocation, while in other species, such as Solanum photeinocarpum and Boehmeria nivea, ABA severs the opposite effect. Interestingly, differences in the methods and concentrations of ABA addition also triggered the opposite result of Cd uptake and translocation in Sedum alfredii. The regulatory mechanism of ABA involved in Cd uptake and accumulation in plants is still not well-established. Therefore, we summarized the latest studies on the ABA synthesis pathway and comparatively analyzed the physiological and molecular mechanisms related to ABA uptake, translocation, and detoxification of Cd in plants at different ABA concentrations or among different species. We believe that the control of Cd uptake and accumulation in plant tissues can be achieved by the appropriate ABA application methods and concentrations in plants.

Assessment of the Heavy Metal Contamination of Roadside Soils Alongside Buddha Nullah, Ludhiana, (Punjab) India

The present study was carried out to determine the physico-chemical characteristics and heavy metal contents in roadside soil samples collected during 2 sampling periods (September 2018 and April 2019) from 8 different roadside sites lying parallel to the Buddha Nullah, an old rivulet, flowing through Ludhiana, (Punjab) India. The contents (mg/kg) of seven metals (cadmium, chromium, cobalt, copper, lead, nickel and zinc) were estimated using a flame atomic absorption spectrophotometer. Among the metals analyzed, the contents of Cd, Co, Cu, Pb and Zn were found above the permissible limits. The results of the index of geoaccumulation (Igeo), contamination factor (CF), contamination degree (Cdeg), modified contamination degree (mCdeg), the Nemerow pollution index (PI) and pollution load index (PLI) indicate a moderate to high heavy metal contamination of the analyzed soil samples. The results of the potential ecological risk factor (ERi) and potential ecological risk index (RI) indicate a low to moderate risk of heavy metals in the studied soil samples. The Pearson correlation analysis revealed that most of the variables exhibited a statistically significant correlation with one or more variables during the two samplings. Multivariate analysis demonstrates that contents of heavy metals in the study area are influenced by anthropogenic and geogenic factors.

Land Use Change and Its Impact on Landscape Ecological Risk in Typical Areas of the Yellow River Basin in China

The basic premise of regional ecological construction would be to scientifically and effectively grasp the characteristics of land use change and its impact on landscape ecological risk. The research objects of this paper are the typical areas of the Yellow River Basin in China and "process-change-drive" as the logical main line. Moreover, this paper is based on multi-period land use remote sensing data from 2000 to 2020, the regional land use change process and influencing factors are identified, the temporal and spatial evolution and response process of landscape ecological risk are discussed, and the land use zoning control strategy to reduce ecological risk is put forward. The results indicated: (1) The scale and structure of land use show the characteristics of "many-to-one" and "one-to-many"; (2) the process of land use change is affected by the alternation of multiple factors. The natural environment and socio-economic factors dominate in the early stage and the location and policy factors have a significant impact in the later stage; (3) the overall landscape ecological risk level and conversion rate show a trend of "high in the southeast, low in the northwest", shift from low to high and landscape ecological risks gradually increase; and (4) in order to improve the regional ecological safety and according to the characteristics of landscape ecological risk and spatial heterogeneity, we should adopt the management and control zoning method and set different levels of control intensity (from key intensity to strict intensity to general intensity), and develop differentiated land use control strategies.

Assessment of Heavy Metal Pollution Levels in Sediments and of Ecological Risk by Quality Indices, Applying a Case Study: The Lower Danube River, Romania

It is a well–known fact that heavy metal pollution in sediments causes serious problems not only in the Danube basin, but also in the large and small adjacent river streams. A suitable method for assessing the level of heavy metals and their toxicity in sediments is the calculation of pollution indices. The present research aims to assess heavy metal pollution in the Lower Danube surface sediments collected along the Danube course (between 180 and 60 km) up to the point where the Danube River flows into the Danube Delta Biosphere Reserve (a United Nations Educational, Scientific and Cultural Organization—UNESCO, protected area). In addition, this monitored area is one of the largest European hydrographic basins. Five heavy metals (Cd, Ni, Zn, Pb, Cu) were analyzed in two different seasons, i.e., the autumn of 2018 and the spring of 2019, using the Inductively Coupled Plasma Mass Spectrometry (ICP– MS) technique. Our assessment of heavy metal pollution revealed two correlated aspects: 1. a determination of the potential risks of heavy metals in sediments by calculating the Potential Ecological Risk Index (RI), and 2. an evaluation of the influence of anthropogenic activities on the level of heavy metal contamination in the surface sediments, using three specific pollution indices, namely, the Geo–Accumulation Index (Igeo), the Contamination Factor (CF), and the Pollution Load Index (PLI). The results of this pioneering research activity in the region highlighted the presence of moderate metal (Ni and Cd) pollution and a low potential ecological risk for the aquatic environment.