Ecological Risk Of Heavy Metals Research Articles

Geospatial Visualization and Ecological Risk Assessment of Heavy Metals in Rice Soil of a Newly Developed Industrial Zone in Bangladesh

With rapid industrialization in Gazipur areas of Bangladesh, untreated industrial effluents have been polluting rice soils which could exert potential ecological risk. Therefore, four different types of industries including chemical (SL), textile and paints (MIX), dyeing (CK), and sweater and dyeing (RD) were selected to monitor the intensity of heavy metal pollution in rice soils and ecological risk assessment. The di-acid digestion method was used for the determination of Pd, Cd, and Ni, and the DTPA extraction method was used for Fe, Zn, and Cu. ArcGIS was used to visualize the spatial patterns of heavy metal pollution, and different pollution indices were calculated to assess the ecological risk. The highest concentration (mg kg−1) of Cd (0.72), Pb (104.20), and Ni (5.02) was found in soils of the MIX industrial area. The highest concentration (mg kg−1) of Fe (147.65) and Zn (11.27) was found in the SL industry, while the highest Cu (7.67) was found in the CK industry. It was evident from the spatial distribution that the soils of paddy fields adjacent to the different industries are more contaminated than background soil. Although the potential ecological risk of heavy metal was low, different pollution indices indicated low to high pollution. Thus, the adjacent rice field soil of different industries is being contaminated by different heavy metals which may raise ecological risk.

Reconstruction of heavy metal(loid) pollution history based on dendrochemistry in Jiuzhaigou World Natural Heritage site, southwestern China

Heavy metal(loid)s are widely regarded as important environmental pollutants and have attracted extensive attention. In addition to such areas with frequent human activities as cities and industrial areas, the heavy metal(loid) pollution in remote areas lacking long-term monitoring data also deserves attention. In this study, Chinese pine (Pinus tabuliformis) in Jiuzhaigou World Natural Heritage was sampled to analyze concentration of Pb, Zn, Cu, As, Cd, Co, Cr, and Ni and to reconstruct pollution history. Source analysis and evaluation of the potential ecological risk of heavy metal(loid)s were also performed. Results showed that Jiuzhaigou has been polluted by heavy metal(loid)s at a relatively high level and concentrations were the highest at the location with intensive human activities (Nuorilang). Tree growth was inhibited by increased heavy metal(loid) concentration and this situation was more pronounced at high concentrations. The increased heavy metal(loid) concentrations were attributed to human activities such as forest logging, infrastructure construction, and tourism development. Heavy metal(loid) pollution reached a very high level of ecological harm at Nuorilang and a high level of ecological harm in Shuzheng and Heye villages. Overall, even at low concentrations, we demonstrated that Chinese pine can be used not only as a bioindicator for heavy metal(loid) pollution but also to infer pollution history over a relative long-term period and to enhance our understanding of the biogeochemical cycle of heavy metal(loid)s in forest ecosystems.

Evaluation of ash /slag heavy metal characteristics and potassium recovery of four biomass boilers

The utilization of biomass combustion for electricity generation has grown an importance and popularity. However, effective management of ash produced during biomass combustion is a major challenge. To analyze the ecological risk of heavy metals and ash characteristics in biomass ash, an inductive coupled plasma emission spectrometer (ICP) and X-ray diffraction (XRD) were used. The effects of temperature (20 °C, 40 °C, 60 °C), stirrer time (1h, 2h, 3h), and water-ash ratio (1:1, 2:1, 3:1) on potassium extraction were studied. The results show that the ecological risk index (RI) values of the fly ash and slag samples are very high, and all samples have very high risk (VHR) mainly due to Cd higher toxicity than other heavy metals. The main constituents of slag are aluminosilicate and SiO2, whereas fly ash contains CaSO4, KCl, SiO2, and KAlSi3O8. The fly ash from straw-fired biomass boiler contains more potassium, making it the most suitable raw material for the actual potassium extraction. In addition, temperature and stirrer time have little effect on potassium solubility while the effect of water-ash ratio is significant. Therefore, the most cost-effective potassium extraction method is water washing at room temperature with a stirrer time of about 1 h, a water-ash ratio of about 2:1, and leaching fly ash multiple times with incorporating the water recycling.

Heavy Metals in Sediments of Hulun Lake in Inner Mongolia: Spatial-Temporal Distributions, Contamination Assessment and Source Apportionment

The spatial and temporal distributions, contamination evaluation, and source apportionment of Cu, Zn, As, Pb, Cd, and Cr in the sediments of Hulun Lake were explored in this work. The pollution characteristics of six heavy metals were assessed by single factor pollution index (PI) and geo-accumulation index (Igeo). The sources of heavy metals in the surface sediments were analyzed by the positive definite matrix factorization (PMF) and Pearson correlation analysis. The sedimentary records of heavy metals in core sediments were reproduced by radioisotopes. The average concentrations of 6 heavy metals except Cd were lower than the corresponding background values. The spatial distributions of Cu, Zn, Cr, Cd and As were generally similar and showed higher abundances in the southwestern part of the lake. With the use and import of heavy metals, the concentration of heavy metals in core sediments increased with the fluctuation of years. The peak of heavy metal concentration was related to the high growth rate of gross domestic product in 2003-2008. The single factor pollution index and geo accumulation index results showed that the surface sediment was mainly polluted by Cd, followed by Zn and As. Natural parent material, agricultural activities and industrial activities were the main sources of heavy metal pollution in the sediments, accounting for 17.03%, 26.34%, and 56.63% of the total heavy metal accumulation, respectively. Pb was derived mainly from natural parent material. Cd and As were closely associated with agricultural activities. Cu and Zn were mainly attributed to industrial mining activities. Source apportionment of the ecological risks of heavy metals illustrated that industrial sources were the primary ecosystem risk sources (66.1%), followed by agricultural sources (23.75%) and natural sources (10.15%). The results will also provide reference data for future studies of heavy metals pollution in sediments from Hulun Lake and other lakes.

Comprehensive distribution characteristics and risks of heavy metals in typical intertidal zones and their relationship with urban economic indicators

Human activities have increased heavy metal pollution in intertidal environments. However, the comprehensive ecological risks of heavy metals in the active zones and their relationship with urban economic indicators are still poorly understood. This study investigated the multiphase distribution characteristics of heavy metals (Cr, Ni, Cu, Zn, Pb, and Cd) in 14 typical intertidal zones in the Guangdong–HongKong–Macao Greater Bay Area. The results showed that the concentrations of heavy metals varied greatly among different cities, and the highest average concentrations in Dongguan city were 695.27, 243.79, 1482.36, 980.24, 66.36 and 4.95 mg.kg−1, respectively. The proportion of bioavailable state Cd was the highest as 54.20%, followed by Zn > Cu > Pb > Ni > Cr. The comprehensive ecological risks (RCER) of the two intertidal zones in Dongguan were 1.45 ∼ 7.70 times higher than those of other sampling areas, indicating a very high ecological risk. Correlation analysis showed that total organic carbon in surface water, ammonia nitrogen in pore water, and solid organic carbon and the proportion of clay in sediments were significantly correlated with RCER values, and the linear regression coefficients were 0.784, 0.919, 0.962 and 0.914, respectively. The modified environmental Kuznets curve (EKC) model was used to describe the relationship between RCER values and urban economic indicators, and an inverted U shaped curve relationship was found, indicating that regional heavy metal pollution seemed to have reached a peak and entered a period of emission reduction. Nevertheless, given the increasing proximity of the intertidal zone to human daily life, long-term follow-up assessments are recommended.

Risk Assessment and Source Analysis of Heavy Metal Pollution in Surface Sediments from Major River Systems in Maoming City, Guangdong Province

In order to understand the spatial distribution and sources of heavy metals in surface sediments of MaoMing city and to reasonably evaluate the ecological risk of heavy metals in sediments of the study area, the contents of heavy metals (As, Hg, Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn) in surface sediments of eight rivers and three reservoirs were detected, and the risks of heavy metals were assessed using the geo-accumulation index (Igeo), potential ecological disk index (RI), and potential adverse biological impacts (ΣTUs). The sources of heavy metals were analyzed via correlation, principal component analysis (PCA), and positive matrix factorization (PMF). The results showed that the ω(Zn) (147.56 mg·kg-1) and ω(Hg) (0.20 mg·kg-1) were 3.72 and 2.25 times the background value, respectively, and the spatial distributions of Cd, Co, Cu, Mn, Ni, and Zn were in the order of northern>central>western>southeast. The geo-accumulation index results showed that Zn was at a moderate pollution level, 76.6% of the sampling sites of Hg were at a light-heavy pollution level, and other heavy metals were at a non-light pollution level. The results of potential ecological risk and potential adverse biological impacts indicated that the potential ecological risk index and toxicity effect of Gaozhou Reservoir were higher than those of other rivers, and Hg was the major contributor to heavy metal pollution. The three factors extracted from principal component analysis and positive matrix factorization represented natural sources, agricultural sources, and industrial sources, respectively. Therefore, in order to reduce the health hazards caused by heavy metals in sediments, a prevention and control system for the Hg element should be established.

Distribution Characteristics and Pollution Assessment of Heavy Metals in Soils of a Testing Range

Heavy metal pollution in testing ranges is one of the most widely concerning environmental problems. The ammunition static detonation test area, the bomb falling area, and the living area of a testing range in Jilin were selected as the study objects. The contents of heavy metals (As, Cd, Cr, Cu, Ni, Pb, and Zn) in 112 topsoil samples and two soil profiles were analyzed, and their distribution characteristics and sources were analyzed in detail. After that, the pollution degree and potential ecological risk of heavy metals were investigated using multiple pollution index assessment methods. The results showed that the average contents of As, Cd, Cu, Ni, and Zn in the soil of the ammunition static detonation test area were higher than the soil background values in Jilin province, and the contents of Cu, Zn, As, and Cd showed strong spatial heterogeneity. The average concentrations of As, Cd, and Ni in the soil of the bomb falling area exceeded their background values. The average contents of As and Cd in the soil of the living area were higher than the background values, and the variation coefficients of Pb, Cd, Zn, and Cr were relatively high, indicating that they may have been affected by human activities. In different test areas, the contents of As, Cr, Cu, Ni, and Zn in the soil samples were significantly different (P<0.05). The ammunition static detonation test area was more strongly affected by the test activities than the bomb falling area, and the heavy metal contents in the surface layer of the soil profile were significantly higher. There was no obvious vertical migration of heavy metals in the soil profiles. The results of multivariate statistics and source identification analysis using absolute principal component score-multiple linear regression (APCS-MLR) showed that Zn, Pb, and Cd were mainly affected by pollution sources related to test activities; Cr and Ni were mainly affected by natural sources of soil forming materials; and the sources of As and Cu were more complicated. The geo-accumulation index showed that Cd in the three areas and Ni in the bomb falling area belonged to pollution level 1 (uncontaminated to moderately contaminated). The Nemerow comprehensive pollution index showed that the pollution levels among the different functional areas were:living area>ammunition static detonation test area>bomb falling area, and the three functional areas were slightly polluted. The potential ecological risk index showed that the study area was at moderate ecological risk level, and Cd was considered to be the main soil pollution factor.

Ecological risk assessment and heavy metals accumulation in agriculture soils irrigated with treated wastewater effluent, river water, and well water combined with chemical fertilizers

Contaminated irrigation water can increase trace heavy metals concentration in agricultural soil. The present research aimed to investigate the effect of three types of irrigation water sources, including treated wastewater effluent, Gharasoo river water, and well water with chemical fertilizer, on the accumulation and ecological risk of heavy metals in agricultural soils. Soil samples were collected before and after crop irrigation to evaluate heavy metal concentrations. The samples were analyzed to determine the presence of arsenic, nickel, cadmium, iron, chromium, zinc, lead, copper, and manganese. Based on the results, the concentration of essential metals in the soil before the irrigation process was more than toxic metals. The different irrigation sources increased the concentration of all heavy metals in the soil, and the accumulation of Cr, Ni, and Cd significantly elevated more than others. Irrigation resources' effectiveness in transferring heavy metals to the soil was obtained as treated wastewater effluent < well water with fertilizer < river water. Furthermore, the potential ecological risk index (RI) for irrigated soil was in a high-risk category. Therefore, it is recommended that the river water should not be used to irrigate vegetables to the utmost possible. Finally, the low heavy metals concentration and the presence of nutrients in treated wastewater effluent make this source the most suited source of irrigation because it eliminates the need for chemical fertilizers by farmers and transfers fewer heavy metals to the soil.

Combined impacts of algae-induced variations in water soluble organic matter and heavy metals on bacterial community structure in sediment from Chaohu Lake, a eutrophic shallow lake

Many lakes are suffering from eutrophication and heavy metals-contamination. However, the combined impacts of algae bloom and its induced variations in heavy metals on microbial community in sediment from eutrophic lakes remain unclear. In this study, we performed field experiments to investigate how algae bloom impacted water soluble organic matter (WSOM) and heavy metals in sediment from Chaohu Lake, a eutrophic shallow lake, and probed their combined impacts on sediment bacterial community structure. The results showed that algae bloom increased WSOM quantity, in particular, the soluble microbial by-product-like (SMP) and fulvic acid-like (Fa-L) components markedly enhanced by 203.70 % and 70.17 %, respectively. We also found that algae bloom redistributed the spatial patterns of heavy metals and altered their chemical species in sediment, then promoted contamination degree and potential ecological risk of heavy metals in sediment. Moreover, sediment bacterial community richness and diversity obviously decreased after algae bloom, and the variance partitioning analysis (VPA) results showed that combined impacts of algae-induced changes in WSOM and heavy metals explained 66.56 % of the variations in bacterial community structure. These findings depicted how algae bloom influence sediment WSOM and heavy metals, and revealed the combined impacts of algae-induced variations on microbial community structure in shallow eutrophic lake.

Ecological risk assessment and early warning of heavy metal cumulation in the soils near the Luanchuan molybdenum polymetallic mine concentration area, Henan Province, central China

The Luanchuan molybdenum polymetallic mine concentration area is rich in mineral resources and has a long history of mining. The environmental impact of long-term mining activities cannot be ignored. It is of great significance to study the ecological risk and the accumulation trends of heavy metals in the soil of mining areas for scientific prevention and control of heavy metal pollution. Taking the Taowanbeigou River Basin in the mine concentration area as the research object, the ecological pollution risk and cumulative effect of heavy metals in the soil of the basin were studied by using the comprehensive pollution index method, potential ecological risk assessment method and geoaccumulation index method. On this basis, the cumulative exceeding years of specific heavy metals were predicted by using the early warning model. The comprehensive potential ecological risk of heavy metals in the soil near the Luanchuan mine concentration area is moderate, and the single element Cd is the main ecological risk factor, with a contribution rate of 53.6%. The overall cumulative degrees of Cu and Pb in the soil are “none-moderate”, Zn and Cd are moderate, Mo has reached an extremely strong cumulative level, Hg, As and Cr risks are not obvious, and the overall cumulative risks order is Mo>Cd>Zn>Cu>Pb>Hg. According to the current accumulation rate and taking the risk screening values for soil contamination of agricultural land as the reference standard, the locations over standard rates of Cu, Zn and Cd will exceed 78% in 90 years, and the over standard rate of Pb will reach approximately 57% in 200 years. The cumulative exceeding standard periods of As, Cr and Hg are generally long, which basically indicates that these elements do not pose a significant potential threat to the ecological environment. Mining activities will accelerate the accumulation of heavy metals in soil. With the continuous development of mining activities, the potential pollution risk of heavy metals in the soil of mining areas will also increase.©2023 China Geology Editorial Office.

Ecological risks of heavy metals in soil under different cultivation systems in Northwest China

The increasing population worldwide and high demand for food have changed the conventional open-field cultivation system (OFS) to plastic shed cultivation system (PSS), resulting in serious concern about soil contamination by heavy metals due to the intensive planting in PSS. However, there is limited research on heavy metals ecological risk after converting the cultivation system from OFS to PSS in Northwest China. Therefore, a total number of 341 soil samples were collected in Shaanxi province to measure heavy metals contents (As, Cd, Cr, Cu, Hg, Pb, and Zn) and assess the ecological risk. In this study, the PSS cultivation system exhibited more severe contamination than the OFS; whereas the heavy metals pollution in different regions was in the following order: southern Shaanxi (SS) > central Shaanxi (CS) > northern Shaanxi (NS). Although the mean values of the selected heavy metals were below the national limited standard, Cd and Pb posed considerable accumulation in both cultivation systems and the growing cultivation years increased the Cd, Hg and Zn contents in soils of PSS. The results of correlation analysis revealed a significant correlation between total phosphorus (TP) and Cd in PSS cultivation systems. However, soil organic matter (SOM), total nitrogen (TN), total phosphorus (TP), and total potassium (TK) had different interactions with other heavy metals in each region under both cultivation systems due to the variations in crop management techniques such as planting intensity and fertilizer input. Partial least square path model (PLS-PM) analysis showed that the different cultivation regions had a greater impact than the type of cultivation system, which should be carefully taken into account in mitigating pollution risk. Additionally, research on heavy metals species and fractions in connection to their bioavailability under various agricultural production systems is advised for improved food safety.

Heavy metal pollution and risk assessment of tailings in one low-grade copper sulfide mine

Analyzing the pollution level and ecological risk of heavy metals in tailings is a necessary step for conducting revegetation after a tailings pond’s closure. Herein, we determined the heavy metal pollution status and ecological risk in one low-grade copper sulfide tailings pond using chemical and mineralogical analysis, chemical extraction, and ecological risk assessment. The results showed that the low-grade copper sulfide tailings displayed a low pollution status and exhibited a very low ecological risk. Among six heavy metals (Cu, Pb, Zn, As, Cr, and Cd), only Cu (53.7 mg/kg) slightly exceeded its standard value limit (50 mg/kg), and was the main pollutant in the tailings. Due to its high toxicity, As had the maximum contribution to the potential ecological risk in the tailings. Pb, Zn, Cr, and Cd in the tailings were practically of no pollution, and at low or none potential ecological risk. In order to conduct revegetation in the tailings pond, more attention should be paid to the acidity change of tailings and its impact on the chemical activity and bioavailability of Cu and As. This research provides a theoretical basis for heavy metals risk control and revegetation in the low-grade copper sulfide tailings pond.

Health and ecological risks assessment of heavy metals and metalloids in surface sediments of Urmia Salt Lake, Northwest of Iran.

Urmia Lake, in the northwest of Iran, is the largest body of saline water in the Middle East, which has been desiccated in recent decades. To investigate the pollution status and ecological-health risks of heavy metals and metalloids in the surface sediments of this lake, 26 sediment samples were collected along the salt marshes of the lake and were analyzed for heavy metals and metalloid concentrations. The potential ecological risk assessment was carried out using enrichment factor (EF), geo-accumulation index (Igeo), contamination factor (CF), and potential ecological risk (Eri) standard indices. The average concentrations (mg kg-1) of heavy metals and metalloids were as follows: Fe (11,714) > Sr (320.8) > Mn (274.3) > V (28.5) > Cu (24.7) > Zn (21.2) > As (17.3) > Ni (14.8) > Cr (12.6) > Pb (11) > Co (4.0) > U (1.7), Hg (0.6) > Mo (0.36). The concentrations of As, Hg, and Sr in lake sediments were higher than geochemical background values. The non-carcinogenic risks caused by heavy metals and metalloids were insignificant regarding health risks. Levels of carcinogenic risk for metal(loid)s were in the acceptable ranges (10-6-10-4). The ecological risk was low, except for As, Sr, and Hg which showed moderate to significant EF, Igeo, and CF values. Arsenic and Sr were enriched in the surface sediments in desiccated parts of the lake due to complete lake water evaporation. It seems that further drying of the lake increases the potential ecological risk of heavy metals and metalloids in the surface sediments of Urmia Lake.

Nematode as a biomonitoring model for evaluating ecological risks of heavy metals in sediments from an urban river

Heavy metals have attracted much attention due to their irreversibility, persistence, concealment and bioaccumulation. Biomonitoring method combined chemical analysis can be well evaluate health risks of heavy metals in the environment. In this study, eleven sediments and water samples were collected along Xihe River, which was polluted by heavy metals in Shenyang city of China. The content of multiple heavy metals in these samples was determined by inductively coupled plasma mass spectrometry. 18S rRNA gene sequencing was performed to identify the composition and diversity of nematodes in fine River sediments. The biological toxicity of water-soluble extracts from the samples was further assessed by referring to different endpoints of Caenorhabditis Elegans. The results indicated that the risk of heavy metals in Xihe River was high (potential ecological risk index = 308.75), in which Hg and Cd are the main contributing factors. The relative abundance of nematodes complemented the chemical analysis result, Enoplida, Mononchida, Triplonchida, and Chromadorida nematodes presented a significant positive correlation with the concentration of heavy metals. Specially, Chromadorida nematodes were sensitive to changes in heavy metals in Xihe River, which was significant positively correlated with As, Pb and V. Therefore, nematodes such as Chromadorida can be applied in environmental monitoring to evaluate the health risks of heavy metals.

Spatial Distribution Characteristics and Potential Risk Assessment of Heavy Metals in Sludge of Shanghai Sewage Treatment Plant: A Case Study

Sewage treatment is an important indicator of the urban environment and an important method of sustainable development. In this paper, the spatial distribution characteristics of 8 heavy metals in sewage sludge from 44 sewage treatment plants in Shanghai were analyzed. The pollution degree and potential ecological risk of heavy metals in sludge were evaluated by the Nemerow comprehensive pollution index and Hakanson potential ecological risk index. First, the single factor pollution index of heavy metals was ranked. The Nemerow comprehensive pollution index showed that five sewage treatment plants in Nanxiang, Dongqu, Liantang, Songjiang west, and Xinhe were heavily polluted. Second, the single factor potential ecological risk index of each heavy metal was analyzed. Finally, it is concluded that in the monitoring and control of sewage treatment, Shanghai should pay attention to the sewage treatment plants with high potential ecological risks and gain an excellent performance in the reduction in the emissions of pollution sources, so as to improve environmental quality and reduce the potential ecological risks. This paper provides the basis for studying the characteristics of heavy metal pollution of sewage sludge.

Co-gasification of municipal sewage sludge and cotton stalk enhanced by metal-enriched texture dyeing sludge additives for syngas production

In this study, co-gasification characteristics of municipal sewage sludge (MSS) and cotton stalk (CS) for syngas production enhanced by using metal-rich texture dyeing sludge (TDS) pyrolysis residues as additives wereinvestigated in a TGA and a fixed bed reactor. Kinetic analysis results showed that the addition of TDS residue prepared at 600 °C (TDS-600) resulted in the reduction of activation energy of MSS/CS co-pyrolysis to the maximum extent. The syngas yield greatly increased with the rising temperature and steam volume fraction (fH2O). However, the excessive steam at high temperature may lead to the decrease of syngas yield due to the gas expansion effect. The maximum syngas yield of 0.808 m3/kg could be obtained at an optimal gasification temperature of 850 °C and a fH2O of 20 %. In the co-gasification of MSS and CS, the syngas yield increased from 0.683 without TDS-600 to 0.903 kJ/mol with 20 % TDS-600 and the tar content decreased from 40.15 % to 26.45 %, suggesting the outstanding catalytic effect of TDS-600 on promoting syngas yield and tar decomposition. The possible ecological risk of heavy metals in ashes after co-gasification was evaluated by the potential ecological risk index (RI). The calculated RI values of all samples were <50, demonstrating the safe application of ashes in agriculture industry.

Spatial Distribution and Risk Assessment of Heavy Metals in Surface Sediments from the Middle and Upper Reaches of the Yangtze River

The hydrological regime of rivers significantly changes after dam impoundment, which in turn affects the particle composition and heavy metal fractions of the river sediments. From June to July 2019, the sediments from 26 sampling sections were collected along the main stream of the Yangtze River from Panzhihua City in the upper reaches of the Yangtze River to Hukou City in the middle reaches of the Yangtze River. The concentrations and fractions of As, Cd, Co, Cr, Cu, Ni, Pb, and Zn were measured using the BCR three-step extraction procedure. The pollution status and potential ecological risk of heavy metals in sediments were evaluated using the geo-accumulation index, the sediment quality guideline, and the risk assessment coding method (RAC). The results showed that the average particle size of sediments in the upper reaches of the Yangtze River (Jinsha River cascade reservoir section and the Three Gorges reservoir section) decreased from upstream to downstream, the total concentrations of As and Zn increased, and the variation trend in the middle reaches was not obvious. The content of clay particles was significantly positively correlated with the acid-soluble fraction concentrations of Cd and Ni. Cd was mainly in the residual fraction (59.26%) and acid-soluble fraction (24.67%). Large parts of Cr and Ni were residual fractions accounting for 92.41% and 83.41%, respectively. As, Co, Cu, Pb, and Zn were mainly in the residual fraction and the reducible fraction. The order of decrease for the pollution degree (Igeo) of As, Cd, Co, Cr, Ni, and Zn was the Jinsha River, the middle reaches of the Yangtze River, and the Three Gorges Reservoir. The decrease order of bioavailability (RAC) of Cd, Co, Cr, Cu, Ni, and Zn was the Three Gorges Reservoir, the Jinsha River, and the middle reaches of the Yangtze River. The bioavailability of As and Pb decreased in the order of the middle reaches of the Yangtze River, the Three Gorges, and the Jinsha River. According to the classification of the RAC, Cd in the Three Gorges Reservoir area exhibited a high risk with the RAC accounting for 48.44%. Cu, Ni, and Zn showed a low or medium risk.

Ecological and health risk assessment of heavy metals: a case study of residential waste sites in Umuahia, South-East Nigeria

This study assessed the human health hazards and ecological risks of heavy metals from waste sites in residential vicinity. The heavy metals analyzed were Cr, Pb, Cd, Ni, Cu, and Zn. A total of 40 soil samples were collected from waste sites in two residential estates located in the urban and suburb areas of Umuahia, Abia state. Results revealed a trend in concentrations of the heavy metals for both sites in the following order: Cu > Ni > Zn > Cr > Cd > Pb. The concentrations of heavy metals were higher in rural soils than in urban soil. The contamination factor (CF) indices for Pb, Cr, Cu, Ni, and Zn were less than 1 for both sites, signifying a low contamination scenario. The contamination factor for Cd (6 > CF) for both sites indicated a very high contamination status. The estimated degree of contamination (Cdeg) was less than the lower threshold of 8.0, denoting a low degree of contamination. Cd was the highest contributor to ecological risk with Er index value of 184.2 among measured heavy metals. The overall potential ecological risk index for urban and rural sites are 187.1 and 196.1 respectively, classifying the sites as moderate risk. The overall non-carcinogenic hazard index values (HI) for adults and children in urban and rural soils are 0.00248, 0.0198 and 0.0028, 0.0223 respectively, which are below the acceptable limit (HI < 1), indicating that the exposed residents are unlikely to experience any apparent adverse health hazards. However, children are more susceptible to non-carcinogenic hazards than adults in the study areas.

Pollution and ecological risk assessments for heavy metals in coastal, river, and road-deposited sediments from Apia City in Upolu Island, Samoa

This study was the first to investigate the pollution and ecological risks of heavy metals in coastal, river/stream and road-deposited sediments (RDS) from Apia in Samoa. Cr and Ni concentrations in sediment samples were higher than those of other metals. River sediments and RDS had relatively high EF values around the intensive commercial areas, with a moderate to significant enrichment of Cu, Zn, Cd, and Pb. The results indicate that Cr and Ni have a natural origin from volcanic parent materials, while Cu, Zn, Cd, and Pb originated from anthropogenic activities, such as traffic emissions and the discharge of municipal wastewater. The assessments of pollution and ecological risk revealed that coastal sediments adjacent to the river are anthropogenically contaminated and present a moderate ecological risk. This study demonstrates that metals that have accumulated in the urban impermeable layer and river/stream bed have flowed into the coastal environment through runoff.

Environmental Risk Assessment, Principal Component Analysis, Tracking the Source of Toxic Heavy Metals of Solid Gold Mine Waste Tailings, South Africa

This study collected 21 soil samples from 30 to 120 cm depth, from 9 solid gold mine waste dumps in the Witwatersrand basin, South Africa. The samples were analysed using ICP-OES method to determine the concentrations of heavy metals. Principal component analysis (PCA) was performed to track sources of heavy metals, migration passages, their distributions and spatial variations at the study sites. The results of this study showed that the soil screening values (mg/kg) ranged from 2.20–7,070.00 Pb, 0.20–11.00 As, 0.06–2,630.00 Hg, 1.00–69.00 U, 0.02 − 4.20 Cd, and exceeded the background concentrations of the continental crust. The study results further showed that the average concentrations (mg/kg) of Pb (432.08), U (13.75), Tl (4.41), Ag (1.07), Cd (0.34) were highest at Durban Deep. Arsenic (59.86) and Sn (2.03) were highest at Krugersdorp, Kagiso, New Canada, and Shaft 17. The average values of Hg (625.56 µg/kg) and Au (17.67 µg/kg) were highest at Mogale City, Fleurhof, Krugersdorp, Shaft 17, and Davidsonville. These values reflected moderate to extreme contamination, supported by geoaccumulation index (Igeo), pollution load index (PLI), and contamination factor (Cf i) values. According to PCA, F1 was responsible for heavy metal generations from the local gold processing and waste dumping facilities. The F1 loading for Cd and Pb was 0.845 and 0.835, respectively, whereas F1 and F2 contribution of the variable % were greater than 0.70 for Ag, As, Au, Cd, Pb, Sn, Tl, and U, suggesting that they were generated from the waste dumps, transported by rain water and subsequently deposited in downstream soil. The heavy metal concentrations were traced upstream at the dumps where the highest averages were recorded, whereas the lowest values were measured from downstream samples. Thus, the gold mine tailing dumps are considered the primary sources of the high measured values of the heavy metals in the study sites. The ecological risk values were ranked in the order of As > Cd > Hg > Pb and exceeded the permissible health risk value suggested by the South African and global standards. Excessive Hg concentration with 160 ≤ E r i < 320 was recorded at Krugersdorp, whilst Pb with 320 ≤ E r i was recorded at Durban Deep. Thus, the estimated high E r i values insinuate higher ecological risk of heavy metals that can accumulate in the human body through absorption, inhalation and ingestion of dust, or ingestion of food grown from the contaminated soil.