Distribution, sources and influence factors of polycyclic aromatic hydrocarbon at different depths of the soil and sediments of two typical coal mining subsidence areas in Huainan, China

Distribution, sources, and risk assessment of polycyclic aromatic hydrocarbons in surface soils and plants from industrial and agricultural areas, Junggar Basin, Xinjiang

The contamination characteristics of Polycyclic Aromatic Hydrocarbons (PAHs) in different environmental functional areas are different. In this study, the contamination of PAHs in soils and common plants in typical mining and farmland areas in Xinjiang, China, was analyzed. The results showed that the contamination levels of PAHs in mining soils were significantly higher than those in farmland soils, and the mining soils were dominated by 4-5-ring PAHs and farmland soils by 3-4-ring PAHs. Analysis of their sources using a positive definite factor matrix model showed that PAHs in mining soils mainly originated from coal and natural gas combustion, and transportation processes; while farmland soils mainly came from biomass and coal combustion, and fossil fuel volatile spills. The cancer risk of PAHs in soils was evaluated using a combination of the Monte Carlo and the lifetime carcinogenic risk models, and the results showed that the overall level of cancer risk for mining soils was higher than that for farmland soils, and can put some people in high risk of cancer. For plant samples, except for individual crop samples, the contamination levels of mining plants and crops were similar, with 4-5-ring PAHs dominating in desert plants in mining areas and the highest proportion of 3-ring PAHs in crops in agricultural fields, and PAHs in both plants were mainly from biomass and coal combustion. The results of correlation analysis showed that 2-ring PAHs in crop roots were significantly positively correlated with it in corresponding soils, and some high-ring PAHs in crop leaves were significantly negatively correlated with it in corresponding soils. Therefore, there were significant differences in the pollution characteristics of PAHs in soils and common plants in mining and agricultural areas. Human health risks and ecological risks are mainly concentrated in mining areas, and appropriate intervention measures should be taken for pollution remediation.

Distribution of mercury and methylmercury in aquacultured fish in special waters formed by coal mining subsidence

In China, fence net aquaculture practices have been established in some subsidence waters that have been formed in coal mining subsidence areas. Within this dynamic ecological context, diverse fish species grow continuously until being harvested at the culmination of their production cycle. The purpose of this study was to investigate diverse factors influencing the bioavailability and distribution of mercury (Hg) and methylmercury (MeHg), which have high physiological toxicity in fish, in the Guqiao coal mining subsidence area in Huainan, China. Mercury and MeHg were analyzed in 38 fish samples of eight species using direct mercury analysis (DMA-80) and gas chromatography-cold vapor atomic fluorescence spectrometry (GC-CVAFAS). The analysis results show that the ranges of Hg and MeHg content and methylation rate in the fish were 7.84-85.18 ng/g, 0.52-3.52 ng/g, and 0.81-42.68 %, respectively. Meanwhile, conclusions are also summarized as following: (1) Monophagous herbivorous fish that were fed continuously in fence net aquaculture areas had higher MeHg levels and mercury methylation rates than carnivorous fish. Hg and MeHg contents were affected by different feeding habits of fish. (2) Bottom-dwelling fish show higher MeHg levels, and habitat selection in terms of water depth also partially affected the MeHg content of fish. (3) The effect of fence net aquaculture on methylation of fish in subsidence water is mainly from feed and mercury-containing bottom sediments. However, a time-lag is observed in the physiological response of benthic fishes to the release of Hg from sediments. Our findings provides baseline reference data for the ecological impact of fence net aquaculture in waters affected by soil subsidence induced by coal mining in China. Prevalent environmental contaminants within coal mining locales, notably Hg, may infiltrate rain-induced subsidence waters through various pathways.

Source-specific ecological risk analysis and critical source identification of heavy metal(loid)s in the soil of typical abandoned coal mining area

Long-term coal mining activities in abandoned coal mining areas have resulted in the migration of large quantities of heavy metals into the surrounding soil environment, posing a threat to the regional ecological environment. This study focuses on the surface soil collected from a typical abandoned coal mining area. Methods such as the pollution index (PI) and potential ecological risk index (RI) were used to comprehensively evaluate the pollution levels and ecological risks of soil heavy metals. Geostatistical analysis and the APCS-MLR model were used to quantify the sources of soil heavy metals, and Nemerow integrated ecological risk (NIRI) model was coupled to apportion the ecological risks from different pollution sources. The results indicate that the average concentrations of Cd, As, and Zn are 4.58, 2.44, and 1.67 times the soil background values, respectively, while the concentrations of other heavy metals are below the soil background values. The soil of study area is strongly polluted by heavy metals, with the pollution level and ecological risk of Cd being significantly higher than those of other heavy metals. The NIRI calculation results show that the overall comprehensive ecological risk level is considerable, with sample points classified as relatively considerable, moderate, and low at 60.53 %, 36.84 %, and 2.63 %, respectively. The sources of soil heavy metals can be categorized into four types: traffic activities, natural sources, coal gangue accumulation, and a combined source of coal mining and agricultural activities, with contribution rates of 35.3 %, 36.1 %, 19.5 %, and 9.1 %, respectively. The specific source ecological risk assessment results indicate that coal gangue accumulation contributes the most to ecological risk (36.4 %) and should be prioritized for pollution control, with Cd being the priority control element for ecological risk. The findings provide theoretical support for the refined management of soil heavy metal pollution in abandoned coal mining areas.

Polycyclic aromatic hydrocarbons (PAHs) in coal preparation plant products: A contributor to environmental pollution

Coal and coal gangue are petrogenic sources of polycyclic aromatic hydrocarbons (PAHs), which cause adverse impacts on the environment. Raw coal, cleaned coal, slime, slack gangue, and lump gangue from the Pingshuo No. 1 Coal Preparation Plant, China, were analyzed to determine the concentrations and compositions of 16 priority parent PAHs (16PAHs) and their alkylated derivatives (aPAHs). The ∑16PAH and ∑aPAH concentrations in the samples ranged from 18.7 to 139.2 mg/kg and 22.2 to 262.3 mg/kg, respectively, and ranked as follows: cleaned coal > raw coal > slime > lump gangue > slack gangue. Coal gangues had a higher proportion and lower degree of alkylation of 4-6-ring PAHs than coals. A summary analysis of references related to coal and coal gangue diagnostic ratios showed that their ratios could not be used to differentiate them from other PAH sources, indicating that the release of particulate coal and coal gangue would increase the uncertainty of environmental PAH identification results. The diagnostic ratios of coal gangue were relatively concentrated, and comparing the ratio distribution could reveal the coal gangue source PAHs. The toxicity risk of slack gangue was higher than that of lump gangue based on the benzo[a]pyrene-equivalent concentration; hence, more attention should be given to its escape to the environment.

An overview of the impacts of coal mining and processing on soil: assessment, monitoring, and challenges in the Czech Republic

Coal mining activities are causing an extensive range of environmental issues at both operating and abandoned mine sites. It is one of the most environmentally destructive practices, with the capability to eliminate fauna and flora, impact the groundwater system, and pollute the soil, air, and water. The Czech Republic relies almost exclusively on coal as its primary domestic source of energy. The combined reserves of hard and brown coals in this country are 705 million tons. About 50 million tons of coal is produced annually, making it the 14th biggest producer in the world. Soil degradation is an inevitable outcome of the coal production from surface coal mining procedures in the Czech Republic. Significant changes have taken place in soil productivity, hydraulic characteristics, horizon, and texture as a result of soil pollution, bioturbation, compaction, and weathering. The current review has evaluated the impact of reclamation and coal mining on soil characteristics, including biological, chemical, and physical properties. Additionally, the study has outlined the process of soil formation in reclamation areas in the Czech Republic. In nutshell, research gaps and future directions in understanding coal mining areas and their influences on soils in the Czech Republic are identified.

How do rotifer communities respond to floating photovoltaic systems in the subsidence wetlands created by underground coal mining in China?

Along with the increasing demand for energy and pressure to reduce carbon emissions, floating photovoltaic (FPV) systems are increasingly built on the surface of water bodies with the aim to produce clean energy. However, little is known about how FPV systems influence freshwater ecosystems, e.g., their zooplankton communities. We investigated how rotifer communities responded to FPV systems in subsidence wetlands created by underground coal mining in the North China Plain. Diversity metrics of the rotifer communities were compared between wetlands with and without FPV systems. The density of rotifers was higher in wetlands without FPV systems. In contrast, rotifer diversity as represented by Shannon-Weiner and Pielou evenness indices was higher in the FPV-covered wetlands, while there was no difference in species richness between the two types of wetlands. Furthermore, community structures differed between the two types of wetlands, in large part reflecting differences in the relative abundance of five dominant species found in both types of wetlands. These differences in rotifer assemblages were in large part explainable from environmental changes caused by the FPV panels, notably reduced light availability and water temperature, leading to reduced phytoplankton production. These findings show that FPV systems cause major changes to rotifer communities in these subsidence wetlands and likely in wetlands more generally, and monitoring of the longer-term effects is recommended given the fundamental role of zooplankton in freshwater ecosystems.

Seasonal succession of microbial community co-occurrence patterns and community assembly mechanism in coal mining subsidence lakes

Coal mining subsidence lakes are classic hydrologic characteristics created by underground coal mining and represent severe anthropogenic disturbances and environmental challenges. However, the assembly mechanisms and diversity of microbial communities shaped by such environments are poorly understood yet. In this study, we explored aquatic bacterial community diversity and ecological assembly processes in subsidence lakes during winter and summer using 16S rRNA gene sequencing. We observed that clear bacterial community structure was driven by seasonality more than by habitat, and the α-diversity and functional diversity of the bacterial community in summer were significantly higher than in winter (p < 0.001). Canonical correspondence analysis indicated that temperature and chlorophyll-a were the most crucial contributing factors influencing the community season variations in subsidence lakes. Specifically, temperature and chlorophyll-a explained 18.26 and 14.69% of the community season variation, respectively. The bacterial community variation was driven by deterministic processes in winter but dominated by stochastic processes in summer. Compared to winter, the network of bacterial communities in summer exhibited a higher average degree, modularity, and keystone taxa (hubs and connectors in a network), thereby forming a highly complex and stable community structure. These results illustrate the clear season heterogeneity of bacterial communities in subsidence lakes and provide new insights into revealing the effects of seasonal succession on microbial assembly processes in coal mining subsidence lake ecosystems.

Phytoplankton-Zooplankton Community Structure in Coal Mining Subsidence Lake

Land subsidence from coal mining has shaped new artificial aquatic ecosystems, these subsidence lakes are known for their restricted ecological system, water pollution, and extreme habitat conditions. However, knowledge concerning the community structure of plankton in these types of water bodies is still limited. Therefore, both phytoplankton and zooplankton communities' abundance, distribution, and diversity, as well as relations of these communities to physicochemical water quality variables were analyzed, alongside the interaction between phytoplankton and zooplankton groups. The results indicate zooplankton abundance was 842.375 to 186,355.0 ind./L. Biomass ranged from 0.3408 to 10.0842 mg/L. Phytoplankton abundance varied between 0.541 × 10⁶ cell/L and 52.340 × 10⁶ cell/L while phytoplankton wet biomass ranged from 0.5123 to 5.6532 mg/L. Pearson correlation analysis revealed that both the zooplankton and phytoplankton total densities were significantly correlated with nutrients (TN, TP, PO₄^3-) and COD_cr; zooplankton abundance was significantly correlated with phytoplankton abundance. According to the biodiversity index of Shannon-Wiener, both phytoplankton and zooplankton revealed less biodiversity in the subsidence water region than in the Huihe river system and Xiangshun canal, with values ranging from 0.20 to 2.60 for phytoplankton and 1.18 to 2.45 for zooplankton; however, the phytoplankton community showed lower biodiversity index values compared to the zooplankton community. Overall, the knowledge gleaned from the study of plankton community structure and diversity represents a valuable approach for the evaluation of the ecological conditions within the subsidence lakes, which has significant repercussions for the management and protection of aquatic environments in mining areas.

Alkylated Polycyclic Aromatic Hydrocarbons Are the Largest Contributor to Polycyclic Aromatic Compound Concentrations in the Topsoil of Huaibei Coalfield, China

Alkyl polycyclic aromatic hydrocarbons (APAHs) are more toxic and persistent than their parent compounds. Here, the concentrations, composition profiles, and spatial distribution of polycyclic aromatic compounds (PACs) in 127 topsoil samples from Huaibei coalfield were analyzed. The PAC concentrations in different functional areas were significantly different: mining area > industrial area > residential area > agricultural area. APAHs were the major contributors to PACs, accounting for 71-83% of total PACs. Alkylnaphthalenes and alkylphenanthrenes were the primary APAH components, accounting for 83-87% of APAHs. Principal component analysis showed that petrogenic source, coal and biomass combustion, and vehicle emissions were the primary sources of PACs. By comparing the fingerprint information of soil, coal, and coal gangue, it was hypothesized that the petrogenic source of PAC pollution in typical mining areas and surrounding areas are coal particle scattering and coal gangue weathering. Some coal mining and industrial areas potentially pose risks to children, whereas others do not. There are limited evaluation criteria for alkyl PAHs; hence, the estimated risk is likely lower than the actual risk. In addition to the conventional 16 PAHs, it is critical to consider a broader range of PACs, especially APAHs.

Distribution, sources, and ecological risk assessment of HCHs and DDTs in water from a typical coal mining subsidence area in Huainan, China

Coal mining subsidence areas are a special and widespread ecosystem in China and many developing countries in the world. However, limited research has focused on HCHs and DDTs in coal mining subsidence areas. Investigating the concentration, distribution, and sources of HCHs and DDTs at the Yangzhuang coal mining subsidence area in Huainan, China, is the object of this study. Water samples from different depths were collected from this region to detect and analyze HCHs and DDTs using gas chromatography-mass spectrometry. The result showed that the concentrations of HCHs and DDTs increased with increasing water depth, and the average concentrations of HCHs and DDTs in the top (T-layer), middle (M-layer), and bottom (B-layer) layers were 152, 169, and 182 ng∙L^-1, respectively. Spatial distribution of HCH and DDT concentrations in the study area revealed that the concentrations gradually decreased in the direction of water flow, and the highest concentration was observed at the entrance of the Nihe River. The T-layer was easily influenced by environmental and human activities, while the M-layer and B-layer were mainly influenced by sediment. Using principal component analysis and diagnostic ratios, we found that HCHs and DDTs in the study area mainly originated due to natural and human activities (such as pesticide use). Hexachlorocyclohexanes (HCHs) were mainly derived from lindane, and dichlorodiphenyltrichloroethanes (DDTs) mainly originated due to the recent agricultural use of dicofol; both of these are directly related to agricultural activities. Based on a comparison of reported concentrations of HCHs and DDTs in the rivers and lakes throughout China, we found that the overall ecological risk of HCHs and DDTs in the study area was elevated. The results are important for further understanding the transfer characteristics of HCHs and DDTs as well as the ecological health of the water in coal mining subsidence areas.

Influence of Solar Photovoltaic System on the Concentration and Environmental Risks of Heavy Metals in Subsidence Pond Water from Coal Mining Area: A Case Study from Huainan Subsidence Pond

The subsidence pond is an important water resource for coal mining areas in China. In order to take full advantage of the subsidence pond, a floating photovoltaic cover or a pillaring photovoltaic cover were installed on the surface water of the subsidence pond in the Huainan coal field. Different photovoltaic systems (floating/pilling cover) equipped in the subsidence pond may affect the water quality; thus, assessing the metals in the subsidence pond with the solar photovoltaic system is of great importance for environment control. In this research, surface water samples were collected from three different subsidence ponds, with or without the solar photovoltaic system. The concentrations of Pb, Cr, Ni, Cu, As, Mn, and Zn in the water of the subsidence pond were determined using ICP-MS and AFS. Then, the health risk posed by the heavy metal in different subsidence pond waters via the ingestion pathway was evaluated and analyzed using the assessment model recommended by USEPA. The results indicated that the mean concentrations of Pb, Cr, Ni, Cu, As, Mn, and Zn in the water of different subsidence ponds were less than the environmental quality standards for surface water (China, Grade II). Cr showed a higher non-carcinogenic risk than the other metals, and the photovoltaic cover actually decreased the total non-carcinogenic risk in the photovoltaic subsidence pond compared with the natural subsidence pond. Non-carcinogenic risks of single and total heavy metals in the subsidence ponds with or without solar photovoltaic systems were below 1; thus, these risks in different subsidence ponds were considered to be at an acceptable level. However, the potential single carcinogenic risks of Cr, Ni, and As; and the multielement carcinogenic risks of Pb, Cr, Ni, and As exceeded the limits of 1 × 10−6 and 1 × 10−4, respectively, suggesting that these metals showed single and total potential health risks in the subsidence pond, with or without the solar photovoltaic system. Further, the subsidence pond with the photovoltaic cover showed higher total carcinogenic risks in comparison with the natural subsidence pond. Therefore, a subsidence pond with a solar photovoltaic system should be monitored periodically to ensure the water safety.

The risk assessment of inorganic and organic pollutant levels in an urban area affected by intensive industry

The city of Litvínov (North Bohemia, Czech Republic) is seriously affected by coal mining, coal processing, and intensive industrial activities. Within the urban area, the potential environmental hazard of risk elements (in soil and vegetation) and polycyclic aromatic hydrocarbons (PAHs, in soils) was estimated using selected environmental and human health hazard indices. In total, 24 sites were sampled, including the city center, residential areas, industrialized zone, and areas close to operating and/or abandoned coal mines. The results showed elevated values of As, Cd, Cu, Ni, Pb, and Zn in soils (the maximum levels of individual pollution indices varied between 3 and 5 for As, Pb, and Zn); the risk assessment code (RAC) values indicated high bioaccessibility of Cd and Zn. The high mobility of Cd was confirmed by their bioaccumulation factors (BAF) in the aboveground biomass of Taraxacum sect. Ruderalia and Polygonum aviculare, reaching up to 1.9 and 2.9, respectively. The Cd content in plants presents a substantial health hazard for herbivores such as Oryctolagus cuniculus living within the urban area. The PAH levels in the soils also showed elevated values; the contents of benzo(a)pyrene exceeded more than 2-fold the indicative values for potential health risk for biota, especially near the abandoned coal mines. The incremental lifetime cancer risks (ILCR) for ingestion of the contaminated soil showed only low or negligible cancerogenic risk, varying between 6.7 × 10^-7 and 1.6 × 10^-5 for children, and between 9.9 × 10^-7 and 2.7 × 10^-6 for adults. However, the potential health impact of the inhalation of the contaminated particulate matter should be included in the further research. Although the contamination level in the investigated area does not represent an imminent environmental and health risk, the potential remediation measures should be considered in the future.

An ecological scenario prediction model for newly created wetlands caused by coal mine subsidence in the Yanzhou, China

The ecological model we developed can simulate the state of wetlands and predict ecosystem development by varying both parameter settings and forcing functions. The newly created wetland resulting from large-scale coal mining is a distinct type of wetland, but existing ecological models for this wetland type are limited in number and scope. The Yanzhou coalfield, located in Shandong Province in China, contains a typical newly created wetland that came into being after coal mining subsidence. We developed an ecological model for this wetland that estimates values for four state variables: phytoplankton biomass (A), zooplankton biomass (Z), sediment biomass (D), and hydrophyte biomass (H). Analysis of the results showed that the model was sensitive to changes in nutrient loading. As nutrient loads increased, plankton biomass increased, and the ratio of zooplankton biomass to phytoplankton biomass (Z/A) decreased. We defined three prediction scenarios for the wetland and calculated their eco-exergies to compare the ecological effects for each scenario. The most effective measures to improve the state of the ecosystem are to reduce the subsidence depth and to decrease nutrient loading.

Occurrence, risk and influencing factors of polycyclic aromatic hydrocarbons in surface soils from a large-scale coal mine, Huainan, China

Coal is one of the most important fossil fuels for energy, but it can cause serious polycyclic aromatic hydrocarbon (PAH) pollution to the environment. In this work, the distribution, sources, influencing factors, and risk assessment of PAHs were studied in a soil of typical coal resource city, Huainan, China. The total concentration of 16 PAHs classified by USEPA in 47 soils ranged from 109.94 to 1105.30 ng/g with a mean concentration of 528.06 ng/g. The PAH concentration was higher in soil of this area than most of the agricultural, urban and industrial soils and lower than some coal mine and coal-fired power plant areas in the world. The principal component analysis (PCA) and diagnostic ratios demonstrated that PAHs in soils were mainly from the coal combustion and refined petroleum products. The total organic carbon (TOC, p < 0.01) and black carbon (BC, p < 0.01) can significantly influence PAH inventories in soils, particularly for PAHs with high molecular weight. In addition, the significantly positive correlations between PAHs in feed coal (p < 0.05), fly ash (p < 0.01), particulate matter (PM_1-2.5 and PM_2.5-10, p < 0.01) and PAHs in soils revealed that the emission sources and deposition processes were also the main factors affecting PAH contents in soils. The estimated values of incremental lifetime cancer risk (ILCR) for children and adults were higher than 10^-4 at all sampling sites, suggesting high carcinogenic risks for local residents, and the most important exposure route for PAHs was dermal absorption. These findings are valuable for assessing the health risk of PAHs in soils around typical coal mine and coal-fired power plants and highlight the urgency of taking actions to control and reduce the carcinogenic risks for local residents.

Distribution, Origins and Hazardous Effects of Polycyclic Aromatic Hydrocarbons in Topsoil Surrounding Oil Fields: A Case Study on the Loess Plateau, China

The Loess Plateau has one of the most vulnerable ecological environments in the world, but it also contains abundant oil and gas resources that are regularly exploited, which has resulted in serious environmental problems. Therefore, it is important to analyze the polycyclic aromatic hydrocarbons (PAHs) present in the topsoil of this region. The ∑16PAHs concentrations between 1980–1999 and 2000–2019 ranged from 1134.20–15871.04 and 1010.67–18,068.80 µg kg⁻¹, with average values of 5021.30 and 5662.82 µg kg⁻¹. All samples displayed heavy pollution levels according to European soil quality standards. In addition, among the measured physicochemical properties, the soil organic carbon (SOC) had the greatest influence on PAHs, while soil particle size distribution had the smallest effect. Source apportionment indicated that the two main sources were petroleum source (37.57%) and vehicular traffic source (25.88%). Lastly, an assessment of the carcinogenic risks illustrated that more focus should be placed on the dermal pathway in which the human body is exposed to soil PAHs. Overall, the carcinogenic risks in different populations did not exceed 10⁻⁴, but there was still a potential carcinogenic risk in some age groups, especially in adult women.

Spatial distribution of polycyclic aromatic hydrocarbon contamination in urban soil of China

Soil pollution is becoming increasingly prominent and polycyclic aromatic hydrocarbons (PAHs) are key pollutants in urban areas. Understanding the sources of PAH pollution is an effective step toward its control and reduction. The main purpose of this review was to collate the spatial distribution, pollution level, pollution sources, and potential risks of PAHs in urban soils of different regions of China. Relevant data of PAH soil contamination in Chinese provinces and cities were extracted from studies published from 2000 to 2018. The concentrations of total PAHs (Σ₁₆PAHs) ranged from 65.01 to 23603.05 μg/kg for urban soils with a mean of 2801.98 μg/kg. According to the Maliszewska-Kordybach classification criteria, about 47% of the regions of China were heavily contaminated, 23% of the regions were contaminated, and 17% of the regions were weakly contaminated, while only 13% of regions were not contaminated. Based on the results of the total PAHs data from 30 provinces and cities and the results of individual compounds from 27 cities, 18 provinces and cities were classified as "severely" contaminated with a Nemero Comprehensive Index (PI) > 3.0. The results of this review indicate that the main sources of PAH pollution in urban soils of China are coal combustion and automobile exhaust emissions, followed by oil, biomass, and coke tar combustion. This review comprehensively collates the spatial distribution of PAH concentration, their composition, and dominant sources in urban soils of North and South China. Coal and oil combustion contribute more to total PAHs in North China while vehicle emissions and biomass combustion contribute more in South China. This regional difference suggests that PAH pollution in urban soils is a side-effect of a combination of regional development levels and human activities, which differ between North and South China. Risk assessment based on the benzo[a]pyrene toxicity equivalent factor indicates that the concentration of PAHs is low in most parts of China; however, several sensitive areas should receive increased attention. This review aims to provide improved decision-making support toward soil pollution control and monitoring based on the distribution and main pollution sources of PAHs in urban soil of China.

Assessing heavy metal pollution in paddy soil from coal mining area, Anhui, China

Heavy metal pollution in agricultural soil has negative impact on crop quality and eventually on human health. A total of 24 top soil samples were collected from paddy field near the Zhangji Coal Mine in Huainan City, Anhui Province. Seven heavy metals (Cu, Zn, As, Cr, Cd, Pb, and Ni) were selected to evaluate the pollution status through total content and chemical speciation, geo-accumulation index (I_geo), and risk assessment code (RAC) and investigate leaching behavior of heavy metals under simulated rainfall. The results of present study indicated that mining activities were responsible for elevated Cu and Cd in surrounding paddy soil. Based on the results of chemical speciation, most heavy metals were associated with the residual fraction, and the environmental risk of heavy metals in soil was sequenced as Pb > Cd > Ni > As > Zn > Cu > Cr. It revealed that Pb in soil would pose a higher environmental risk due to its higher reducible fraction, then followed by Cd, Ni, As, and Zn, which would pose a medium risk. The result of simulated rainfall leaching analysis showed that heavy metals could be categorized into two groups: concentrations of Cu, Ni, Cd, Zn, and Cr in the leachates displayed a continuous decrease tendency with the increase in accumulative simulated rain volume; whereas leachable tendency of As and Pb was enhanced with increasing leaching time and rain volume. Generally, the leaching percentage of heavy metals followed the sequence of As > Zn > Ni > Cd > Cr > Cu > Pb. More attention should be paid to the higher environmental risk of Pb and higher leaching percentage of As with regard to ecosystem safety and human health.

Spatiotemporal distribution, source apportionment and ecological risk assessment of PBDEs and PAHs in the Guanlan River from rapidly urbanizing areas of Shenzhen, China

In this study, nine congeners of polybrominated diphenyl ethers (PBDEs) and sixteen congeners of polycyclic aromatic hydrocarbons (PAHs) were measured in water samples to elucidate their spatial distribution, congener profiles, sources and ecological risks in the Guanlan River during both the dry season (DS) and the wet season (WS). The concentration of Σ₉PBDE ranged from 58.40 to 186.35 ng/L with an average of 115.72 ng/L in the DS, and from 8.20 to 37.80 ng/L with an average of 22.15 ng/L in the WS. Meanwhile, the concentration of Σ₁₆PAHs was ranged from 121.80 to 8371.70 ng/L with an average of 3271.18 ng/L in the DS and from 1.85 to 7124.25 ng/L with an average of 908.11 ng/L in the WS. The concentrations of PBDEs and PAHs in the DS were significantly higher than those in the WS, probably due to the dilution of the river during the rainy season. Moreover, the spatial distribution of pollutants revealed decreasing trend in the concentration from upstream to downstream and almost identical pattern was observed during both seasons. The source apportionment suggested that penta-BDE and to some extent octa-BDE commercial products were major sources of PBDEs in the study area. However, the sources of PAHs were mainly comprised of fossil fuels and biomass burning, followed by the petroleum products and their mixtures. The results of the ecological risk assessment indicated PBDEs contamination posed high ecological risks, while PAHs exhibited low or no ecological risks in the study area. Consistent with the environmental levels, the ecological risks of pollutants were relatively lower in the WS, compared to that in the DS. The results from this study would provide valuable baseline data and technical support for policy makers to protect the ecological environment of the Guanlan River.

Health risk assessment of potentially harmful elements in subsidence water bodies using a Monte Carlo approach: An example from the Huainan coal mining area, China

Enrichment of potentially harmful elements in surface water results in ecological risk to the surrounding environment. Assessing the environmental risk of these elements is of great importance. In this study, surface water samples from 6 different subsidence water bodies in the Huainan coal mining area were collected. The concentrations of Cu, Ni, Pb, Cd, Co, Cr, V, Fe, Mn and Zn were measured by atomic absorption spectrophotometry, and those of As and Hg were analyzed by atomic fluorescence spectrometry. Then, human health risks through the ingestion and dermal contact pathways were assessed and analyzed on the basis of a Monte Carlo simulation. The mean and 95th percentile risks were reported. The results showed that the total carcinogenic risk values in every subsidence water body summed for Cr, Ni and As via two exposure pathways were greater than the maximum acceptable level (1 × 10^-4), and Xinji'er water body had the highest carcinogenic risk. Among three elements, Ni was the highest contributor to carcinogenic risk. All non-carcinogenic health risk (hazard quotients) values except for one water area of Co (Xinji'er) were less than 1; however, the total non-carcinogenic health risks of two water bodies (Xinji'er, Xinjiyi) summed for all the elements based on mean concentrations were higher than 1. Xinji'er had the highest hazard index. The extent of the impacts of the total hazard quotients followed the order of Co > As > Cd > Hg > Pb > V >Fe > Ni > Mn > Zn > Cr. Furthermore, the total hazard quotients of Co and As via ingestion pathway summed for the six subsidence water areas were greater than 1, which should be a concern.

Assessing pollution and risk of polycyclic aromatic hydrocarbons in sewage sludge from wastewater treatment plants in China's top coal-producing region

Managing and disposing of sewage sludge have been a severe environmental challenge around the world. China produces hundreds of million tons of sewage sludge annually, and a better understanding of the extent and risk of the associated pollution is of critical importance for implementing environmentally safe regulations and practices. The present study examined the quantity, composition, source, and risk of polycyclic aromatic hydrocarbons (PAHs) in sewage sludge from 18 wastewater treatment plants (WWTPs) in Shaanxi, one of China's top coal-producing provinces. The total concentrations of 16 PAHs varied from 778 to 3264 ng/g dry weight, which is below the upper safety limit (5000 ng/g dry weight) set for the disposal of sludge from municipal wastewater treatment plants for agricultural use in China. However, the concentration of individual PAH compound exceeded the acceptable level prescribed by the Netherland Soil Standard. Three-ring PAHs were the most abundant constituent (50% of total PAHs on average), followed by four-ring PAHs averaging 25%. Relative to sludge PAHs in the same region a decade ago, the total concentrations decreased by more than 27% and the composition shifted to a more pronounced dominance by low molecular weight compounds. This compositional shift suggests higher contributions of petrogenic sources, which may reflect China's increasing consumption of petroleum products over the past decade. The flux of sludge PAHs from each WWTP was positively correlated with the corresponding city's GDP and population, and the total flux amounted to over 100 kg each year for WWTPs in the Xi'an city. The mean toxicity equivalent quantity (TEQ) value was more than twice higher than the value recommended by the Netherlands Soil Standard, and seven carcinogenic PAHs were the primary contributor (i.e., 89-99%) of the TEQ. Collectively, our findings demonstrate that sewage sludge PAHs in Shaanxi constitute a significant source of environmental pollution and toxicity, which cautions against the direct discharge and reuse of sewage sludge and further highlights challenges in managing and disposing of the vast quantities of sewage sludge in China.