Risk assessment and driving factors of trace metal(loid)s in soils of China

Improving prediction of soil heavy metal(loid) concentration by developing a combined Co-kriging and geographically and temporally weighted regression (GTWR) model

The study of heavy metal(loid) (HM) contamination in soil using extensive data obtained from published literature is an economical and convenient method. However, the uneven distribution of these data in time and space limits their direct applicability. Therefore, based on the concentration data obtained from the published literature (2000-2020), we investigated the relationship between soil HM accumulation and various anthropogenic activities, developed a hybrid model to predict soil HM concentrations, and then evaluated their ecological risks. The results demonstrated that various anthropogenic activities were the main cause of soil HM accumulation using Geographically and temporally weighted regression (GTWR) model. The hybrid Co-kriging + GTWR model, which incorporates two of the most influential auxiliary variables, can improve the accuracy and reliability of predicting HM concentrations. The predicted concentrations of eight HMs all exceeded the background values for soil environment in China. The results of the ecological risk assessment revealed that five HMs accounted for more than 90% of the area at the "High risk" level (RQ ≥ 1), with the descending order of Ni (100%) = Cu (100%) > As (98.73%) > Zn (95.50%) > Pb (94.90%). This study provides a novel approach to environmental pollution research using the published data.

Impact of economic development on soil trace metal(loid)s pollution: A case study of China

Recently, intensive anthropogenic activities, while promoting economic growth, have also exacerbated soil trace metal(loid) (TM) pollution. To explore the impact of economic development on soil TM pollution, a time-weighted method was introduced to calculate the average concentrations of eight TMs in Chinese topsoil from 2001 to 2020, and panel data on TMs and economic factors of 31 provinces were used for regression analysis. The results revealed that the average concentrations of soil TMs all exceeded their respective soil background values. Meanwhile, the spatial distribution of soil TMs was characterized by obvious regional heterogeneity, with economically developed areas being heavily polluted and having high ecological risks. In addition, the results derived from panel data models showed that the relationship between soil TM pollution and economic development in China presented a continuous growth curve, but with an N-shaped pattern in eastern China, a U-shaped pattern in central China, and a positive linearity in western China. Four control variables were also introduced to evaluate their impact on TM pollution, and the results indicated that the proportion of secondary industry and the road area per capita were the major influencing factors. Ultimately, the inflection point estimation results suggested that the soil TM pollution level will increase in eastern China, central China and western China with ongoing economic growth. Our findings contribute to the current understanding of the relationship between soil TM pollution and anthropogenic activities, and provide a scientific basis for adjusting and planning industrial development and layout according to the characteristics of soil TM pollution.

Pollution and source-specific risk analysis of potentially toxic metals in urban soils of an oasis-tourist city in northwest China

Source-specific risk apportionment for soil potentially toxic metals (PTMs) is of great significance for contamination prevention and risk management in urban environments. Eighty-five urban soil samples were obtained from an oasis-tourist city, China and examined for eight PTMs (As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn). The pollution levels, sources, and ecological risk of soil PTMs were quantified, and their source-specific ecological and human health effects were also estimated using the multi-proxy approaches. The results demonstrated that accumulation of Cd, Hg, Pb, Cr, Cu, and Zn in soils was observed compared to their background levels, and the soils experienced varying degrees of PTMs pollution, especially at sites with high-intensity anthropogenic activities. Natural sources, atmospheric deposition, industrial sources, vehicular emissions, and comprehensive inputs were the principal sources, with contributions of 29.28%, 25.86%, 20.13%, 16.50%, and 8.23%, respectively. The integrated ecological risks of PTMs in soils were moderate at most sites, with atmospheric deposition being the dominant contributor to ecological risks. Children exhibited pronounced non-cancer risks, but adults had no notable non-cancer risks. Moreover, there were potential carcinogenic risks for both children and adults within the study region. Non-cancer and carcinogenic risks were more significant for children than adults, and traffic emissions were the primary contributor to non-cancer risks (adults: 20.53%, children: 20.49%) and carcinogenic risks (adults: 22.95%, children: 22.08%). The industrial and traffic activities were considered as priority control sources for soil pollution control and risk management, with Hg, Cd, Zn, and Pb corresponding to the priority elements. This study highlights the source-specific ecological and human health effects of PTMs pollution in urban soils, thereby providing valuable information for targeted pollution control and priority source management.

Human activities contributing to the accumulation of high-risk trace metal(loid)s in soils of China's five major urban agglomerations

Rapid urbanization has accelerated the accumulation of trace metal(loid)s (TMs) in soils, but the relationship between this accumulation and human activities remains largely unknown. Therefore, based on 775 published literatures (2001-2020), this study aimed to identify the influence of human activities on TM accumulation. Results showed that all soil TM concentrations were higher than their corresponding Chinese soil background values. The pollution risk assessment indicated that the soil TMs in the study area were at moderate levels, and the value of Pollution load index was 2.10. According to the assessment of health risks, the non-carcinogenic risks for adults were at the "Negligible risk" level; while the carcinogenic risk was not negligible for all populations, with children being more susceptible than adults. Meanwhile, six high-risk TMs were identified based on the grading of Contaminating factors (CF ≥ 3) and contribution to health risk (≥ 75%), including four high pollution risk TMs (Cd, Hg, Cu, and Pb) and two high health risk TMs (Cr and As) . In addition, in accordance with the results of the Random forest model, the accumulation of soil high-risk TMs was closely related to influencing factors associated with human activities. The accumulation of Hg and Cr among five major urban agglomerations had the same influencing factors (the number of industrial companies and the amount of industrial wastewater discharge for Hg; the amount of pesticide application and highway mileage for Cr). However, there were significant differences in the factors influencing the accumulation of the other four high-risk TMs (including Cd, As, Cu and Pb), due to the different characteristics of each urban agglomeration. Our results provide new insights into the relationship between human activities and soil TM accumulation.

Distribution, sources, and risk analysis of heavy metals in sediments of Xiaoqing River basin, Shandong province, China

The accumulation of heavy metals in river sediment poses a major threat to ecological safety. The Xiaoqing River originates in western Jinan, with higher population density and per capita gross domestic product (GDP) in its basin compared to the Shandong province average. This study analyzed the spatial characteristics, ecological risk, human health risk, and contamination sources of heavy metals by collecting sediment samples from Xiaoqing River. We use the methods such as geo-accumulation index (Igeo), ecological risk assessment based on the interval number sorting method, and health risk assessment to evaluate the risk of heavy metals in sediments. The research finding suggests heavy metals including Pb, As, Ni, and Cr are low ecological risks, while Hg and Cd have reached high and extreme ecological risks. Correlation analysis and principal component analysis were used to analyze the correlation and sources of different heavy metals. The six heavy metals were categorized into three groups. Factor 1, comprising Hg, Cr, and Pb, was identified as a mixed source with a contribution rate of 37.76%. Factor 2 is an agricultural source and comprises Ni, Cd, and As with a contribution rate of 27.05%. Factor 3 includes Pb and Ni contributing to 15.30% as a natural source. This study offers valuable insights for the prevention of heavy metal pollution, as well as promoting sustainable urban development.

Water quality pollution assessment and source apportionment of lake wetlands: A case study of Xianghai Lake in the Northeast China Plain

Surface water pollution has always posed a serious challenge to water quality management. Improving water quality management requires figuring out how to comprehend water quality conditions scientifically and effectively as well as quantitatively identify regional pollution sources. In this study, Xianghai Lake, a typical lake-type wetland on the Northeast China Plain, was taken as the research area. Based on a geographic information system (GIS) method and 11 water quality parameters, the single-factor evaluation and comprehensive water quality index (WQI) methods were used to comprehensively evaluate the water quality of the lake-type wetland in the level period. Four key water quality parameters were determined by the principal component analysis (PCA) method, and more convenient comprehensive water quality evaluation models, the minimum WQI considering weights (WQImin-w) and the minimum WQI without considering weights (WQImin-nw) were established. The multiple statistical method and the absolute principal component score-multiple liner regression (APCS-MLR) model were combined to analyse the lake pollution sources based on the spatial changes in pollutants. The findings demonstrated that the WQImin-nw model's water quality evaluation outcome was more accurate when weights were not taken into account. The WQImin-nw model can be used as a simple and convenient way to comprehend the variations in water quality in wetlands of lakes and reservoirs. It was concluded that the comprehensive water quality in the study area was at a "medium" level, and CODMn was the main limiting factor. Nonpoint source pollution (such as agricultural planting and livestock breeding) was the most important factor affecting the water quality of Xianghai Lake (with a comprehensive contribution rate of 31.65%). The comprehensive contribution rates of sediment endogenous and geological sources, phytoplankton and other plants, and water diversion and other hydrodynamic impacts accounted for 25.12%, 19.65%, and 23.58% of the total impact, respectively. This study can provide a scientific method for water quality assessment and management of lake wetlands, and an effective support for migration of migratory birds, habitat protection and grain production security.

Soil heavy metal(loid) pollution and health risk assessment of farmlands developed on two different terrains on the Tibetan Plateau, China

The quality of farmland soils on the Tibetan Plateau is important because of the region's ecological vulnerability and their close link with local food security. Investigation on the pollution status of heavy metal (loid)s (HMs) in the farmlands of Lhasa and Nyingchi on the Tibetan Plateau, China revealed that Cu, As, Cd, Tl, and Pb were apparently enriched, with the soil parent materials being the primary sources of the soil HMs. Overall, the farmlands in Lhasa had higher contents of HMs compared to those in the farmlands of Nyingchi, which could be attributed to the fact that the former were mainly developed on river terraces while the latter were mainly developed on the alluvial fans in mountainous areas. As displayed the most apparent enrichment, with the average concentrations in the vegetable field soils and grain field soils of Lhasa being 2.5 and 2.2 times higher compared to those of Nyingchi. The soils of vegetable fields were more heavily polluted than those of grain fields, probably due to the more intensive input of agrochemicals, particularly the use of commercial organic fertilizers. The overall ecological risk of the HMs in the Tibetan farmlands was low, while Cd posed medium ecological risk. Results of health risk assessment show that ingestion of the vegetable field soils could pose elevated health risk, with children facing greater risk than adults. Among all the HMs targeted, Cd had relatively high bioavailability of up to 36.2% and 24.9% in the vegetable field soils of Lhasa and Nyingchi, respectively. Cd also showed the most significant ecological and human health risk. Thus, attention should be paid to minimize further anthropogenic input of Cd to the farmland soils on the Tibetan Plateau.

Soil Chromium Accumulation in Industrial Regions across China: Pollution and Health Risk Assessment, Spatial Pattern, and Temporal Trend (2002-2021)

This study conducted a nationwide specific assessment of soil chromium (Cr) contamination status in 506 of China's industrial regions. The overall soil Cr concentrations were 0.74-37,967.33 mg/kg, and the soil Cr content in 4.15% of the regions exceeded the reference screening value (2500 mg/kg). Geochemical accumulation index (I_geo) and monomial potential ecological risk index (E) revealed Cr salt production and tanning were the primary control industries. The non-carcinogenic risks posed by Cr salt production and tanning industries were higher than the national average values, and children were the most vulnerable groups. The heavily polluted regions were mainly located at the Yangtze River Delta, the Bohai Rim, the Pearl River Delta, the Yangtze River Basin, and the Yellow River Basin. The Yangtze River Delta was further identified as the high priority control area based on the class distribution of I_geo and E. Regression analysis showed the soil Cr concentrations in industrial regions increased during 2002-2009 and then turned into a declining trend in 2009-2021. This paper gives detailed insights into soil Cr pollution status in industrial regions across China and the results may serve as references for formulating tailored control measures for different industries and areas.

Spatio-temporal characteristics of soil Cd pollution and its influencing factors: A Geographically and temporally weighted regression (GTWR) method

Soil Cd pollution is the result of the combined influence of various human activities over a long period of time, and then quantifying the influence is essential for the prevention and control. Based on published literature data during 2000-2020, this study investigated the pollution characteristics and influencing factors of soil Cd in the Yangtze River Delta. The results were as follows: (1) The average Cd concentration was higher than the Chinese soil criteria value (0.30 mg/kg), and the proportion of Cd concentration exceeding its background value was 87.43%. (2) The assessment results using Contamination factor (CF) and Geo-accumulation index (I_geo) indicated that the soil Cd pollution risk could not negligible in the study area. (3) The pollution center shifted significantly owing to the combined effect of human activities. (4) The main influencing factors of Cd pollution obtained by Geographically and temporally weighted regression (GTWR) model were GDP per capita, Consumption of chemical fertilizer, Output value of primary industry, and Output value of secondary industry, but there were significant differences in the dominant factors for different provinces. Our findings contribute to the current understanding of the relationship between Cd pollution and human activities, and provide a scientific basis for pollution control.

Distribution, sources and health risks of heavy metals in indoor dust across China

The potential effects of heavy metals on human health have attracted increasing attention as most people spend up to 90% of their time indoors. Human exposure to heavy metals in indoor dust have only been characterised for limited regions in China, and full-scale data for different functional areas are not available. Therefore, this review analysed the concentrations, contamination characteristics, and potential health risks of seven heavy metals (including zinc (Zn), lead (Pb), copper (Cu), chromium (Cr), nickel (Ni), arsenic (As), and cadmium (Cd)) in indoor dust at 3392 sampling sites in 55 cities across 27 provincial regions of China based on literature data. Results revealed that the median heavy metal concentrations in indoor dust throughout China decreased in the following order: Zn > Pb > Cu > Cr > Ni > As > Cd. Traffic emissions and decorative materials are the primary sources of heavy metal pollution in indoor dust. No considerable non-carcinogenic risk was found for Zn, Cu, Cr, Ni, and Cd in indoor dust, while Pb and As exhibited potential non-carcinogenic risks to children, primarily distributed in cities across Southern China. Meanwhile, the carcinogenic risks posed by Cr and Ni were higher than those posed by As and Cd, especially in Southern China. Therefore, effective measures in Southern China should prioritised for controlling Pb, Cr, Ni and As pollution in indoor dust to reduce human health risk. This review is useful for policy decision-making and protecting human from exposure to heavy metals in indoor dust across China.

Pollution Profiles, Source Identification and Health Risk Assessment of Heavy Metals in Soil near a Non-Ferrous Metal Smelting Plant

Heavy metal pollution related to non-ferrous metal smelting may pose a significant threat to human health. This study analyzed 58 surface soils collected from a representative non-ferrous metal smelting area to screen potentially hazardous heavy metals and evaluate their health risk in the studied area. The findings demonstrated that human activity had contributed to the pollution degrees of Cu, Cd, As, Zn, and Pb in the surrounding area of a non-ferrous metal smelting plant (NMSP). Cu, Cd, As, Zn, Pb, Ni, and Co pollution within the NMSP was serious. Combining the spatial distribution and Spearman correlations with principal component analysis (PCA), the primary sources of Cd, As, Pb, and Zn in surrounding areas were related to non-ferrous metal smelting and transportation activities. High non-cancer (THI = 4.76) and cancer risks (TCR = 2.99 × 10^-4) were found for adults in the NMSP. Moreover, heavy metals in the surrounding areas posed a potential cancer risk to children (TCR = 3.62 × 10^-6) and adults (TCR = 1.27 × 10^-5). The significant contributions of As, Pb, and Cd to health risks requires special attention. The construction of a heavy metal pollution management system will benefit from the current study for the non-ferrous metal smelting industry.