A questionnaire based probabilistic risk assessment (PRA) of heavy metals in urban and suburban soils under different land uses and receptor populations

High-efficiency combination washing agents with eco-friendliness simultaneously removing Cd, Cu and Ni from soil of e-waste recycling site: A lab-scale experiment

Soil washing technology plays an important role in the removal of heavy metals, and the efficacy of this process depends on the washing agent used. Due to the difficulty in treating soils contaminated by multiple heavy metals, there is still a need for further exploration of efficient washing agents with low environmental impact. Although single washing agents, such as chelators, can also effectively remove heavy metals from soil, combining efficient washing agents and determining their optimal washing conditions can effectively improve their removal efficiency for multiple heavy metals in soil simultaneously. Based on the previous research, the present study was carried out to combine different types of washing agents to remediate contaminated soils at a commonly e-waste recycling site. The objectives were to investigate their efficient washing conditions and assess the impact of the washing process on the speciation distribution and pollution level associated with heavy metals in soil. The results showed that the combination of HEDP (1-hydroxyethylidene-1,1-diphosphonic acid) and FeCl3 at a ratio of 6:4 exhibited the most effective removal of Cd, Cu and Ni from the contaminated soil at an e-waste recycling site. Under optimal washing conditions, with a soil-to-liquid ratio of 1:20 and a washing time of 48 h, the removal rates of Cd, Cu and Ni were 96.72%, 69.91% and 76.08%, respectively. It needed to be emphasized that the combination washing agents were able to remove most of the acid-soluble, reducible and oxidizable fractions of heavy metals, and even the removal rates of the stable residual fraction (e.g., of Cd) was at a relatively high level. In addition, the washing process significantly reduced the pollution level associated with heavy metals in soil. This study aid in the development of combined efficient washing agents and explores optimal washing strategies for the remediation of Cd, Cu, and Ni-contaminated soil at e-waste recycling sites. The findings may play a role in enhancing the remediation capabilities for soils contaminated with multiple heavy metals, due to its characteristics of and high-efficiency and environmental friendliness.

Emerging nitrate contamination in groundwater: Changing phase in a fast-growing state of India

The consumption of nitrate-contaminated groundwater is often associated with potential health risks, particularly in children. This study aimed to assess the hydrochemistry and nitrate contamination in groundwater of Kerala state, India for the years 2010 and 2018 and evaluate the potential human health risks due to nitrate exposure in adults, and children through oral ingestion and dermal contact pathways. Nitrate-contaminated zones were identified by spatial mapping of nitrate concentration based on groundwater quality data of 324 wells. Groundwater is typically acidic to slightly alkaline, and the electrical conductivity (EC) varied from 33 to 1180 μS/cm in 2010 and 34.6-2500 mg/L in 2018 indicating a noticeable increase over the years. Most samples fall within low salt enrichment category. The nitrate concentration in groundwater varied from 0 to 173 mg/L with a mean of 15.4 mg/L during 2010 and 0 to 244 with a mean of 20.3 mg/L during 2018. Though nitrate concentrations show uneven spatial distributions due to both natural and anthropogenic sources, the spatial clustering of higher concentrations remains almost same in both periods. In 2010, non-carcinogenic risk, as measured by Health Index Total (HITotal) values in groundwater for the investigated region, ranged from 0.005 to 4.170 (mean of 0.349) for males, 0.005 to 4.928 (mean of 0.413) for females, and 0.008 to 7.243 (mean of 0.607) for children, while in 2018, the corresponding values varied from 0.001 to 5.881 (mean of 0.501) for males, 0.002 to 6.950 (mean of 0.592) for females, and 0.003 to 10.215 (mean of 0.870) for children, indicating a substantial increase in risk, for females and children. Greater health risk is observed in children during both the periods. The findings emphasize the need for proper water quality management, especially in regions with higher vulnerability to nitrate pollution, to safeguard human health and well-being.

Evaluating the protective capacity of soil heavy metals regulation limits on human health: A critical analysis concerning risk assessment - Importance of localization

Heavy metal pollution of agricultural soil is a major global concern, prompting the establishment of maximum allowable limits (MALs) to ensure food safety and protect human health. This study collected and compared MALs for six heavy metals (As, Cd, Hg, Pb, Zn, and Cu) in agricultural soils from representative countries and organizations (EU and WHO/FAO). The research evaluated the critical health risks and efficacy of these MALs under the hypothetical scenario of metals concentrations reaching the maximum allowable level. Safe thresholds for heavy metals were then derived based on maximum acceptable health risk levels. The comparative analysis revealed significant variations in the specific limit values and terms of MALs across countries and organizations, even for the same metal. This suggests that there is no consensus among countries and organizations regarding the level of metal-related health risks. Furthermore, the risk analysis of metal concentrations reaching the maximum level accentuated heightened risks associated with As, suggesting that the current risk of soil As exposure was underestimated, particularly for children. However, soil Cu, Cd, and Zn limits generally resulted in low health risks, implying that the current limits may overestimate their hazard. Overall, the results highlight that the current MALs for soil heavy metals may not fully safeguard human health. There is a critical need to optimize current soil MALs based on localized risks and the actual impact of these metals on human health. It is suggested to appropriately lower the limits of metals (such as As) whose impact on health risks is underestimated, and cautiously increase the limits of metals (such as Cu, Cd, and Zn) that currently pose minor health risks. This approach aims to reduce both over and insufficient protection problems of soil heavy metal MALs, emphasizing the importance of considering the locality in setting these limits.

Pollution sources and risk assessment of potentially toxic elements in soils of multiple land use types in the arid zone of Northwest China based on Monte Carlo simulation

The concentration of potentially toxic elements (PTEs) in soils of different land-use types varies depending on climatic conditions and human. Topsoil samples were collected in Northwest China to investigate PTE pollution and risk in different land uses, and thereby estimate the risk of various pollution sources. The results showed that human activity had an impact on PTE concentrations in the study area across all land use types, with farmland, grassland, woodland, and the gobi at moderate pollution levels and the desert at light pollution levels. Different PTE sources pose different risks depending on the land-use type. Apart from deserts, children are exposed to carcinogenic risk from a variety of sources. A mixed natural and agricultural source was the main source of public health risk in the study area, contributing 38.7% and 39.0% of the non-carcinogenic and 40.7% and 35.5% of the carcinogenic risks, respectively. Monte Carlo simulations showed children were at a higher health risk from PTEs than adult s under all land uses, which ranked in severity as farmland > woodland > grassland > gobi > desert. As and Ni has a higher probability of posing both a non-carcinogenic and a carcinogenic risk to children. Sensitivity analysis showed that the contribution of parameters to the assessment model of PTEs exhibited the following contribution pattern: concentration > average body weight > ingestion rate > other parameters. The PTEs affecting the risk assessment model were not common among different land use types, where the importance distribution pattern of each parameter was basically the same in woodland, grassland, and farmland, and Ni contributed the most to carcinogenic risk. However, Cr contributed the most to the carcinogenic risk in the desert and gobi.

Source identification and health risk assessment of heavy metals with mineralogy: the case of soils from a Chinese industrial and mining city

Understanding the precise sources of heavy metals (HMs) in soil and the contribution of these sources to health risks has positive effects in terms of risk management. This study focused on the HMs in the soil of five land uses in an industrial and mining city. The sources of HMs in soils were identified, and the soil mineralogical characteristics and health risks of HMs were discussed. The results showed that the HMs (Cu, Zn, Ni, Cd, Pb) found in the soil of the five land uses were affected by human activities. For example, the Cu in grassland, gobi beach, woodland, green belt, and farmland is 22.3, 3.5, 22.5, 16.7, and 21.3 times higher than the soil background values in Gansu Province, respectively. The Positive Matrix Factorization model (PMF) results revealed that traffic emissions and industrial and agricultural activities were the primary sources of HMs in the soil, with industrial sources accounting for the largest share at 55.79%. Furthermore, various characteristics proved that the studied HMs were closely related to smelting products. Concentration-oriented health risk assessments showed that HMs in the different soil types held non-carcinogenic and carcinogenic risks for children and adults. Contamination source-oriented health risk assessments of children and adults found that industrial activities controlled non-carcinogenic and carcinogenic risks. This study highlighted the critical effects of smelting on urban soil and the contribution of pollution sources to health risks. Furthermore, this work is significant in respect of the risk control of HMs in urban soils.

Introducing a land use-based weight factor in regional health risk assessment of PAHs in soils of an urban agglomeration

The high heterogeneity of land uses in urban areas has led to large spatial variations in the contents and health risks of polycyclic aromatic hydrocarbons (PAHs) in soils. A land use-based health risk assessment (LUHR) model was proposed for soil pollution on a regional scale by introducing a land use-based weight factor, which considered the differences in exposure levels of soil pollutants to receptor populations between land uses. The model was applied to assess the health risk posed by soil PAHs in the rapidly industrializing urban agglomeration of Changsha-Zhuzhou-Xiangtan Urban Agglomeration (CZTUA). The mean concentration of total PAHs (∑PAHs) in CZTUA was 493.2 μg/kg, and their spatial distribution was consistent with emissions from industry and vehicles. The LUHR model suggested the 90th percentile health risk value was 4.63 × 10-7, which was 4.13 and 1.08 times higher than those of traditional risk assessments that have adopted adults and children as default risk receptors, respectively. The risk maps of LUHRs showed that the ratios of the area exceeding the risk threshold (1 × 10-6) to the total area were 34.0 %, 5.0 %, 3.8 %, 2.1 %, and 0.2 % in the industrial area, urban green space, roadside, farmland, and forestland, respectively. The LUHR model back-calculated the soil critical values (SCVs) for ∑PAHs under different land uses, resulting in values of 6719, 4566, 3224, and 2750 μg/kg for forestland, farmland, urban green space, and roadside, respectively. Compared with the traditional health risk assessment models, this LUHR model identified high-risk areas and drew risk contours more accurately and precisely by considering both the spatial variances of soil pollution and their exposure levels to different risk receptors. This provides an advanced approach to assessing the health risks of soil pollution on a regional scale.

Estimation of heavy metal soil contamination distribution, hazard probability, and population at risk by machine learning prediction modeling in Guangxi, China

Due to superposition of diverse pollution sources, soil heavy metal concentrations have been detected to exceed the recommended maximum permissible levels in many areas of Guangxi province, China. However, the heavy metal contamination distribution, hazard probability, and population at risk of heavy metals in the entire Guangxi province remain largely unclear. In this study, machine learning prediction models with different standard risk values determined according to land use types were used to identify high-risk areas and estimate populations at risk of Cr and Ni based on 658 topsoil samples from Guangxi province, China. Our results showed that soil Cr and Ni contamination derived from carbonate rocks was relatively serious in Guangxi province, and that their co-enrichment during soil formation was associated with Fe and Mn oxides and alkaline soil environment. Our established model exhibited excellent performance in predicting contamination distribution (R² > 0.85) and hazard probability (AUC>0.85). Pollution of Cr and Ni exhibited a pattern of decreasing gradually from the central-west areas to the surrounding areas with the polluted area (I_geo>0) of Cr and Ni accounting for approximately 24.46% and 29.24% of total area in Guangxi province, respectively, but only 10.4% and 8.51% of total area was classified as Cr and Ni high-risk regions. We estimated approximately 1.44 and 1.47 million people were potentially exposed to the risk of Cr and Ni contamination, which were mainly concentrated in the Nanning, Laibin, and Guigang. These regions are main heavily-populated agricultural regions in Guangxi, and thus heavy metal contamination localization and risk control in these regions are urgent and essential from the perspective of food safety.

Environmental behavior, human health effect, and pollution control of heavy metal(loid)s toward full life cycle processes

Heavy metal(loid)s (HMs) have caused serious environmental pollution and health risks. Although the past few years have witnessed the achievements of studies on environmental behavior of HMs, the related toxicity mechanisms, and pollution control, their relationship remains a mystery. Researchers generally focused on one topic independently without comprehensive considerations due to the knowledge gap between environmental science and human health. Indeed, the full life cycle control of HMs is crucial and should be reconsidered with the combination of the occurrence, transport, and fate of HMs in the environment. Therefore, we started by reviewing the environmental behaviors of HMs which are affected by a variety of natural factors as well as their physicochemical properties. Furthermore, the related toxicity mechanisms were discussed according to exposure route, toxicity mechanism, and adverse consequences. In addition, the current state-of-the-art of available technologies for pollution control of HMs wastewater and solid wastes were summarized. Finally, based on the research trend, we proposed that advanced in-operando characterizations will help us better understand the fundamental reaction mechanisms, and big data analysis approaches will aid in establishing the prediction model for risk management.

Estimating accumulation rates and health risks of PAHs in residential soils of metropolitan cities

Predicting temporal changes in PAH concentrations in urban soils and their corresponding health risk is essential for developing appropriate management measures to prevent those risks. Concentrations of PAHs in soils of residential areas with different building ages in three metropolitan cities were determined to estimate the accumulation rates of PAHs in soil. The mean concentrations of total PAHs (∑PAHs) were 1297 ng/g in Shanghai, 865 ng/g in Beijing, and 228 ng/g in Shenzhen. The primary sources of the PAHs were traffic and coal combustion for industrial activity and space heating. The high PAH concentrations in Shanghai were attributed to the relatively high average building age of the sampled residential areas and the low annual temperature in the city. The overall annual accumulation rates of PAHs in the soils were estimated from linear regressions between the PAH concentrations and building age of the residential areas. The annual accumulation rate of PAHs in the soils was 64.7 ng/g in Beijing, 24.2 ng/g in Shanghai, and 3.3 ng/g in Shenzhen. The higher rate in Beijing was due to the higher intensity of PAH emissions and the lower temperature. The regression estimations suggest that health risks posed by PAHs in residential soils of the metropolitan cities increase considerably with time.

Contamination, sources and health risks of toxic elements in soils of karstic urban parks based on Monte Carlo simulation combined with a receptor model

Understanding the health risks of toxic elements (TEs) in urban park soils and determining their priority control factors are crucial for public health and pollution management. Soil samples were collected from 33 urban parks in Guiyang, a typical karstic city. For each park, 15-45 topsoil samples were collected according to the area and then thoroughly mixed to obtain a representative sample. The results showed that the mean concentrations of TEs in park soils (22.5, 0.37, 88.6, 43.7, 0.26, 39.9, 44.7, and 101.0 mg/kg for As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn, respectively) were higher than their background values. Approximately 54.5% and 33.3% of enrichment factor (EF) values reached moderately enriched to significantly enriched levels for Cd and Hg, respectively. Moreover, 54.5% and 42.4% of monomial potential ecological index (EI) values were at considerable to high risk levels for Cd and Hg, respectively. These results illustrate that Cd and Hg pose high ecological risks. According to the potential ecological risk index (RI) values, 21.2% of the parks were exposed to considerable ecological risk and 48.5% were at moderate risk. Based on the positive matrix factorization (PMF) model, four sources governing TE contamination (including coal combustion, natural sources, traffic emissions, and industrial activities) were identified, with contribution rates of 32.3%, 31.0%, 19.6%, and 17.1%, respectively. A probabilistic health risk assessment showed acceptable non-carcinogenic risks and high levels of carcinogenic risk in all populations. Based on the source-specific health risk assessment, arsenic from coal combustion was determined to be a major contributor to human health risks. Although several efforts have been made by the local government to eliminate coal-borne arsenicosis, our results revealed that the accumulation of arsenic in the soil due to coal combustion poses a potential threat to human health.

Human health risk-based soil environmental criteria (SEC) for park soil in Beijing, China

Urban parks are important places that allow urban residents to experience nature but are also associated with the risk of exposure to contaminated soil. Therefore, it is necessary to establish appropriate soil environment criteria (SEC) to manage park soil quality. Studies on the demographic characteristics and behavioral patterns of urban park visitors are helpful for the selection of sensitive receptors and the determination of parameters in the establishment of SEC. This study explored the park visitors' demographic characteristics and behavioral patterns, and applied the results to derive SEC. Eighty-six parks in Beijing were selected, and mobile phone data were obtained to analysis the demographic characteristics and residence time of the visitors. Kruskal-Wallis test, kernel density estimation and random forest model were used for data analysis. The CLEA model was used to derive SEC. The results showed that the demographic characteristics and behavioral patterns of visitors in different types of parks were quite different. Parks were mostly used by males and visitors aged 31-45. Most visitors stayed in the park for 1-2 h, and the distance from a given visitor's home to the park was the most important factor affecting stay time. Then, several parameters such as the parameters related to the receptors and occupation period were optimized, and the SEC of sensitive parks and non-sensitive parks were derived. Exposure frequency may be the main reason for the difference of SEC between the two types of parks. The SECs of sensitive parks were higher than the soil screening values (SSVs) for class 1 land in GB36600-2018, indicating that the current SSVs for some parks may be too conservative. This study provides a reference for the formulation and revision of soil environmental standards for park land, and suggests strengthening research on human behavioral patterns.

Conjunctive use of synchrotron X-ray diffraction and Rietveld refinement in Fe-oxide clays for forensic applications

Soils have distinctive chemical, physical, mineralogical and biological properties, which make it possible to differentiate them in different environments and also to test for an association of a particular questioned item with a crime scene. Mineral compositions and structures in the soil clay fraction can reflect a distinct characteristic when analyzed by powerful techniques. In this way, the aim of this study was to compare the discriminative power of Fe-oxides concentrated clay samples from the same soil class with and without differences in parent material when analyzed using the Rietveld method and two sources of X-ray diffraction: conventional and high-resolution synchrotron radiations. Clay samples were Fe concentrated (kaolinite and gibbsite removal) to clarify mineralogical composition of 12 samples from three simulated crime scenes, developed under claystone and granite. By Rietveld refinement, detailed crystallographic data were obtained to discriminate samples according their provenance. By synchrotron radiation, mineral data demonstrated the power of quantitative (crystallite size and minerals contents) and qualitative (identification of majoritarian and accessory minerals) analysis by Rietveld refinement, which provides well-resolved data able to discriminate samples from different and same geology. The techniques can be applied in other criminal investigations given their potential of discrimination.

Source Identification and Apportionment of Potential Toxic Elements in Soils in an Eastern Industrial City, China

The extensive pattern of economic growth has an inestimable negative impact on the ecological environment, which causes the soil pollution problem to become increasingly prominent. In order to improve the effectiveness and rationality of prevention and control of heavy metal pollution in regional soil, it is necessary to understand the current situation of pollution, identify pollution sources and clarify future pollution risks. In this paper, an industrially developed city in eastern China was taken as the study region. The positive matrix factorization model (PMF) model and Unmix model was applied to identify and apportion the pollution sources of soil potential toxic elements after evaluating the ecological risk of soil potential toxic elements. The PMF model identified six factors, including single source and composite source. The Unmix model also identified six sources, including sources of nature, industrial discharge and traffic emissions. The comparison between the two models showed that Hg and Ni pollution, as well as Cr enrichment in the study region, were related to the industrial discharge from enterprises and factories. Cd pollution was related to traffic emission sources. Cu and Zn pollution were related to the multiple sources mixed with soil parent material, traffic emissions and industrial discharge from electronic enterprises. Pb pollution was related to natural sources (e.g., soil pH) but also to industrial sources (e.g., industrial wastes discharge). Enrichment was related to soil parent material and agricultural inputs. Our study also implies that soil heavy metal pollution or enrichment in the study region was mainly from anthropogenic sources and supplemented by natural sources.

Priority Soil Pollution Management of Contaminated Site Based on Human Health Risk Assessment: A Case Study in Southwest China

The human risk assessment model can serve as a tool for regional contaminated site comprehensive management. However, site-specific risk assessment is still seldom applied in China as a basis for making decisions on risk management actions. In this study, a total of 112 soil samples were collected from ten polluted sites in Southwest China. The human health risk assessment method was used to assess the risk of Cd, As, Cu, Pb, Cr, Zn, and Hg pollution. According to the findings, the average concentrations of As, Zn, and Pb in contaminated sites are substantially higher than those of Cu, Cd, Cr, and Hg. Further studies conclusively showed the soil at contaminated site in its present condition pose risk to human health to potential future receptors. The main contribution of non-cancer and cancer risks was through incidental soil and dust ingestion. The priority control site remediation order is Region VI > Region V > Region IV > Region III > Region VII > Region X > Region IX > Region VIII > Region I > Region II. Finally, management recommendations are made, including reducing pollutant intake, implementing a stringent monitoring scheme, utilizing bioremediation, and strengthening the implementation of relevant laws. This study provides a case for the comprehensive evaluation of soil pollution at contaminated sites in China.

Pollution Assessment and Source Apportionment of Soil Heavy Metals in a Coastal Industrial City, Zhejiang, Southeastern China

In this research, Ningbo City, a typical industrial city in southeastern China, was selected as the study area, and the concentrations of 12 heavy metals (Cd, Cr, Ni, Pb, Zn, Cu, Hg, As, Co, V, Se, and Mn) were measured at 248 sampling points. Pollution index methods were used to assess the status of soil heavy metal contamination, and the Positive Matrix Factorization (PMF) model and Unmix model were integrated to identify and apportion the sources of heavy metal contamination. The results indicated that nearly 70% of the study area was polluted by heavy metals, and that Ni, Cr, and Zn were the main enriched heavy metals. The five sources identified using the PMF model were a geological source, an atmospheric deposition source, a transportation emissions source, a mixed source of agriculture and industry, and a mixed source of geology and industry. The four sources identified using the Unmix model were a mixed source of geology, agriculture, and industry (14.27%); a transportation emissions source (4.76%); a geological source (14.7%); and a mixed source of geology and industry (66.28%). These results have practical significance, as they can help to carry out pollution source risk assessment and give priority to the management of pollution source control.

Indoor Nanoparticle Characterization in Construction Waste Recycling Companies over Time

Building activity is a significant source of atmospheric contamination by ultrafine dust. Cognizant of this fact, those active in the use and recycling of construction materials must be aware of the risks associated with exposure to nanoparticles (NPs) and ultra-fine particles (UFPs), as well as the associated health impacts. This work analyzed NPs and UFPs generated in a small building-material recycling company using high-resolution electron microscopes and X-ray Diffraction. A self-made passive sampler (LSPS) that can obtain particulate samples without physical and morphological changes, especially where there is a suspension of particulate material, was used in this study. A total of 96 particulate samples, using the LSPS for three months in four seasons, were collected during the study. Thus, the dry deposition of the particles, which are considered highly harmful to human health, was found in each of the four seasons of the year. It is suggested that for future research, the toxicological evaluations of the particulates in the construction industry should be investigated through the consideration of measures to control and mitigate the health risks of workers regarding exposure to NPs and UFPs.

Distribution Characteristics and Risk Assessment of Heavy Metals in Soil and Street Dust with Different Land Uses, a Case in Changsha, China

Rapid urbanization and industrialization have led to the accumulation of heavy metals in urban areas. The distribution and health risk of heavy metals in soil and street dust were studied by collecting the samples in pairs from different land uses in Changsha, China. The results showed that the average contents of the heavy metals Pb, Cd, Cu, Zn, Cr and Ni in the soil were 45.3, 0.69, 46.3, 220.4, 128.7 and 32.9 mg·kg-1, and the corresponding heavy metal contents in the street dust were 130.1, 3.9, 130.8, 667.2, 223.2, 50.5 mg·kg-1, respectively. The soils in the parks and roadsides have higher heavy metal contents than those in the residential and agricultural areas. The street dust collected from parks, roadsides and residential areas contained higher heavy metal contents than agricultural areas. Significant correlations were found between heavy metals, suggesting similar sources. However, most of the heavy metals in the soil were uncorrelated with those in the street dust. The contents of heavy metals in soil are the results of long-term pollution. Street dust is easily affected by natural or human disturbances, reflecting pollution emissions in a short period. The health risks posed by heavy metals in the soil are acceptable, but the street dust may threaten children's health, especially in residential areas. Pb, Cr and Cd are the main risk contributors. Reducing the emissions from industrial plants and traffic may reduce the risk of exposure to heavy metals in the street dust.