A causation-based method developed for an integrated risk assessment of heavy metals in soil

Fluoride and acid enrichment in coal fire sponges in the Wuda coalfield, Inner Mongolia, Northern China

Coal fire sponges (CFSs) are a type of sponge-like contaminated soil bulge common in coal fire areas. However, the impacts of CFSs on the local environment are not yet understood. Thus, this study investigated soil samples from CFSs in the Wuda coalfield, Inner Mongolia, China, focusing on the acidity, sulfate, and fluorine content. The results showed that the CFSs were highly acidic, with an average pH of 0.76, and contained high levels of SO42- (257.29 × 103 μg/g), total fluorine (TF, 2011.6 μg/g), and water-soluble fluorine (WF, 118.94 μg/g), significantly exceeding those in the regional background soil and indicating that CFSs are a point source of heavy pollution. Soils in the 8000 m2 reclamation zone showed elevated acidity and high SO42- (129.6 × 103 μg/g), TF (1237.8 μg/g), and WF (43.05 μg/g) levels, which was likely the result of the weathering and dissemination of CFS. The CFS samples were rich in hydrogen fluoride, releasing 202.05 ppb of it when heated to 40 °C. Correlation analysis indicated that the acid sulfate soils in CFSs are likely caused by HSO4-/SO42-. Time-of-flight secondary ion mass spectrometry detected four characteristic ions (F-, H3O+, H2SO4+, and HSO4-) in all micro-domains of each sample, indicating that ionic fluorine compounds and sulfuric acid hydrate were found in the CFS samples. Sulfate minerals detected in CFSs included CaSO4, Fe2(SO4)3, CdSO4, NH4HSO4, and Na2SO4. Thus, the results identified CFSs as a transmission channel for contamination, with erosional surface soils as the carrier, for the first time. CFSs pose a serious threat of contamination, albeit over limited areas.

Identification and hazard analysis of heavy metal sources in agricultural soils in ancient mining areas: A quantitative method based on the receptor model and risk assessment. JOURNAL OF HAZARDOUS MATERIALS 2023;445:130528. [PMID: 37055956 DOI: 10.1016/j.jhazmat.2022.130528]

Industry in ancient mining areas caused significant heavy metal pollution (HMP) in agricultural soils. This study measured the hazards of specific sources of heavy metals (HMs) in an ancient mining areas agricultural soil. Firstly, we identified the major pollution sources based on the PMF model. Then, the proposed single-factor pollution load index (SPLI_zone) and ecological load index (SELI_zone) analyzed the integrated pollution and ecological risks of various elements. Finally, the source-specific soil contamination levels and ecological risks were quantified by combining the source assignment and single-factor assessment processes. SPLI_zone and SELI_zone showed that Cu and Cd were the most contaminated elements. Five factors were determined as the major sources of HMs, including mining, natural, smelting industry, agricultural and traffic sources. The mining sources contributed the most soil contamination (33.73%). However, the largest contributor to ecological risk was the smelting industrial (42.18%). Lower soil contamination may contain higher ecological risk. Smelting industrial and traffic are the most critical sources that need to be controlled at present. This study proposes a quantitative method for assessing the hazards of HM sources, which provides a beneficial reference for the study and management of HMP.

Source-specific risk assessment for cadmium in wheat and maize: Towards an enrichment model for China

Cadmium (Cd) pollution of agricultural soil is of public concern due to its high potential toxicity and mobility. This study aimed to reveal the risk of Cd accumulation in soil and wheat/maize systems, with a specific focus on the source-specific ecological risk, human health risk and Cd enrichment model. For this we investigated more than 6100 paired soil and grain samples with 216 datasets including soil Cd contents, soil pH and grain Cd contents of 85 sites from China. The results showed that mining activities, sewage irrigation, industrial activities and agricultural practices were the critical factors causing Cd accumulation in wheat and maize cultivated sites. Thereinto, mining activities contributed to a higher Cd accumulation risk in the southwest China and Middle Yellow River regions; sewage irrigation influenced the Cd accumulation in the North China Plain. In addition, the investigated sites were classified into different categories by comparing their soil and grain Cd contents with the Chinese soil screening values and food safety values, respectively. Cd enrichment models were developed to predict the Cd levels in wheat and maize grains. The results showed that the models exhibited a good performance for predicting the grain Cd contents among safe and warning sites of wheat (R² = 0.61 and 0.72, respectively); while the well-fitted model for maize was prone to the overestimated sites (R² = 0.77). This study will provide national viewpoints for the risk assessments and prediction of Cd accumulation in soil and wheat/maize systems.

Accumulation and risk assessment of heavy metals in rice: a case study for five areas of Guizhou Province, China

In the present study, the concentration and accumulation abilities of five heavy metals (Cd, Hg, As, Pb, Cr) in rice were assessed and their human health risk to local citizens had been evaluated. Soil and rice samples (125 samples) were collected from Guiyang (GY), Qiannan (QN), Bijie (BJ), Tongren (TR), and Zunyi (ZY) in Guizhou Province. Heavy metals were measured by inductively coupled plasma-mass spectrometry (ICP-MS) after microwave digestion. The mean concentrations of Cd, Hg, As, Pb, and Cr were 0.58, 0.65, 12.31, 38.70, and 87.30 mg/kg in soil and were 0.05, 0.005, 0.11, 0.07, and 0.34 mg/kg in rice, respectively. The bioconcentration factors (BCF) decreased with the order Cd > Hg > As > Cr > Pb. Non-carcinogenic risk in this study was evaluated using the method of the hazard quotient (HQ) and hazard index (HI). The mean HQ values for Cd, Hg, Pb, and Cr were all lower than the standard limit (1.0) for children and adults, except As with the mean HQ for children of 2.79. The mean HI values for children and adults were 4.22 and 1.42, which exceeded 1.0. The mean carcinogenic risk (CR) values of As and Pb for children and adults were higher than the upper limit of the acceptable range (1 × 10^-4) established by the United States Environmental Protection Agency (USEPA). In a conclusion, the non-carcinogenic and carcinogenic risks induced by heavy metals for children were higher than that for adults. This study revealed that consumption of rice in study areas may pose potential non-carcinogenic and carcinogenic risks to humans, and As was the largest contributor.

Grid-Scale Regional Risk Assessment of Potentially Toxic Metals Using Multi-Source Data

Understanding the risks posed by potentially toxic metals (PTMs) in large regions is important for environmental management. However, regional risk assessment that relies on traditional field sampling or administrative statistical data is labor-intensive, time-consuming, and coarse. Internet data, remote sensing data, and multi-source data, have the advantage of high speed of collection, and can, thereby, overcome time lag challenges and traditional evaluation inefficiencies, although, to date, they are rarely applied. To evaluate their effectiveness, the current study used multi-source data to conduct a 1 km scale assessment of PTMs in Yunnan Province, China. In addition, a novel model to simulate potentially hazardous areas, based on atmospheric deposition, was also proposed. Assessments reveal that risk areas are mainly distributed in the east, which is consistent with the distribution of mineral resources in the province. Approximately 3.6% of the cropland and 1.4% of the sensitive population are threatened. The risk areas were verified against those reported by the government and the existing literature. The verification exercise confirmed the reliability of multi-source data, which are cost-effective, efficient, and generalizable for assessing pollution risks in large areas, particularly when there is little to no site-specific contamination information.

Bioaccumulation of heavy metals in Stachys inflata and Scariola orientalis affected by particulate matters of a cement factory in central Iran

Industrial activities can affect accumulation of pollutants (e.g., heavy metals (HMs)) by plants and influence their entrance to the food chain. This research was carried out on accumulation of HMs including chromium (Cr), lead (Pb), and zinc (Zn) by two plants Stachys inflata and Scariola orientalis grown in natural grasslands in vicinity of a national park where they are influenced by dispersion of particulate matter (PM) through Sarooj Cement Factory in central Iran. The PM spatial dispersion of the factory was determined using the AERMOD model. Soil and vegetation samples were collected based on the modeled PM levels to analyze their HM contents. Bioconcentration factor (BCF) and transfer factor (TF) from root to shoot were determined in two widespread plants of the region: Stachys inflata and Scariola orientalis. The mean concentration of HMs in the soil samples was as follows: Zn (145.39 mg/kg) > Pb (78.52 mg/kg) > Cr (32.69 mg/kg) which was significantly correlated with simulated PM concentrations. This indicated the common source and distribution pattern of HMs which affected their accumulation in plants. TF and BCF values of the HMs were higher in Scariola orientalis than those of Stachys inflata, especially for Cr showing potentially higher risk to enter the food chain. The results showed that HM concentration in the soil as well as their accumulation by plants were correlated with the simulated PM deposition and not with linear distance from the factory.

Development of a new framework to estimate the environmental risk of heavy metal(loid)s focusing on the spatial heterogeneity of the industrial layout

Industrialization and urbanization have increased the risk of heavy metal(loid)s coming from a wide range of pathways and processes. Regional environmental risk assessment mainly focuses on the regional functional layout, industrial orientation, and enterprise location. These aspects may generate immense environmental risks and hazards. However, many gaps in regional environmental risk assessment remain, particularly concerning the spatial heterogeneity of environmental processes and mechanisms affected by the industrial layout. Most of the risk estimation often neglected the risk factor interaction. Here, we developed a framework to estimate the environmental risk of heavy metal(loid)s focusing on the spatial heterogeneity of the industrial layout. This framework was operationalized by performing an integrated risk detection of heavy metal(loid)s, spatial heterogeneity identification of the industrial layout, the power of risk factors and factor interaction examination, risk factor condition quantification and key risk source apportionment. Shaoguan city, one of six trial zones for China's pollution prevention and control of heavy metal(loid)s, was taken as a case study. Among all of the natural and socioeconomic factors, the running time of the industry was the most important risk factor of the Cd, As and Pb in soil and rice in all subregions. These subregions were divided based on the spatial heterogeneity of the industrial layout. The threshold of the running time of the industry for soil Cd was 11.97 years. The power of other dominant risk factors was different in different subregions, and the joint risk of the dominant risk factors was larger than the single risk of the running time of the industry. Our results suggest that the environmental risk of heavy metal(loid)s in Shaoguan could be mitigated by adjusting the industrial structure and controlling the running time of enterprises. Our study also indicates that estimating the regional environmental risk of heavy metal(loid)s focusing on the spatial heterogeneity of the industrial layout can help define specific strategies to achieve environmentally friendly industrial development.

Interactive effects of multiple heavy metal(loid)s on their bioavailability in cocontaminated paddy soils in a large region

Heavy metal(loid) pollution in large regions is often highly complex due to the coexistence and interactions of metal(loid)s and complex soil environments. However, the interaction effects of heavy metal(loid)s on their bioavailability in large regions remain obscure. Here, we identified the interaction effects of Pb, Cd and As on their bioavailability in cocontaminated paddy soils of Shaoguan City, China. The results showed that pH (12.40%) was the most important impact factor among the key soil properties of the pH, CEC, and SOM for the bioconcentration factor (BCF) of Cd. As the soil Pb content decreased and the soil Cd content increased, the interaction of soil Pb and Cd increased the BCF of Pb. As the soil Pb content increased and the soil Cd content decreased, the interaction of soil Pb and Cd increased the BCF of Cd. The synergistic interaction of Pb and Cd in soil promoted the accumulation of both Pb and Cd in rice under certain soil conditions. Specifically, when the average pH and CEC were below 6.19 ± 0.82 and above 7.23 ± 2.55 cmol (+)/kg, respectively, the average BCF of Cd varied from 0.70 ± 0.80 to 1.47 ± 0.62 due to the interactive effect of soil Cd and Pb on the BCF of Cd. When the average pH was above 6.19 ± 0.82 and the average SOM was below and above 27.12 ± 20.34 mg/kg, respectively, the corresponding average BCF of Cd varied from 0.70 ± 0.63 to 0.10 ± 0.26. As the average soil Cd and As contents increased, the interactive effect of soil As and Cd on the average BCF of As decreased. The negative interaction of As and Cd in soil mitigated As accumulation in rice at certain soil Cd and As contents. Our results suggest that to achieve the large-scale control of heavy metal(loid) pollution, the interactions among multiple metal(loid)s and soil properties should be considered.