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.

Health risk assessment of trace metal(loid)s in agricultural soil using an integrated model combining soil-related and plants-accumulation exposures: A case study on Hainan Island, South China

Traditional health risk assessment of trace metal(loid)s (TMs) in agricultural soil exclusively considers direct soil-related exposure and may underestimate the health risks they pose. In this study, the health risks of TMs were evaluated using an integrated model that combined soil-related and plant-accumulating exposures. A detailed investigation of common TMs (Cr, Pb, Cd, As, and Hg) coupled with probability risk analysis based on a Monte Carlo simulation was conducted on Hainan Island. Our results showed that, except for As, the non-carcinogenic risk (HI) and carcinogenic risk (CR) of the TMs were all within the acceptable ranges (HI < 1.0, and CR < 1E-06) for direct soil-related exposure to bio-accessible fractions and indirect exposure via plant accumulation (CR substantially lower than the warning threshold 1E-04). We identified crop food ingestion as the essential pathway for TM exposure and As as the critical toxic element in terms of risk control. Moreover, we determined that RfDo and SFo are the most suitable parameters for assessing As health risk severity. Our study demonstrated that the proposed integrated model combining soil-related and plant-accumulating exposures can avoid major health risk assessment deviations. The results obtained and the integrated model proposed in this study can facilitate future multi-pathway exposure research and could be the basis for determining agricultural soil quality criteria in tropical areas.

Using multiple normalization procedures and contamination indices in the assessment of trace metal(loid) contents of the surface sediments of Lake Xingyun, southwestern China

Trace metal(loid) (TM) contamination, especially of aquatic ecosystems, is a global ongoing environmental problem. Fully and accurately determining their anthropogenic sources is a key requirement for formulating remediation and management strategies. Herein, we developed a multiple normalization procedure, combined with principal component analysis (PCA) to assess the influence of data-treatment and environmental factors on the traceability of TMs in surface sediments of Lake Xingyun, China. Multiple contamination indices, i.e., Enrichment factor (EF), Pollution Load Index (PLI), Pollution Contribution Rate (PCR) and Exceeded multiple discharge standard limits (BSTEL) suggest that contamination is dominated by Pb with the average EF exceed 3, especially within the estuary aeras with the PCR >40 %. The analysis demonstrates that the mathematical normalization of data, which adjusts it for various geochemical influences, has a significant effect on analysis outputs and interpretation. Routine (Log) and extreme (outlier removing) transformations may mask and skew important information contained within the original (raw) data, which create biased or meaningless principal components. Granulometric and geochemical normalization procedures can obviously identify the influence of grain size and other environmental impact on TM contents in principal components, but incorrectly explains the potential sources and contamination on different sites. Reducing the influence of organic matter by normalization allowed the mineralogy, bio-degradation, salinity, and anthropogenic sources associated with local sewage and anthropogenic smelting to be identified and interpreted more clearly. Moreover, the co-occurrence network analysis also confirms that the influence of grain size, salinity, and organic matter content are the primary factors controlling the spatial variability in the type and concentrations of TMs.

Machine learning based on the graph convolutional self-organizing map method increases the accuracy of pollution source identification: A case study of trace metal(loid)s in soils of Jiangmen City, south China

Rapid economic development and industrialization may include environmentally harmful human activities that cause heavy-metal accumulation in soils, ultimately threatening the quality of the soil environment and human health. Therefore, accurate identification of pollution sources is an important weapon in efforts to control and prevent pollution. The self-organizing map (SOM) method is widely used in pollution source identification because of its capacity for visualization of high-dimensional data. The SOM ignores the graph structure relationship among chemical elements in soils; the SOM analysis of pollution sources has high uncertainty. Here, we propose a new analysis method, i.e., the graph convolutional self-organizing map (GCSOM), which uses a graph convolutional network (GCN) to extract the graph structure relationship among the chemical elements in soils, then performs data visualization using an SOM. We compared the performances of GCSOM and SOM, then assessed the pollution source characteristics of trace metal(loid)s (TMs, mostly heavy metals) in Jiangmen City using the GCSOM. Our experimental results showed that the GCSOM is superior to the SOM for identification of TM sources, while the TMs in the soil of Jiangmen originate from three main sources: agricultural activities (mainly in Taishan City, Jiangmen), traffic emissions (mainly in Xinhui and Pengjiang Districts), and industrial activities (mainly in Xinhui District). The risk assessment indicated that the risk of all TMs was within threshold.

Short- and long-term exposure to trace metal(loid)s from the production of ferromanganese alloys by personal sampling and biomarkers

The environmental exposure to trace metal(loid)s (As, Cd, Cu, Fe, Mn, Pb, and Zn) was assessed near a ferromanganese alloy plant using filters from personal particulate matter (PM) samplers (bioaccessible and non-bioaccessible fine and coarse fractions) and whole blood as short-term exposure markers, and scalp hair and fingernails as long-term biomarkers, collected from volunteers (n = 130) living in Santander Bay (northern Spain). Bioaccessible and non-bioaccessible metal(loid) concentrations in coarse and fine PM from personal samplers were determined by ICP-MS after extraction/digestion. Metal(loid) concentration in biomarkers was measured after alkaline dilution (whole blood) and acid digestion (fingernails and scalp hair) by ICP-MS as well. Results were discussed in terms of exposure, considering the distance to the main Mn source, and sex. In terms of exposure, significant differences were found for Mn in all the studied fractions of PM, As in whole blood, Mn and Cu in scalp hair and Mn and Pb in fingernails, with all concentrations being higher for those living closer to the Mn source, with the exception of Cu in scalp hair. Furthermore, the analysis of the correlation between Mn levels in the studied biomarkers and the wind-weighted distance to the main source of Mn allows us to conclude that scalp hair and mainly fingernails are appropriate biomarkers of long-term airborne Mn exposure. This was also confirmed by the significant positive correlations between scalp hair Mn and bioaccessible Mn in coarse and fine fractions, and between fingernails Mn and all PM fractions. This implies that people living closer to a ferromanganese alloy plant are exposed to higher levels of airborne metal(loid)s, mainly Mn, leading to higher levels of this metal in scalp hair and fingernails, which according to the literature, might affect some neurological outcomes. According to sex, significant differences were observed for Fe, Cu and Pb in whole blood, with higher concentrations of Fe and Pb in males, and higher levels of Cu in females; and for Mn, Cu, Zn, Cd and Pb in scalp hair, with higher concentrations in males for all metal(loid)s except Cu.

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

Recently, with the rapid development of China's economy, the pollution of trace metal(loid)s (TMs) in soils has become increasingly severe and attracted widespread attention. Based on 1,402 published papers from 2000 to 2021, this study aimed to analyze the pollution intensity, ecological risk and driving factors for eight TMs (As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) in Chinese soils. Results showed that the average concentrations of eight TMs in Chinese soils all exceeded background values, and the pollution of Cd and Hg was the most serious. Based on Principal component analysis of pollution intensity and ecological risk, the priority control TMs were identified for the heavily polluted provinces. The results of Geo-detector model suggested that Urban development factors contributed most to the TM accumulation in Chinese soils. Further, spatial analysis using bivariate Moran's I indicated that industrial activities contributed most to soil TM accumulation in the middle and lower reaches of the Yangtze River, while soil TM pollution in the southwest and northwest provinces was mainly caused by mining and metal smelting. This study investigated the relationship between soil TM pollution and anthropogenic activities, thus providing a scientific basis for controlling soil TM pollution at a large-scale level.

Do trace metal(loid)s in road soils pose health risks to tourists? A case of a highly-visited national park in China

Nowadays, more people tend to spend their recreational time in large national parks, and trace metal(loid)s in soils have attracted long-term attention due to their possible harm to human health. To investigate the pollution levels, potential sources and health risks of trace metal(loid)s in road soils, a total of eight trace metal(loid)s (including As, Cd, Cr, Cu, Ni, Pb, Zn and Hg) from 47 soil samples along roads were studied in the Huangshan National Park in Southeast China. The results showed that the concentrations of As, Cd, Pb, Zn and Hg appeared different degrees of pollution compared with their corresponding background values. According to the pollution indices, Hg and Cd were recognized as significant pollutants presenting moderate to high ecological risk. Combining principal component analysis and positive matrix factorization model, the results showed that traffic, industrial, agricultural and natural sources were the potential origins of trace metal(loid)s in this area, with contribution rates of 39.93%, 25.92%, 10.53% and 23.62%, respectively. Non-carcinogenic risks were all negligible, while the carcinogenic risk of As was higher than the limit (1 × 10^-6). Moreover, children were more susceptible to trace metal(loid)s by ingestion which appeared to be a more important exposure pathway than dermal contact and inhalation. The contribution rates of different sources to non-carcinogenic risks and carcinogenic risks were similar among children and adults, while traffic and industrial sources have a significant impact on health risks. This study will give more insights to control the environmental risks of trace metal(loid)s in national parks.

Spatiotemporal variations, health risks, pollution status and possible sources of dissolved trace metal(loid)s in the Karasu River, Turkey

The Karasu River is the main tributary of the Euphrates River, which is the longest river in Southwest Asia. Domestic and industrial wastewater discharges, agricultural practices and mining activities in the basin can cause potential toxic metal pollution in the Karasu River. However, very little is known about the levels of dissolved trace metal(loid)s (TMs) in the river. In this study, levels of ten TMs (Fe, Al, Cd, Ni, Cu, Zn, Pb, As, Mn and Cr) in water samples taken monthly from 8 stations along the Karasu River between January 2019 and December 2019 were measured and compared with water quality guidelines. In addition, spatial and seasonal variations, health risks, pollution status and possible sources of the TMs were assessed. The 90th percentile levels of the TMs were below the drinking water standards. The highest total concentration was recorded at the most upstream station due to weathering processes, and rain and snowmelt runoff. The total metal concentration showed an increasing trend from winter to summer due to the combined effect of natural and anthropogenic sources. Metal pollution indices indicated that river water quality is suitable for potable uses. The results of factor and cluster analyses revealed that Ni, Fe, Mn and Cr are controlled by both lithogenic sources and anthropogenic activities, while other TMs are controlled by lithogenic sources. The hazard quotient (HQ) of each TM for both water ingestion and dermal contact pathways for residents was below the risk level. However, the hazard index (sum of HQs of all TMs) for water ingestion for children was higher than the risk level, indicated that the ingestion of ten TMs in the Karasu River may pose non-carcinogenic health risks to children. The carcinogenic risk results of As and Cr for both water ingestion and dermal absorption were within or below the acceptable carcinogenic risk range.

Pollution status, potential sources and health risk assessment of arsenic and trace metals in agricultural soils: A case study in Malatya province, Turkey

We measured the concentrations of arsenic and 11 trace metals in the soils from vegetable fields in Malatya province (Turkey) and assessed health risks for residential adults and children. Also, we assessed their potential sources, contamination status and ecological risks. Median concentrations of only As, Co, Ni and Cr exceeded the world soil average values, while those of Cd, As, Ni and Cu exceeded the upper continental crust contents. Contamination factor, enrichment factor and geoaccumulation index results indicated that the study region was contaminated with Cd, As, Ni and Cu likely due to use of irrigation water contaminated with industrial wastewaters and use of fertilizers and pesticides. Also, the study region had "high potential ecological risk" for Cd, whereas "low potential ecological risk" for the other trace metal(loid)s (TMs). Factor and hierarchical cluster analyses revealed that As and Cu were from anthropogenic sources, Cd and Ni from both natural and anthropogenic sources, while other TMs from natural sources. The hazard quotient values of all TMs and total hazard index values for both children and adults were lower than the risk level of 1, indicating that non-carcinogenic health risks are not expected for residents. Also, the cumulative carcinogenic risk results were within the acceptable risk range. Our results indicated that application of multivariate statistics, pollution, ecological and health indices together provide valuable knowledge for assessing soil pollution in a particular region.

Trace metal(loid)s contamination in paddy rice (Oryza sativa L.) from wetlands near two gold mines in Côte d'Ivoire and health risk assessment

This study examined the concentrations of arsenic (As), cadmium (Cd), and mercury (Hg) in rice grains grown in wetlands associated with gold mining in central-southern of Côte d'Ivoire to evaluate potential health risks exposure via rice consumption. In total, 30 rice grains were sampled around Agbaou and Bonikro gold mines. Arsenic and cadmium concentrations were determined using an inductively coupled plasma-optical emission spectrometer (ICP-OES), while atomic absorption spectrometry (AAS) was used for mercury. Results showed that As and Hg average concentrations in rice were above the permissible limits, while Cd average concentrations were below the permissible limit established by FAO/WHO in both sites. Except for Hg at Agbaou, no significant (p < 0.05) difference was found between trace metal concentrations in the two sites. The average daily intake (ADI) of As via rice consumption exceeded the USEPA reference dose (RfD) of 0.0003 μg g^-1 day^-1, indicating that rice ingestion is a pathway of As exposure for adults and children in the area. The average values of non-carcinogen (HQ) for As and carcinogen (CR) for As and Cd risks index suggest that potential health risks exist for both adults and children due to rice consumption at Agbaou and Bonikro. The maximum safe weekly consumption (MSWC) of rice relative to As, Cd, and Hg was estimated for the study area. Overall, this study provides strong evidence that As could threaten local population health in Côte d'Ivoire regions where gold mine extraction is occurring through rice ingestion.

Understanding how methodological aspects affect the release of trace metal(loid)s from urban dust in inhalation bioaccessibility tests

The bioaccessibility of metal(loid)s in ambient particulate matter (PM) has been recently used to represent the risk of inhalation exposure. Nevertheless, different methodological factors affect the bioaccessibility values; among these, the type and composition of surrogate biological fluids and the liquid to solid ratio have been revealed to be the most important. To better understand how these methodological aspects affect the bioaccessibility, a reference material corresponding to urban dust (SRM1648a) was contacted with synthetic biological fluids commonly used in the literature representing surrogate fluids that may interact with fine (Gamble's solutions, artificial lysosomal fluid (ALF)) and coarse particles (gastric fluid), for liquid to solid (L/S) ratios ranging from 500 to 20,000. Visual MINTEQ 3.1. was used to enhance the discussion on how the solubility of metals in the leaching solution depends on the composition of the simulated fluids and the speciation of metals. The results obtained indicate that a small change in the composition of Gamble's solution (the presence of glycine) may increase significantly the bioaccessibility at a L/S ratio of 5,000. The highest bioaccessibility of most of the studied metal(loid)s at a L/S ratio of 5,000 was found for ALF fluid. The study of the effect of the L/S ratio showed that metal(loid)s bioaccessibility in Gamble's fluid increased logarithmically with increasing L/S ratio, while it remained practically constant in ALF and gastric fluid. This different behavior is explained assuming that the leaching of metal(loid)s in Gamble's solution is solubility-controlled, while in ALF and gastric fluid is availability-controlled.

Combined impacts of Si-rich rice residues and flooding extent on grain As and Cd in rice

Increasing plant-availability of Si through soil amendment of Si-rich rice residues can decrease inorganic As without affecting Cd levels in grain under flooded soil conditions. However, the impacts of Si amendments on Cd and As uptake by rice under different flooding extents have not been reported. We investigated the effects of different flooding extent on As and Cd uptake by rice and accumulation in grain in well-weathered soil amended with Si-rich rice husk (Husk) or mixed charred/ashed rice husk (Ash). Our results show that Husk and to a lesser extent Ash amendments decreased grain As under both flooded (~40% and 20% decrease, respectively) and nonflooded (~75% decrease) conditions due to increased Si. Under flooded conditions grain As and yield is higher, and Husk amendment additionally decreased grain inorganic As by ~45%. Under nonflooded conditions grain Cd is higher and yield is lower, and Ash amendment decreased grain, husk, and straw Cd by ~40-50% not due to Si, but due to increased aboveground biomass and an increase in soil pH, which helped to retain Cd in soil. These data illustrate that rice residue addition to paddy soil can lower human health risk under both flooded and nonflooded conditions without affecting grain Zn and Fe.

Opportunities and risks of biofertilization for leek production in urban areas: Influence on both fungal diversity and human bioaccessibility of inorganic pollutants

The influence of biofertilization with arbuscular mycorrhizal fungi (AMF) on trace metal and metalloids (TM) - Pb, Cd and Sb - uptake by leek (Allium porrum L.) grown in contaminated soils was investigated. The effect of biofertilization on human bioaccessibility of the TM in the plants was also examined. Leek were cultivated in one soil with geogenic TM sources and one soil with anthropogenic TM, to assess the influence of pollutant origin on soil-plant transfer. Leek were grown for six months on these contaminated soils, with and without a local AMF based biofertilizer. Fungal communities associated with leek roots were identified by high throughput sequencing (illumina Miseq®) metagenomic analysis. The TM compartmentation was studied using electron microscopy in plants tissues. In all the soils, biofertilization generated a loss of diversity favoring the AM fungal species Rhizophagus irregularis, which could explain the observed modification of metal transfer at the soil-AMF-plant interface. The human bioaccessibility of Sb increased in biofertilized treatments. Consequently, this latter result highlights a potential health risk of the use of this fertilization technique on contaminated soil since further field investigation is performed to better understand the mechanisms governing (1) the effect of AMF on TM bioaccessibility and (2) the evolution of AMF communities in contaminated soils.