Soil heavy metal contamination and health risks associated with artisanal gold mining in Tongguan, Shaanxi, China

Metal(loid)s Spatial Distribution, Accumulation, and Potential Health Risk Assessment in Soil-Wheat Systems near a Pb/Zn Smelter in Henan Province, Central China

To understand the influence of Pb/Zn smelter on surrounding environment, 110 soil and 62 wheat grain samples (62 paired samples) were collected nearby a Pb/Zn smelter in Jiaozuo City, Henan Province, China. The content and spatial distribution of metal(loid)s in the soil-wheat system, and the potential health risk via consumption of wheat grains were determined. Results showed that the average content of Pb, Cd, As, Cu, Zn, and Ni in soil were 129.16, 4.28, 17.95, 20.43, 79.36, and 9.42 mg/kg, respectively. The content of Cd in almost all soil samples (99.1%) exceeded the national limitation of China (0.6 mg/kg). Spatial distribution analysis indicated that atmospheric deposition might be the main pollution source of Pb, Cd, As, and Zn in soil. In addition, the average content of Pb, Cd, As, Cu, Zn, and Ni in wheat grain were 0.62, 0.35, 0.10, 3.7, 35.77, and 0.15 mg/kg, respectively, with the average Pb and Cd content exceeding the national limitation of China. The average bioaccumulation factor of these metal(loid)s followed the following order: Zn (0.507) > Cu (0.239) > Cd (0.134) > Ni (0.024) > Pb (0.007) > As (0.006). Health risk assessment indicated that the average noncarcinogenic risk of children (6.78) was much higher than that of adults (2.83), and the carcinogenic risk of almost all wheat grain is higher than the acceptable range, with an average value of 2.43 × 10−2. These results indicated that humans who regularly consume these wheat grains might have a serious risk of noncarcinogenic and carcinogenic diseases.

Spatial distribution and ecological risk assessment of heavy metals in karst soils from the Yinjiang County, Southwest China

BACKGROUND

Soil heavy metals (HMs) under different land-use types have diverse effects, which may trigger the ecological risk. To explore the potential sources of HMs in karst soils, the spatial distribution and geochemical behavior of HMs based on different land-use types are employed in this study.

METHODS

Soil samples (n = 47) were collected in three suites of karst soil profiles from the secondary forest, abandoned cropland and shrubland in Yinjiang, Southwest China. The concentrations of Ni, Mn, Cr, Pb, Cd and Mo were determined to give a comprehensive understanding of the possible sources of these HMs and evaluate the potential ecological risk in Yinjiang County.

RESULTS

The mean concentrations of HMs in all profiles followed the same order: Mn > Cr > Ni > Pb > Mo > Cd. Meanwhile, the concentrations of most HMs roughly increased with the depth. Additionally, the concentrations of HMs were mostly correlated with soil pH and SOC, rather than with clay and silt proportions. By contrast, with the enrichment factors (EF), geo-accumulation (Igeo) and potential ecological risk index (PERI) of HMs in soil under different land-use types, the results indicated that these HMs exhibited non-pollution (Igeo < 0) and no ecological risk (PERI < 30) to human health in soils of Yinjiang County.

CONCLUSIONS

The distribution of HMs is dominated by weathering in the karst area, and the effects of agricultural inputs on the enrichment of soil HMs in Yinjiang County are limited. This further state that the arrangement of the local agricultural structure is reasonable.

Effects of Application of Pig Manure on the Accumulation of Heavy Metals in Rice

Pig manure (PM) is often highly enriched in heavy metals, such as Cu and Zn, due to the wide use of feed additives. To study the potential risks of heavy metal accumulation in the soil and rice grains by the application of PM and other organic manure, a four-year field experiment was conducted in the suburb of Shanghai, southeast China. The contents of Cu, Zn, Pb, and Cd in the soils and rice plants by the treatments of PM and fungal culturing residues (FCR) show a trend of annual increase. Those in the soils and rice by the PM treatment are raised even more significantly. Cu and Zn contents in the soil and rice roots by the PM are significantly higher than those by the non-fertilizer control (CK) during the four years, and Pb and Cd also significantly higher than CK in the latter two years. Heavy metals taken up by the rice plants are mostly retained in the roots. Cu and Zn contents in the rice plants are in the decreasing order of roots > grains > stems > leaves, and Pb and Cd in the order of roots > stems > leaves > grains. Cu, Zn, Pb, and Cd contents in the soils by the PM treatment increase by 73%, 32%, 106%, and 127% on annual average, and those in the brown rice by 104%, 98%, 275%, and 199%, respectively. The contents of Cu, Zn, Pb, and Cd in the brown rice of the treatments are significantly correlated with those in the soils and rice roots (p < 0.05), suggesting the heavy metals accumulated in the rice grains come from the application of PM and FCR. Though the contents of heavy metals in the brown rice during the four experimental years are still within the safe levels, the risks of their accumulative increments, especially by long-term application of PM, can never be neglected.

Estimation of metal elements content in soil using x-ray fluorescence based on multilayer perceptron

X-ray fluorescence (XRF) is widely used to rapidly detect heavy metals in soil. Spectra processing has been an important research topic to improve accuracy. In this study, 80 soil samples were analyzed by XRF under indoor conditions, where different preprocessing and quantitative analysis methods were compared in terms of prediction accuracy. Denoising algorithms were used to preprocess the soil spectra before establishing prediction models for As, Pb, Cu, Cr, and Cd in soil. The influence of denoising methods on the prediction effects of different models was compared and discussed. The results on five heavy metal spectra show that the proper spectral preprocessing method can effectively improve the prediction performance of the model. The multilayer perceptron model provides promising analysis and modeling for the five metal elements. The determination coefficients (R²) of the models were 0.857, 0.976, 0.977, 0.995, and 0.886, respectively. The proposed method provides the potential to support accurate quantitation by XRF analysis.

Source Apportionment and Geographic Distribution of Heavy Metals and as in Soils and Vegetables Using Kriging Interpolation and Positive Matrix Factorization Analysis

Food security and cultivated land utilization can be seriously affected by heavy metal (HM) pollution of the soil. Therefore, identifying the pollution sources of farmland is the way to control soil pollution and enhance soil quality effectively. In this research, 95 surface soil samples, 34 vegetable samples, 27 irrigation water samples, and 20 fertilizer samples were collected from the Wuqing District of Tianjin City, China and was used to determine their HMs accumulation and potential ecological risks. Then, kriging interpolation and positive matrix factorization (PMF) were utilized to identify the sources of soil HMs. The results indicated that soil HMs in the study area were contaminated at a medium level, but that the pollution of Cd was more severe, and the Cd content in vegetables was slightly higher than the permissible threshold (0.02 mg·kg⁻¹). Furthermore, a non-homogeneous distribution was observed, with higher concentrations of HM contaminants concentrated in the southwest of the study area, where many metal manufacturing industries are located. Our results suggest that the Cd originated from industrial activity; As and Pb from agricultural practices; Ni, Cu, Cr, and As mainly from natural sources; Zn and Cu from organic fertilizer; Pb and Cd mainly from traffic discharge; and Cr, Ni, and Pb from sewage irrigation. Obviously, the accumulation of soil HMs in the study area could be mainly attributed to industrial activities, implying the need for implementation of government strategies to reduce industrial point-source pollution.

Related health risk assessment of exposure to arsenic and some heavy metals in gold mines in Banmauk Township, Myanmar

Exposure to heavy metals in mining activities is a health issue among miners. This study was carried out at three small-scale gold mining sites situated in Banmauk Township, Myanmar and aims to assess the occupational health risks of small-scale gold miners who are exposed to arsenic (As), cadmium (Cd), mercury (Hg) and lead (Pb) in the soil through the dermal route. Soil samples were analyzed through atomic absorption spectroscopy (AAS). The concentrations of the heavy metals in soils found As, ranged 1.04 mg/kg to 22.17 mg/kg, 0.13 mg/kg to 3.07 mg/kg for Cd, 0.15 mg/kg to 77.44 mg/kg for Hg, and 7.67 mg/kg to 210.00 mg/kg for Pb. In this study, 79% of the participants did not use any form of personal protective equipment (PPE) while working in gold mining processes. Regarding noncancer risk assessment, the results found all hazard quotient were lower than acceptable level (HQ < 1). In addition, all hazard index (HI) was lover than 1, the highest HI was found as 5.66 × 10⁻¹ in the amalgamation process. On the other hand, the result found cancer risk ranged from 8.02 × 10⁻⁸ to 1.75 × 10⁻⁶, and the estimated cancer risks for 9 years ranged from 4.78 × 10⁻⁷ to 1.04 × 10⁻⁵. Therefore, the cancer risks of the miners were greater than the United State Environmental Protection Agency (U.S. EPA) acceptable cancer risk level, 1 × 10⁻⁶, and the miners may be at risk of developing carcinogenic diseases. The suggestion is to educate miners about the health risks of heavy metals and to encourage the use of proper PPE all the time while working in gold mine.

Citric acid-assisted phytoextraction of trace elements in composted municipal sludge by garden plants

Sludge landscaping after compost stabilization is a popular recycling process; however, until trace elements (TEs) are extracted by plants and reduced to safe concentrations, they present a potential exposure risk. Three garden plants, Liriope platyphylla Wang et Tang (L. platyphylla), Iris tectorum Maxim (I. tectorum), and Photinia x fraseri Dress (P. x fraseri), were selected for field experiments, and their ability to phytoremediate TEs and the promotion effect of citric acid (CA) were studied over 3 months of observation. Among the three kinds of plants, L. platyphylla had the highest biomass per unit soil area, and the CA treatment further increased the biomass of this plant per unit soil area as well as the uptake of TEs. When treated with 3 mmol kg^-1 CA, L. platyphylla showed increases in the bioconcentration factors of Cu, Zn, Pb, and Cd by 24%, 63%, 27%, and 123%, respectively. Because of the large biomass and high concentrations of TEs, L. platyphylla had high phytoremediation indexes for Zn, Cu, Pb, Ni, and Cd, which reached 18.5, 3.7, 3.2, 2.2, and 0.4 mg m^-2, respectively, and were further improved by 60%-187% by the CA treatment. These advantages indicate the potential usefulness of L. platyphylla for phytoremediation. The results provide basic data and technical support for the use of sludge-based compost and phytoremediation by garden plants.

Potentially Toxic Element Contaminations and Lead Isotopic Fingerprinting in Soils and Sediments from a Historical Gold Mining Site

Lead (Pb) isotopes have been widely used to identify and quantify Pb contamination in the environment. Here, the Pb isotopes, as well as the current contamination levels of Cu, Pb, Zn, Cr, Ni, Cd, As, and Hg, were investigated in soil and sediment from the historical gold mining area upstream of Miyun Reservoir, Beijing, China. The sediment had higher ²⁰⁶Pb/²⁰⁷Pb ratios (1.137 ± 0.0111) than unpolluted soil did (1.167 ± 0.0029), while the soil samples inside the mining area were much more variable (1.121 ± 0.0175). The mean concentrations (soil/sediment in mg·kg⁻¹) of Pb (2470/42.5), Zn (181/113), Cu (199/36.7), Cr (117/68.8), Ni (40.4/28.9), Cd (0.791/0.336), As (8.52/5.10), and Hg (0.168/0.000343) characterized the soil/sediment of the studied area with mean I_geo values of the potentially toxic element (PTE) ranging from −4.71 to 9.59 for soil and from −3.39 to 2.43 for sediment. Meanwhile, principal component analysis (PCA) and hierarchical cluster analysis (HCA) coupled with Pearson’s correlation coefficient among PTEs indicated that the major source of the Cu, Zn, Pb, and Cd contamination was likely the mining activities. Evidence from Pb isotopic fingerprinting and a binary mixing model further confirmed that Pb contamination in soil and sediment came from mixed sources that are dominated by mining activity. These results highlight the persistence of PTE contamination in the historical mining site and the usefulness of Pb isotopes combined with multivariate statistical analysis to quantify contamination from mining activities.

Human risk associated with the ingestion of artichokes grown in soils irrigated with water contaminated by potentially toxic elements, Junin, Peru

The contamination of water, air and soil with potentially toxic elements (PTE) compromises the supply of contaminant free food. Vegetables grown in contaminated soils can absorb and accumulate PTE at concentrations that are toxic to human health. In this context, the human risk associated with the intake of artichokes grown in soils irrigated with PTE contaminated water was assessed. 120 samples of surface soil and artichoke heads were collected and the concentrations of Cu, Fe, Pb, Zn and As were determined. The results showed that the concentrations of Cu, Fe and Zn in soil did not exceed the standards of the Ministry of Environment of Peru, but they did exceed those of Pb (125.45 mg kg^-1) and As (28.70 mg kg^-1). The decreasing order of mean PTE concentration in artichoke heads was Fe > Zn > Cu > Pb > As, exceeding the permissible levels of FAO/WHO CODEX Alimentarius. However, the concentrations of As comply with the maximum limits of inorganic contaminants in vegetables (0.3 mg kg^-1) established in the MERCOSUR regulations. The non-carcinogenic and carcinogenic risk of Pb and As indicated that the ingestion of artichoke heads does not represent a health risk.

Spatiotemporal distribution and human health risk assessment of potential toxic species in soils of urban and surrounding crop fields from an agricultural area, Córdoba, Argentina

The spatiotemporal distribution of potentially toxic species was studied in the topsoil of parks, playgrounds, and surrounding crop fields of Marcos Juarez City in Córdoba province, Argentina. The content of available metals and of some pesticides used in the region was determined. The mean values of available metal concentrations in all samples, expressed in mg kg^-1, were 7.99 ± 6.58, 0.89 ± 0.71, 0.35 ± 0.26, and 1.50 ± 1.40 for Pb, Cr, Cd, and Ni, respectively. Pearson's correlation coefficients, coefficient of variation (%), and principal component analysis were used to explore whether variations in metal content were associated with anthropogenic factors. Agrochemicals such as lindane, chlorobenzilate, endosulfan, endrin, permethrin, and chlorpyrifos were found in crop field soil samples. In turn, chlorothalonil, chlordanes, methoxychlor, DDT, permethrin, and chlorpyrifos were detected in park and playground soil samples. The degree of pollution with possible effects on environmental health was evaluated using the Nemerow integrated pollution index (NIPI) and the modified degree of contamination (mCd). In some campaigns, the values obtained from crop fields ranged from low to high pollution levels during periods of agrochemical application. Noteworthy, in periods of low agrochemical application in crop fields, a high level of pollution was observed in parks and playgrounds. For children, the hazard index (HI) values were higher than the threshold value of 1, suggesting a potential health risk. This study provides valuable information regarding land management practices and highlights the importance of monitoring and implementing policies to reduce human health risks.

Application of cadmium prediction models for rice and maize in the safe utilization of farmland associated with tin mining in Hezhou, Guangxi, China

Cadmium (Cd) contamination in soil and crops caused by mining activities has become a prevalent concern in the world. Given that different crops have varying Cd bioaccumulation factors, crops with low Cd bioaccumulation abilities can be selected for the safe usage of Cd -contaminated lands. This study aimed to investigate Cd contamination in soil and crops and the influencing factors of soil Cd activity in a tin mining area (TMA) and control area (CA) and to put forward suggestions for the safe usage of farmlands by developing prediction models of Cd content in different crop grains. We collected 72 and 40 pairs of rice and maize grain samples, respectively, along with their rhizosphere soil samples and 6176 topsoil samples. The results showed that compared with the CA, the Cd pollution was more severe in the cultivated soil and crop grains around TMA. Furthermore, rice has a strong ability to transport Cd from soil to grains, whereas maize has a poor Cd uptake ability. The total organic carbon, CaO, pH, and Mn in soil play key roles in the transfer of Cd from soil to crop grains. Using these parameters and Cd concentration in soil, two sets of accurate Cd prediction models were developed for maize and rice. Based on the Cd concentration in the topsoil and predicted Cd concentration in crop grains, the safe utilization scheme of farmland was proposed. The proportions of priority protection, safe exploitation, planting adjustment, and strict control were 72.59%, 22.77%, 3.16%, and 1.48% in the TMA, respectively. The values reached 80.51% (priority protection), 19.12% (safe exploitation), 0.37% (planting adjustment), and 0% (strict control) in the CA. Thus, given the difference between Cd accumulation in rice and maize, adjustment of planting crops in contaminated farmlands can be applied to maximize the use of farmland resources.

[Progress of sample preparation and analytical methods of dried fruit foods]

坚果、果脯等干果类食品含有丰富的营养成分,深受国内外广大消费者的喜爱。但这些食品在果实生产、加工、储运时会使用农药或产生霉变等,造成干果中农药、重金属、霉菌毒素或添加剂等有害成分残留,甚至超过国家限量要求,带来严重的食品安全问题。因此,加强干果类食品的质量监督具有重要的经济和社会意义。但干果类食品基质复杂,有害物质种类多,结构和性质差异大,含量低,其分析检测需要快速高效的样品前处理技术和准确灵敏的分析检测方法。该文主要综述了近十年来干果类食品中有害物质的样品前处理及分析检测方法研究进展。其中样品前处理方法主要包括各种场辅助萃取法、相分离法和衍生化萃取方法等。场辅助萃取法主要是借助超声波和微波场等外场(协同)作用加快干果中有害物质的溶出速度,提高其萃取效率。相分离法,包括固相(微)萃取、分散固相萃取和液相(微)萃取法等,具有溶剂消耗少、分离富集效率高的优势,是干果样品分析中较常使用的前处理方法。该文还重点介绍了干果中各类有害成分分析检测技术,主要包括色谱、原子光谱、无机质谱、电化学分析等常规实验室方法,以及一些适用于现场分析的快速检测技术,并以此为基础,展望了干果类食品中有害物质分析检测技术的发展趋势。

Source-specific ecological and health risks of potentially toxic elements in agricultural soils in Southern Yunnan Province and associated uncertainty analysis

Source-specific risk apportionment is critical to prevent and control soil potentially toxic element (PTE) pollution. This study explored source-specific ecological and human health risks of soil PTEs in Southern Yunnan Province. Geochemical baseline values were determined to assess the pollution level of PTEs; then source-specific risk was apportioned combining positive matrix factorization (PMF) with ecological and human health risk assessment. Obvious accumulation of As, Cd, Pb, and Zn was observed in this area, especially Cd in 21.33% of the samples exhibited significant enrichment. Four sources were quantified based on PMF assisted with GIS-mapping: natural sources (41.49%), traffic emissions (24.70%), industrial activities (17.48%), and agricultural activities (16.33%). Industrial activities were the largest source (64.55%) to ecological risk. Agricultural activities were regarded as the major contributor to non-carcinogenic (adults: 75.93%, children: 62.33%) and carcinogenic risks (adults: 55.97%, children: 56.36%). Non-carcinogenic and carcinogenic risks for children were higher than adults, and their health risks showed similar trend. Thus, agricultural activities should be regarded as a priority to reduce health risk, whereas industrial activities should be given priority to control ecological risk. Although source-specific risk was quantified, combination with bioavailability and interactions of PTEs are necessary to obtain more accurate results in future.

Evaluation of phytoremediation potential of native dominant plants and spatial distribution of heavy metals in abandoned mining area in Southwest China

A field investigation on the content of heavy metals in soils and dominant plants was conducted in three sites (A<0.5 km, B<1.0 km, C<1.5 km) with different distances of mine tailings. The spatial distribution of heavy metals and the accumulation in plants were compared, and the candidate species for ecosystem restoration were selected. The results indicated that the soil was polluted by chromium (Cr), Cadmium (Cd), copper (Cu), nickel (Ni) in varying degrees, which is 2.07, 2.60, 1.79, and 4.49 times higher than the Class-Ⅱ standard in China. The concentrate of Ni, Cd, and Zinc (Zn) increased, while Cr, Lead (Pb), and Cu decreased with the distance from the mine tailings. 73 species (34 families) were found and mainly herbaceous plants. The concentrate of Cd, Cu, Cr, and Ni in 29 dominant plants were measured and 66.67%, 21.43%, 100%, 47.62% plants exceeded the normal concentration range. Based on the comparative analysis of heavy metal content, bioconcentration factor, and translocation factor in plants, Polygonum capitatum has good phytoextraction ability, Boehmeria nivea, Chrysanthemum indicum, Miscanthus floridulus, Conyza canadensis, Rubus setchuenensis, Senecio scandens, and Arthraxon hispidus showed remarkable phytostabilization abilities of Cr, Cd, Ni, and Cu, which can be used as potential phytoremediation candidate.

Probabilistic multi-pathway human health risk assessment due to heavy metal(loid)s in a traditional gold mining area in Ecuador

Mining operations are important causes of environmental pollution in developing countries where mining waste management is not adequate. Consequently, heavy metal(loid)s are easily released into the environment, being a potential risk to human health. This study carries out a Bayesian probabilistic human health risk assessment, related to multi-pathway exposure to heavy metal(loid)s in a gold mining area in Southern Ecuador. Concentrations of As, Cd, Cr, Cu, Ni, Pb, and Zn in tap water, surface water, and soil samples, were analyzed to assess the potential adverse human health effects based on the Hazard Index (HI) and Total cancer risk (TCR). Adults and children residents were surveyed to adjust their exposure parameters to the site-specific conditions. Exposure to heavy metal(loid)s resulted in unacceptable risk levels for human health in the two age groups, both carcinogenic (TCR > 1 × 10-5) and non-carcinogenic (HI > 1) through ingestion of tap water and incidental ingestion of surface water. Sensitivity analysis showed that As concentration in waters and exposure frequency were the main contributors to risk outcome. Exposure to soil via accidental ingestion and dermal contact was below the safety limit, not posing a risk to human health. These findings can provide a baseline for the environmental management of the mining area and indicate the need for further research on As pollution in water and its implications on the health of the inhabitants of mining communities.

Spatial distribution, risk assessment, and source identification of pollutants around gold tailings ponds: a case study in Pinggu District, Beijing, China

This work investigated heavy metal and cyanide pollution in surface soils and edible plants around Yanzhuang gold tailings ponds in the region of Yanzhuang Village in Pinggu District, Beijing. Surface soil samples were collected from 33 sites around gold tailings ponds, and concentrations of seven heavy metals (i.e., Sb, As, Cd, Cu, Pb, Zn, and Hg) and cyanide were analyzed to determine their spatial distributions, pollution degrees, and sources. The potential ecological risks of As, Cd, Cu, Pb, Zn, and Hg were preliminarily assessed. The results showed that the mean cyanide, Sb, As, Cd, Cu, and Pb concentrations were higher than the standard values. The pollutant concentrations around the tailings ponds were high and decreased with increasing distance from the ponds. The single pollution index indicated that cyanide, As, and Cd were the main pollutants. The Nemerow pollution index revealed a large region and serious degree of heavy metal pollution in soils. The potential ecological risk level of the study area was moderate, with Cd and As posing the main risks. Multivariate statistical analysis suggested that the heavy metal and cyanide pollution present mainly derived from gold tailings, with agricultural pollution also had a certain effect. However, the 12 edible plants sampled were basically not polluted.

A modelling study of a buffer zone in abating heavy metal contamination from a gold mine of Hainan Province in nearby agricultural area

The establishment of new buffer zone in the mine areas lacks the basis of theoretical model. As a case study, this study presents the partition model of new buffer zone in a small-scale mine area located in the remote mountainous region of Hainan province, China. The investigation carried out by integration of geostatistical interpolation maps using unmanned aerial vehicle has revealed that As, Cd, Pb, Zn, and Hg are mainly distributed near the tailing ponds and the dressing plant, while Cr and Cu are prominent near the agricultural area. The partition model of buffer zone was established in accordance to the transport velocity of the liquid phase heavy metal in soil. The boundary line of buffer zone is integrated by comparing the 'predicted' heavy metal concentrations with the 'measured' heavy metal concentrations. Principal component analysis (PCA) and the variations of heavy metal concentrations with elevation, slope, and distance were performed to further evaluate the reliability of the predicted buffer zone, indicating that the new buffer zone has a significant effect on minimizing transport of heavy metals from the mining area into the agricultural land. This study is suggestive to provide risk control and sustainable development strategy for the ecosystem protection in mine areas.

Geogenic enrichment of potentially toxic metals in agricultural soils derived from black shale in northwest Zhejiang, China: Pathways to and risks from associated crops

Agricultural soils derived from black shale are typically enriched in potentially toxic metals. This is a serious problem, both in terms of the ecological environment and human health. To assess the levels of potentially toxic metals, 90 paired soil-crops samples were collected from the Anji Country, western Zhejiang province, a typical exposed black shale area in China. Concentrations and bioavailability of potentially toxic metals in the soil-crops system were measured, and the associated potential risks were further evaluated. Results showed the enrichment of potentially toxic metals (i.e. Cd, Pb, Cu, Zn and Ni) in the soil and crop samples, especially a significant accumulation of Cd. Sequential extraction data indicated that Cd in soils derived from black shale was the second most dominant element in the exchangeable fraction (mean at 33.42%) and possessed high bioavailability, whereas Pb was mostly retained in the residual fraction (mean at 76.34%) and exhibited low mobility. The total concentration as well as mobility and bioavailability of Cd were the highest in the sampled soils. This resulted in a high potential ecological risk in areas with agricultural soils derived from black shale, which could eventually jeopardize the health of local residents through various exposure pathways. Overall, our findings provide a scientific basis for developing suitable management strategies to mitigate the exposure to potentially toxic metals in high risk areas.

Heavy metal pollution caused by cyanide gold leaching: a case study of gold tailings in central China

It is known that the tailings of gold mines have brought serious heavy metal pollution; however, the heavy metal pollution caused by gold tailings in specific geological environments and extraction processes still must be studied. This study investigated the distribution, speciation, bioaccumulation, and pollution of heavy metals in soils from the Yueliangbao gold tailings area in central China, where gold was extracted by cyanidation. The results show that the concentrations of Cu, Pb, Zn, Mn, Mo, and Cd in the soils of the tailings pond were higher than those in the local background. The concentrations of heavy metals related to mineralization activities, such as Cu, Pb, Zn, and Mo, varied with the distance to the tailings pond center. There was a decreasing trend of tailings pond center > tailings pond entrance > surrounding environment. This study's gold tailings pond differed from those of other regions because of its high content of unextracted Cu remaining in the pond. The proportion of non-residual Cu in the tailing pond soil was much higher than that of residual Cu, indicating it was likely to migrate to the surrounding environment. The pollution assessment indicated that the tailings pond soils were heavily polluted by Cu, and the level of heavy metal pollution in soils was positively correlated with the distance to the tailings pond center. Consequently, this tailings pond may become a source of Cu pollution in the surrounding environment, thus endangering environmental safety and human health. The study of heavy metal concentrations in the dominant plants showed that Chinese brake (Pteris vittata L.), Ramose scouring rush (Equisetum ramosissimum), and Manyflower silvergrass (Miscanthus floridulus) had the potential to be used for the phytostabilization of Cu.

Understanding Potential Heavy Metal Contamination, Absorption, Translocation and Accumulation in Rice and Human Health Risks

Rice is a worldwide staple food and heavy metal contamination is often reported in rice production. Heavy metal can originate from natural sources or be present through anthropogenic contamination. Therefore, this review summarizes the current status of heavy metal contamination in paddy soil and plants, highlighting the mechanism of uptake, bioaccumulation, and health risk assessment. A scoping search employing Google Scholar, Science Direct, Research Gate, Scopus, and Wiley Online was carried out to build up the review using the following keywords: heavy metals, absorption, translocation, accumulation, uptake, biotransformation, rice, and human risk with no restrictions being placed on the year of study. Cadmium (Cd), arsenic (As), and lead (Pb) have been identified as the most prevalent metals in rice cultivation. Mining and irrigation activities are primary sources, but chemical fertilizer and pesticide usage also contribute to heavy metal contamination of paddy soil worldwide. Further to their adverse effect on the paddy ecosystem by reducing the soil fertility and grain yield, heavy metal contamination represents a risk to human health. An in-depth discussion is further offered on health risk assessments by quantitative measurement to identify potential risk towards heavy metal exposure via rice consumption, which consisted of in vitro digestion models through a vital ingestion portion of rice.

Bioremoval of hazardous cobalt, nickel, chromium, copper and cadmium compounds from contaminated soil by Nicotiana tabacum plants and associated microbiome

Contamination of soils with heavy metals leads to reduction of soil fertility, destruction of natural ecosystems and detrimental effects on the health of society by increasing content of metals in the food chains from microorganisms to plants, animals and humans. Bioremediation is one of the most promising and cost-effective methods of cleaning soils polluted with toxic metals. According to current researchers, microorganisms and plants have the genetic potential to remove toxic metals from contaminated sites. The method of thermodynamic prediction was used to theoretically substantiate the mechanisms of interaction of soil microorganisms and plants with heavy metals. According to the our prediction, exometabolite chelators of anaerobic microorganisms may increase the mobility of metals and thereby contribute to the active transport of metals and their accumulation in plants. Plants of Nicotiana tabacum L. of Djubek cultivar were used as plant material for the current investigation. The examined toxicants were heavy metals, namely cobalt (II), nickel (II), chromium (VI), copper (II) and cadmium (II). The aqueous solutions of metal salts were added to the boxes after two months of plants growing to the final super-high concentration – 500 mg/kg of absolutely dry weight of soil. Quantitative assessments of copper and chromium-resistant microorganisms were made by cultivation on agar nutrient medium NA with a gradient of Cu(II) and Cr(VI). The concentration of metals in soil and plant material (leaves, stems and roots) was determined by atomic absorption method. The study revealed that heavy metals inhibited the growth of the examined tobacco plants. This was expressed by the necrosis of plant tissues and, ultimately, their complete death. Despite this, all investigated heavy metals were accumulated in plant tissues during 3–7 days before death of plants. The uptake of metals was observed in all parts of plants – leaves, stems and roots. The highest concentrations of Co(II), Ni(II), Cd(II), Cr(VI) were found in the leaves, Cu(II) – in the roots. The results show that the bioremoval efficiency of the investigated metals ranged 0.60–3.65%. Given the super-high initial concentration of each of the metals (500 mg/kg), the determined removal efficiency was also high. Cadmium was the most toxic to plants. Thus, the basic points of the thermodynamic prognosis of the possibility of accumulation of heavy metals by phytomicrobial consortium were experimentally confirmed on the example of N. tabacum plants and metal-resistant microorganisms. The study demonstrated that despite the high initial metals concentration, rate of damage and death of plants, metals are accumulated inplant tissues in extremely hight concentrations. Soil microorganisms were observed to have high adaptation potencial to Cu(II) and Cr(VI). In anaerobic conditions, microorganisms presumably mobilize heavy metals, which later are absorbed by plants. The obtained results are the basis for the development of environmental biotechnologies for cleaning contaminated soils from heavy metal compounds.

Heavy metal pollution and ecological risk assessment of tailings in the Qinglong Dachang antimony mine, China

The pollution of heavy metals and their harm to human health and the ecological environment have caused widespread concern. In this research, we collected Qinglong antimony mine tailings (8-meter deep) and then analyzed the content changes, geochemical behavior, and ecological risk assessment of 7 heavy metals (Sb, As, Cr, Cd, Cu, Zn, Pb) in the tailing profile, providing a theoretical basis for strengthening the source control and risk control of heavy metals. In addition, the chemical forms of Sb and As were analyzed, and the relationship between their forms and their physical and chemical properties was analyzed by redundancy analysis (RDA). The results showed that the concentrations of Sb (671.97-13896.62 mg/kg), As (287.38-657.36 mg/kg), Cu (27.61-74.48 mg/kg), and Cd (0.49-1.76 mg/kg) in the tailings greatly exceeded their background values, those of Pb (15.67-125.74 mg/kg) and Cr (22.69-185.88 mg/kg) moderately exceed their background values, while that of Zn (41.66-94.48 mg/kg) was slightly below its background value. Among the chemical forms of Sb and As, the residual fraction (F4) had the highest concentration. RDA showed that the pH and tailing particle size were significantly correlated with the chemical species content of Sb and As (p < 0.05). The improved Igeo analysis showed that the tailings were extremely polluted with Sb; highly polluted with As; uncontaminated to moderately polluted with Cd, Cu, and Pb; and uncontaminated with Zn and Cr, and the average Igeo values were in the following order: Sb >As > Pb > Cd > Cu > Zn > Cr. The potential environmental risk index showed that Sb and As imposed a serious risk and Cr, Cd, Cu, Pb, and Zn imposed a low risk, which was basically consistent with the results of the improved Igeo values. This research provides comprehensive theoretical approaches to better understand the source control and risk control of heavy metals in tailing ponds.

Heavy Metals and Pesticides Toxicity in Agricultural Soil and Plants: Ecological Risks and Human Health Implications

Environmental problems have always received immense attention from scientists. Toxicants pollution is a critical environmental concern that has posed serious threats to human health and agricultural production. Heavy metals and pesticides are top of the list of environmental toxicants endangering nature. This review focuses on the toxic effect of heavy metals (cadmium (Cd), lead (Pb), copper (Cu), and zinc (Zn)) and pesticides (insecticides, herbicides, and fungicides) adversely influencing the agricultural ecosystem (plant and soil) and human health. Furthermore, heavy metals accumulation and pesticide residues in soils and plants have been discussed in detail. In addition, the characteristics of contaminated soil and plant physiological parameters have been reviewed. Moreover, human diseases caused by exposure to heavy metals and pesticides were also reported. The bioaccumulation, mechanism of action, and transmission pathways of both heavy metals and pesticides are emphasized. In addition, the bioavailability in soil and plant uptake of these contaminants has also been considered. Meanwhile, the synergistic and antagonistic interactions between heavy metals and pesticides and their combined toxic effects have been discussed. Previous relevant studies are included to cover all aspects of this review. The information in this review provides deep insights into the understanding of environmental toxicants and their hazardous effects.

Bioleaching for detoxification of waste flotation tailings: Relationship between EPS substances and bioleaching behavior

The production of large volumes of waste flotation tailings results in environmental pollution and presents a major ecological and environmental risk. This study investigates bioleaching of waste flotation tailings using Acidithiobacillus ferrooxidans. The experiments were performed with 5.00% solid concentration, pH 2.0 with 100 mL medium for 25 d in the lab. The pH, OPR, metal concentration, dissolved organic matter (DOM) in leachate and extracellular polymeric substances (EPS) were recorded. Bioleaching tailing materials were finally characterized. Results showed that microorganisms, acclimating with mine tailings, effectively accelerated the bioleaching process, achieving maximum Zn and Fe extraction efficiencies of 95.45% and 83.98%, respectively, after 25 days. Compared with raw mine tailings, bioleaching could reduce 96.36% and 95.84% leachable Zn and Pb, and Pb presented a low risk (4.13%), while Zn, Cu, and Cr posed no risk (0.34%, 0.64%, and 0%). Toxicity and environmental risk analysis revealed bioleaching process significantly reduced the environmental risk associated with mine tailings. EPS analysis indicated that the loosely-bound EPS (LB-EPS) and tightly-bound EPS (TB-EPS) fractions contained different organic substances, which played different roles in the bioleaching process. Pearson correlation analysis revealed that EPS was highly correlated with bioleaching behavior (p < 0.05), and EPS was the main factor affecting the bioleaching process, promoting bioleaching in the LB-EPS and TB-EPS fractions.

Potential ecological and health risk assessment of different kiwifruit orchards in Qianjiang district, Chongqing city, China

Heavy metal (HM) pollution in orchards is becoming serious in many countries, and some fruit HMs exceed the safety limits. In this study, contents of 8 HMs (Cd, Hg, As, Pb, Cr, Cu, Ni, and Zn) in 5 kiwifruit orchard soils and the tissues (roots, twigs, leaves, fruits) of 4 kiwifruit varieties collected from Qianjiang district, Chongqing city, China, were determined. Seven HMs could meet priority protection class I, except for Cd with slightly poor environmental quality, including 4% and 53% of the samples belonging to the strict control class III and safe utilization class II, respectively. The potential ecological risk index (235.30) indicated that the HMs in the orchard soil were of medium potential ecological risk. The HMs' migration from rock to soil was very obvious. Kiwifruit was easy to accumulate Cu from soil and it had high Zn and Ni translocations to above-ground parts from roots. Compared with other tissues, HMs' concentrations in fruits were the lowest. From the perspective of human health, about 8.3% and 0.83% of the fruit samples for Cr and Cu exceeded the national maximum permissible levels, respectively; fortunately, the health risk index (HRI) values for all the fruit samples were within the safe limits.

Biomass allocation strategies and Pb-enrichment characteristics of six dwarf bamboos under soil Pb stress

Dwarf bamboos are clonal plants with potential applications in the remediation of heavy metal-polluted soils, although their pollution adaptation strategies are unknown. This study examined the biomass allocation strategies and lead (Pb) enrichment characteristics of various dwarf bamboo tissues by the end of the growing season and explored their potential for phytoremediation of Pb stress in the soils. Six dwarf bamboo genotypes were treated with three levels (0, 300, and 1500 mg kg^-1) of soil Pb stress. The majority of the bamboos adopted two biomass allocation strategies to adapt to Pb stress, namely, "reducing biomass allocation into new bamboo growth" and "increasing/stabilizing biomass allocation into rhizomes". Pb accumulation was highest in the roots, rhizomes, and old stems and showed the following trend: rhizomes/old stems> new roots/old roots> old leaves> new leaves> new stems among various tissues. Moreover, the six bamboos used three different Pb-enrichment strategies, as follows: (i) "rhizome domination and old stem synergy" (Sasaella glabra (Nakai) f. albo-striata Muroi, Sasa auricoma (Mitford) E.G. Camus, Sasa fortunei (Van Houtte) Fiori, and Shibataea lanceifolia C.H. Hu); (ii) "old stem domination and rhizome synergy" (Indocalamus decorus Q.H. Dai); and (iii) "old stem domination and new root synergy" (Sasa argenteostriata (Regel) E.G. Camus). In Pb-contaminated soils, genotypes with TFs greater than 1 were Sasa fortunei (Van Houtte) Fiori, Sasa argenteostriata (Regel) E.G. Camus, and Indocalamus decorus Q.H. Dai; in addition, only S. argenteostriata had BCF values greater than 1. Furthermore, this study provides the first evidence that S. argenteostriata can extract 0.22 and 0.58 mgplant^-1 of Pb ions in soil polluted with 300 and 1500 mg kg^-1 Pb, respectively. S. argenteostriata showed the greatest potential for phytoremediation among the bamboo genotypes in both Pb-contaminated urban and mining sites.

Performance of the emerging biochar on the stabilization of potentially toxic metals in smelter- and mining-contaminated soils

Soil potentially toxic metals (PTMs) pollution caused by anthropogenic activities has become serious concern with respect to the crop safety production. In this study, an emerging biochar derived from kiwi pruning branches waste was employed as amendment aiming to evaluate its remediation potential on smelter- and mining-contaminated soils. The effect of biochar on the soil physicochemical properties, leachability, and chemical fractions acted on stabilization practice of PTMs in soil was investigated. The results showed that the addition of biochar increased the soil pH, cation exchange capacity, organic matter, and enzymatic activities (dehydrogenase, urease, and sucrase) but reduced the extraction toxicity of PTMs in both smelter (Fengxian, FX) and mining (Tongguan, TG) soils. The fraction analysis showed that the maximum reduction of exchangeable fraction of Cd, Zn, and Pb in the 4% biochar amended soils decreased by 11.1, 13.3, and 24.7% in FX soil and 7.67, 22.8, and 7.89% in TG soil, respectively, in comparison with to control (no biochar added). Additionally, the residual fraction of Cd, Zn, and Pb increased by 55.9, 7.14, and 11.0% in FX soil and 23.7, 5.86, and 10.0% in TG soil, respectively. The further greenhouse experiment showed that the Indian mustard (Brassica juncea) production increased with the increasing application dosages of biochar, while the PTMs uptakes in plant notably decreased after amendments. Conversion of kiwi pruning branches waste into emerging biochar benefits the agricultural waste recycling utilization and enhances PTMs-contaminated soil remediation in practice. Graphical abstract.

Bioremediation of Cd-contaminated soil by earthworms (Eisenia fetida): Enhancement with EDTA and bean dregs

The remediation of cadmium (Cd) contaminated soil has become a global problem due to its toxicity to living organisms. In this study, earthworm (Eisenia fetida) alone or combined with EDTA or bean dregs were used for Cd removal from soils. The total and available Cd in soils, soil physicochemical and biological (soil enzyme) properties, Cd accumulation in the earthworm and its antioxidant responses towards Cd, were determined during the 35 days of soil incubation experiment. Our results showed that earthworms were capable of removing Cd from soils, and the remediation process was accelerated by both EDTA and bean dregs. By translocation of Cd from soils, the content of Cd in earthworm steadily increased with the exposure time to 8.11, 12.80, and 9.26 mg kg^-1 on day 35 for T2 (earthworm alone), T3 (EDTA enhancement), and T4 (bean dregs enhancement), respectively. Consequently, a great reduction in the Cd contents in soils was achieved in T3 (36.53%) and T4 (30.8%) compared with T2 (28.95%). The concentrations of water/DTPA extractable Cd were also reduced, indicating the low Cd mobility after amendment. Finally, the soil became more fertile and active after wermi-remediation. The soil pH, EC, NO₃^--N, available P, and K contents increased, while soil SOM, DOC, and NH₄⁺-N contents were decreased. There were higher soil enzyme activities (including acid phosphatase activity, β-glucosidase activity, and urease activity) among treatments with earthworms. Additionally, the operational taxonomic units (OTUs) increased by 100-150 units, and the higher chao1 and Shannon indexes indicated the enhanced microbial community after wermi-remediation, especially among treatment with EDTA and bean dregs. Therefore, we concluded that earthworms, alone or combined with EDTA and bean dregs, are feasible for the remediation of Cd-contaminated soil.

Activated mineral adsorbent for the efficient removal of Pb(II) and Cd(II) from aqueous solution: adsorption performance and mechanism studies

Activated mineral adsorbent (AMA) was prepared via double salts (Na₂SO₄ and CaCO₃) heat treatment activation of solid-state potassium feldspar. Adsorption performance of AMA for Cd(II) and Pb(II) was investigated by batch mode and factors affecting adsorption including pH value, initial concentration of adsorbate, contact time, adsorbent dosage and temperature on adsorption performance for Cd(II) and Pb(II) were studied. The results indicated that the adsorption process was pH dependent, endothermic and spontaneous. When the adsorption process of Cd(II) and Pb(II) on AMA reached equilibrium, the maximum saturated adsorption capacities were 263.16 and 303.03 mg/g for Cd(II) and Pb(II) ions, respectively, showing higher adsorption removal efficiency. The Langmuir adsorption isotherm and pseudo second kinetic equation could well fit the adsorption process of Cd(II) and Pb(II) by AMA. Besides, Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques were also performed to further reveal the adsorption mechanism. The results indicated that ion exchange, precipitation and adsorption played an important role in adsorption process. From the investigation, it was concluded that AMA was an excellent adsorbent with the advantages of environment-friendly, inexpensive, facile preparation and higher adsorption capacity of toxic Cd(II) and Pb(II) ions.

Contamination of stream waters, sediments, and agricultural soil in the surroundings of an abandoned copper mine by potentially toxic elements and associated environmental and potential human health-derived risks: a case study from Agrokipia, Cyprus

Abandoned mining areas have left a legacy of environmental damage with potential public health implications. The present study aimed at (1) assessing the level of contamination of the sites surrounding the Agrokipia abandoned copper mine in Cyprus through the mobilization of potentially toxic elements (PTEs), (2) correlating results with the mineralogy of the area, (3) discussing potential ecological and human health risks, and (4) proposing regeneration strategies. To this effect, the levels of 22 PTEs and other major elements were assessed in the acidic water of pit lakes, the tailings, the waters, and sediments of several streams originating from the mining site and flowing through the village of Agrokipia, and from agricultural soil from an impacted adjacent olive orchard. The pH values of water (pH < 2.7) in the pit lakes uncovered the acidic and oxidizing conditions that prevailed in the area. The acidity and the examined PTE concentrations in stream waters followed a decreasing trend with increasing distance from the tailing, reaching background values in a distance of 1500 m. The tailing spoil-heap was significantly enriched with Cu, Zn, Pb, Cd, Cr, and Ag (e.g., enrichment factor values up to 29 for Cu and 120 for Ag). Stream sediments and agricultural soil were contaminated with PTEs (mainly Cu, Zn, Pb, Cd, Cr, Ag, and Li), as evident by several contamination indices (i.e., enrichment and contamination factor). The level of contamination was correlated with the reported mineralogy of the site. The values of the degree of contamination (Cdeg = 62) and pollution load index (PLI = 2.4) indicated contamination of the sediments of the Voulgarides stream flowing through the village, suggesting potential public health implications to the local community. In addition, the values of the ecological risk factor suggested that the studied streams pose moderate ecological risks, mainly mediated by Cd and Cu. Overall, the results highlighted the need for undertaking regeneration measures for safeguarding environmental sustainability and public health.

Environmental and health risk assessment of agricultural areas adjacent to uranium ore fields in Brazil

To investigate the risks posed by trace and rare earth elements (REEs) in two tropical uranium ore fields, metal concentrations from 50 vegetable samples (corn and soybean) and their corresponding agricultural soils were evaluated in a U mining area and a U-rich coal mining area in Brazil. Samples from both areas had metal concentrations (REE: La to Lu, and trace elements: As, Pb, Cd, Ni, Cu, Cr, Mn, Zn, Ba, U, Sr) that were higher than the guidelines proposed by the Brazilian environmental agency. Soils from the U mining area (Poços de Caldas) generally had higher contents of trace elements than the coal mining area (Figueira), with the exception of Ni and Cr, indicating a higher risk of pollution, which was confirmed by a pollution load index that was greater than unity. For both sites, concentrations of uranium in the soil and plants, its hazard quotients and the soil contamination factor were higher in agricultural fields closer to the mines, indicating that contamination and the consequent risks to human health were distance dependent. REE concentrations averaged 52.8 mg kg^-1 in the topsoils and 0.76 mg kg^-1 in the grains for Figueira, whereas higher values of 371 mg kg^-1 (topsoils) and 0.9 mg kg^-1 (grains) were found in Poços de Caldas. Based upon corn and soybean consumption, the estimated intake dose of the REE was lower than the intake dose predicted to be problematic for human health for both sites, indicating limited risk related to the ingestion of REE.

Optimization of Cr6+ Removal by Bacillus subtilis Strain SZMC 6179J from Chromium-Containing Soil

The removal rate of Cr⁶⁺ has been explored by the optimized removal conditions. Five Cr-resistant strains were isolated from chromium-contained soil. The most efficient strain S1 was identified as Bacillus subtilis strain SZMC 6179J through 16S rDNA. Response surface methodology (RSM) was used to investigate the effects of four independent variables, including initial pH, initial Cr⁶⁺ concentration (mg/L), time (h) and inoculation percentage (%). RSM revealed that when pH was 5.02, time was 24.0 h, inoculation percentage was 4.64% (v/v) and initial concentration of Cr⁶⁺ was 55.0 mg/L, the optimal condition was obtained. Under the optimum conditions, the actual response values for Bacillus subtilis strain SZMC 6179J was 93.50%. The pH was the most significant factor towards removal rate of Cr⁶⁺. The result showed that the removal mechanism of Cr⁶⁺ by Bacillus subtilis strain SZMC 6179J was reduction under normal conditions. The removal mechanism of Cr⁶⁺ by Bacillus subtilis strain SZMC 6179J was adsorption under adverse conditions.

Multi-pathway human exposure risk assessment using Bayesian modeling at the historically largest mercury mining district

The largest mercury (Hg) mining district in the world is located in Almadén (Spain), with well-known environmental impacts in the surrounding ecosystem. However, the impact of mercury on the health of the inhabitants of this area has not been documented accordingly. This study aims to carry out a probabilistic human health risk assessment using Bayesian modeling to estimate the non-carcinogenic risk related to Hg through multiple exposure pathways. Samples of vegetables, wild mushrooms, fish, soil, water, and air were analyzed, and adult residents were randomly surveyed to adjust the risk models to the specific population data. On the one hand, the results for the non-carcinogenic risk based on Hazard Quotient (HQ) showed unacceptable risk levels through ingestion of Hg-contaminated vegetables and fish, with HQ values 20 and 3 times higher, respectively, than the safe exposure threshold of 1 for the 97.5th percentile. On the other hand, ingestion of mushrooms, dermal contact with soil, ingestion of water, dermal contact with water and inhalation of air, were below the safety limit for the 97.5th percentile, and did not represent a risk to the health of residents. In addition, the probabilistic approach was compared with the conservative deterministic approach, and similar results were obtained. This is the first study conducted in Almadén, which clearly reveals the high levels of human health risk to which the population is exposed due to the legacy of two millennia of Hg mining.

Spatial distribution and assessment of the human health risks of heavy metals in a retired petrochemical industrial area, south China

Petrochemical industries are widely distributed in China. As a negative consequence, heavy metals in petrochemical area can result in soil contamination. However, the relevant research of heavy metals contamination in petrochemical area was few. In this study, a total of 103 topsoil samples (<20 cm) and 25 profile soil samples were collected and examined in a retired petrochemical industrial area, South China. The results showed the mean contents of Hg, Cd, As, Pb, Ni and Cu were 0.18, 0.69, 16.22, 47.24, 31.62 and 93.06 mg kg^-1, respectively. The spatial distribution of six metals in topsoil was largely attributed to the industrial activities during the petroleum refining and transshipment process. Ni was the main pollutant in the petroleum refining process. While, the contamination of other metals mainly were caused by the leakage of the oil during transshipment. The migration of six metals to subsoil layers was also observable. In accordance, Hg, Cd, As, Pb, Cu, and Ni dropped by 95.02, 71.91, 89.45, 90.88, 99.22, and 65.07%, respectively, compared to their contents in topsoil. The contamination of the heavy metals was mainly caused during the process of petroleum refining and transshipment. The distribution of heavy metals in the factory was mainly affected by the industrial activities or the lateral infiltration of Lianhuashan River. Soil ingestion was the primary pathway for children and adults exposure to heavy metals. The total non-cancer human health risk induced by heavy metals was within the limit of USEPA (10^-6 a^-1). While the cancer risks alone induced by As through soil ingestion to children was 1.14 × 10^-6 a^-1, which exceeded the limit of USEPA. This study indicated that not only petroleum hydrocarbon but also heavy metals can cause soil contamination in a retired petrochemical industrial area, which provides a novel cognition. Altogether, measures should be taken in practice to substantially improve the soil quality in petrochemical industrial area.

Accumulation of potentially toxic elements in agricultural soil and scenario analysis of cadmium inputs by fertilization: A case study in Quzhou county

Fertilizer application has greatly increased crop yield, however impurities in mineral or organic fertilizers, such as heavy metals, are being added to agricultural soils, which would pose a high risk for soil and crop production. 115 soil samples were collected from Quzhou, a typical agricultural county in the North China Plain, to investigate the total content of cadmium (Cd), arsenic (As), lead (Pb), nickel (Ni), copper (Cu), zinc (Zn) and chromium (Cr) in soils. The contamination levels and source apportionment of studied elements were explored by the pollution indices, multivariate statistical approaches and geostatistical analysis. The ranges of Cd, As, Pb, Ni, Cu, Zn and Cr were between 0.08 and 0.35, 5.34-15.9, 7.34-38.9, 12.9-61.3, 7.80-27.0, 31.4-154, and 17.0-50.5 mg/kg and with the mean values 0.16, 9.20, 16.0, 24.7, 17.6, 61.1, and 29.5 mg/kg, respectively. The studied area was slightly polluted mainly by Cd, and higher pollution was found in soils under vegetable crops. The application of mineral phosphate fertilizer and livestock manure were the main source of Cd and Zn, and other elements (As, Pb, Ni and Cu) might originate from soil parent materials. Scenario analyses were performed using the R programming language, based on the cadmium contents in mineral phosphate fertilizers and livestock manures. The results showed that the long-term application of phosphate fertilizers would lead to some Cd enrichment in soil without risk of substantial pollution. Compared to pure mineral fertilizers, the long-term application of blended fertilizers (30% livestock manures and 70% phosphate fertilizers) or livestock manures would incur a higher Cd pollution risk within a short period, with a maximum probability of Cd risk of 55.21%. Mitigation measurements and scientific agronomic practices should be developed to minimize the risk of potential toxic elements in agricultural soil.

The systematic exploration of cadmium-accumulation characteristics of maize kernel in acidic soil with different pollution levels in China

Cadmium is a toxic element with a half-life of more than a few decades that can be absorbed by crops and threaten human health. The problem of food security caused by cadmium through soil-crop systems has received great attention in China. Maize is a staple food widely cultivated throughout the world. However, the lack of systematic study makes it difficult to draw an accurate conclusion on its exact characteristics of cadmium accumulation and the corresponding health risk assessment. The availability of cadmium increased with the decrease of soil pH in acidic soil, enhancing the uptake of cadmium by crops and thus posing a major threat to food safety. In this study, the performance of kernel cadmium accumulation in abundant maize inbred and important hybrid lines were analyzed on acidic fields with different pollution levels in China. It was found that the kernel cadmium concentration both in inbred and hybrid lines showed left skewed distribution and concentrated significantly in a low interval under different soil cadmium gradients with good correlation. The classification of cadmium risk level in maize germplasm and cultivars and the analysis of soil cadmium threshold for maize safe planting can provide references to utilize the crop more feasibly and effectively. Maize may be an important staple crop to reduce human exposure to cadmium in agricultural soil.

Ecological Effects of Heavy Metal Pollution on Soil Microbial Community Structure and Diversity on Both Sides of a River around a Mining Area

The objectives of this study were to understand the characteristics of heavy metal pollution caused by mining activities on the two sides of the Shun'an river and the response of soil microorganisms to the habitats by different contamination levels and vegetation. This paper selected soil samples from the banks of the Shun'an River near the Shizishan mining area, which is at the left of the river, in Tongling, Anhui Province, China. Using Illumina MiSeq 2500 technology, we analyzed the relationship between environmental factors and microbial communities. As the distance from the mining area increased, the heavy metal comprehensive pollution and potential risk value decreased. Additionally, the pollution severity and risk value of the left bank, where the mining area lies, were generally higher than those of the right bank. Because the symmetric sampling points on both banks of the river had similar planting types, their environmental factors and microbial community structure were similar and clustered. However, under different vegetation, the paddy soils tended to have a higher nutrient content and community richness and diversity than the vegetable fields or the abandoned land. It was found that soil microbial communities in this area were mostly affected by pH and Nemerow pollution index (P_N). The pH significantly affected the abundance and structure of most microorganisms. In addition, Proteobacteria, Acidobacteria, and Bacteroidetes had significant tolerance to Zn, Pb, and Cd. By exploring the potential use of these tolerant microorganisms, we seek to provide strains and the theoretical basis for the bioremediation of areas contaminated by heavy metal.

A theorem on a product of lognormal variables and hybrid models for children's exposure to soil contaminants

This study developed hybrid Bayesian models to investigate the modeling process for children's exposure to soil contaminants, which involves the intrinsic uncertainty of the exposure model, people's judgments regarding random variables, and limited data resources. A hybrid Bayesian p-box was constructed, which was facilitated by a multiple integral dimensionality reduction (MIDR) theorem. The results indicated that exposure frequency (EF) dominated the exposure dose. The hybrid Bayesian p-box for the Frequentist-Bayesian (F-B) model at the 95th percentile of the simulated average daily dose (ADD) values corresponded to a 4.40 order-of-magnitude difference between the upper and lower bounds of the p-box. This considerable uncertainty was magnified by the combination of the highest posterior density (HPD) regions for three groups of the distribution parameters. For the Interior-Bayesian (I-B) hybrid model, the uncertainty of the outcomes, namely, [1.75 × 10^-8, 2.18 × 10^-8] mg kg^-1d^-1, was limited by the HPD regions for only one parameter unless the hyperparameters for the variables' distributions were further evaluated. It was concluded that the hybrid models could provide a novel understanding of the complexity of the exposure modeling process compared to the traditional modeling method.

Critical risk analysis of metals toxicity in wastewater irrigated soil and crops: a study of a semi-arid developing region

Toxic elemental exposure through consumption of contaminated crops is becoming a serious concern for human health. Present study is based on the environment and health risk assessment of wastewater irrigated soil and crops in a semi-arid region Faisalabad, Pakistan. The concentrations of potentially toxic elements (Cu, Cr, Mn, Fe, Pb, Zn, Ni) were analysed by atomic absorption spectrometer in five different crops (Corn, rice, wheat, sugarcane and millet), while, their topsoil's and multi targeted risks analysis were assessed. Results showed, the mean values of Pb and Zn were higher in crop than Food and Agriculture Organization guidelines for food additives and contaminants. A strong positive correlation was found among wastewater and crop's toxic metals (r2 values in Cu, Zn, Pb, Ni and Cr were 0.913, 0.804, 0.752, 0.694, 0.587 respectively). Whereas, a strong correlation was also found among soil and wastewater lead (r2 = 0.639). The calculations of Nemerow Integrated Pollution Index (NIPI) showed the soil samples maximum pollution limit (NIPI > 3) and Potential Ecological Risk Index (PERI) was found to be higher than maximum limit (PERI > 600) for all samples. While, for non-carcinogenic risk, Hazard Index (HI) values in adult were near threshold (HI > 1) for all crop samples. In children, the HI values for Corn, Rice and Wheat were above threshold limit and for Sugarcane and Millet, these were near to threshold. Cancer risk values for Cr found higher than safe limit (1 × 10-6) in adult and children for crop samples. Crop irrigation by wastewater irrigation is a prominent alternative option for water scarce countries, however prior testing and treatment of such wastewater streams must be employed to minimize the adverse impacts on human health and environment.

Pollution characteristics and ecological risk assessment of heavy metals in paddy fields of Fujian province, China

To analyze the concentration, spatial distribution patterns, and ecological risks of heavy metals (Cd, Cr, Pb, As, Cu, Ni and Co), 272 topsoil samples (0–20 cm) were collected from paddy fields in Fujian province in July 2017. The results revealed that the mean concentration of all heavy metals exceeded the background values in Fujian province, with the mean concentration of Cd being 5.20 times higher than its background. However, these concentrations of heavy metals were lower than their corresponding national standards (GB 15618-1995). Spatially, for Cd, the high concentration areas were located mainly in southeast of Sanming city and northeast of Quanzhou city. For Pb and As, the places of highest concentration were mainly in southeast of Quanzhou city and Zhangzhou city, and the main areas of high Ni concentration were distributed southeast of Nanping city. The geo-accumulation index (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${I}_{geo}$$\end{document}Igeo) of Cd and As were indicative of moderate contaminations, and the index of Co, Cu and Cr suggested that these were practically uncontaminated. The nemerow integrated pollution index (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${P}_{n}$$\end{document}Pn) showed that the entire study area was prone to a low level of pollution, but at the county level, Yongcun county and Zhaoan county are in an warning line area of pollution. According to the potential ecological risk (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$RI$$\end{document}RI), the ecological risk belongs to the low risk of paddy fields in Fujian province. However, Cd should be given attention (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${E}_{r}$$\end{document}Er = 25.09), as it contributed to the majority of potential ecological risks in Fujian province.

Application Research of Biochar for the Remediation of Soil Heavy Metals Contamination: A Review

Soil contamination by heavy metals threatens the quality of agricultural products and human health, so it is necessary to choose certain economic and effective remediation techniques to control the continuous deterioration of land quality. This paper is intended to present an overview on the application of biochar as an addition to the remediation of heavy-metal-contaminated soil, in terms of its preparation technologies and performance characteristics, remediation mechanisms and effects, and impacts on heavy metal bioavailability. Biochar is a carbon-neutral or carbon-negative product produced by the thermochemical transformation of plant- and animal-based biomass. Biochar shows numerous advantages in increasing soil pH value and organic carbon content, improving soil water-holding capacity, reducing the available fraction of heavy metals, increasing agricultural crop yield and inhibiting the uptake and accumulation of heavy metals. Different conditions, such as biomass type, pyrolysis temperature, heating rate and residence time are the pivotal factors governing the performance characteristics of biochar. Affected by the pH value and dissolved organic carbon and ash content of biochar, the interaction mechanisms between biochar and heavy metals mainly includes complexation, reduction, cation exchange, electrostatic attraction and precipitation. Finally, the potential risks of in-situ remediation strategy of biochar are expounded upon, which provides the directions for future research to ensure the safe production and sustainable utilization of biochar.

Bioimmobilization of toxic metals by precipitation of carbonates using Sporosarcina luteola: An in vitro study and application to sulfide-bearing tailings

Metal release from mining wastes is a major environmental problem affecting ecosystems that requires effective, low-cost strategies for prevention and reclamation. The capacity of two strains (UB3 and UB5) of Sporosarcina luteola was investigated to induce the sequestration of metals by precipitation of carbonates in vitro and under microcosm conditions. These strains carry the ureC gene and have high urease activity. Also, they are highly resistant to metals and have the capacity for producing metallophores and arsenophores. SEM, EDX and XRD reveal that the two strains induced precipitation of calcite, vaterite and magnesian calcite as well as several (M²⁺)CO₃ such as hydromagnesite (Mg²⁺), rhodochrosite (Mn²⁺), cerussite (Pb²⁺), otavite (Cd²⁺), strontianite (Sr²⁺), witherite (Ba²⁺) and hydrozincite (Zn²⁺) in vitro. Inoculation of the mixed culture of UB3+UB5 in tailings increased the pH and induced the precipitation of vaterite, calcite and smithsonite enhancing biocementation and reducing pore size and permeability slowing down the oxidation of residual sulfides. Results further demonstrated that the strains of S. luteola immobilize bioavailable toxic elements through the precipitation and coprecipitation of thermodynamically stable (M²⁺)CO₃, Fe-Mn oxyhydroxides and organic chelates.

Bioelectrochemical remediation of Cr(VI)/Cd(II)-contaminated soil in bipolar membrane microbial fuel cells

Heavy-metal contaminated soils post great environmental and health concerns. In this study, Cr and Cd which are frequently observed in contaminated soils, were selected as representatives of hazardous heavy metals because of their different redox potentials and electric charges. Cr(VI)-, Cd(II)-, Cr(VI)/Cd(II)-contaminated soils were remediated in two-chamber air-cathode MFCs, in order to investigate the remediation of soil contaminated by single heavy metal and mixed heavy metals. Four ion exchange membranes (IEMs) were first evaluated to find out that bipolar membrane (BPM) was able to well maintain pH in both anolyte and catholyte, which was beneficial to support biological metabolism and heavy metal removal. It was also found that heavy metal ions (Cr, Cd or Cr/Cd) could migrate toward the cathode forming a concentration gradient under the weak electric field. The interaction between negatively charged Cr and positively charged Cd had no major effect to hinder each other on the migration, suggesting that the reduction reaction and electric field should be the main motivation for metal ion migration. The remediation performance of mixed heavy metal contaminated soil was superior to that of single heavy metal contaminated soil, for the possible reason of smaller internal resistance under mixed heavy metal condition.

Ecological drivers of methanotrophic communities in paddy soils around mercury mining areas

Methanotrophs play a crucial role in mitigating methane (CH₄) emission by oxidizing produced CH₄ in paddy soils; however, ecological drivers of methanotrophic community in the soils around heavy metal contaminated areas remain unclear. In this study, we evaluated the effects of heavy metal pollution and soil properties on the abundance, diversity and composition of methanotrophic community in paddy soils from two typical mercury (Hg) mining regions in southwest China. The results of random forest and structure equation models suggest that both heavy metal content and soil nutrients greatly influenced the attributes of methanotrophic community. In general, the abundance and diversity of methanotrophs were negatively related to soil Hg content, but showed positive correlation with soil organic carbon content. However, the other metals (cadmium (Cd), nickel (Ni), lead (Pb), arsenic (As), zinc (Zn)) had inconsistent associations with the microbial indexes of methanotrophic community in the soil. Elevated levels of heavy metal and nutrients in the soils shifted the community composition of methanotrophs. For example, Pb, As and Zn contents had negative associations with the relative abundance of Methylocaldum. In addition, changes in the relative abundance of ecological clusters within the co-occurrence network of methanotrophs were related to metal contents and soil properties. Together, our findings provide novel insights into understanding ecological drivers of methanotrophic community in paddy soils around Hg mining regions, with important implications for mitigating CH₄ emissions in terrestrial ecosystems.

Statistical analyses on effective removal of cadmium and hexavalent chromium ions by multiwall carbon nanotubes (MWCNTs)

In this work, multiwall carbon nanotubes (MWCNTs) developed from cobalt-ferrite catalyst on activated carbon (from castor seed), was used as an adsorbent for the removal of cadmium and hexavalent chromium ions. The effectiveness of the adsorbent for the uptake of Cd(II) and Cr(VI)ions from aqueous solution was investigated in a process batch adsorption study. The developed activated carbon and MWCNTs were characterized by Brunauer-Emmett-Teller (BET) surface area analysis, Fourier Infrared Spectroscopy (FT-IR) and Scanning Electron Microscopy (SEM) for the determination of surface area, functional group, and surface morphology, respectively. The BET surface area of activated carbon and developed adsorbent from Co–Fe/AC was 230.24 and 372.42 m²/g, respectively. The operational parameters evaluated on the adsorption efficiency were solution pH, temperature, adsorbent dosage initial metal ions concentration, and contact time. The adsorption of Cd(II) and Cr(VI) were found to have attained equilibrium positions in 60 min for the concentration range tested, respectively. The four linearized adsorption isotherm models; Langmuir, Freundlich, Temkin and Dubinin Radushkevich (D-R) tested, when compared, revealed that Langmuir isotherm fitted well to the experimental data judging from the higher correlation coefficient values (R²) and lower values of the error functions (chi-square (χ²), the sum of square error (ERRSQ/SSE) and the sum of absolute error (EABS))with monolayer adsorption capacities of 404.858 and 243.902 mg/g for Cd(II) and Cr(VI) ions, respectively. Adsorption kinetic models investigated by pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion showed the conformity of pseudo-second-order model to the process adsorption as informed by the higher values R² and Adj, R², maximum log-likelihood and smaller ERRSQ/SSE, χ², Akaike information criterion (AIC), Bayesian information criterion (BIC), and Hannan-Quinn information criterion (HQIC). The intraparticle diffusion model plots indicated that intraparticle diffusion was not the only rate-limiting step. Thermodynamic adsorption parameters (ΔH^o and ΔG^o, ΔS^o) showed that the adsorption of Cd (II) and Cr (VI) ions was spontaneous, endothermic, and increased in randomness between the adsorbate-adsorbent. The mean adsorption energy (E), the heat of adsorption (ΔH^o), and activation energy (E_a) values, revealed the adsorption mechanism of Cd(II) and Cr(VI) onto MWCNTs as a combination of chemical and physical adsorption but dominated more by chemical adsorption.