High Background Areas Research Articles

An Exposure to Natural Background Radiation in Eastern Nepal

Monitoring natural background radiation is important to locate the high background area. The objective of the work is to find the average background radiation in the Morang district and to observe the effects of cosmic radiation at high altitudes. In this study, background radiation was measured in 17 different municipalities of Morang with the help of a GM counter of model GMC-300E plus. The result showed that the annual effective dose of Morang was 0.24±0.02mSv/y and was below the recommended value of 1 mSv/y set by ICRP for public health. The radiation level was slightly higher in the hospital area. The frequency distribution indicates that there is a good fit of observed data with a known Gaussian distribution. The variation of background radiation with an altitude from 381 to 2550m showed an increasing trend. The best-fitted line depicted that background radiation increased by 16% with 1000m in altitude and it was slightly higher than the literature’s result of 10-12%. The comparative study of the present work showed that the effective dose was the least value in the Morang (0.24mSv/y) and the highest in the Pokhara Valley (0.81mSv/yr).

Co-exposure of heavy metals in rice and corn reveals a probabilistic health risk in Guizhou Province, China

The adverse effects of heavy metals have arousing concern in the high geological background area, especially in southwestern Guizhou, China. However, the pollution status of heavy metals are still unclear when exposed to rice and corn in Guizhou province. Therefore, the concentration, pollution level, spatial distribution, and probabilistic health risks of Ni, Cr, Pb, Cu, and Zn are estimated in rice and corn. A total of 241 samples (117 for rice and 124 for corn) were collected from Guizhou province and measured by a method of inductively coupled plasma-mass spectrometry (ICP-MS). The results showed that rice and corn were contaminated with Ni and Cr. High concentrations of Ni were presented in the southeast of rice. It indicated that 22.0 % of rice samples were contaminated with Ni. HI values for children and adults exceeded 1.0 in rice and corn, suggesting that humans might be subject to probabilistic non-carcinogenic risks. FTCR demonstrated that rice and corn might cause probabilistic carcinogenic risks to children and adults, which were both greatly higher than 1.0 × 10−4. Moreover, the contributions of Ni to the HI and FTCR were the highest for adults and children. Therefore, more attention should be paid to the exposure of heavy metals in rice and corn, especially in Ni. The results would provide a novel prospective for pollution control and be helpful for environmental regulation.

Spatial-temporal variation, source apportionment and risk assessment of lead in surface river sediments over ∼20 years of rapid industrialisation in the Pearl River Basin, China

Lead (Pb) is a highly toxic element and is not essential to the human body. Lead pollution caused by human activities and a high geological background is considered a global environmental issue. According to the China Geochemical Baseline (CGB) project, the Pearl River Basin had the highest Pb content in alluvial sediments of 30 first-level basins in China. For this reason, it is of great significance to determine the temporal and spatial variations in Pb and their influencing factors in the Pearl River Basin. In this study, 956 stream sediment samples collected in the 1980 s (early stage) and 129 river sediment samples collected from 2008 to 2010 (late stage) were used to study the background value and spatial-temporal variation characteristics of Pb in river sediments in the Pearl River Basin. The Pb source apportionment and an ecological risk assessment were also carried out. The background value of Pb (36.2 mg·kg–1) in the river sediments of the Pearl River Basin was significantly higher than that in China (22.1 mg·kg–1). The parent rocks determine the Pb background in sediments and the high Pb background areas mainly comprised carbonate rocks and acid volcanic rocks. Over 20 years of rapid industrialisation, the average Pb increased from 43.3 to 68.3 mg·kg–1 in the Pearl River Basin. The BCR analysis revealed that Pb mainly existed in the reducible phase (48 % on average) and residue phase (42 % on average). The enrichment factor and geo-accumulation index indicated that the late-stage sediments experienced more Pb pollution than the early-stage sediments. However, the risk assessment code (RAC) showed that there was a low ecological risk of Pb in the late-stage sediments. The factor analysis results for the two rounds of data were significantly different. The Pb content in early-stage sediments was closely related to Al2O3 and Zr, while Pb in the late-stage sediments was mainly related to Zn, As, Sb, Au and Hg, indicating that the increase in Pb in the later samples was mainly influenced by human activities. The Pb isotope composition of the late-stage sediments confirmed that low Pb content was mainly controlled by natural sources, while high Pb content was significantly affected by anthropogenic sources. Combining the results of spatial-temporal variation, chemical speciation and source apportionment indicated that the rapid rise of Pb in late-stage sediments in certain areas could be attributed to mining and smelting activities during the process of industrialisation over 20 years. The anthropogenic exogenous Pb could be immobilised by Fe-Mn (hydro)oxides when it entered the soil, so although there was a high background the ecological risk of Pb in river sediments was low. In the future, Pb pollution control and remediation needs to be strengthened in the Pearl River Basin to avoid the outbreak of potential ecological risks linked to Pb.

Transfer of heavy metals from soil to tea and the potential human health risk in a regional high geochemical background area in southwest China

Tea is one of the most consumed nonalcoholic beverages. The collaborative analysis of heavy metals soil-to-tea transfer and the associated potential risk to human health is important. This study features a survey of As, Cd, Pb and Cr in 144 paired soils and tea leaves from six main tea-growing regions (Fengqing, Linxiang, Yongde, Mangshi, Longling, and Yunlong) in Yunnan, China. The data showed soil acidification (pH = 4.77–5.17) in tea plantations, affecting heavy metals bioavailability thereby the transfer to tea leaves. Soil total and bioavailable As, Cd, Pb and Cr concentrations were 1.45–117, 0.025–0.67, 15.2–153, 3.8–409 mg kg−1 and 0.03–0.22, 0.011–0.38, 0.59–17, 0.013–0.47 mg kg−1, respectively. Specifically, As concentration in 20.8 % of the soil samples exceeded the standard value at 40 mg kg−1, while the standard-exceeding ratio of Cr was low at 9 %. Besides, Cd showed high bioavailability at 44–56.1 %, while Cr was low at 0.12–0.34 %. Arsenic, Cd, and Pb in tea leaves were within the standard values at 2, 1 and 5 mg kg−1. However, though soil Cr was low in standard-exceeding ratio and bioavailability, Cr accumulation in tea showed high standard-exceeding ratio (72.2 %). This indicated that soil heavy metals concentration and bioavailability are not necessarily to predict the pollution risk in tea leaves. Besides, tea favors to accumulate Cd, with 16 % showing BAF > 1. Though Cr in tea leaves was highly standard-exceeded and Cd was uptake-preferred, the target hazard quotients (THQ; <1) and aggregate risk hazard indexes (HI; 0.046) suggested that there was no potential risks to human health. This indicated that high pollution risk in tea leaves is not necessarily to induce risk to human health. The information helps to better understand the efficiency and influencing factors for heavy metals soil-to-tea leaves transfer and strategize how to more accurate evaluate the risks in soil pollution, food safety and human health.

Bioavailability, Sources, and Transfer Behavior of Heavy Metals in Soil–Crop Systems from a High Geological Background Area Impacted by Artisanal Zn Smelting in Guizhou Province, Southwest China

The environmental risk posed by heavy metals in agricultural soil is primarily influenced by their sources, bioavailability, and geochemical transfer behavior. This study focused on Weining County, a region in Guizhou province, Southwest China, with a high geological background and long-term impact from artisanal Zn smelting. Vertical soil profiles, crop, and rhizospheric soil samples were collected and analyzed for heavy metal concentration (As, Cd, Co, Cr, Cu, Hg, Ni, Pb, V, and Zn) including the total concentration and chemical fraction. The results revealed elevated concentrations of Cd (range: 0.7–6.9 mg·kg−1), Co (range: 19.3–120.0 mg·kg−1), Cu (range: 71.6–386.0 mg·kg−1), Ni (range: 51.0–121.0 mg·kg−1), and V (range: 310.0–721.0 mg·kg−1) in all soil samples compared to the background values of Guizhou Province. Chemical fractionation analysis indicated that Cr, Ni, As, Cu, and Zn were predominantly present in the residual fraction, while Hg and Pb were predominantly found in the potentially bioavailable fraction. Cd exhibited the highest bioavailability, accounting for 58.5% of its total concentration. Enrichment factor analysis suggested that artisanal Zn smelting activities were the main sources of Cd, Pb, and Zn contamination. Furthermore, Cd, Pb, and Zn were found to be highly accumulated in the surface soil layer (0–20 cm). Notably, 90.0% of potato and 9.4% of maize grain samples exceeded the food hygiene standards for Cd concentration, posing potential health risks to consumers. The bioconcentration factor (soil-to-root) and translocation factor (root-to-grain) analyses indicated that maize roots had a higher tendency to accumulate Cd from the soil, while Zn and Cu showed a significant transferability from roots to maize grains. These findings offer valuable insights for devising heavy metal remediation strategies in similar areas.

Accumulation Pathway of Cd, Pb, and Zn in Chinese Cabbage under the Condition of Exogenous Pollution Superposition in High Geological Background Area

Northwest Guizhou is a karst area with a high geological background. Affected by historical soil zinc smelting, the heavy metal content of atmospheric dust in the region is high, and soil pollution is severe. In order to explore the accumulation pathway of heavy metals in leafy vegetables, Chinese cabbage was used as the test crop, and the geological high background soil and zinc smelting-contaminated soil with the same contents of Cd, Pb, and Zn were selected. A pot experiment was carried out in the polluted area of zinc smelting and the non-polluting control area. The heavy metal content, enrichment coefficient (BCF), and transport coefficient (TF) of Chinese cabbage were studied under open-air, plastic mulching film, and greenhouse cultivation conditions. The results showed that the contents of Cd, Pb, and Zn in Chinese cabbage in the polluted area and the control area were 0.10-1.01 and 0.10-0.91 mg·kg-1, 0.31-0.62 and 0.23-0.37 mg·kg-1, and 7.50-32.74 and 4.88-21.79 mg·kg-1, respectively. Overall, the contents of heavy metals in the polluted area were relatively high. The contents of Cd and Pb in Chinese cabbage planted in soil with a high geological background met the requirements of the national food safety standard limits. Affected by atmospheric deposition, the contents of Pb and Zn in Chinese cabbage in the polluted area were significantly higher than that in the control area, and the difference in Cd was insignificant. The proportions of weak acid-soluble Cd, Pb, and Zn in the contaminated soil were 48%, 3.0%, and 16%, respectively, which were 3.15, 1.01, and 1.57 times higher than those in the control soil with a high geological background. Affected by the activity of heavy metals, the contents of Cd and Zn in Chinese cabbage planted in the contaminated soil exceeded the national standard and were significantly higher than those in the control soil. The root-soil BCF of Cd, Pb, and Zn in polluted soil was significantly higher than that in the control soil, and the BCF of Cd and Zn was higher than that of Pb. The TF aboveground root Cd and Zn in Chinese cabbage was significantly higher than in the control soil, whereas the TF aboveground root Pb in the polluted area was significantly higher than that in the control area. The Pb content of Chinese cabbage in the two study areas showed open field>plastic mulching film>greenhouse cultivation. In conclusion, the content of Cd and Zn in Chinese cabbage was greatly affected by the activity of heavy metals in soil, and the main accumulation pathway was root absorption and transportation. In addition to root absorption, atmospheric deposition was an important accumulation pathway of Pb. Therefore, in areas with high geological backgrounds, attention should be paid to controlling the exposure risk of Cd and Zn in leafy vegetables planted on exogenously polluted soils. Additionally, greenhouse cultivation could effectively reduce the accumulation of Pb.

Heavy Metal Regularity of Carboniferous Weathered Black Shale in Qiziqiao Area, Central Hunan

The Hunan region is a high geological background area of black rock series rich in various metallic elements; accordingly, local heavy metal pollution is severe. Previous studies on black shale have primarily focused on the lower Cambrian strata, while research on Carboniferous black shale remains scarce. To better explore the activity law of heavy metals during Carboniferous black shale weathering, this study analyzed the elemental components of samples through field observations of outcrops in the Qiziqiao area of central Hunan province, China using inductively coupled plasma mass spectrometry and X-ray fluorescence spectrometry. The results showed that the heavy metal content of black shale under different degrees of weathering varied greatly, with different heavy metals maintaining distinct migration and enrichment rules throughout this process. The heavy metal content in Carboniferous black shale and soils of central Hunan was generally less than that of the regional lower Cambrian black shale and soil; however, the Cd content in the black shale soil was slightly higher than background values, while the Sr content was substantially higher than background values. Heavy metals V, Cr, Co, Ni, Cu, and Pb were not generally leached or released during weathering, and may undergo relative enrichment or secondary enrichment. Comparatively, Zn, Cd, and Ba can be more readily leached and released, and may undergo secondary enrichment. The lithophilic element Sr tended to leach out overall and expressed strong activity, whereas the chemical activities of the high-field-strength elements, Zr and Hf, were relatively stable. During soil formation, all heavy metal elements save Sr were significantly enriched. The enrichment factor analysis of different degrees of weathered black shale reveals that the heavy metals Ba, Hf, and Sr in black shale soil originate from the parent rock. V, Cr, Co, Ni, Cu, Zn, Cd, and Pb are influenced by both natural and anthropogenic factors, with Cd being significantly impacted by human activities. The evaluation of soil heavy metals using the geoaccumulation index method indicates that V, Cr, Co, Ni, Cu, Zn, Zr, Ba, Hf, and Pb are non-polluted, Cd exhibits moderate pollution, and Sr shows moderately heavy pollution. From a geochemical perspective, it can be inferred that heavy metals in black shale soil are likely to be secondarily enriched in clay and iron oxide minerals.

Comprehensive Quality Assessment of Soil-Maize Heavy Metals in High Geological Background Area

The aim of this study was to analyze the pollution degree and causes of soil and agricultural products in high geological background areas and to provide a basis for the safe production of agricultural products and the risk control of soil heavy metals. A total of 36 sets of soil-corn collaborative samples were collected in the farming area of Baolong Town, Wushan County, Chongqing City; the contents of heavy metals (Cd, Hg, Pb, As, and Cr) and soil pH in the soil-maize were analyzed, the pollution degree of heavy metals in the soil-maize was evaluated using the Nemerow comprehensive pollution index method (PN) and comprehensive quality impact index (IICQ). The sources of heavy metals in the soil and the influencing factors of heavy metal excess in corn were also analyzed. The results showed that the average value of soil heavy metal content in the study area was higher than the national and Chongqing soil background values, and the soil heavy metal enrichment effect was obvious. Cd was the main factor of soil-maize exceeding the standard, and the overall exceeding rates of soil and corn Cd were 91.67% and 30.55%, respectively. The evaluation results of the Nemerow comprehensive pollution index showed that the soil was dominated by heavy pollution, accounting for 63.89%. The soil-maize comprehensive quality impact index was dominated by moderate and severe pollution, accounting for 44.44% and 47.22%, respectively. From the perspective of the spatial distribution of heavy metal pollution, corn and soil pollution areas were inconsistent. Soil heavy metal pollution was mainly affected by the Permian and Triassic strata and was related to the secondary enrichment of black rock series and limestone areas. The Cd content of maize was mainly affected by soil pH, and maize was relatively safe under alkaline conditions. It is suggested that the soil in the study area should be divided into risk zones according to the stratum distribution, and the planting structure should be adjusted in the high-risk areas. For the low- and medium-risk areas, it is recommended to strengthen the monitoring of agricultural inputs and reduce the input of heavy metals in the soil. Additionally, we recommend carrying out agronomic regulation in acidic soil areas to improve soil acidification, plant corn varieties with low accumulation of heavy metals, and reduce the risk of agricultural products exceeding the standard.

Source Analysis and Pollution Assessment of Soil Heavy Metals in Typical Geological High Background Area in Southeastern Chongqing

In order to understand the pollution characteristics of soil heavy metals in typical geological high background areas in southeastern Chongqing, analyze its pollution sources, and put forward risk management and control suggestions, 211 topsoil samples (0-20 cm) were collected in Xinglong Town and Muye Township in the north of Youyang County, Chongqing City, and the contents of eight heavy metals (As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) and the soil pH value in the surface soil were analyzed. Additionally, mathematical statistics, pollution load index (P), potential ecological risk index (RI), correlation analysis, and the positive matrix factorization (PMF) model were used to study the content and spatial distribution characteristics of heavy metals in the topsoil, and pollution assessment and source analysis of heavy metals were carried out. The results showed that the average concentrations of heavy metals in the surface soil all exceeded the soil background value in Chongqing, showing different levels of enrichment. Among them, the proportion of Cd exceeding the screening value in the "soil environmental quality risk control standard for soil contamination of agricultural land" (GB 15618-2018) was as high as 83.41%, the proportion of exceeding the control value was 7.58%, and the potential risk was relatively high. The evaluation results of the pollution load index method showed that the study area was slightly polluted as a whole, and the evaluation results of the potential ecological risk index showed that the overall ecological risk of the study area was relatively high. Among them, the contribution rates of heavy metals Hg, Cd, and As were 50.27%, 28.63%, and 11.70%, respectively. The PMF results showed that there were three main sources of heavy metals in the soil in the study area:natural parent material sources, agricultural sources, and mixed sources of industrial activities and traffic emissions, accounting for 40.49%, 29.12%, and 30.39%, respectively. The quantitative source analysis results of soil heavy metals in the study area have important reference significance for soil heavy metal pollution control in geologically high background areas.

Refining health risk assessment of arsenic in wild edible boletus from typical high geochemical background areas: The role of As species, bioavailability, and enterotoxicity

Arsenic (As) is easily accumulated in wild Boletus. However, the accurate health risks and adverse effects of As on humans were largely unknown. In this study, we analyzed the total concentration, bioavailability, and speciation of As in dried wild boletus from some typical high geochemical background areas using an in vitro digestion/Caco-2 model. The health risk assessment, enterotoxicity, and risk prevention strategy after consumption of As-contaminated wild Boletus were further investigated. The results showed that the average concentration of As was 3.41–95.87 mg/kg dw, being 1.29–56.3 folds of the Chinese food safety standard limit. DMA and MMA were the dominant chemical forms in raw and cooked boletus, while their total (3.76–281 mg/kg) and bioaccessible (0.69–153 mg/kg) concentrations decreased to 0.05–9.27 mg/kg and 0.01–2.38 mg/kg after cooking. The EDI value of total As was higher than the WHO/FAO limit value, while the bioaccessible or bioavailable EDI suggested no health risks. However, the intestinal extracts of raw wild boletus triggered cytotoxicity, inflammation, cell apoptosis, and DNA damage in Caco-2 cells, indicating existing health risk assessment models based on total, bioaccessible, or bioavailable As may be not accurate enough. Given that, the bioavailability, species, and cytotoxicity should be systematically considered in accurate risk assessment. In addition, cooking mitigated the enterotoxicity along with decreasing the total and bioavailable DMA and MMA in wild boletus, suggesting that cooking could be a simple and effective way to decrease the health risks of consumption of As-contaminated wild boletus.

Accurate derivation and modelling of criteria of soil extractable and total cadmium for safe wheat production

It is significant to establish an accurate model to predict cadmium (Cd) criteria for safe wheat production. More importantly, for better evaluation of the risk of Cd pollution in high natural background areas, the soil extractable Cd criteria are needed. In the present study, the soil total Cd criteria were derived using the method of cultivars sensitivity distribution integrated with soil aging and bioavailability as affected by soil properties. Firstly, the dataset that meet the requirements was established. Dataset from thirty-five wheat cultivars planted in different soils published in literature of five bibliographic databases were screened using designated search strings. Then, the empirical soil-plant transfer model was used to normalize the bioaccumulation data. Afterwards, the soil Cd concentration for protecting 95 % (HC5) of the species was calculated from species sensitivity distribution curves, and the derived soil criteria were obtained from HC5 prediction models that based on pH. The process of derivation for soil EDTA-extractable Cd criteria was the same way as the soil total Cd criteria. Soil total Cd criteria ranged from 0.25 to 0.60 mg/kg and soil EDTA-extractable Cd criteria ranged from 0.12 to 0.30 mg/kg. Both the criteria of soil total Cd and soil EDTA-extractable Cd were further validated to be reliable using data from field experiments. The results suggested that the criteria of soil total Cd and soil EDTA-extractable Cd in the study can ensure the safety of Cd in wheat grains and thereby enable local agricultural practitioners to develop appropriate management for croplands.

Mercury and selenium co-ingestion assessment via rice consumption using an in-vitro method: Bioaccessibility and interactions

Mercury (Hg) was reported to accumulate in rice grains, and, together with the selenium (Se) was found in rice, the co-exposure of Hg-Se via rice consumption may present significant health effects to human. This research collected rice samples containing high Hg:high Se and high Se:low Hg concentrations from high Hg and high Se background areas. The physiologically based extraction test (PBET) in vitro digestion model was utilized to obtain bioaccessibility data from samples. The results showed relatively low bioaccessible for Hg (<60%) and Se (<25%) in both rice sample groups, and no statistically significant antagonism was identified. However, the correlations of Hg and Se bioaccessibility showed an inverse pattern for the two sample groups. A negative correlation was detected in the high Se background rice group and a positive correlation in the high Hg background group, suggesting various micro forms of Hg and Se in rice from different planting locations. In addition, when the benefit-risk value (BRV) was calculated, some “fake” positive results showed while Hg and Se concentrations were directly used, which indicated that bioaccessibility should not be neglected in benefit-risk assessment.

Source Analysis and Ecological Risk Assessment of Heavy Metals in the Arable Soil at the Geological High Background, Based on the Township Scale

Due to the extensive development of carbonate rocks in southwest China, heavy metals are naturally occurring elements that have high natural background levels in the environment. Therefore, it is important to conduct ecological risk assessments and identify potential sources of heavy metals in the geological high background area. Based on the township scale, a total of 307 surface soil samples were collected in Qinglong Town, Fengjie County, Chongqing. The concentrations of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn and pH were analyzed and determined. The spatial distribution and source of soil heavy metals were discussed using the geostatistical analysis and an absolute principal component score-multiple linear regression (APCS-MLR) model in the studied area. The results showed that the average values of seven heavy metals (As, Cd, Cr, Cu, Hg, Ni, and Zn) in the arable soil exceeded the background values of Chongqing, and the cumulative effect of Cd and As was obvious. The concentrations of Cd significantly exceededthe screening values in The Risk Control Standard for Soil Environmental Quality and Soil Pollution in Agricultural Land (GB 15618-2018), with the over-standard rates of 52.12%. The spatial characteristics of soil heavy metal contents exhibited a pattern of high in the south and low in the north. PCA and APCS-MLR modeling revealed that the contributions of natural sources to Cr, Cu, Ni, and Zn were 86.62%, 64.34%, 76.44%, and 85.46%, respectively. As, Pb, and Hg mainly derived from industrial activities, which accounted for 74.63%, 61.90%, and 73.49%, respectively, and Cd was affected by both natural sources and industrial activities (accounting for 47.74% and 39.56% of the total Cd content, respectively). The evaluation of the soil by the Nemerow comprehensive index (P) showed that Cd pollution was relatively serious, accounting for 27.04% of soil pollution. The potential ecological hazard index showed that Cd and Hg were the main ecological hazard elements, and the distribution range of RI was 51.77 to 2228, indicating mainly mild and moderate risks, and the moderate and above risk areas in the study area were mainly located around the southern industrial source area. Altogether, our results revealed that in the study area, the heavy metal pollution was mainly caused by industrial activities, and the heavy metal pollution caused by geological background was mainly light to moderate. In conclusion, the medium and above risk areas in the study area were mainly caused by mineral and industrial activities, whereas the heavy metal pollution caused by geological background was mainly light to moderate pollution.

Evaluation and Source Identification of Heavy Metal Pollution in Black Soils, Central-Eastern Changchun, China

Black soils are vital agricultural resources, and assessing heavy metal contamination in black soils is of great significance to the sustainable development of agriculture and the environment. In this study, 1246 surface soil samples were collected from the central-eastern part of Changchun, where phaeozems and chernozems are widely distributed, and the As, Hg, Cr, Cd, and Pb concentrations were determined to investigate the pollution status in the black soils by the geoaccumulation index (Igeo). To eliminate the influence of background variation and improve the calculation accuracy of the Igeo values, the local background values of these five elements were estimated after classifying the samples into three clusters with the k-means clustering method. The Igeo calculated with the local background values not only identified the pollution that is difficult to recognize in the low-background areas but also eliminated the easily misidentified pollution in the high-background areas. The Igeo results show that the black soils are mainly contaminated with Hg, followed by Cd and Pb, and are almost free from the pollution of As and Cr. The further the sampling sites are from urban areas, the milder the soil pollution is. A positive matrix factorization (PMF) analysis shows that industrial activities and coal burning contributed the most to the heavy metal pollution in the black soils, followed by agricultural activities, which should be paid more attention to.

Contamination levels of and potential risks from metal(loid)s in soil-crop systems in high geological background areas

Soil metal(loid)s in high geological background areas occur mainly in the residual form with low bioavailability, and whether these potentially toxic elements (PTEs) in agricultural soils are harmful to human health is of considerable public concern. A paired survey using both soil and crop samples was conducted using 437 contaminated sites in east Yunnan province, southwest China. The concentration, distribution, and source of PTEs (arsenic (As), copper (Cu), zinc (Zn), lead (Pb), cadmium (Cd), and chromium (Cr)) in agricultural soils, and the contamination levels of and potential health risks from PTEs from different pollution sources were evaluated. Soil Pb, Cu, Zn, Cd, Cr, and As concentrations were higher than the Chinese screening values (GB 15618-2018) of 10.98, 36.16, 24.71, 86.96, 14.19, and 6.64 %, respectively, and Cd greatly exceeded the screening values. Spatial distribution maps indicate that areas with high concentrations of Pb, Cu, Cd, and As were located mainly in mining areas. However, the Zn and Cr concentrations were relatively homogeneous and more dependent on natural processes. The source identification of PTEs shows that Zn and Cr in soils were controlled mainly by the geological background, Pb and As were closely related to anthropogenic activities, and Cu and Cd were related to both sources. Different pollution sources affected crop PTE contents, with average concentrations of Zn, Cd, Cr, and As in high geological background areas significantly lower than in anthropogenic activity areas (p < 0.001), while Cu and As did not differ significantly. Although soil PTEs in high geological background areas represent a relatively high potential risk, they had little impact on crop quality. The hazard indices of different crop products for adults and children followed the sequence: cereals > leafy vegetables > rootstalk vegetables > fruit vegetables. Rootstalk and fruit vegetables are recommended to be grown in the study areas because they are safe for human consumption.

Identification of soil parent materials in naturally high background areas based on machine learning

Recently, farmlands with high geological background of Cd derived from carbonate rock (CA) and black shale areas (BA) have received wide attention. However, although both CA and BA belong to high geological background areas, the mobility of soil Cd differs significantly between them. In addition to the difficulty in reaching the parent material in deep soil, it is challenging to perform land use planning in high geological background areas. This study attempts to determine the key soil geochemical parameters related to the spatial patterns of lithology and the main factors influencing the geochemical behavior of soil Cd, and ultimately uses them and machine-learning methods to identify CA and BA. In total, 10,814 and 4323 surface soil samples were collected from CA and BA, respectively. Hot spot analysis revealed that soil properties and soil Cd were significantly correlated with the underlying bedrock, except for TOC and S. Further research confirmed that the concentration and mobility of Cd in high geological background areas were mainly affected by pH and Mn. The soil parent materials were then predicted using artificial neural network (ANN), random forest (RF) and support vector machine (SVM) models. The ANN and RF models showed higher Kappa coefficients and overall accuracies than those of the SVM model, suggesting that ANNs and RF have the potential to predict soil parent materials from soil data, which might help in ensuring safe land use and coordinating activities in high geological background areas.

Availability of Se-rich Arable Land in High Geological Background Area and Suggestions for Zoning

In order to promote the results of land quality geochemical surveys to serve the development of characteristic land resources and realize the safe utilization of Se-rich resources in high geological background areas, Wuli Town, Qianjiang District, Chongqing City were taken as the research object to evaluate the Se-rich level and heavy metal content of soil crops and carry out research on Se-rich cultivated area division and the availability method system in the high geological background area, in order to improve the utilization efficiency of Se-rich resources and provide ideas for the safe utilization of Se-rich resources in high geological background areas. The results showed that the soil and crops in the study area were rich in Se and had the potential to develop Se-rich resources, but some samples had the problem of excessive Cd. Soil pH was a key factor affecting the content of Se and Cd in crops, and alkaline conditions were conducive to the safe utilization of Se-rich resources. The areas of Class A-E (A:selenium-enriched arable land, B:crops that were not selenium-enriched but were safe, C:crops that were selenium-enriched but unsafe, D:crops that were not selenium-enriched and unsafe, and E:soil selenium content less than the selenium-enriched threshold and soil heavy metals not exceeding the standard)cultivated land were 0.72, 0.75, 0.28, 0.13, and 0.56 km2, respectively. It is recommended to develop safe and Se-rich resources in the distribution area of Class A cultivated land and to carry out soil acidification conditioning and low-accumulation crops in the distribution area of Class C and D cultivated land; other agronomic measures should be taken to reduce the risk of excessive heavy metals in crops and strengthen the protection of cultivated land in the region to prevent the input of new pollutants.

Derivation and validation of soil cadmium thresholds for the safe farmland production of vegetables in high geological background area

Excessive dietary intake of cadmium (Cd) poses toxicity risks to human health, and it is therefore essential to establish accurate and regionally appropriate soil Cd thresholds that ensure the safety of agricultural products grown in different areas. This study investigated the differences in the Cd accumulation in 32 vegetable varieties and found that the Cd content ranged from 0.01 to 0.24 mg·kg−1, and decreased in the order of stem and bulb vegetables > leafy vegetables > solanaceous crops > bean cultivars. A correlation analysis and structural equation model showed that pH, soil organic matter, and the cation exchange capacity had significant effects on Cd accumulation in the vegetables and explained 72.1 % of the variance. In addition, species sensitivity distribution (SSD) curves showed that stem and bulb vegetables were more sensitive to Cd than other types of vegetables. Using the Burr Type III function for curve fitting, we derived Cd thresholds of 6.66, 4.15, and 1.57 mg·kg−1 for vegetable soils. These thresholds will ensure that 20 %, 50 %, and 95 % of these vegetable varieties were risk–free, respectively. The predicted threshold of soil Cd was more than twice that of China's current National Soil Quality Standard (GB 15618–2018) for Cd values. Therefore, soil scenarios and cultivars should be considered comprehensively when determining farmland soil thresholds. The present results provide a new model for setting soil Cd criteria in high geological background areas.

Heavy metal ecological-health risk assessment under wheat–maize rotation system in a high geological background area in eastern China

A high geological background can increase the ecological and health risks associated with crop production; therefore, it is essential to assess the heavy metals and their impact. In this study, ecological and health risk impacts of heavy metal contamination, in combination with positive matrix factorization was assessed for an area with high geological background with wheat–maize cropping system, to provide a quantitative understanding of the effects of heavy metals, enabling its prevention and control. This study revealed that the comprehensive ecological risk (RIwheat–maize) is 56.21 (low), with industries being the biggest contributors (34.22%). Comprehensive health risk (non-carcinogenic) assessment showed that industrial (40.98–49.30%) and natural (23.96–37.64%) factors were the primary (particularly of Cd and Zn) and secondary (particularly of Cr and Ni) contributors, respectively in eastern China. Comprehensive health risk (HIwheat–maize) for children and adults were 0.74 and 0.42, respectively, indicating that non-carcinogenic risks were at an acceptable level. Soil ingestion was the primary pathway for health risks (62.23–73.00%), especially for children. Based on soil heavy metal sources and crop systems, source-ecological risk assessment and source-health risk assessment were used to provided valuable insights on making strategies to protect human health in high geological background areas.

Source Identification and Superposition Effect of Heavy Metals (HMs) in Agricultural Soils at a High Geological Background Area of Karst: A Case Study in a Typical Watershed.

Exogenous sources and the superposition effect of HMs in agricultural soils made the idenfication of sources complicated in a karst area. Here, a typical watershed, a research unit of the karst area, was chosen as the study area. The smaller-scale study of watersheds allowed us to obtain more precise results and to guide local pollution control. In this study, sources of HMs in agricultural soil were traced by a CMB model. Superposition effects were studied by spatial analysis of HMs and enrichment factor (EF) and chemical fraction analysis. The average concentrations of Cd, Pb, Cr, Cu, Ni and Zn in surface soils were 8.71, 333, 154, 51.7, 61.5 and 676 mg∙kg−1, respectively, which exceeded their corresponding background values. The main sources of Cd, Pb and Zn in agricultural soil were rock weathering, atmospheric deposition and livestock manure, and their contributions were 47.7%, 31.0% and 21.2% for Cd; 7.63%, 78.7% and 13.4% for Pb; and 17.0%, 52.3% and 28.1% for Zn. Cr mainly derived from atmospheric deposition (73.8%) and rock weathering (20.0%). Cu and Ni mainly came from livestock manure (81.3%) and weathering (87.5%), respectively, whereas contributions of pesticides and fertilizers were relatively limited (no more than 1.04%). Cd, Pb, Zn and Cu were easily enriched in surface soils near the surrounding pollution sources, whereas Cr and Ni were easily enriched in the high-terrain area, where there was less of an impact of anthropogenic activities. The superposition of exogenous sources caused accumulation of Cd, Pb and Zn in topsoil, contaminated the subsoil through leaching and improved bioavailability of Cd and Pb, causing high ecological risk for agricultural production. Therefore, Cd and Pb should be paid more attention in future pollution control.