Machine learning can identify the sources of heavy metals in agricultural soil: A case study in northern Guangdong Province, China.

Source tracing of heavy metals in agricultural soils is of critical importance for effective pollution control and targeting policies. It is a great challenge to identify and apportion the complex sources of soil heavy metal pollution. In this study, a traditional analysis method, positive matrix fraction (PMF), and three machine learning methodologies, including self-organizing map (SOM), conditional inference tree (CIT) and random forest (RF), were used to identify and apportion the sources of heavy metals in agricultural soils from Lianzhou, Guangdong Province, China. Based on PMF, the contribution of the total loadings of heavy metals in soil were 19.3% for atmospheric deposition, 65.5% for anthropogenic and geogenic sources, and 15.2% for soil parent materials. Based on SOM model, As, Cd, Hg, Pb and Zn were attributed to mining and geogenic sources; Cr, Cu and Ni were derived from geogenic sources. Based on CIT results, the influence of altitude on soil Cr, Cu, Hg, Ni and Zn, as well as soil pH on Cd indicated their primary origin from natural processes. Whereas As and Pb were related to agricultural practices and traffic emissions, respectively. RF model further quantified the importance of variables and identified potential control factors (altitude, soil pH, soil organic carbon) in heavy metal accumulation in soil. This study provides an integrated approach for heavy metals source apportionment with a clear potential for future application in other similar regions, as well as to provide the theoretical basis for undertaking management and assessment of soil heavy metal pollution.

Status of arsenic accumulation in agricultural soils across China (1985-2016).

Based on 1677 published studies, 1648 sites across China collected from 1985 to 2016 were used to research the concentrations of arsenic in agricultural soils. In order to understand the status of arsenic pollution in agricultural soils in China over the past three decades, and to learn about the arsenic stocks in agricultural soils in various regions, and compared the relationship with annual arsenic emissions in China, and finally evaluated the potential ecological risks and human health risks. The median arsenic concentration in the surface agricultural soils of China was 10.40 mg Kg-1, and it ranged from 0.4 mg Kg-1 to 175.8 mg Kg-1. The inventory of arsenic in Chinese agricultural surface soils was estimated to be 3.71 × 106 t. In this study, the arsenic concentrations were found to be higher in Central, South, and Southwest China than those in other regions. The trend of arsenic pollution in agricultural soils has gradually increased over the past three decades. However, the growth rate of arsenic concentrations pollution in farmlands agricultural in China slowed during 2012-2016. The ecological risk index and geoaccumulation index revealed that arsenic in Chinese agricultural soil poses a low risk to the ecosystem. For human health assessment, the dietary pathway was the main pathway of exposure to arsenic in farmland soil of China. However, children's soil intake also contributed 34.48% to the exposure to arsenic, owing to their behavior. This study can provide a reference for the management of arsenic agricultural pollution in farmland soils in China.

Organophosphate Flame Retardants in Soils of Zhejiang Province, China: Levels, Distribution, Sources, and Exposure Risks.

Organophosphate flame retardants (OPFRs) are an emerging class of pollutants. In this study, 62 soil samples were collected from Zhejiang Province China, and screened for 8 typical OPFRs. All compounds were detected in soil at 100% detection frequency, except for triethyl phosphate (TEP) compounds (93.6%). The sum of the eight OPFR concentrations ranged from 9.15 to 132 ng/g dry weight (dw), with mean and median values of 24.9 and 19.0 ng/g dw, respectively. Triphenyl phosphate (TPHP) was identified as the most abundant analog, with a median concentration of 9.94 ng/g dw, followed by tris(2-ethylhexyl)phosphate (TEHP). Significantly higher OPFR concentrations were detected in northern Zhejiang; concentrations decreased sharply from the north to the south. OPFR concentrations in soils from cities or economically developed counties were much higher than those from rural areas. OPFR sources in Zhejiang Province mainly originated from PVC-made products and traffic emissions.  Dermal absorption of OPFRs via soil was the primary pathway for human exposure. Health risks due to exposure to OPFRs through soil ingestion were found to be negligible.

Inventories of heavy metal inputs and outputs to and from agricultural soils: A review.

Heavy metal pollution of agricultural soils is an important issue around the world. To understand the overall pollution process, accurate determination of every input and output pathway of heavy metals to and from soils is essential. Hence, input and output inventory, a quantitative analysis method of heavy metals balance in agricultural soils, has been widely used. However, due to differences in geography, climate, socioeconomic factors, industrial and agricultural production, substantial variation exists among existing input and output inventories for different countries and regions. In this study, we systematically analyzed these differences and the findings will improve the compilation of inventories worldwide.

Would it be better for partition prediction of heavy metal concentration in soils based on the fusion of XRF and Vis-NIR data?

Heavy metal (HM) contamination in soil necessitates effective methods to diagnose suspected contaminated areas and control rehabilitation processes. The synergistic use of proximal sensors demonstrates significant potential for rapid detection via accurate surveys of soil HM pollution at large scales and high sampling densities, and necessitates the selection of appropriate data mining and modeling methods for early diagnosis of soil pollution. The aim of this study is to evaluate the performance of a subarea model based on geographically partitioned and global models based on high-precision energy dispersive X-ray fluorescence (HD-XRF) and visible near-infrared (vis-NIR) spectra using a random forest model for predicting soil Cu and Pb concentrations. A total of 166 soil samples are acquired from a contaminated plot in Baiyin, Gansu Province, China. The soil samples are subjected to HM analysis and proximal sensor scanning in a laboratory. Vis-NIR spectral data are preprocessed using the Savitzky Golay (SG) and first-order derivative with Savitzky Golay (SGFD) methods. The results show that for predicting Cu and Pb concentrations in soil, the subarea models performs better than the global models in terms of quantitative prediction, based solely on individual HD-XRF data. For the subarea and global models, the R2 values are 0.961 and 0.981, respectively; the RMSE values are 27.8 and 79.6, respectively; and the RPD values are 4.96 and 7.38, respectively. However, making use of the random forest algorithm trained with data fusion obtained from the HD-XRF and vis-NIR sensors, the global model achieves the best predictions for Cu and Pb concentrations via HD-XRF + vis-NIR (SGFD) and HD-XRF + vis-NIR (SG), respectively. The results will provide a new perspective for modeling approaches to rapidly invert HM concentrations based on proximal sensor data fusion within a large scope of the study area.

Using multi-technology to characterize transboundary Hg pollution in the largest presently active Hg deposit in China.

Active Hg mines are primary sources of Hg contamination in the environment of mining districts and surrounding areas. Alleviation of Hg pollution requires knowledge of pollution sources, migration, and transform pathways across various environmental media. Accordingly, the Xunyang Hg-Sb mine, the largest active Hg deposit in China, presently was selected as the study area. GIS, TIMA, EPMA, µ-XRF, TEM-EDS, and Hg stable isotopes were adopted to investigate the spatial distribution, mineralogical characteristics, in situ microanalysis, and pollution sources of Hg in the environment medium at the macro- and micro-levels. The total Hg concentration in samples showed a regional distribution, with higher levels in areas close to the mining operations. The in situ distribution of Hg in soil was mainly associated with the mineralogical phases of quartz, and Hg was also correlated with Sb and S. Hg was also found to be rich mainly in quartz minerals in the sediment and showed different distributions of Sb. Hg hotspots had S abundances and contained no Sb and O. The contributions from the anthropogenic sources to soil Hg were estimated to be 55.35%, among which 45.97% from unroasted Hg ore and 9.38% from tailing. Natural input of soil Hg due to pedogenic processes accounted for 44.65%. Hg in corn grain was mainly derived from the atmosphere. This study will provide a scientific basis for assessing the current environmental quality in this area and minimizing further impacts that affect the nearby environmental medium.

Dual-drug codelivery nanosystems: An emerging approach for overcoming cancer multidrug resistance.

Multidrug resistance (MDR) promotes tumor recurrence and metastasis and heavily reduces anticancer efficiency, which has become a primary reason for the failure of clinical chemotherapy. The mechanisms of MDR are so complex that conventional chemotherapy usually fails to achieve an ideal therapeutic effect and even accelerates the occurrence of MDR. In contrast, the combination of chemotherapy with dual-drug has significant advantages in tumor therapy. A novel dual-drug codelivery nanosystem, which combines dual-drug administration with nanotechnology, can overcome the application limitation of free drugs. Both the characteristics of nanoparticles and the synergistic effect of dual drugs contribute to circumventing various drug-resistant mechanisms in tumor cells. Therefore, developing dual-drug codelivery nanosystems with different multidrug-resistant mechanisms has an important reference value for reversing MDR and enhancing the clinical antitumor effect. In this review, the advantages, principles, and common codelivery nanocarriers in the application of dual-drug codelivery systems are summarized. The molecular mechanisms of MDR and the dual-drug codelivery nanosystems designed based on different mechanisms are mainly introduced. Meanwhile, the development prospects and challenges of codelivery nanosystems are also discussed, which provide guidelines to exploit optimized combined chemotherapy strategies in the future.

The design and straightforward synthesis of multifunctional DNA microgels for the improved targeted delivery of antitumor drugs.

Multifunctional drug delivery platforms represent ideal approaches to reliably targeting pharmacological agents of interest to the complex tumor microenvironment (TME), yet the complicated synthesis processes, high costs, and toxicities associated with these agents have hindered their clinical application to date. In this study, the properties of the TME are leveraged to develop a multifunctional pNAB/AS DNA microgel that is able to actively target tumors. This microgel is generated by a straightforward one-step free radical precipitation polymerization procedure, exhibiting extremely high drug encapsulation efficiency (∼90%), and is responsive to three environmental stimuli including temperature, reduction, and an acidic pH while showing minimal drug leakage under physiological conditions. Through a synergistic combination of appropriate size and aptamer recognition, this microgel is able to reliably facilitate intratumoral drug accumulation and nuclear drug delivery. Critically, pNAB/AS-Dox treatment is associated with specific antitumor activity in vitro and in vivo while retaining a good biosafety profile and causing lower levels of off-target toxicity as compared to free drug treatment. Together, these findings emphasize the potential value of this multifunctional pNAB/AS DNA microgel as a platform amenable to targeted drug delivery to the TME, providing a foundation for further efforts to readily develop multifunctional drug delivery systems.

Evaluation of Pollution Level, Spatial Distribution, and Ecological Effects of Antimony in Soils of Mining Areas: A Review.

The first global-scale assessment of Sb contamination in soil that was related to mining/smelting activities was conducted based on 91 articles that were published between 1989 and 2021. The geographical variation, the pollution level, the speciation, the influencing factors, and the environmental effects of Sb that were associated with mining/smelting-affected soils were analyzed. The high Sb values mainly occurred in developed (Poland, Italy, Spain, Portugal, New Zealand, Australia) and developing (China, Algeria, Slovakia) countries. Sb concentrations of polluted soil from mining areas that were reported in most countries significantly exceeded the maximum permissible limit that is recommended by WHO, except in Turkey and Macedonia. The soil Sb concentrations decreased in the order of Oceania (29,151 mg/kg) > North Africa (13,022 mg/kg) > Asia (1527 mg/kg) > Europe (858 mg/kg) > South America (37.4 mg/kg). The existing extraction methods for Sb speciation have been classified according to the extractant, however, further research is needed in the standardization of these extraction methods. Modern analytical and characterization technologies, e.g., X-ray absorption spectroscopy, are effective at characterizing chemical speciation. Conditional inference tree (CIT) analysis has shown that the clay content was the major factor that influenced the soil Sb concentration. Non-carcinogenic risks to the public from soil Sb pollution were within the acceptable levels in most regions. An Sb smelter site at the Endeavour Inlet in New Zealand, an abandoned open-pit Sb mine in Djebel Hamimat, Algeria, an old Sb-mining area in Tuscany, Italy, and Hillgrove mine in Australia were selected as the priority control areas. Cynodon dactylon, Boehmeria, Pteris vittata, and Amaranthus paniculatus were found to be potential Sb accumulators. All of the values of bioaccumulation factors for the crops were less than one. However, ingestion of Sb through crop consumption posed potential non-carcinogenic health risks, which should not be neglected. The soil variables (pH, Eh, total sulfur, carbon nitrogen ratio, total organic carbon, and sulfate), the total Sb and the bioavailable Sb, and heavy metal(loid)s (As, Pb, and Fe) were the major parameters affecting the microbial community compositions.

Accumulation, regional distribution, and environmental effects of Sb in the largest Hg-Sb mine area in Qinling Orogen, China.

In this study, knowledge gaps on Sb concentration in rocks, ores, tailings, soil, river water, sediments, and crops of mine areas were identified and discussed in terms of contamination levels, spatial distribution, and environmental effects. Accordingly, Xunyang Hg-Sb mine, the largest Hg-Sb deposit in China as research region in this study, field sampling and laboratory analysis were conducted. The results showed elevated concentrations of Sb in the soil, sediment, and river water. The X-ray diffraction analysis indicated that the main minerals of the rocks were quartz, dolomite, calcite, and margarite. Based on the TESCAN integrated mineral analyzer analysis, the main ore minerals in the Gongguan mine were dolomite (93.97%), cinnabar (2.50%), stibnite (2.48%), calcite (0.38%), and quartz (0.38%). The µ-XRF analysis indicated that Sb distribution was similar to those of S and O, instead of those of Hg and As. The clear spatial variation of Sb concentration in environmental media, mines, tailings, and settling ponds affected Sb accumulation. Actinobacteriota, Proteobacteria, Acidobacteriota, and Chloroflexi were the dominant phyla in the soil. Patescibacteria, Proteobacteria, and Bdellovibrionota were negatively correlated with Sb in the soil (p < 0.05). Exposure to Sb through maize grain and cabbage consumption poses serious non-carcinogenic health risk for residents. This work provides a scientific basis for the environmental quality assessment of Sb mine areas and development of applicable guidelines.

Heavy metals in indoor dust: Spatial distribution, influencing factors, and potential health risks.

Given the large proportion of time that people spend indoors, the potential health risks posed by heavy metals in the indoor environment deserve greater attention. A global-scale assessment of heavy metal contamination in indoor dust was conducted in this study based on >127 articles published between 1985 and 2019. The pollution levels, spatio-temporal variations, sources, bioaccessibilities, influencing factors, and health risks of heavy metals associated with indoor dust were analyzed. Children's blood lead levels (BLLs) were also estimated using the integrated exposure uptake biokinetic model. The results indicated that the median concentrations of Cu and Zn in 71.9% and 71.0% of the study sites surpassed the corresponding permissible limits, 100 and 300 mg/kg, respectively; thus, their control should be given priority. Heavy metal concentrations in indoor dust from different areas of the world varied greatly, which was closely associated with the type of local human activities, such as mining, melting, e-waste recycling and Pb-related industries. The bioaccessibilities of some key elements, e.g., Pb, Cd, Cu, and Zn, in household dust were high. The levels of heavy metals in indoor dust were mainly affected by a combination of outdoor and indoor sources and related critical factors, and future studies should focus on quantifying the contributions of different sources. Based on the health risk assessment, dust Pb exposure is a major health concern in e-waste recycling areas, which warrants greater attention. 49.8%, 36.8% and 14.4% of study sites showed BLLs exceeding 35 µg/L (threshold limit in Germany), 50 µg/L (threshold limit in the USA), or 100 µg/L (threshold limit in China), respectively. Finally, Pb exposure from indoor dust represents a major contributor to children's blood Pb poisoning in many developing countries. This study details the overall heavy metal contamination status of indoor dust and provides insights for policymakers with respect to pollution prevention measures.

Status of chromium accumulation in agricultural soils across China (1989-2016).

The first national-scale assessment of chromium (Cr) contamination in China's agricultural soils was performed based on 1625 sites analysed with 1799 previously published papers. Spatial and temporal variations were assessed, and the ecological risk was estimated. The range of Cr concentrations in farmland soil is 1.48-820.24 mg/kg. At approximately 4.31% and 0.12% of the sampling sites, Cr concentrations exceeded the screening value (150 mg/kg) and the control value (800 mg/kg), respectively (GB15618-2018). Cr concentrations decreased in the following order: Southwest > Northwest > East > South > Northeast > Central > North China. Moreover, the Cr accumulation rate in agricultural soils may have decreased during 2011-2016, possibly due to government-led changes in China's industrial structure and policies limiting the discharge of polluted industrial wastes. Linear correlations were observed between the application amounts of fertilizers and Cr concentrations in the soil, indicating that the application of nitrogen, phosphorus and potassium fertilizers is an important contributor of Cr in agricultural soils. Additionally, geoaccumulation index (Igeo) values for Cr showed that more than 83.4% of the sampling sites were uncontaminated, with high Igeo values distributed in some areas, especially those with mining and electroplating industries. Overall, this study details the Cr contamination status of agricultural soils in China and provides insights for policymakers enacting measures to prevent pollution.

Soil-air exchange of mercury from agricultural fields in Zhejiang, East China: Seasonal variations, influence factors, and models of fluxes.

Mercury exchange between soil and air is an important processe governing the biogeochemical cycling of Hg. This study investigated the in situ soil-air Hg fluxes in agricultural soils of Quzhou, Zhejiang Province, China, using a dynamic flux chamber coupled with a Hg vapor analyzer. Soil-air Hg exchange fluxes were overall emission for all seasons, indicating that agricultural soil was a Hg source for the atmosphere. Seasonal variations in soil-air Hg flux were observed, with low values in winter, elevated values in spring, peak values in summer, and a decline in autumn. Mercury emissions from soils showed a clear diurnal pattern where Hg released into the atmosphere reached a maximum at 11 a.m. and declined to a minimum at 2:00 and 20:00 in spring and summer, respectively. Meanwhile, soil-air Hg flux peaked at 1 p.m. and declined to a minimum at 6:00 and 23:00 in autumn and winter, respectively. The impact of each factor on the Hg exchange between soil and air varied in different seasons. Soil temperature was the major variable controlling the Hg flux in winter and spring; soil temperature and total gaseous Hg evidently affected the Hg flux in summer, and ozone (O3) played a dominant role in influencing the Hg flux in autumn. Models for estimating the Hg evasive flux from soils were developed, and the atmospheric O3 concentration was used for the first time as a parameter in these models. The measured and modeled Hg fluxes showed significant linear correlations (R2 = 0.61; P < 0.001).

Mass balance-based inventory of heavy metals inputs to and outputs from agricultural soils in Zhejiang Province, China.

It is important to understand the status and extent of soil contamination with heavy metals to make sustainable management strategies for agricultural soils. Input and output inventory of heavy metals in agricultural soil of Zhejiang Province was systematically studied. The results showed that atmospheric deposition was responsible for 47.88% and 76.87% of the total Cr and Pb inputs, respectively. Livestock manures accounted for approximately 54-85% of the total As, Cu, and Zn inputs. Livestock manure and irrigation were the main sources of Hg, contributed 50.25% and 38.63% of the total inputs, respectively. Ni was derived mainly from atmospheric deposition (57.86%), followed by irrigation (22.69%). As for Cd, the relative contributions of atmospheric deposition, irrigation, and livestock manure were similar. Crop harvesting and leaching were found to be the dominant output pathways of the soil elements Cd, Cu, Hg, and Zn, being responsible for 74.43-83.62% of the total outputs. Surface runoff was the dominant output pathway for As, Cr, Ni, and Pb, accounting for approximately 73.36%, 46.32%, 54.16%, and 48.11% of the total outputs, respectively. According to prediction and early warning, Cd is the priority control pollutant in agricultural soil. This work will assist in developing strategies for reducing heavy metal inputs to agricultural soil and effectively targeting policies to protect soil environment from long-term heavy metal accumulation.

Status of lead accumulation in agricultural soils across China (1979-2016).

The first national-scale assessment of lead (Pb) contamination in agricultural soils across China was conducted based on >1900 articles published between 1979 and 2016. Pb concentrations, temporal and spatial variations, and influencing factors were analyzed. Children's blood lead levels (BLLs) were also estimated using the integrated exposure uptake biokinetic (IEUBK) model. Pb concentrations in different areas of China varied greatly, which was closely associated with the distribution of Pb-related industries, especially Pb-zinc mine smelting, non-ferrous polymetallic mine smelting, e-waste recycling, and leaded gasoline consumption. The year 2000 was a significant transition year for Pb concentrations, with a rapid increase pre-2000 and a subsequent slow upward trend. Pb concentrations were found to be strongly associated with indicators of economic and social development including gross domestic product (GDP), population size, and vehicle ownership. Leaded gasoline, coal combustion, and non-ferrous smelting were the main sources of atmospheric Pb during the different periods. Predicted BLLs were higher in South China than those in the north. This study details the overall Pb contamination status of agricultural soils in China, and thus provides insights for policymakers with respect to pollution prevention measures.

Status of cadmium accumulation in agricultural soils across China (1975-2016): From temporal and spatial variations to risk assessment.

Based on 1186 published studies, the first national-scale assessment of cadmium (Cd) contamination in agricultural soils across China was conducted. Cd concentrations, temporal and spatial variations, and ecological and health risks resulted from Cd exposure were analyzed. A small part of sampling sites with Cd concentration surpass the screening value and the control value (GB15618-2018), respectively. Soil Cd concentrations in South China were higher than other regions. Ecological risks resulting from Cd contamination were low. Soil Cd concentrations accumulated gradually from 1981 to 2016. Cd mainly came from anthropogenic activities, such as mining, smelting, sewage irrigation, and fertilization. Linear correlations were observed between application amounts of fertilizers and Cd concentrations in soil, indicating that the application of nitrogen, phosphorus, potassium, and compound fertilizers is an important contributor of Cd in soils. This study details the overall Cd contamination status of agricultural soils in China, thus can provide insights for policymakers regarding contamination prevention measures.

Residuals, bioaccessibility and health risk assessment of PAHs in winter wheat grains from areas influenced by coal combustion in China.

Polycyclic aromatic hydrocarbons (PAHs) contamination in atmospheric and soil was serious, which is mainly due to high level of emission of PAHs in China resulted from the predominating use of coal in energy consumption and continuous development of economy and society for years. However, the status of PAHs in winter wheat grains from the areas influenced by coal combustion in China was still not clear. During harvest season, the winter wheat grains were collected from agricultural fields surrounding coal-fired power plants located in Shaanxi and Henan Provinces. This study found that the mean concentrations of 15 priority PAHs ranged from 69.58 to 557.0µgkg-1. Three-ring PAHs (acenaphthene, acenaphthylene, fluorene, phenanthrene and anthracene) were dominant in the grains, accounting for approximately 70-81% of the total PAHs. The bioaccessibility of low molecular weight (LMW, 2-3 ring) PAHs (51.1-52.8%), high molecular weight (HMW, 4-6 ring) PAHs (19.8-27.6%) and total PAHs (40.9-48.0%) in the intestinal condition was significantly (p<0.001) higher than that (37.4-38.6%; 15.6-22.5%; 30.7-35.5%) in the gastric condition, respectively. Based on total PAHs, the values of incremental lifetime cancer risk (ILCR) for children, adolescents, adults and seniors were all higher than the baseline value (10-6) and some even fell in the range of 10-5-10-4, which indicated that most grains from the areas affected by coal combustion possessed considerable cancer risk. The present study also indicated that the children were the age group most sensitive to PAHs contamination. The pilot research provided relevant information for the regulation of PAHs in the winter wheat grains and for the safety of the agro-products growing in the PAHs-contaminated areas.

Variation in foliar uptake of polycyclic aromatic hydrocarbons in six varieties of winter wheat.

To investigate intraspecific variations of foliar uptake of polycyclic aromatic hydrocarbons (PAHs) of winter wheat (Triticum aestivum L.), leaves of six varieties including Changwu 521 (CW), Hedong TX-006 (HD), Jiaomai 266 (JM), Xiaoyan 22 (XY), Yunong 949 (YN), and Zhongmai 175 (ZM) were exposed to three levels of (0, 0.25, and 1.5 mg L-1) mixture of six selected PAHs (phenanthrene, anthracene, pyrene, benz[a]anthracene, benzo[a]pyrene, and benzo[g,h,i]perylene). After 10 consecutive days of application, all the six selected PAHs (Σ6 PAHs) were determined in the leaves of the six varieties of the winter wheat. There were apparent intraspecific differences in foliar uptake of PAHs in the winter wheat. The highest concentrations of Σ6 PAHs in the leaves of YN variety (64.6 mg kg-1) were approximate two times of the lowest concentrations in the leaves of HD variety (29.6 mg kg-1). Both individual PAHs and Σ6 PAHs in the cuticular waxes were significantly (p < 0.01) higher than those in leaves and far higher than those in roots, indicating that the cuticular waxes could play significant role in foliar uptake of PAHs. The present results also showed that the concentrations PAHs in leaves were positively (p < 0.05) correlated with the water solubility of the six selected PAHs. In addition, the present study suggested that there was basipetal translocation of PAHs in the winter wheat after foliar application of PAHs, although the mechanism was yet to be further studied.