Using machine learning to predict selenium and cadmium contents in rice grains from black shale-distributed farmland area.

Cadmium (Cd) and selenium (Se) are widely enriched in soil at black shale outcropping areas, with Cd levels exceeding the standard (2.0 mg/kg in 5.5 < pH ≤ 6.5) commonly. The prevention of Cd hazards and the safe development of Se-rich land resources are key issues that need to be urgently addressed. To ensure safe utilization of Se-rich land in the CdSe coexisting areas, 158 rice samples, their corresponding rhizosphere soils, and 8069 topsoil samples were collected and tested in the paddy fields of Ankang City, Shaanxi Province, where black shales are widely exposed. The results showed that 43 % of the topsoil samples were Se-rich soil (Se > 0.4 mg/kg) wherein 79 % and 3 % of Cd concentrations exceeded the screening value and control value, respectively, according to the GB15618-2018 standard. Meanwhile, 63 % of the rice samples were Se rich (Se > 0.04 mg/kg) and the Cd content exceeded the prescribed limit (0.2 mg/kg) in Se-rich rice by 26 %. There was no significant positive correlation between the Se and Cd contents in the rice grains and the Se and Cd contents in the corresponding rhizosphere soil. The factors influencing Se and Cd uptake in rice were SiO2, CaO, P, S, pH, and TFe2O3. Accordingly, an artificial neural network (ANN) and multiple linear regression model (MLR) were used to predict Cd and Se bioaccumulation in rice grains. The stability and accuracy of the ANN model were better than those of the MLR model. Based on survey data and the prediction results of the ANN model, a safe planting zoning of Se-rich rice was proposed, which provided a reference for the scientific planning of land resources.

Influencing factors of selenium transformation in a soil-rice system and prediction of selenium content in rice seeds: a case study in Ninghua County, Fujian Province.

Selenium (Se) is an essential element for human and animal health and has antioxidant, anticancer, and antiviral effects. However, more than 100 million people in China do not have enough Se in their diets, resulting in a state of low Se in the human body. Since the absorption of Se by crop seeds depends not only on the Se content in soil, there are many omissions and misjudgments in the division of Se-rich producing areas. Soil pH, total iron oxide content (TFe2O3), soil organic matter (SOM), and P and S contents were the main factors affecting Se migration and transformation in the soil-rice system. In this study, we compared the performance of the back propagation neural network (BP network) and multiple linear regression (MLR) using 177 pairs of soil-rice samples. Our results showed that the BP network had higher accuracy than MLR. The accuracy and precision of the prediction data met the requirements, and the prediction data were reliable. Based on the Se data of surface paddy fields, 26,900 ha of Se-rich rice planting area was planned using this model, accounting for 77% of the paddy field area. In the planned Se-rich area for rice, the proportion of soil Se content greater than 0.4 mg·kg-1 was only 5.29%. Our research is of great significance for the development of Se-rich lands.

Spatially varying relationships of soil Se concentration and rice Se concentration in Guangxi, China: A geographically weighted regression approach.

In recent years, the biogeochemical behavior and environmental impact of Selenium (Se) on soil-plant systems have received widespread attention, and traditional statistical methods reveal generally positive correlations between rice Se and soil Se. However, that initial positive relationship may have been obscured by local external factors. Using local scale data from the geochemical evaluation of land quality project, this work employed geographically weighted regression (GWR) to examine the spatial variation of rice Se (as the dependent variable) and soil Se (as the independent variable) in Guangxi. Strong and weak correlation coefficients occur between rice Se and soil Se, thereby indicating that their relationships are spatially varying. Guangxi is characterized by significantly positive correlations in most areas, with weak correlations mostly found in the south-western and central-eastern regions. Areas with weak correlation can be divided into two patterns: high soil Se with low rice Se and high rice Se with low soil Se. The unique patterns are correlated with distinct natural factors, particularly the abundance of Fe-rich soils in the carbonate area; by contrast, sandstone areas in central Guangxi may have been affected by anthropogenic activities. To reveal the spatially varying relationships at the local scale, we employed GWR, an effective tool that allowed us to identify the association between environmental variables and influencing factors and explore spatially varying relationships between them. This study breaks through the existing understanding that soil Se is completely positively correlated with rice Se for the first time, and concludes that their correlation is spatially variable, providing an effective approach for the study of complex relationships.

Soil selenium enrichment in the Loess Plateau of China: Geogenic evidence, spatial distribution, and it's influence factors.

The selenium (Se)-deficient soil belt in China has gained widespread attention. During large-scale soil surveys in China, Se-rich soils within low-Se belts have been identified. However, the sources of Se in those soils and the controlling factors for their enrichment remain unclear. Here we summarize Se concentrations and spatial distributions in the Yuanzhou district of the Loess Plateau. We evaluated Se variations in soil profiles, Se migration into water bodies, and considered soil indicators, topographic characteristics and the influence of land-use types on soil Se concentrations. The average Se concentration in the topsoil of the Yuanzhou district was 0.164 µg/g. High-Se soils (>0.222 µg/g) were found in the western valley plain and the southern red bed hilly area, as well as sporadically in higher elevation forestland and grassland areas in the east. Enrichment of Se in the topsoil in the eastern and southern areas was primarily due to Se adsorption and accumulation by soil organic matter as well as enrichment in gypsum, berlinite, and clay minerals during soil formation. Widespread enrichment in the southern area was linked to high Se concentrations in red Tertiary sedimentary rocks. In the western area, enrichment of Se in topsoil was found on both sides of the Qingshui River at low elevations with gentle slopes, with river water being the primary carrier of Se enrichment. These findings provide valuable insights into the epigenetic geochemical behavior of soil Se in China's low-Se belt that accounts for development of Se-rich soils in the region.

Linking health to geology-a new assessment and zoning model based on the frame of medical geology.

With the growing concerns about the Earth's environment and human health, there has been a surge in research focused on the intersection of health and geology. This study quantitatively assesses the relationship between human health and geological factors using a new framework. The framework considers four key geological environment indicators related to health: soil, water, geological landform, and atmosphere. Results indicate that the atmospheric and water resource indicators in the study area were generally favorable, while the scores of geological landforms varied based on topography. The study also found that the selenium content in the soil greatly exceeded the local background value. Our research underscores the importance of geological factors on human health, establishes a new health-geological assessment model, and provides a scientific foundation for local spatial planning, water resource development, and land resource management. However, due to varying geological conditions worldwide, the framework and indicators for health geology may need to be adjusted accordingly.

Identification of the spatial patterns and controlling factors of Se in soil and rice in Guangxi through hot spot analysis.

Selenium (Se) is essential to human health, anti-cancer, possessing antioxidant, and antiviral properties. In this study, the spatial patterns of rice Se and their varying relationship with soil Se on a regional scale were studied using hot spot analysis for the agricultural soils in Guangxi. According to the hot and cold spot maps, rice Se correlates positively with soil Se in Guangxi agricultural soils. High rice Se accompanies high soil Se in the central part of Guangxi (e.g., Liuzhou, Laibin), and low rice Se is in line with low soil Se in the western part (e.g., Baise). However, the hot spot analysis maps indicate that southwestern Guangxi exhibits a special characteristic of low rice Se with high soil Se (e.g., Chongzuo). This special pattern is strongly associated with the high concentrations of Fe2O3 (ferromanganese nodules) in the carbonate rock area. The hot spot analysis proves useful in revealing the spatial patterns of rice Se in Guangxi and identifying the hidden patterns.

Probability of cultivating Se-rich maize in Se-poor farmland based on intensive field sampling and artificial neural network modelling.

Selenium (Se) is a necessary micronutrient for humans, and its supplementation from crop grains is important to address the ubiquitous Se deficiency in people worldwide. Se uptake by crops largely depend on soil bioavailable Se rather than soil total Se content, which provides possibilities to explore the Se-rich crops in Se-poor area. Here, the possibility of cultivating Se-rich maize grains in Se-poor farmland was tested based on intensive field sampling and mathematical modelling. Sampling was conducted at county scale, and a total of 7779 topsoil samples and 109 maize samples with paired rhizosphere soils samples were collected. Results showed that although the soil Se content in the study county from southwestern China was at a low level (0.01-2.75 mg kg-1), 54.1% of the maize grain samples satisfied the standard for Se-rich products (0.02-0.30 mg kg-1). Soil organic matter, iron oxide, and phosphorus levels were correlated negatively with Se bioconcentration factor (BCF) of maize grain. Compared with the multivariate linear regression model, the artificial neural network (ANN) model was more accurate and reliable in predicting maize Se BCF. Prediction using the ANN model showed that 22.7% of the county's farmland was suitable for cultivating naturally Se-rich maize, which increased 21.3% growing areas than that from cultivation based on simply soil total Se. This study provided a new methodological framework for natural Se-rich maize production and verified the probability of cultivating naturally Se-rich maize in Se-poor farmland.

Analysis of phosphorus and sulfur effect on soil selenium bioavailability based on diffusive gradients in thin films technique and sequential extraction.

Human intake of selenium (Se) mainly occurs through the food chain, and is largely dependent on the bioavailability of soil Se. Sulfur (S) and phosphorus (P) also as essential nutrients for plants, their antagonistic with Se effects on Se bioavailability should be considered. We conducted pot experiments to investigate the interaction effect on the bioavailability of Se in the soil using a sequential extraction method and diffusive gradients in thin films (DGT). The results showed that the root and shoot Se of pak choi increased at most 340%-360% with S and P application, while the Se uptake by pak choi was slightly inhibited when S and P application was 100 mg kg-1. With high S and P application, pak choi Se had a high bioaccumulation factor (BAF) and low translocation factor (TF), and soil Soluble-Se (SOL-Se) increased 178%-299%, which due to the competitive adsorption of S, P with Se and changes in soil pH that lead to the transformation of soil Se fractions. In addition, the available Se concentration in soil measured by the DGT (CDGT-Se) increased by 866% with exogenous S and P application, and its source was HA-Se. However, CDGT-Se failed to show a good linear relationship with the Se content of pak choi. The application of DGT to assess the bioavailability of Se in soils where Se is present in the steady state needs to be further explored. We discuss the effect of S and P application on the bioavailability of soil Se and provide evidence for agricultural production and rational fertilizer use on Se-rich land.

Safe utilization and zoning on natural selenium-rich land resources: a case study of the typical area in Enshi County, China.

Selenium (Se) is an essential trace element. However, Se in soil is often accompanied by heavy metals, such as cadmium (Cd), because of geological background. The safe utilization of such Se-rich land resources remains a challenge. A typical Se-rich area located in Enshi County, China, was systematically investigated with geochemical and epidemiological methods. The results show that Se in the topsoil is 0.84 ± 1.39 µg/g, whereas that of Cd is 0.93 ± 1.63 µg/g. And the concentration of Se and Cd in corn is 0.22 ± 0.96 µg/g and 0.15 ± 0.32 µg/g, respectively, which is mainly related to the high concentrations in soil. The benchmark dose limit of urinary Cd for ß2-microglobulin in subjects (n = 160) was calculated as 3.27 µg/g Cr. In view of crop-human dose effect and combining the relationship among the concentrations of crops and human biomarkers and the concentrations of crops and topsoil, this study established the models of land resource safety zoning. With that, the risk screening value of Cd in the soil could be obtained as 0.98 µg/g in this typical area. The proportions of priority utilization, safe utilization, and strict management of agricultural land area were 58.85%, 22.90%, and 18.25%, respectively, in Enshi, China. These results could provide scientific support for local agricultural development and ecological sustainability.

Application of ecogeochemical prediction model to safely exploit seleniferous soil.

Seleniferous soil and crops have recently attracted attention worldwide. Cultivating seleniferous crops in the absence of heavy metals is greatly challenging. This study aimed to develop approaches for the safe exploitation of seleniferous soil. We collected 246 pairs of rice grain samples and their corresponding rhizosphere soil samples and 8542 topsoil samples from Binyang and Xingbin in Guangxi. The Cd, Cu, Hg, Pb, Zn, and Se contents of soil and rice grain samples were tested. Several soil properties, including CaO, Mn, Mo, and S contents; total organic carbon content; and pH were also measured. Soil and rice grain samples that were classified as seleniferous accounted for 85.77% and 88% of all samples, respectively. More than 30% of soil and rice grain samples were potentially polluted by Cd. The percentage of seleniferous rice grain samples increased as soil Se concentration increased. Notably, however, the percentage of Cd-polluted rice grain samples decreased with the increase in soil Cd concentration. Models for the prediction of BAFs of heavy metal and Se were accurately established on the basis of significant partial correlations between log10 (BAFs) and log10 (soil properties). Farmlands with seleniferous soil under preferential protection and with safely exploited seleniferous soil accounted for 82.61% of the total study area. Sites that require remediation or land-use changes accounted for only 14.7% of the total study area and were mainly distributed in the center of the study area.

Constraint on selenium bioavailability caused by its geochemical behavior in typical Kaschin-Beck disease areas in Aba, Sichuan Province of China.

Kaschin-Beck disease (KBD), an endemic osteoarthropathy, is distributed in the low-selenium (Se)-belt that stretches from northeast to southwest China. However, very few studies have investigated the relationship between low bioavailabitity of Se and KBD. The present study examined the behavior of Se and other elements in areas with varying levels of KBD prevalence using pedological and geochemical methods. Rhizosphere soil samples obtained from the KBD-stricken Aba area were classified into Ustic Isohumisols (J2), Udic Luvisols (L4), Stagnic Gleysols (I2), and Cryic Cambisols (M1) and the integrated constraints on selenium bioavailability in these soils were analyzed. We found that Se concentration in soil profiles from a typical KBD area ranged between 0.08 µg · g(-1) and 0.215 µg · g(-1), indicating absent and marginal bioavailability, respectively. This suggested that low Se bioavailability may be a feature that soils inherit from their Se-deficient parent materials. Moreover, the soil types examined showed different geochemical behaviors such as eluviation for soluble Se(VI), migration of Se(IV) for its adsorption on clay and sesquioxide, and extreme redox conditions. In conclusion, a higher level of Se bioavailability in environment might be related to a lower risk of KBD, and our results offer a foundation for scientific theory on ecological geochemistry and improve our understanding of KBD.

Evaluation of potential effects of soil available phosphorus on soil arsenic availability and paddy rice inorganic arsenic content.

The transfer of arsenic from paddy field to rice is a major exposure route of the highly toxic element to humans. The aim of our study is to explore the effects of soil available phosphorus on As uptake by rice, and identify the effects of soil properties on arsenic transfer from soil to rice under actual field conditions. 56 pairs of topsoil and rice samples were collected. The relevant parameters in soil and the inorganic arsenic in rice grains were analyzed, and then all the results were treated by statistical methods. Results show that the main factors influencing the uptake by rice grain include soil pH and available phosphorus. The eventual impact of phosphorus is identified as the suppression of As uptake by rice grains. The competition for transporters from soil to roots between arsenic and phosphorus in rhizosphere soil has been a dominant feature.

Inputting history of heavy metals into the inland lake recorded in sediment profiles: Poyang Lake in China.

The temporal and spatial distribution of heavy metals (Cd, Hg, Pb, As and Cr) in Poyang Lake, the largest freshwater lake (3050 km(2)) in China, were studied based on the sedimentary profiles. For this purpose, eight sedimentary cores were selected which located at lake area, outfall of lake and the main branch rivers, respectively. High-resolution profiles with interval 2 cm were used for analyzing the concentration of metals, and the ages of them were determined by (210)Pb and (137)Cs isotopic dating. While studying the change of metals concentration with the age in profile, it is found that the concentration of them in sediments was influenced not only by the sources in history but also by the sediment types. Based on this detailed work, the inventory and burden of heavy metals per decade were estimated in lake area during the past 50 years. Significantly, rivers-contribution ratio per decade was estimated to distinguish each river's contribution of heavy metals into lake while river-flux in history and metals concentration in profiles were considered as calculating factors. So, our research provides a proof to well understand the sedimentary history and the inputting history of heavy metals from main rivers into an inland lake.