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BACKGROUND As the significant factor of the accumulation of heavy metals in farmland soils, mineral activities such as mining, traffic and mineral processing and smelting allow heavy metals to spread into the surrounding environment by water or atmospheric deposition, and finally collected into the soil, causing heavy metal pollution in the surrounding farmland soil. Heavy metals pollution in soils especially in farmland soils around the mining area thus has received great attention in the field of environmental pollution. Located in the middle reaches of the Yellow River watershed, the gold mining area in western Henan is an extremely important gold deposit area with great prospecting potential in China for the strong late Yanshan acidic magmatic activity and the extremely favorable metallogenic geological conditions, in which more than 40 large, medium or small gold deposits have been discovered. Under the background of ecological protection and high-quality development in the Yellow River watershed, the western Henan gold mining area, with a long history of gold mining development, lacks more attention to the accumulation, spatial distribution and ecological risk of heavy metals in farmland soil around the mining area during the years of mining, beneficiation and processing. It is particularly necessary to study the heavy metal pollution in soil, find out the impact of mining activities on heavy metals in surrounding farmland soil, and provide a scientific basis for prevention and control of heavy metal pollution in farmland soil. OBJECTIVES To clearly understand the impact of mining activities in the western Henan mining area on heavy metals in the surrounding farmland soil, provide necessary basic data for supporting the safe production of key mineral resources, the surrounding agricultural safety, and prevent and control heavy metal pollution in farmland soil. METHODS 375 topsoil samples from the farmland around the western Henan gold mining area at a depth of 0-20cm were systematically investigated and analyzed with reference to Code of Practice for Soil Geochemical Survey (DZ/T 0145—2017). The contents and spatial distribution characteristics of Cd, Cu, Zn, Pb, Hg, As, Cr, Ni were analyzed. The heavy metal pollution and ecological risk were evaluated by the geo-accumulation index method and potential ecological risk index method. RESULTS (1) The contents variation range of Cu, Pb, Zn, Ni, As, Hg, Cd, Cr are 1.00-71.72, 2.00-524.79, 8.00-320.37, 2.00-52.77, 2.29-24.64, 0.0067-0.268, 0.04-1.30, 28.20-107.93, respectively, and the average are 35.33, 74.43, 137.69, 31.60, 12.39, 0.064, 0.43, 76.27, respectively, showing significant differences between the 8 heavy metals. Compared with the soil background value in the middle reaches of the Yellow River, the average contents of Cu, Pb, Zn, Ni, As, Hg, Cd, Cr are 1.47, 3.24, 2.06, 1.05, 1.03, 1.52, 2.77 and 1.07 times of them, respectively, but lower than the value of risk screening values for soil contamination of agricultural land.(2) The characteristics of coefficients of variation show that Pb(90.72%)>Hg(85.25%)>Cd(65.65%)>Zn(44.0%)>Cu(33.66%)>As(31.72%)>Ni(24.23%)>Cr(13.61%), the Pb, Hg, Cd are the primary factors causing the soil pollution as the external input by mineral activities for the high coefficients of variation and special relation with mining. The main ore-forming elements in the gold deposit area are Au and Mo, and the associated elements are Cu, Pb, Zn, Ni, As, Hg, Cd, which may diffuse into the surrounding environment during ore transportation, waste rock and slag piling along the river, and processing. Alongside the Daping River, the two gold mining areas and concentrators are distributed around the farmland, and the gold ore heap leaching site on the east side is located at the top of the hillside and hill. The heavy metals produced by mining activities can diffuse in the downstream agricultural areas through atmospheric deposition, rainwater leaching, river drainage, and can accumulate in the surrounding agricultural soil, causing heavy metal pollution in the agricultural soil around the mining area.(3) The geo-accumulation index of 8 heavy metals is -0.1, 0.74, 0.33, -0.56, -0.60, -0.29, 0.62, -0.49 with the order Pb>Cd>Zn>Cu>Hg>Cr>Ni>As, in which Cu, Hg, Cr, Ni, As show no influence to the quality of soils for the average geo-accumulation index lower than 0, and Pb, Cd, Zn show moderate pollution for the average geo-accumulation index between 0-1. Among them, the proportion of samples with a Cd element of medium or higher impact grade is 20.27%, the proportion of samples with medium to strong impact grade is 7.73%, and the proportion of samples with strong impact grade is 1.07%. The proportion of samples with a Pb element above the moderate impact level is 18.93%, and the proportion of samples with moderate to strong impact level is 10.40%. Hg and Zn also have 7.46% and 13.33% of the samples reaching the moderate impact level, indicating that Hg, Cd and Pb in the soil at local sampling sites have different degrees of impact on farmland soil quality.(4) The average value of the single-factor potential ecological risk index of eight heavy metals is between 2.06 and 83.62, among which the single-factor potential ecological risk index of As, Cr, Ni, Cu and Zn is a slight potential ecological risk. Pb is mainly subject to slight potential ecological risks for 92% of samples, moderate potential ecological risks for 7.47% of samples and strong potential ecological risks for 0.53% of samples. Cd is dominated by moderate potential ecological risks, with 46.14% of samples, and there are 25.33% and 10.93% of samples reaching strong and very strong potential ecological risks respectively. For the ecological risk index of Hg, there are 35.47%, 11.46%, 4.27% and 3.20% of the samples that reach moderate, strong, very strong and very strong degree. The comprehensive potential ecological risk index (RI) ranges from 51.66 to 689.64, with an average of 192.07. The proportion of samples with slight, moderate, strong and very strong impact degree is 46.40%, 41.07%, 11.20% and 1.33%, respectively. The overall comprehensive potential ecological risk index shows moderate potential ecological risks. CONCLUSIONS Compared with the risk screening values for soil contamination of agricultural land, the contents of Cd, Cu, Zn, Pb, Cr, Ni, As, Hg are all lower than the standard, indicating low risk for the soil environment. There were different degrees of accumulation surrounding the intense mining area of Cd, Pb, and Zn by longtime mineral development. Cu, Ni, As, Hg, and Cr were influenced by the natural factor. The farmland area with strong and very strong comprehensive potential ecological risks is 349.4 hectares and 11.71 hectares, respectively. Cd and Hg are the main contributing elements, with higher risk to the soil ecology, which should be monitored and controlled from source to avoid the further accumulation of heavy metal elements in the soil.

BACKGROUND Selenium is one of the essential trace elements for humans. Eating agricultural products containing selenium is an important way for humans to obtain selenium. It is of great significance for the utilization of selenium-enriched soil resources and the development of selenium-enriched agricultural products to investigate the content characteristics of soil selenium, delimit selenium-enriched soil areas, and determine the influencing factors of soil selenium spatial distribution, migration and enrichment. OBJECTIVES To discuss the content, distribution characteristics and influencing factors of soil selenium in the study area. METHODS Tangchang Town in the Pidu District of Chengdu City was chosen as the study area. 788 surface soil samples (0-20cm) and 46 profile soil samples (100-150cm) were collected. The pH values and contents of Se, As, Hg, Cu, Pb, Zn, Ni, Cr, CD, TP, TK, TN and TOC in soil were determined by AFS, XRF and ICP-MS/OES. Geostatistical analysis, variance analysis, correlation analysis and geographic detectors were applied to systematically determine the content, distribution characteristics and influencing factors of soil selenium. RESULTS (1) Results showed that surface soil selenium content of Tangchang Town ranged from 0.082 to 1.10mg/kg, with an arithmetic mean value of 0.337mg/kg, which was 1.47, 4.02 and 1.16 times the average Se content of soil in Chengdu, Sichuan and China, respectively. (2) The Se-sufficient and Se-enriched topsoil reached 99.2% of Tangchang Town. In the profile soil samples, the soil selenium content decreased with increasing depth. In the spatial distribution, high selenium concentrate areas generally showed a northwest zonal distribution trend in Zhanqi Village, Baimu Village, Dayun Village, and Zhulin Village. (3) Correlation analysis showed that lead, chromium, nickel, cadmium, mercury, arsenic, total potassium, total nitrogen, pH, TOC and altitude were factors affecting spatial distribution variability of the soil selenium but varied in extent (P < 0.01). (4) The factor detection showed that TOC was the highest in the effect, explaining 0.29 of the variability, followed by Zn, which was 0.18, and the third was Cd, which was 0.16. Interaction detection showed the interpretation degree of the interaction between soil TOC and 17 influencing factors was more than 0.30, which was the dominant factor of spatial differentiation of selenium in topsoil. CONCLUSIONS The town is characterized by selenium-enriched soil resources; it is suggested to organically combine the selenium-enriched area with the characteristic industries of chives in Tangyuan to build an ecological chain of selenium-enriched industry, and further carry out collaborative analysis on the influencing factors of selenium migration and enrichment in soil crops.

BACKGROUND Water quality security and human health are important to ensure rural revitalization of old liberated areas. The continuous development and utilization of ion-adsorption type REE deposits in northern Ganzhou aggravate trace elements from ores and tailings to the water cycle, thereby endangering the sanitation and safety of drinking water. OBJECTIVES To investigate and evaluate health risk and water quality on the watershed scale of rare earth ore concentration area in the Huangpi River Basin. METHODS The contents of manganese, cadmium and other elements were determined by inductively coupled plasma-optical emission spectrometry/mass spectrometry(ICP-OES/MS). By choosing "standards for drinking water quality" (GB 5749—2006) as the evaluation basis, the water quality index (WQI), hazard quotient (HQ), and cancer risk (CR)were adopted to evaluate water quality and human health risks through analyzing 9 indices including Pb and Mn. RESULTS NH3-N and Mn were anomaly indices whether in surface water or groundwater. The average values of NH3-N were 750μg/L and 4533μg/L in surface water and groundwater, respectively. Index values of Mn were 207μg/L and 4009μg/L in surface water and groundwater, respectively. Arsenic, class I carcinogen published by the World Health Organization, had no abnormality in surface water and groundwater. Moreover, 85.7% of surface water and groundwater was found to be suitable for drinking upon analyzing the WQI values. The HQ average value of NH3-N was less than 1 in surface water and groundwater so it had no harmful effects on human health. However, the HQ average value of Mn was more than 1, which may be harmful to human health. CR values of As varying from 10-6 to 10-4 were also calculated, and the risk of cancer was acceptable. CONCLUSIONS It is suggested that relevant departments should pay attention to the status of NH3-N and heavy metal elements in water during the reclamation evaluation of rare earth mines. The research detailed in this paper confirms that the groundwater monitoring system of manganese should be improved.

As strategic emerging mineral resources supported by the state, niobium and tantalum are the functional and structural materials needed for the development of emerging industries. Therefore, conducting research on the determination of niobium and tantalum in related materials is of great significance. Unfortunately, niobium and tantalum have similar physical and chemical properties, making it difficult to separate them. However, they are easy to hydrate. Geological samples are difficult to be decomposed, thus the determination of niobium and tantalum has always been a difficult issue. Sample pre-treatment technology and modern analytical techniques are reviewed in this paper. Sample pre-treatment is the key step for niobium and tantalum analysis, therefore a suitable sample digestion and preconcentration method combined with analytical methods and sample characteristics is the premise of accurate determination of niobium and tantalum. Instrument analysis is the mainstream of modern analytical technology. Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) are the most widely used methods for the determination of niobium and tantalum, but it is necessary to solve problems such as coexisting component interference, matrix effects and salt influence. Laser Ablation (LA), X-ray Fluorescence Spectrometry (XRF), and Neutron Activation Analysis (NAA) are the development direction of tantalum and niobium analysis, due to the fact that they avoid the complicated sample pre-treatment and addition of impurities by solid sample introduction.