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BACKGROUND The quality of soil is directly related to human health and the safety of agricultural products, which has important references for agricultural planting and land planning. As an important vegetable basket base in Chengdu, Tangchang Town has developed agricultural planting, but the recent soil quality in the region is still unclear. OBJECTIVES In order to accurately understand the current content of nutrient and heavy metal elemental characteristics and soil quality grade of topsoil in the Tangchang agricultural planting area. METHODS According to 1∶50000 soil quality geochemical survey, 810 topsoil samples were collected. The contents of N, P, K, As, Cd, Hg, Pb, Cr, Ni, Cu, Zn, Se and pH in these soil samples were determined by X-ray fluorescence spectrometry, inductively coupled plasma-mass spectrometry, atomic fluorescence spectrometry, element analyzer and ion selective electrode method. The element geochemical characteristics and soil nutrient grade, soil environmental quality grade and comprehensive soil geochemical grade were then evaluated. RESULTS (1) Compared with the general topsoil in China, Zn and Pb in the topsoil of the study area are slightly enriched, Se is relatively enriched, N, P, Cd and Hg are strongly enriched. The topsoil is generally weakly acidic. (2) The comprehensive grade of soil nutrients is rich in second grade, accounting for 88.0% of the area, and the soil fertility is rich. The proportion of the first grade soil area in the environmental quality grade of the eight heavy metal elements in the soil is more than 96.0%, and the comprehensive environmental quality grade is dominated by first grade clean type, accounting for 98.06%. The comprehensive quality of soil is mainly grade one, accounting for 85.85%. (3) The area of selenium-rich soil in the region is 2.49km2, accounting for 3.7%, sporadically distributed in the central study area. Copper-rich soil area is 63.13km2, accounting for 94.0%, and zinc-rich soil area is 63.31km2, accounting for 94.17%. CONCLUSIONS In summary, the nutrients of topsoil in Tangchang Town are rich, the soil environment is clean and the comprehensive quality of the soil is high.

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 Three acids and four acids dissolution methods are the two main dissolution methods for determination of rare earth, cobalt, hafnium, indium, manganese, niobium, tantalum, thallium, chromium, cadmium, gallium, germanium, vanadium and tin in geological samples by inductively coupled plasma-mass spectrometry (ICP-MS). However, the composition of geological samples is complex, the content of rare earth and other metal elements is low, and the properties of each element are different, which makes the measurement results of volatile elements such as vanadium, chromium, cadmium, gallium and tin unstable, and rare earth elements such as lanthanum, cerium, praseodymium and neodymium are not completely dissolved by three acids or four acids. OBJECTIVES To improve the four acids dissolution system for the determination of 28 elements including rare earth elements and rare metal elements. METHODS The method of HCl-HNO3-HF-HClO4-H2SO4 was developed by addition of H2SO4 in the dissolution system of HCl-HNO3-HF-HClO4. A new analysis method has been developed for the certified reference material of stream sediment, soil and rock, and 28 elements including rare earth elements in samples were determined simultaneously by ICP-MS with 10ng/mL 103Rh and 185Re as the internal standard by on-line injections. RESULTS The accuracy of volatile elements such as vanadium, chromium, cadmium, gallium and tin was improved by 1.4%-14.6%, and that of rare earth elements such as lanthanum and cerium was improved by 0.2%-8.9%. The certified reference materials of stream sediment (GBW07301a), soil (GBW07408) and rock (GBW07107) were analyzed to test the method. The determined values were in good agreement with the certified values. The standard deviations (RSD) of the method were 1.14%-9.84% and accuracy (△lgC) was not higher than 0.1. CONCLUSIONS This method is rapid, simple, and accurate and can meet the requirements for determining the content of rare earth, cobalt, hafnium, indium, manganese, niobium, tantalum and other metal elements in large quantities of geological samples.

The polymetallic mineral samples in Pan-Xi region are rich in rare earth resources, and exploring an efficient and accurate analysis method is of great significance for their comprehensive utilization. In this study, the samples were decomposed by three methods, namely closed acid dissolution, open acid dissolution with five acid and alkali fusion with sodium peroxide, and the 15 REE were determined by inductively coupled plasma mass spectrometry (ICP-MS) with Rh and Re as internal standard correction elements. The comparative experiments were conducted using standard substances, and the results showed: (1) The detection limit of closed acid dissolution method was low with relative standard deviation (RSD) ranging from 2.51% to 9.56% and the accuracy of method (ΔlgC) ranging from 0.006 to 0.073, while the sample processing was long, and the results of some REE were low. (2) The RSD of open acid dissolution with five acid method ranged from 1.93% to 7.96%, and ΔlgC ranged from 0.004 to 0.045 with low results of the determination results of REE. (3) The alkali fusion with sodium peroxide method eliminated the influence of matrix effects by selecting instrument optimization, sample dilution, appropriate internal standard elements, etc. The RSD ranged from 1.24% to 6.49%, and ΔlgC ranged from 0.001 to 0.032. In conclusion, alkali fusion with sodium peroxide method has a fast analysis process, complete sample dissolution, and the accuracy and precision of test results can meet the requirements of specification (DZ/T0011-2015), which is most suitable for the analysis of REE in polymetallic mineral samples from Pan-Xi region. [ABSTRACT FROM AUTHOR]

In order to obtain the full spectrum information of the sample, improve the resolution and sensitivity, and save materials and reagents, an upgraded CCD-1 photoelectric direct reading emission spectrometer was adopted, and the mixture of potassium pyrosulfate, sodium fluoride, alumina, carbon and germanium dioxide was used as the spectrum buffer. When the ratio of the sample to the spectrum buffer was 1 : 1, it was evenly mixed and compacted in the lower electrode, and the problem of sampling was solved by opening a side hole in the lower electrode. At the same time, the selection of upper electrode specifications was investigated, the excitation current and exposure time were optimized, and an analytical method for the determination of trace silver, boron and tin in geochemical samples by solid sampling-CCD photoelectric direct reading emission spectrometry was established. The results showed that the excitation current wass 5 A for 3 s in the pre-combustion stage, and 14 A for 35 s in the excitation stage. The interference spectrum could be corrected accurately, the background was deducted automatically, and the baseline fluctuation of the sample was observed in real time. The calibration curve was drawn by using synthetic silicate reference materials for spectral analysis. The detection limits (3S) of silver, boron and tin in the six national first-class reference materials were 0. 01, 0. 55 and 0. 12 mg/kg respectively, and the relative standard deviations (w=12) were 2. 4%--8. 7%, 5. 8%--9. 4%, and 5. 2%--8. 7% respectively. The measured values were consistent with the standard values, and all the indexes of the method met the requirements of "Quality Management Standard for Laboratory Testing of Geology and Mineral Resources" (DZ/T 0130.4--2006). [ABSTRACT FROM AUTHOR]

The geographical detector is a new statistical method to detect spatial stratified heterogeneity and reveal the driving factors behind it. It can not only reveal the influence of a single factor on dependent variables but also evaluate the influence of two-factor interactions and does not need to consider linearity, while also avoiding the influence of multivariate collinearity. Without strong model assumptions, it solves the limitations of traditional methods in analyzing category variables. The research on the spatial differentiation of heavy metals in soil is increasingly widely used. This study collected 40 research reports on the spatial differentiation of soil heavy metals via geographical detector, combed the discrete methods of independent variables, research scale, dependent variables and types of independent variables, factor detection, exchange detection, risk detection, and ecological detection and put forward the problems that need to be clarified in the future application of this research. It is expected to provide support for the deep application of geo-detector in the field of spatial differentiation of soil heavy metals.

Geographic detectors can quickly detect spatial stratified heterogeneity and quantitatively reveal the intensity of driving factors of heavy metal content, which is of great significance for the prevention, control, and remediation of soil heavy metal pollution. In order to reveal the spatial differentiation and influencing factors of soil heavy metal content on the town-scale, 788 topsoil samples were collected from a town in the hinterland of Chengdu Plain. Soil heavy metal (Cd, Hg, As, Cu, Pb, Cr, Zn, and Ni) pollution risk assessments were carried out by using the geo-accumulation index method. Additionally, based on the geographic detector model, 15 factors such as soil properties, topography, soil forming factors, and distance were taken as independent variables, and the contents of each heavy metal element were taken as dependent variables to explore the spatial differentiation and influencing factors of heavy metal content in soils. The results showed that:the average contents of Hg, As, Pb, Cr, Cu, Ni, and Zn in the study area were 1.06-1.93 times the background value of Chengdu, and the content of Cd was lower than the background value; among them, Hg reached the light pollution level, and the other seven heavy metals were at the non-pollution level. The spatial distribution of eight heavy metals was significantly different, the correlation among the elements was significant, and a significant correlation was found between most heavy meals with soil properties; however, the correlation with distance factor and topographic factor was relatively weak. The factor detection showed that TP, TK, pH, TOC, elevation, and distance from the railway had the most significant explanatory power for the heavy metal contents. Interaction detection showed that the interaction between soil properties and other factors was the dominant factor for the spatial variation in heavy metals, and elevation, distance from residential area, distance from railways, and distance from industrial areas were also important factors. Risk detection showed that Hg had the most significant difference in the subregion of elevation and distance from railway, whereas the other seven heavy metals had the most significant difference in the sub-regions of influencing factors of soil properties. The spatial distribution of heavy metals varied significantly in soil at the town-scale, which was closely related to soil properties, topography, and human activities in the study area.

Three tropical forest soils were collected from Haikou, Qionghai and Tunchang in Hainan Island. Soil particle size fractionations were conducted using the standard dry-sieving procedure. Distribution of heavy metals in bulk samples and particle size fractions was determined by ICP-MS. The distribution characteristics and the response to organic carbon and iron were discussed. The results showed that the distribution of heavy metals was highly associated with the particle size fractions and variable patterns were found, which decreased with the increasing size. The accumulation of Cr, Ni, Cu, Zn, Cd and Cd was predominantly contributed by the particles finer than < 53 microm in diameter, whereas As mainly accumulated in particle size of 53-1 000 microm. Generally, the microaggregate (< 250 microm) contributed 14.38%-65.04% of heavy metals to the contents in bulk soil and the silt-clay aggregates (< 53 microm) contributed 2.61% -32.01%. The content of heavy metals except for As and Cd and Pb in Haikou soil in these different size fractions were controlled by the organic carbon and iron contents, which increased with the decreasing particle size.