[Quantifying the Contribution of Soil Heavy Metals to Ecological and Health Risk Sources].

Quantifying the risk of soil heavy metal sources can identify the main pollution sources. It can provide a scientific basis for reducing the ecological and human health risks of soil heavy metals. Taking the shallow soil in a Pb-Zn mine watershed in northern Guangxi as a research object， ecological and human health risk assessments were conducted using potential ecological risk assessment （RI） and human health risk assessment （HRA）， and the source apportionment of soil heavy metals was completed using the absolute principal component-multiple linear regression receptor （APCS-MLR） model and random forest （RF） model. Then， a combined risk assessment model， consisting of RI， HRA， and APCS-MLR， was used to quantify the risk of soil heavy metal sources. The results showed that the contents of Pb， Zn， Cu， and Cd exceeded the environmental screening values for agricultural land with mean values of 342.77， 693.34， 61.27， and 3.08 mg·kg-1， respectively， and there was a certain degree of contamination. Pb， Cr， and As were the main health risk impact factors， with higher health risks for children than for adults. Three sources were identified： mining activities （Source Ⅰ）， soil parent material sources and original formation （Source Ⅱ）， and unknown sources. Pb， Zn， Cu， and Cd were mainly derived from Source Ⅰ， and Cr and As were controlled by unknown sources and Source Ⅱ. The source risk assessment results of soil heavy metals indicated that the potential ecological risk and non-carcinogenic risk were mainly from Source Ⅰ and Source Ⅱ， and carcinogenic risk was mainly from unknown sources. The unknown sources had a high proportion in source apportionment and risk assessment， and should be further researched to provide scientific basis for soil heavy metal control. The combined risk assessment model based on source analysis， focusing on the risk characteristics of different sources， can accurately identify high-risk pollution sources. It is a more reasonable and reliable risk assessment method.

[Analysis of Influencing Factors on the Accumulation and Distribution of Heavy Metals in Soil of a Typical Lead-zinc Mine Watershed].

Taking a typical lead-zinc mining area watershed in northern Guangxi as the research object, the total amount and morphology of nine heavy metals(Zn, Pb, Cd, Fe, Mn, Cu, Cr, Sb, and As) and fine soil property indicators(pH, conductivity, cation exchange, organic matter, and particle size) in the surface soils of the Yangshuo lead-zinc mine were analyzed and determined. The accumulation and distribution of soil heavy metals and their main controlling factors were revealed using correlation, redundancy(RDA), and GeoDetector analyses. In the analytical data of soil samples, the mean values of As, Cd, Fe, Cu, Mn, Pb, and Zn exceeded the background values, in which Cd, Mn, Pb, and Zn were 4.01, 3.15, 5.53, and 9.72 times higher than the background values, respectively, indicating that they were significantly enriched in the surface soil. There were more noticeable spatial differences in distribution, which were higher in the alluvial floodplain accumulation area(1-6) than those in the other areas(7-9). The available states(K) of Pb and Mn were 48.8% and 57.2%, respectively, with high bioavailability and average potential migration capacity(PMI 0.015-0.068 and 0.036-0.082, respectively). The Zn and Cu had some bioavailability degree, with available states(K) of 30.9% and 16.8% and moderately available states of 10.9% and 13.6%, respectively. The difference was that Zn had a strong migration capacity(PMI 0.160-0.203), and Cu had an average potential migration capacity(PMI 0.017-0.084). Fe and Cr had a difficult-to-use state(N)>95%, low bioavailability, and weak migration capacity(PMI<0.005). The results of the analysis of the main controlling factors affecting accumulation and distribution showed that Cr was controlled by cation exchange capacity(CEC) and clay; Fe was controlled by sand; As was controlled by electrical conductivity(EC) and pH; Cu, Zn, Cd, and Sb were controlled by pH and clay; Pb accumulation was controlled by pH and soil organic matter(SOM); Mn was controlled by pH. This study quantified the main controlling factors affecting the accumulation and distribution of soil heavy metals, which can provide a scientific basis for decision making in the prevention and control of soil heavy metal pollution.

The relationships between fractal parameters of soil particle size and heavy-metal content on alluvial-proluvial fan.

The particle size distribution (PSD) of soil is an important factor in determining heavy-metal content, mobility, and transformation. One method of describing the soil PSD is applying fractal theory. This study explored the use of fractal theory to characterize soil PSD in the alluvial-proluvial fan located downstream of the Yangshuo lead­zinc mine. The relationships between fractal parameters of soil PSD and heavy-metal content were analyzed. The results showed that soil in front of the mountain (FM) had higher clay content than soil on the mountain slope (MS) or in the middle of the alluvial-proluvial fan (MF). Among the different sections of the alluvial-proluvial fan, MS had the largest capacity dimension D(0), information dimension D(1), correlation dimension D(2), single fractal dimension D, spectral width Δα, and D(1)/D(0), whereas MF had the greatest symmetry degree Δf. Soil of MS had the highest ω (Cr) and ω (Fe), while FM had the highest ω (Zn), ω (Mn), ω (Pb), ω (Cu), ω (As), ω (Sb), and ω (Cd). Fractal parameters of soil PSD and soil mechanical composition were significantly correlated, while both variables were correlated with heavy-metal content. Fractal parameters can be used to indicate heavy-metal content when heavy metals migrate due to migration of particle size. This study thus introduces an empirical method for evaluating heavy-metal content in soil and analyzing the mechanisms of their migration, making a strong contribution to developing strategies that limit heavy-metal pollution.

[Spatial Distribution and Sources of Heavy Metals in Soil of a Typical Lead-Zinc Mining Area, Yangshuo].

Taking a typical lead-zinc mining area in Yangshuo county, Guangxi as the research object, the contents of 10 metal elements (Cr, Mn, Ni, Cu, Zn, As, Cd, Sb, Hg, and Pb) in the surface soil of Sidihe River basin in Yangshuo were analyzed and determined. Pearson correlation analysis, principal component analysis (PCA), positive definite matrix factorization (PMF), and other methods were comprehensively used to quantitatively analyze their contributions and identify pollution sources. In total, 168 surface soil samples were collected across the study area. The mean concentrations of Zn, Cd, Hg, and Pb in the soils were higher than the National Environmental Quality Standards for Soils in China. The mean contents of Sb, Cd, Cu, Pb, and Zn were higher than their corresponding local background values by approximately 1.01, 5.50, 3.29, 9.11, and 10.67 times, respectively, indicating that heavy metals have been enriched in topsoil. The Igeo showed that the major pollutant element in the soils was Hg, followed by Pb, Zn, and Mn. Correlation analysis and principal component analysis showed that the sources of metal pollution in surface soil in the study area were complex and mainly from human activities. Cu, Zn, Cd, Sb, As, and Pb were mainly derived from mining activities; Hg, Cr, and Ni were controlled by soil parent material sources; and Mn and Cd were mainly derived from mining activities and agricultural activities. PMF model analysis results showed that the metal pollution sources in the surface soil were jointly affected by these three sources. Mining activities, natural sources, and a mixed source of mining activities and agricultural activities were the main sources of heavy metal pollution in the soils, accounting for 58.0%, 13.5%, and 28.6% of the total heavy metal accumulation, respectively. Ni, Cu, Zn, As, Sb, Hg, and Pb were derived mainly from mining activities. Cr, Ni, and Hg were mainly attributed to natural sources, such as soil parent materials and rainfall erosion (44.6%, 23.2%, and 21.0%, respectively), and Mn and Cd were associated with a mixed source of mining activities and agricultural activities (75.4% and 70.4%).

Characteristics of denitrification and microbial community in respect to various H2 pressures and distances to the gas supply end in H2-based MBfR.

The hydrogen-based hollow fiber membrane biofilm reactor (H2-based MBfR) has shown to be a promising technology for nitrate (NO3 --N) reduction. Hollow fiber membranes (HFM) operating in a closed mode in an H2-based MBfR often suffer from reverse gas diffusion, taking up space for the effective gas substrate and resulting in a reduction in the HFM diffusion efficiency, which in turn affects denitrification performance. In this work, we developed a laboratory-scale H2-based MBfR, which operated in a closed mode to investigate the dynamics of denitrification performance and biofilm microbial community analysis at different H2 supply pressures. A faster formation of biofilm on the HFM and a shorter start-up period were found for a higher H2 supply pressure. An increase in the H2 pressure under 0.08 MPa could significantly promote denitrification, while a minor increase in denitrification was observed once the H2 pressure was over 0.08 MPa. Sequencing analysis of the biofilm concluded that (i) the dominant phylum-level bacteria in the reactor during the regulated hydrogen pressure phase were Gammaproteobacteria and Alphaproteobacteria; (ii) when the hydrogen pressure was 0.04-0.06 MPa, the dominant bacteria in the MBfR were mainly enriched on the hollow fiber membrane near the upper location (Gas inlet). With a gradual increase in the hydrogen pressure, the enrichment area of the dominant bacteria in MBfR gradually changed from the upper location to the distal end of the inlet. When the hydrogen pressure was 0.10 MPa, the dominant bacteria were mainly enriched on the hollow fiber membrane in the down location of the MBfR.