Microbial diversity and community assembly in heavy metal-contaminated soils: insights from selenium-impacted mining areas.

Microbial community succession in soils under long-term heavy metal stress from community diversity-structure to KEGG function pathways

Environmental problems caused by the exploitation of mineral resources are worsening, especially the heavy metal pollution in soil. Food safety caused by heavy metal pollution in soil has become the focus of increasing attention.Sampling points were selected in Hunan Province. By sampling the soil and rice point by point, the total concentration and the concontration in rice were monitored. The results showed that the mean concentration of Cd, Cu, Hg, Pb and Zn were 1.31 mg/kg, 45.3 mg/kg, 0.61 mg/kg, 49.15 mg/kg and 133.3 mg/kg. The soils were contaminated in some parts of the 85 investigated sites in Hunan Province.Also, the analysis results showed that the average of PI (pollution index) descended in the order of Cd (2.58) > Hg (1.05) > Cu (0.52)> Zn (0.51)> Pb (0.41).The NIPI values of the research area were 28.59, belong to the high-level pollution, which mainly caused by Cd. The pollution ratio of soil samples were 100.0% in Zhuzhou-Xiangtan and Changning, 94.1%, 90.9% and 88.2% in Changde, Yiyang and Yongzhou. According to the potential ecological risk evaluation result, there was a medium level risk in the investigation area of Hunan and the potential ecological risk mainly caused by Cd.

The accumulation of heavy metals in vegetables has become a key factor affecting residents’ health. Samples of soil and vegetables surrounding a pyrite mine in Tongling, China, were collected in this study to investigate the contaminant characteristics from heavy metals. Multiple elements were measured to evaluate pollution risks. Results showed that the respective concentrations of Cr, Ni, Cu, Zn, Pb, and Cd were 80.84, 22.39, 149.75, 234.21, 135.70, and 3.86 mg kg−1 in soil. Cd contributed most to the integrated pollution index, followed by Cu, Pb, and Zn. Regarding vegetables, Cd contamination was most pronounced in the eggplant and green soybean samples; no heavy metal levels exceeded pollutants’ value limits in the potato and radish samples. This study demonstrates a complex relationship between soil and vegetables in terms of heavy metals; in our case, no significant correlation was observed between heavy metals in vegetables and in soil. Health risk assessment and sensitivity analysis, based on vegetable intake, indicated that Cd in vegetables most prominently affected locals’ health among the considered pollutants: it posed cancer risks for adults and children along with non-cancer risks for children. As heavy metal pollution in soil and vegetables around this mining area threatens the ecological environment and residents’ health, mitigation is necessary.

Due to the emerging environmental issues related to heavy metals, concern about the soil quality of farming lands near manufacturing district is increasing. Investigating the function of soil microorganisms exposed to long-term heavy metal contamination is meaningful and important for agricultural soil utilization. This article studied the potential influence of several heavy metals on microbial biomass, activity, abundance, and community composition in arable soil near industrial estate in Zhuzhou, Hunan province, China. The results showed that soil organic contents (SOC) were significantly positive correlated with heavy metals, whereas dehydrogenase activity (DHA) was greatly depressed by the heavy metal stress. Negative correlation was found between heavy metals and basal soil respiration (BSR), and no correlation was found between heavy metals and microbial biomass content (MBC). The quantitative PCR (QPCR) and polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis could suggest that heavy metal pollution has significantly decreased abundance of bacteria and fungi and also changed their community structure. The results could contribute to evaluate heavy metal pollution level in soil. By combining different environmental parameters, it would promote the better understanding of heavy metal effect on the size, structure, and activity of microbial community in arable soil.

Chemical and microbial characterisations of particle-size fractions (PSFs) from a rice paddy soil subjected to long-term heavy metal pollution (P) and nonpolluted (NP) soil were performed to investigate whether the distribution of heavy metals (Cd, Cu, Pb and Zn) regulates microbial community activity, abundance and diversity at the microenvironment scale. The soils were physically fractionated into coarse sand, fine sand, silt and clay fractions. Long-term heavy metal pollution notably decreased soil basal respiration (a measurement of the total activity of the soil microbial community) and microbial biomass carbon (MBC) across the fractions by 3-45% and 21-53%, respectively. The coarse sand fraction was more affected by pollution than the clay fraction and displayed a significantly lower MBC content and respiration and dehydrogenase activity compared with the nonpolluted soils. The abundances and diversities of bacteria were less affected within the PSFs under pollution. However, significant decreases in the abundances and diversities of fungi were noted, which may have strongly contributed to the decrease in MBC. Sequencing of denaturing gradient gel electrophoresis bands revealed that the groups Acidobacteria, Ascomycota and Chytridiomycota were clearly inhibited under pollution. Our findings suggest that long-term heavy metal pollution decreased the microbial biomass, activity and diversity in PSFs, particularly in the large-size fractions.

Investigations of gut microbiomes have shed light on the diversity and genetic content of these communities, and helped shape our understanding of how host-associated microorganisms influence host physiology, behavior, and health. Despite the importance of gut microbes to metazoans, our understanding of the changes in diversity and composition across the alimentary tract, and the source of the resident community are limited. Here, using community metagenomics and 16S rRNA gene sequencing, we assess microbial community diversity and coding potential in the foregut, midgut, and hindgut of a juvenile Panchlora cockroach, which resides in the refuse piles of the leaf-cutter ant species Atta colombica. We found a significant shift in the microbial community structure and coding potential throughout the three gut sections of Panchlora sp., and through comparison with previously generated metagenomes of the cockroach’s food source and niche, we reveal that this shift in microbial community composition is influenced by the ecosystems in which Panchlora sp. occurs. While the foregut is composed of microbes that likely originate from the symbiotic fungus gardens of the ants, the midgut and hindgut are composed of a microbial community that is likely cockroach-specific. Analogous to mammalian systems, the midgut and hindgut appear to be dominated by Firmicutes and Bacteroidetes with the capacity for polysaccharide degradation, suggesting they may assist in the degradation of dietary plant material. Our work underscores the prominence of community changes throughout gut microbiomes and highlights ecological factors that underpin the structure and function of the symbiotic microbial communities of metazoans.

Abstract. The heavy metal pollution of urban soil of industrial area and its impact on human healths becoming one of the environmental problems in Ulaanbaatar city of Mongolia. The purpose of this study was to determine spatial distribution and health risk of heavy metal pollution in soils surrounding area of leather processing factory and wastewater treatment plants (WWTP) of Ulaanbaatar city. Mapping the spatial distribution of contaminants in soils is the basis of pollution evaluation and risk control. Interpolation methods are extensively applied in the mapping processes to estimate the heavy metal (As, Zn, Pb, Cd, Cr, Cu) concentrations of topsoils. The average concentrations of Cr, Ni, Pb, Zn, Cu and As were 1986.9, 110.5, 111.0, 110.5, 53.5, 16.4 mg/kg, respectively. According to result as the soil pollution index with spatial distribution, a high pollution level for Cr while Zn, Cu and Pb have medium pollution levels. The soil pollution index (PI) values of heavy metals of study areas are, following descending orders Cr > Zn > Cu > Pb > As > Ni. The potential ecological risk of Cr, Cu, Pb, As indicated high ecological risk in the study area. The Hazard index values for almost all the metals were higher than 1, it is indicating a carcinogenic risk for children and adults. The risk index values of two metals (Cr, As) were contribute to a higher risk of development of cancer in humans. Heavy metal contamination can occur when soil particles are swept away from the initial pollution areas by the wind. Therefore, it is necessary to take measures to reduce soil pollution and encourage rehabilitation.

Soil carbon fractions drive microbial community assembly processes during forest succession.

Heavy metal pollution in agricultural soils due to anthropogenic activities like industries and agrochemicals is a major concern all over the world. This study aims to evaluate soil fertility and heavy metal pollution in selected sites of the Sandila area, Uttar Pradesh, India. The composite soil samples were collected in industrial sites (I), surrounding agricultural farmlands (F) in Sandila, and the CIMAP farm as a control (C). The physicochemical properties, heavy metal content, and soil pollution indices like the geo-accumulation index, single pollution index, enrichment factor, contamination factor, and ecological risk factor were analyzed. Soil pH varied across sites—acidic in industrial (I), alkaline in farmland (F), and neutral in control (C). Nutrient levels differed significantly: available nitrogen was low in I (188.16 kg/ha) but high in F (616.75 kg/ha) and moderate in C (292.7 kg/ha). Phosphorus (P₂O₅) and potassium (K₂O) ranged from high (99 kg/ha, 309.44 kg/ha) in I to medium (27.93–252.52 kg/ha) in F and lower (22.35–126.03 kg/ha) in C. The mean elemental concentration in soils was in decreasing order as Zn > Pb > Cu> Cr > Ni > Ba > Fe > Mn > Co. Pb and Cu were major heavy metals contaminated in I and F sites. To mitigate heavy metal contamination, phytoremediation using aromatic crops is recommended. Keywords: Enrichment factor, Geo-accumulation index, Heavy metals, PCA, Single pollution index.

This article is a Commentary on Böttner et al. (2023), 239: 1475–1489.

Response of soil microbial communities and microbial interactions to long-term heavy metal contamination

In this study, the effects of pollution levels and heavy metal pollution on soil microbial diversity in karst tea plantations are reported. Four tea plantations from plateau hills, under forests, by lakesides and on steep slopes in the South China karst were used as research regions. Soil samples were taken from these tea plantations, the soil heavy metals Cd, Cr, Pb, Zn, Ni and Cu were tested using inductively coupled plasma-mass spectrometry, and Hg and As were tested via atomic fluorescence spectrometry. The soil microbes were analyzed via high-throughput sequencing technology. Heavy metal pollution was evaluated via the single factor index and pollution load index, and the correlation between soil heavy metals and the microbial community was analyzed via SPSS 18.0 and Canoco 5.0 software. The results showed that the studied tea plantation soils were greatly polluted by the heavy metals, Cd and Hg, to a low to moderate degree. The comprehensive pollution of multiple heavy metals occurred only in lakeside tea plantations, in which pollution reached a low degree. It is also suggested that Hg and Cd were the major contributors, followed by Cu. The soil microbial diversity in soil samples from lakeside tea plantations was the highest; however, the discrepancy in its dominant species composition was also the highest. When the pollution load index was close to 0.6, the microbial diversity decreased sharply. Afterward, the diversity and heterogeneity generally gently increased, and the dominant composition was more obvious. These results reveal that the impact of heavy metal pollution on soil microbial diversity was not very distinct, but the impact on the dominant microbial community composition was obvious. In addition, the heavy metals, Cd, Hg and Cu, were the key factors that impacted the soil microbial community composition.

Fertilization is a vital approach to increase the crop yield by enhancing soil fertility, but some of the fertilizer sources such as pig manure contain non-essential toxic heavy metals, which can produce the environmental and public health risk. Therefore, the purpose of this study was to investigate the soil fertility and heavy metal pollution risk under long-term fertilization in acidic paddy soil. Fertilizer treatments that were arranged in randomized complete block design (RCBD) included CK (no fertilization), NK (inorganic nitrogen and potassium fertilization), NPK (inorganic NK and phosphorus fertilization), NPKM1 (70% of NPK and 30% pig manure application), NPKM2 (50% of NPK and 50% of pig manure application), and NPKM3 (30% of NPK and 70% of pig manure application). The rice grain yield and soil nutrient contents were highest under NPKM3 treatment. Long-term addition of manure significantly (P ≤ 0.05) increased soil pH and SOC content compared to the NPK fertilization. Soil available and total Cr, Cd, and Hg contents were highest under NPKM3 treatments, while soil total and available Pb content was significantly (P ≤ 0.05) higher under NPK treatment. Highest ecological risk (IR) was (1904) under NPK treatment and highest pollution load index (PLI) was 1.5 under NPKM3 treatment. Cd concentration in rice grain exceeded the maximum permissible limit of 0.1 mg kg−1 under combined application of manure and inorganic fertilization treatments. Grain Cr, Hg, and Pb contents were within safe limits of their concentration in all treatments. Moreover, biological accumulation coefficients of Cr, Cd, Hg, Pb, Zn, and Cu were highest under NPK treatment. Redundancy analysis (RDA) showed that soil pH and nutrient contents showed significant correlation with heavy metal concentrations in soil. Soil pH showed significant (P ≤ 0.05) positive effect on Cd accumulation in rice grain. Heavy metals in pig manure should be monitored before application to the field to reduce the risk of heavy metal pollution in soil and plant. Furthermore, combined application at the rate of 70% inorganic fertilization and 30% of manure could be better strategy to produce high crop yield with minimum risk of heavy metal contamination in soil and food crops.

Heavy metal pollution in soils of development zones has attracted wide attention. In this study, soil heavy metal pollution levels and health risks in 15 selected development zones in Shandong Province were investigated for the first time. Geo-accumulation and potential ecological risk indexes were used to assess pollution levels, and health risk was assessed using the US Environmental Protection Agency model. The soil was contaminated by various heavy metals, among which Hg was dominant. A total of 19% of the monitoring sites showed moderate ecological risk level, and low risk level was observed in general. Pollution control of Hg and Cd in each development zone must be strengthened. Health risk analysis showed that noncarcinogenic and carcinogenic risk levels for adults and children were acceptable or nearly acceptable. Positive matrix factorization model was used to identify three possible sources of heavy metal pollution, namely, industrial sources, atmospheric deposition, and transportation. Some specific measures should be taken to prioritize the control of Hg, As, and Cr for protecting the soil environment and human health, especially vulnerable groups, such as children.

Speciation of heavy metals in soils and their immobilization at micro-scale interfaces among diverse soil components