Patterns in utilization of carbon sources in soil microbial communities contaminated with mine solid wastes from San Luis Potosi, Mexico

TRIAD method to assess ecological risks of contaminated soils in abandoned mine sites

Site-specific soil ecological risk assessment is important for protecting soil ecosystems because it reflects the environmental factors at the site to detect ecological risks and develop risk management measures. This study assessed the ecological risks from chemical pollutants in abandoned mine sites using the TRIAD approach, evaluating its overall applicability, including the tiered system of assessment. A site-specific soil ecological risk assessment was conducted for five abandoned mine sites (Sites 1-4 and R, the reference site); integrated risks (IRs) for each site were calculated. Our results of the Tier 2 assessment showed that IRs at Sites 1-4 were 0.701, 0.758, 0.840, and 0.429, respectively. The IR classification was moderate, high, high, and low risk, in that order for Sites 1-4, the same as that for Tier 1. The IR had more varied analyses, emphasizing the significance of conducting higher tiered analyses under TRIAD while maintaining a balance between soil ecosystem protection and socioeconomic costs. Multiple analyses reduced the uncertainty of IR, thus enabling efficient risk management decision-making to protect soil ecosystems. Our study provides a basis for using the TRIAD for soil assessment and establishing policies for site-specific soil ecological risk assessments.

Health risk assessment of heavy metal pollution and its sources in agricultural soils near Hongfeng Lake in the mining area of Guizhou Province, China

Background

Accelerated modern industrial processes, extensive use of pesticides and fertilizers and remaining issues of wastewater irrigation have led to an increasingly severe composite pollution of heavy metals in arable land. Soil contamination can cause significant damage to ecological environments and human health. Mineral resource mining can result in varying degrees of heavy metal pollution in surrounding water systems and soil. As a plateau lake, Hongfeng Lake has a fragile watershed ecosystem. Coupled with the rapid development of the current socio-economy and the ongoing activities of mining, urbanization and agricultural development, the water and soil environment of the lake and arable land are facing serious heavy metal pollution. Therefore, the situation warrants attention.

Methods

This study focused on characterizing soil types and conducted sampling and laboratory testing on the farmland soil in Hongfeng Lake. The integrated Nemero comprehensive pollution assessment and potential ecological pollution assessment methods were used to evaluate the heavy metal pollution status. The APCS-MLR model was employed to explore the sources of heavy metal pollution. In addition, the human health risk model was used to analyze the association between heavy metal content in cultivated land and human health risks.

Results

The single-factor pollution of each element was ranked in descending order: Hg > As > Pb > Cr > Cd, with Hg being the main pollutant factor. The entire area was subjected to mild pollution according to the pollution index. Pollution source analysis indicated two main pollution sources. Hg, As, Pb and Cr pollution mainly resulted from Source 1 (industrial and natural activities), accounting for 71.99%, 51.57%, 67.39% and 68.36%, respectively. Cd pollution was mainly attributed to Source 2 (agricultural pollution source), contributing 84.12%. The health risk assessment model shows that heavy metals posed acceptable carcinogenic risks to humans rather than non-carcinogenic risks. As was the main non-carcinogenic risk factor, while Cr was the main carcinogenic risk factor, with higher risks in children than adults.

Conclusion

Our study identified the heavy metal pollution in farmland soil in Hongfeng Lake, evaluated and analyzed the pollution sources and identified the heavy metal elements in cultivated lands that have the greatest impact on human health risks. The aim of this study is to provide a scientific basis for soil heavy metal pollution control.

Unravelling the ultramafic rock-driven serpentine soil formation leading to the geo-accumulation of heavy metals: An impact on the resident microbiome, biogeochemical cycling and acclimatized eco-physiological profiles

In the present study, we have underpinned the serpentine rock, serpentinized ultramafic soil and rhizosphere's microbial communities, signifying their heavy metals-exposed taxa signatures and functional repertoires in comparison to non-serpentine soils. The results revealed that the serpentine rock embedded soil highlighted the geo-accumulation of higher amount of Cr and Ni impacting soil microbial diversity negatively by metal stress-driven selection. Biolog Ecoplate CLPP defined a restricted spectrum of C-utilization in the higher heavy metal-containing serpentine samples compared to non-serpentine. The linear discriminant analysis (LDA) score identified a higher abundance of Desulfobacterota, Opitutales, and Bacteroidales in low Cr and Ni-stressed non-serpentine-exposed samples. Whereas the abundance of Propionibacteriales and Actinobacteriota were significantly enriched in the serpentine niche. Further, the C, N, S, Fe, and methane biogeochemical cycles linked functional members were identified, and showing higher functional diversity in low Cr and Ni concentration-containing rhizosphere JS-soils. The Pearson correlation coefficient (r) value confirmed the abundance of functional members linked to specific biogeochemical cycle, positively correlated with relevant pathway enrichment. Ultimately, this study highlighted the heavy metal stress within a serpentine setting that could limit the resident microbial community's metabolic diversity and further select the bacteria that could thrive in the serpentine-associated heavy metal-stressed soils. These acclimatized microbes could pave the way for the future applications in the soil conservation and management.

Arsenic resistance and horizontal gene transfer are associated with carbon and nitrogen enrichment in bacteria

Coastal waters are confluences receiving large amounts of point and non-point sources of pollution. An attempt was made to explore microbial community interactions in response to carbon, nitrogen and metal pollution. Additionally, experiments were designed to analyze the influence of these factors on horizontal gene transfer (HGT). Shift in bacterial diversity dynamics by arsenic stress and nutrient addition in coastal waters was explored by metagenomics of microcosm setups. Phylogenetic analysis revealed equal distribution of Gammaproteobacteria (29%) and Betaproteobacteria (28%) in control microcosm. This proportional diversity from control switched to unique distribution of Gammaproteobacteria (44.5%)> Flavobacteria (17.7%)> Bacteriodia (11.92%)> Betaproteobacteria (11.52%) in microcosm supplemented with carbon, nitrogen and metal (C + N + M). Among metal-stressed systems, alpha diversity analysis indicated highest diversity of genera in C + N + M followed by N + M > C+M> metal alone. Arsenic and ampicillin sensitive E. coli XL1 blue and environmental strains (Vibrio tubiashii W85 and E. coli W101) were tested for efficiency of uptake of plasmid (P) pUCminusMCS (arsB^Ramp^R) under varying stress conditions. Transformation experiments revealed that combined effect of carbon, nitrogen and metal on horizontal gene transfer (HGT) was significantly higher (p < 0.01) than individual factors. The effect of carbon on HGT was proved to be superior to nitrogen under metal stressed conditions. Presence of arsenic in experimental setups (P + M, P + N + M and P + C + M) enhanced the HGT compared to non-metal counterparts supplemented with carbon or nitrogen. Arsenic resistant bacterial isolates (n = 200) were tested for the ability to utilize various carbon and nitrogen substrates and distinct positive correlation (p < 0.001) was found between arsenic resistance and utilization of urea and nitrate. However, evident positive correlation was not found between carbon sources and arsenic resistance. Our findings suggest that carbon and nitrogen pollution in aquatic habitats under arsenic stress determine the microbial community dynamics and critically influence uptake of genetic material from the surrounding environment.

Soil Microbial Community Profiling and Bacterial Metabolic Activity of Technosols as an Effect of Soil Properties following Land Reclamation: A Case Study from the Abandoned Iron Sulphide and Uranium Mine in Rudki (South-Central Poland)

The aims of the study were (1) to recognize the structure of bacteria diversity in Technosols developed from mine spoils containing iron (Fe) sulphides with the use of culture-independent technique, and (2) to determine microbial metabolic activities, in the context of their potential to be an adequate indicators of soil properties being the consequence of land reclamation. The study site was located in the vicinity of the abandoned Fe sulphide and uranium mine in Rudki village (Holy Cross Mts., Poland). Three soil profiles with different chemical properties (pH, content of carbonates, soil salinity, content of total organic carbon and total nitrogen) were studied. Biodiversity was determined with the use of meta-barcoding of 16S rRNA community profiling analysis based on the hypervariable V3-V4 region of 16S rRNA gene (MiSeq, Illumina). The catabolic fingerprinting of soil microbial communities was evaluated with the use of Biolog®EcoPlates™ System. It was evidenced that changes in microbial structure and their metabolic activity were the consequence of a combined effect of both the soil depth and soil chemical properties being the final result of reclamation process. Consequently, microbial indicators (from phyla to genera level) indirectly testifying about success or ineffectiveness of reclamation in technogenic soils were recommended. To our best knowledge, the present study is the first insight into Polish Technosols biodiversity and catabolic activity.