Comparative transcriptomics revealed the mechanism of Stenotrophomonas rhizophila JC1 response and biosorption to Pb2.

Nowadays, there is limited research focusing on the biosorption of Pb2+ through microbial process, particularly at the level of gene expression. To overcome this knowledge gap, we studied the adsorption capacity of Stenotrophomonas rhizophila JC1 to Pb2+, and investigated the physiological mechanism by means of SEM, EDS, FTIR, membrane permeability detection, and investigated the molecular mechanism through comparative transcriptomics. The results showed that after 16 h of cultivation, the biosorption capacity of JC1 for 100 mg/L of Pb2+ reached at 79.8%. The main mechanism of JC1 adsorb Pb2+ is via intracellular accumulation, accounting for more than 90% of the total adsorption. At the physiological level, Pb2+ can precipitate with anion functional groups (e.g., -OH, -NH) on the bacterial cell wall or undergo replacement reaction with cell component elements (e.g., Si, Ca) to adsorb Pb2+ outside of the cell wall, thus accomplishing extracellular adsorption of Pb2+ by strains. Furthermore, the cell membrane acts as a "switch" that inhibits the entry of metal ions into the cell from the plasma membrane. At the molecular level, the gene pbt specificity is responsible for the adsorption of Pb2+ by JC1. In addition, phosphate permease is a major member of the ABC transporter family involved in Pb2+, and czcA/cusA or Co2+/Mg2+ efflux protein plays an important role in the efflux of Pb2+ in JC1. Further, cellular macromolecule biosynthesis, inorganic cation transmembrane transport, citrate cycle (TCA) and carbon metabolism pathways all play crucial roles in the response of strain JC1 to Pb2+ stress.

Exploring the fate of heavy metals from mining and smelting activities in soil-crop system in Baiyin, NW China.

The activity and fate of heavy metals (HMs) from mining and smelting activities in farmland soil is of great significance to effectively prevent the excessive enrichment of HMs in crops. This study focuses on Baiyin area, a typical mining city in northwest China. In this example, the sources, speciation, and fate of HMs in the farmland soil, and the migration and enrichment characteristics of HMs in the different parts of crops planted in different areas were studied in detail combining the chemical sequential extraction and Pb isotope approaches. Results showed that the mean anthropogenic contributions of HMs in farmland soils were approximately 85%, 88%, 76%, and 41% for the ore district (OD), Xidagou sewage irrigation area (XSIA), Dongdagou sewage irrigation area, and the Yellow River irrigation area, respectively, and the risk that HMs were excessively accumulated in crops in OD and XSIA was high. Compared with soil residual fractions, the isotope ratios 206Pb/207Pb in non-residual fractions (1.1304-1.1669) were closer to the values of local ores, suggesting that anthropogenic HMs from mining and smelting activities were mainly enriched in the non-residual fractions. The isotope ratios 206Pb/207Pb in crops (1.1398-1.1686) further confirmed that those anthropogenic HMs were more easily absorbed and concentrated by crops. HMs contents in leaves from OD and XSIA were generally higher than that in roots, suggesting that atmospheric deposition in OD and XSIA had a greater impact on the HMs concentration of crop leaves，while the excess rate of HMs in grain/fruit was the lowest in all parts of crops. The division and classification of crop planting in mining area can effectively help minimize the risk that HMs from anthropogenic source enter the human body through the food chain.

A comprehensive investigation of hazardous elements contamination in mining and smelting-impacted soils and sediments.

Extensive mining and smelting activities in the Baiyin district have resulted in a serious hazardous elements (HEs) contamination in the soils and overbank sediments. In this study, the concentrations and chemical fractions of HEs were analyzed to evaluate the environmental risks of these HEs in the focus areas. In soils, Zn, Cu, Pb, and Cd exhibited an obvious decline compared to the results in 2012, which confirmed that the treatments of the contaminated soils by the government have played a very important role in the remediation of the soils. However, Zn, Cu, and Pb still exceeded the background values, and the study areas were still extremely contaminated with Cd. The spatial distribution of HEs showed that the contaminated areas were mainly focused around the mining and smelting regions and the sewage irrigation regions. Sequential extraction showed that Zn was mainly present as a residue fraction, while the percentages of unstable fractions increased in the sewage irrigation region samples. As for Cd, the bioavailable fractions were extremely high (over 90%) and the ecological risk was much higher than Zn. In the case of the sediments, the concentrations of HEs were extremely high. However, few researches have investigated HEs contamination in the sediments from the study area. With changes in climate and environmental conditions, HEs in sediments will easily release and influence the groundwater and the irrigation water. Furthermore, the available fractions of Zn and Cd were over 80%, which suggests high bioavailability and mobility in sediments. HEs pollution in sediments should receive more attention compared to that in soils.

Lead isotopic fingerprinting as a tracer to identify the pollution sources of heavy metals in the southeastern zone of Baiyin, China.

Baiyin (Gansu Province, China) is a heavily industrialized city with non-ferrous metal mining, ore dressing, and chemical production. The surrounding district has suffered from serious heavy metals (HMs) contamination over half a century. In this study, a Pb isotopic approach was adopted to trace the sources of HMs and explore the environmental behaviors of HMs in the area surrounding Baiyin. HMs concentrations in topsoil showed a clear decrease as the distance from the ore district increased, which suggested that atmospheric transportation is one of the main pathways of HMs dispersal. The Dongdagou irrigation area was an exception where contaminated water from Dongdagou had been used for a long time. The plots of 206Pb/207Pb vs. 208Pb/206Pb and 1/Pb vs. 206Pb/207Pb from the topsoil samples could be described in terms of a binary mixing model with the two average 206Pb/207Pb end-members being (1) the mining and smelting activities (1.1494) and (2) the soil background (1.1992). The relative anthropogenic contribution quickly decreased from 88.3% in the ore district to 30.6% in the Yellow River irrigation area. These results suggested that HMs in the Baiyin District were mainly contributed by anthropogenic mining and smelting activities. The isotope ratios of 206Pb/207Pb in the sediments maintained a consistent low level from the ore district to the Yellow River irrigation area, thereby suggesting that HMs from anthropogenic sources could also be transported over a long distance in the river systems. Moreover, the positive correlation between S content and HMs concentrations in topsoil and sediment confirmed that the HMs mainly originated from the sulfide deposits and smelters.

Sorption of uranyl ions on TiO2: Effects of pH, contact time, ionic strength, temperature and HA.

Sorption of U(VI) onto TiO2 as functions of pH, ionic strength, contact time, soil humic acid (SHA), solid-to-liquid ratio and temperature was studied under ambient conditions using batch and spectroscopic approaches. The sorption of U(VI) on TiO2 was significantly dependent on pH and ionic strength. The presence of SHA slightly enhanced the sorption of U(VI) on TiO2 below pH4.0, while it inhibited U(VI) sorption in the higher pH range. U(VI) sorption on TiO2 was favored at high temperatures, and the sorption process was estimated to be endothermic and spontaneous. Reduction of U(VI) to lower valent species was confirmed by X-ray photo-electron spectroscopy analysis. It is very interesting to find that U(VI) sorption on TiO2 was promoted in solutions with higher back-ground electrolyte concentrations. In the presence of U(VI), higher back-ground electrolyte made more TiO2 particles aggregate through (001) facets, leading more (101) facets to be exposed. Therefore, the reduction of U(VI) was enhanced by the exposed (101) facets and more U(VI) removal was observed.