High-throughput sequencing clarifies the spatial structures of microbial communities in cadmium-polluted rice soils.

Soil microbial communities are affected by environmental factors. Contamination with heavy metals such as cadmium (Cd) can decrease soil microbial species richness and substantially alter soil microbial species composition. Investigations of the microbial communities in Cd-contaminated soils are necessary to obtain data for soil bioremediation efforts. However, depth-associated variations in microbial community composition and structure in Cd-contaminated paddy soils are not well understood. Here, the effects of various degrees of long-term Cd pollution on soil microorganisms were investigated at different soil depths within the plough layer using 16S rRNA gene amplicon sequencing. We found that, in Cd-polluted soils, microbial communities were more similar between the surface soil and the underlying soil. In addition, microbial community richness and/or diversity were significantly reduced in the Cd-polluted underlying soil as compared with the non-polluted underlying soil. However, species richness in the surface layer was significantly greater in the mildly and severely Cd-polluted soils. The soil microbial communities in the same soil layer differed significantly between the non-polluted and polluted soils. Furthermore, Cd contamination affected the microbial communities of different soil layers differently. Soil pH had a synergistic effect on microbial community abundance and composition. The potential functions of the soil microbiota were mainly related to environmental processing, genetic processing, and metabolic pathways. Notably, our identification of the phyla that were differently abundant among sites with different levels of Cd pollution will provide experimental guidance for further explorations of the effects of Cd on soil microbes in natural environments. Our results not only demonstrate that long-term Cd pollution leads to a marked reduction in microbial richness and diversity in the underlying soil layer, but they also help to clarify how long-term heavy metal contamination affects the soil bacterial community.

Characterization and comparison of the bacterial communities of rhizosphere and bulk soils from cadmium-polluted wheat fields.

Cadmium pollution is becoming a serious problem due to its nondegradability and substantial negative influence on the normal growth of crops, thereby harming human health through the food chain. Rhizospheric bacteria play important roles in crop tolerance. However, there is little experimental evidence which demonstrates how various cadmium concentrations affect the bacterial community in wheat fields including rhizosphere microorganisms and nonrhizosphere (bulk) microorganisms. In this study, 16S rRNA amplicon sequencing technology was used to investigate bacterial communities in rhizosphere and bulk soils under different levels of pollution in terms of cadmium concentration. Both the richness and diversity of the rhizosphere microorganism community were higher under nonpolluted soil and very mild and mild cadmium-contaminated soils than compared with bulk soil, with a shift in community profile observed under severe cadmium pollution. Moreover, cadmium at various concentrations had greater influence on bacterial composition than for the nonpolluted site. In addition, redundancy analysis (RDA) and Spearman's analysis elucidated the impact of exchangeable Cd and total Cd on bacterial community abundance and composition. This study suggests that cadmium imposes a distinct effect on bacterial community, both in bulk and rhizosphere soils of wheat fields. This study increases our understanding of how bacterial communities in wheat fields shaped under different concentrations of cadmium.

Pyrolysis of various phytoremediation residues for biochars: Chemical forms and environmental risk of Cd in biochar.

Various phytoremediation residues (PMRs), including Brassica napus L. (BN), Pennisetum sinese (PS) and Lolium perenne L.(LP), were pyrolyzed at 400, 500, 600 and 700 °C, respectively. A series of sequential and single extractions were employed to analyze the chemical speciation and potential environmental risk of Cadmium (Cd) in different phytoremediation residues-derived biochars (PMBs). The results showed that the exchangeable Cd fraction decreased but the residual Cd fraction increased, indicating the inhibition of bioavailability of Cd and low potential ecological risk index of PMBs. When the temperature was over 600 °C, the Cd in biochar was acceptable to the environment and the leaching concentration of Cd extracted by the three extraction methods (distilled water, SPLP and TCLP) were all under the standard limit. Findings from this study illustrated that the treatment of pyrolysis was feasible for the three kinds of PMRs at 600 °C with acceptable environment risk.

A multi-surface model to predict Cd phytoavailability to wheat (Triticum aestivum L.).

The prediction of metal bioavailability in soils is critical to metal risk assessments and the amount of dissolved metal in soils is a key factor determining bioavailability. Because the recently developed geochemical multi-surface models (MSMs) offer a promising tool for the determination of metal partitioning in soils, in this study, a MSM based on generic parameters was used to assess the bioavailability of Cd in wheat (Triticum aestivum L.) growing in 12 soils with a wide range of properties. The amount of MSM-calculated dissolved Cd correlated strongly with the amount of Cd uptake by wheat (R2=0.873 for roots and R2=0.837 for shoots), and the model's performance was better than that of chemical extraction methods (0.01M CaCl2, 0.43M HNO3 and soil total Cd). The reactive fraction of soil organic matter, the soil/solution ratio, and the inclusion/exclusion of background cations influenced the calculation results. The best calculation condition was optimized. The application of the MSM was also examined in 84 wheat-soil samples from the field. The amount of Cd in wheat seeds had a stronger correlation with the amount of MSM-predicted Cd than with the amount of Cd obtained using chemical extraction methods. Our results suggested that MSM-calculated Cd is an effective indicator of the bioavailability of Cd in soils and demonstrated the utility of the method as a tool to assess the risk of Cd contamination in soils.

Spatial Variation of Soil Organic Carbon and Total Nitrogen in the Coastal Area of Mid-Eastern China.

Soils play an important role in sequestrating atmospheric CO2. Coastal tidal flats have been intensively reclaimed for food security and living spaces worldwide. We aimed to identify the changes of soil organic carbon (SOC) and total nitrogen (TN) following coastal reclamation and their spatial variation in the coastal area of mid-Eastern China to provide information for coastal cropland management. We measured SOC and TN of 463 soil samples in the coastal plain of mid-Eastern China. The results showed that SOC and TN increased highly from the uncultivated coastal tidal flat (2.49 g·kg-1 and 0.21 g·kg-1, respectively) to the cropland (10.73 g·kg-1 and 1.3 g·kg-1, respectively). After long-term cultivation, SOC and TN in the old farmland (12.98 g·kg-1 and 1.49 g·kg-1, respectively) were greater than those in the young farmland (5.76 g·kg-1 and 0.86 g·kg-1, respectively). The density of SOC in the uncultivated coastal tidal flat, young farmland, and old farmland were 0.68 kg·C·m-2, 1.52 kg·C·m-2, and 3.31 kg·C·m-2, respectively. The density of TN in the uncultivated coastal tidal flat, young farmland and old farmland were 0.05 kg·N·m-2, 0.23 kg·N·m-2, and 0.38 kg·N·m-2, respectively. The C/N (11.17) in the uncultivated coastal tidal flat was highest comparing to that in the young and old farmland due to lower nitrogen. The C/N increased from 6.78 to 8.71 following cultivation. Reclaimed coastal tidal flats had high carbon and nitrogen sequestration potential that not only mitigated the threat of global warming, but also improved soil fertility for crop production. Coastal management of cropland should consider the spatial distribution of SOC and TN to improve ecosystem services of coastal soils.

Environmental Exposure to Cadmium: Health Risk Assessment and its Associations with Hypertension and Impaired Kidney Function.

Cadmium (Cd) is a toxic metal. This study was aimed to estimate the potential health risks in a Cd-polluted district in China, and examine the relationship between urinary cadmium(UCd) and hypertension and impaired kidney function at low exposure levels (UCd: GM 1.3 µg/g creatinine). Blood pressure measurement, questionnaires, and collection of urinary samples were conducted from 217 residents. Environmental samples, food, and cigarette samples were collected and detected to estimate the risks posed by Cd and the contribution of inhalation, ingestion, and dermal contact pathways to these risks. A logistic regression model was used in examining associations between exposure and hypertension and impaired kidney function. Results show that this population is at high risk. For non-smokers, incremental lifetime cancer risk (ILCR) and hazard quotient (HQ) are 1.74E-04 and 2.96, and for smokers, they are 1.07E-03 and 52.5, respectively. Among all exposure pathways, smoking and foods cause the major increases in ILCR and HQ. UCd is significantly associated with hypertension (odds ratio (OR) = 1.468; 95% confidence interval (CI): 1.104, 1.953; P = 0.008) and impaired kidney function (OR = 1.902, 95% CI: 1.054, 3.432; P = 0.033). The results demonstrate that Cd can potentially lead to adverse health effects.

[Research on the Matrix Interference on Major and Minor Elements in Soil Samples with ICP-AES].

According to the commonly used method of analysis with ICP-AES in geochemistry, to study the influence factors of interference from the analysis results, standard soil substances were selected to be the calibration curve of work, and the same method of digestion with soil samples was used to balance and eliminate the matrix interference. The concentrations of major and minor elements in soil samples were measured; the relative deviation of the results was compared under conditions of soil matrix and non-soil matrix interference; the relations and laws were being analyzed. The relative deviation (RE%) of testing results under non-soil-matrix interference were found floating around zero, the ratios of positive deviation and negative deviation were almost the same. Excluding the factors of spectral interference, the method of matrix matching can effectively eliminate the effects of matrix interference on soil. It was found that the analysis results of major elements, such as Al, Ca, Fe, Mg, P, Ti and Ba, were influenced negatively greatly under the condition of soil matrix interference, The maximum deviation of Mg 279.5 nm was up to -14.49%. The degree of influence ranking showed as Ti, Mg>P, Fe>Ca, Ba>Al. However, there is no obvious effect on other elements, including Na, Cr, Cu, V, Li, Mn, Ni and Sr. Contrary to the original ideas, the matrix interference effected greatly on the results of elements of high content, nevertheless, the effects on minor elements were not significant. As to the comprehensive matrix interference , the large proportion of interference from component self-content appeared of elements of Ca and Mg, because obvious linear correlation was found between component self-content and the relative deviation of the testing results of Ca and Mg. But no linear trend appeared between the self-contents of other elements and the results of matrix interference, indicating that the influence weight from self-content of other elements was very small. It was very important to select the right spectral lines, and remove the factors of interference to determinate the results of measurement. Factors and rules of interference effect has always been the research topic by all of scholars in the research field of ICP spectrum. On the guidance of above research results, the spectral lines will be selected and the accuracy judged reasonably, when soil samples being analyzed by ICP-AES.

[Quantifying the influence of different matrices on Pb accumulation in the soil from Nanjing and suspended matter from the lower of the Yangtze River with Pb isotopic technique].

Lead pollution and its geochemical behavior have an influence on ecological environment and human health. It is of significance to study the characteristics and mechanism of Pb accumulation and to quantify the contributions of different environmental matrices to Pb accumulation in soils and river suspended matter in the representative fluvial delta area, such as the lower of the Yangtze River. The results showed that lead was enriched in the urban topsoil in Nanjing and the suspended matter in the lower of the Yangtze River. The urban topsoil and the river suspended matter showed higher 206Pb/207Pb and lower 208Pb/206Pb relative to the natural matrices, and this was resulted from the influence of the anthropogenic lead. The relative contribution of separate Pb sources was assessed with the Pb geochemical model, 18%-56% (average 35%) Pb in Nanjing urban soil was derived from the anthropogenic matrices, and anthropogenic Pb contributed 22%-46% (average 32%) of total Pb in the Yangtze River suspended matter.

[Coregionalization, spatial-correlation and spatial-factor analysis of soil available heavy metals in a typical region of the Yangtze River Delta].

The method of factorial kriging based on the theory of coregionalization is developed by the combination of multi-statistics, geostatistics and GIS. Soil available heavy metals of 126 topsoil samples in Kunshan city, a typical region of Yangtze River Delta, were analyzed, and the spatial distribution pattern was investigated by the method of factorial kriging. Based on the analysis of multi-scale spatial structure characteristics of available heavy metals, we discussed the pollution source and cause of this spatial distribution by means of spatial scale-correlation analysis and spatial principal component analysis. Our results show that all the available heavy metals distribute normally or lognormally with great variability, and the contamination of available Cd is the biggest. The available heavy metals are categorized into three spatial scales, i.e. nugget, short-range (15 km) and long-range (40 km), respectively, and a linear model of coregionalization comprising these three spatial scales is fitted to the experimental auto-and cross-variograms of the soil available heavy metals. Significant relationship is found between Cd and Zn in the three scales. The spatial correlation of available heavy metals in short-range and long-rang are stronger than it in nugget, while the long-rang has more obvious negative correlation than the other two spatial scales. The results of spatial principal component analysis show the pollution sources are different in the three spatial scales. The kriging interpolation method was applied to work out the distribution maps of first and second principal component of available heavy metal, which indicate that available heavy metal concentrations in the soils are closely related to their industry activity, sewage irrigation and soil characteristics.