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Plant growth promoting (PGP) traits of inoculation in bioaugmentation assisted phytostabilization of heavy metal-contaminated soil have been well documented. The property of inoculation to immobilize heavy metals is another major contributor to phytostabilization efficiency. This study investigated the effects of inoculation with different concentrations of rhizobacteria Bacillus subtilis on the cadmium (Cd) bioavailability and distribution, enzyme activities, and bacterial community structure in soil planted with ryegrass (Lolium multiflorum L.). Addition of a high dosage of Bacillus subtilis decreased plant malondialdehyde (MDA) amount, increased plant antioxidant enzyme and soil nutrient cycling-involved enzyme activities, and subsequently enhanced biomass by 20.9%. In particular, the inoculation reduced the Cd bioavailability in soil, bioaccumulation coefficient (BCF), translocation factors (TF), and accumulation in ryegrass by 39.1%, 36.5%, 24.2%, and 27.9%, respectively. Furthermore, 16S rRNA gene sequencing analysis of rhizosphere soil revealed microbial community structure alterations (e.g., enrichment of Proteobacteria), eight phenotype regulations, and seventeen Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway transformations accounted for the stress mitigation and Cd immobilization in the presence of inocula. Besides, intracellular accumulation and biofilm sequestration were proposed as primary immobilization mechanisms induced by bioaugmentation., Competing Interests: Declaration of competing interest We declare that we have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

This study developed a method to build relationships between chemical fractionations of heavy metals in soils and their accumulations in rice and estimate the respective contribution of each geochemical speciation in the soils from the Yangtze River Delta, China. In contaminated areas, residue and humic acid-bound fractions in soils were the main phases for most heavy metals. The mobility of heavy metals was in this following order: Cd > Pb ≈ Zn > Ni > As ≈ Cr > Hg. Transfer factors calculated by the ratios of specific fractionations of heavy metals in the soil-rice system were used to assess the capability of different metal speciation transfer from soil to rice. The carbonate and Fe/Mn oxyhydroxides bound phase had significant positive correlations with total metal concentrations in rice. Hg uptake by rice might be related to the exchangeable and carbonate-bound fractions of soil Hg. Results of PCA analysis of transfer factors estimated that the labile fractions (i.e. water soluble, exchangeable and carbonate bound) contributed more than 40% of the heavy metal accumulations in rice. Effect of organic matter and residue fraction on metals transfer was estimated to be ~ 25 to  ~ 30% while contribution of humic acid and Fe/Mn oxyhydroxides-bound fractions was estimated to be ~ 20 to  ~ 30%. Modified risk assessment code (mRAC) and ecological contamination index (ECI) confirmed that the soil samples were polluted by heavy metals. Soil Cd contributed more than 80% of mRAC. Contrarily, the main contributors to ECI were identified as As, Hg, Pb and Zn. The average values of total target hazard quotient (TTHQ) and Risk total were above 1 and 10 -4 respectively, implying people living in the study area were exposed to both non-carcinogenic and carcinogenic risk. As and Pb were the main contributor to high TTHQ value while As, Cd and Cr in rice contributed mostly to Risk total value. Spatial changes of ecological risk indexes and human health risk indexes showed that the samples with high TTHQ values distributed in the area with high values of mRAC. Likewise, the area with high ECI values and with high carcinogenic risk overlapped., (© 2021. The Author(s), under exclusive licence to Springer Nature B.V.)

The effects of Bacillus subtilis inoculation on the growth and Cd uptake of alfalfa were evaluated in this research using pot experiments, and the relevant biochemical mechanisms were first investigated by combined microbial diversity and nontarget metabolomics analyses. The results indicated that inoculation with alfalfa significantly decreased the amount of plant malondialdehyde (MDA) and improved the activities of plant antioxidant enzymes and soil nutrient cycling-involved enzymes, thereby promoting biomass by 29.4%. Inoculation also increased Cd bioavailability in rhizosphere soil by 12.0% and Cd removal efficiency by 139.3%. The biochemical mechanisms included enhanced bacterial diversity, transformed microbial community composition, regulated amounts of amino acids, fatty acids, carbohydrates, flavonoids and phenols in rhizosphere soil metabolites, and modulations of the corresponding Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. These responses were beneficial to microbial activity, nutrient cycling, and Cd mobilization, detoxification, and decontamination by alfalfa in soil. This study, especially the newly identified differential metabolites and metabolic pathways, provides new insights into mechanism revelation and strategy development in microbe-assisted phytomanagement of heavy metal-contaminated soils., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)

The study evaluated source apportionment of heavy metals in vegetable samples from the potential sources of fertilizer, water and soil samples collected along the Changjiang River delta in China. The results showed that 25.72% of vegetable samples (Brassica chinensis L.) containing Pb, and Cd, Cu, Hg and Zn at relatively serious levels were from soil. Combined with principle component analysis (PCA) and cluster analysis (CA), the results of the spatial distribution of heavy metals in different environmental media indicated that fertilizer, water and soil were the main sources of heavy metals in vegetables. The results of multivariate linear regression (MLR) using partition indexes (P) showed that fertilizer contributed to 38.5%, 40.56%, 46.01%, 53.34% and 65.25% of As, Cd, Cu, Pb and Zn contents in vegetables, respectively. In contrast, 44.58% of As, 32.57% of Hg and 32.83% of Pb in vegetables came from soil and 42.78% of Cd and 66.97% of Hg contents in vegetables came from the irrigation water. The results of PCA and CA verified that MLR using P was suitable for determining source apportionment in a vegetable. A health risk assessment was performed; As, Cd and Pb contributed to more than 75% of the total hazard quotient (THQ) values and total carcinogenic risk values (Risk total ) for adults and children through oral ingestion. More than 70% of the estimated THQ and Risk total is contributed by water and fertilizer. Therefore, it is necessary to increase efforts in screening limits/levels of heavy metals in fertilizer and irrigation water and prioritize appropriate pollution management strategies., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Consumption of crops grown in cadmium-contaminated soils is an important Cd exposure route to humans. The present study utilizes statistical analysis and in vitro digestion experiments to uncover the transfer processes of Cd from soils to the human body through rice consumption. Here, a model was created to predict the levels of bioaccessible Cd in rice grains using phytoavailable Cd quantities in the soil. During the in vitro digestion, a relatively constant ratio between the total and bioaccessible Cd in rice was observed. About 14.89% of Cd in soils was found to be transferred into rice grains and up to 3.19% could be transferred from rice grains to the human body. This model was able to sufficiently predict rice grain cadmium concentrations based on CaCl 2 extracted zinc and cadmium concentrations in soils (R 2 = 0.862). The bioaccessible Cd concentration in rice grains was also able to be predicted using CaCl 2 extracted cadmium from soil (R 2 = 0.892). The models established in this study demonstrated that CaCl 2 is a suitable indicator of total rice Cd concentrations and bioaccessible rice grain Cd concentrations. The chain model approach proposed in this study can be used for the fast and accurate evaluation of human Cd exposure through rice consumption based on the soil conditions in contaminated regions.

Soil heavy metals and their bioaccumulation in agricultural products have attracted widespread concerns, yet the transfer and accumulation characteristics of heavy metals in different soil-crop systems was rarely investigated. Soil and crop samples were collected from the typical agricultural areas in the Yangtze River Delta region, China. The concentrations of Cu, Pb, Zn, Cd and Hg in the soils, roots and grains of rice (Oryza Sativa L.), wheat (Triticum L.) and canola (Brassica napus L.) were determined in this study. Transfer ability of heavy metals in soil-rice system was stronger than those in soil-wheat and soil-canola systems. The wheat showed a strong capacity to transfer Zn, Cu and Cd from root to the grain while canola presented a restricting effect to the intake of Cu and Cd. Soil pH and total organic matter were major factors influencing metal transfer from soil to rice, whereas soil Al2O3 contents presented a negative effect on heavy metal mobility in wheat and canola cultivation systems. The concentration of Zn and Cd in crop grains could well predicted according to the stepwise multiple linear regression models, which could help to quantitatively evaluate the ecologic risk of heavy metal accumulation in crops in the study area., (Copyright © 2016 Elsevier Inc. All rights reserved.)