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Cadmium (Cd) is an important environmental heavy metal and one of the main soil pollutants in southwest China and even the Yangtze River Basin because of its toxicity to plants and humans. To clarify the potential of Euryops pectinatus L. and Gardenia jasminoides J. and the mechanism they use to remediate Cd-contaminated soil, a soil pot experiment with 0, 5, 10, 20, and 40 mg kg−1 of Cd was used to investigate the accumulation characteristics, subcellular distribution, chemical forms, and the antioxidative defense systems of the two ornamental plants. When the concentration of Cd was below 40 mg kg−1, it promoted the growth of E. pectinatus shoots, and the tolerance index (TI) was >1. However, 20–40 mg kg−1 Cd significantly inhibited the growth of G. jasminoides, and the TI was <1. The shoots of both varieties accumulated more Cd than the roots, and the E. pectinatus shoots accumulated more Cd (1.45 mg plant−1) than those of G. jasminoides (0.71 mg plant−1). The Cd in E. pectinatus and G. jasminoides was primarily distributed in the soluble fraction (52.83–68.97%) and cell walls (44.62–54.98%), respectively. Higher proportions of Cd bound to NaCl and acetic acid (HAc) in E. pectinatus (55.32–73.44%) than in G. jasminoides (42.94–61.58%), while the inorganic and water-soluble proportions of Cd bound in the opposite manner. E. pectinatus maintained high activities of antioxidant enzymes under Cd treatments, and its levels of malondialdehyde (MDA) and relative electrical conductivity (REC) were comparable to those of the control. Nonetheless, G. jasminoides had low levels of activity of antioxidant enzymes, but its levels of MDA and REC were significantly higher than those of the control under the 20–40 mg kg−1 Cd treatment. Therefore, both types of plants have a strong ability to tolerate and accumulate Cd, which makes them suitable for the remediation of Cd-polluted soil. However, E. pectinatus is more effective at remediating Cd and tolerant to it than G. jasminoides. These plants utilize different mechanisms to detoxify Cd. [ABSTRACT FROM AUTHOR]

It is generally accepted that sulfur can passivate the bioavailability of heavy metals in soil, but it is not clear whether high sulfur in cadmium (Cd) and chromium (Cr) contaminated soil has negative effect on soil microbial community and ecological function. In this study, total sulfur (TS) inhibited the Chao 1, Shannon, Phylogenetic diversity (Pd) of bacterial and Pd of fungi in slightly contaminated soil by Cd and Cr around pyrite. TS, total potassium, pH, total chromium, total cadmium, total nitrogen, soil organic matter were the predominant factors for soil microbial community; the contribution of TS in shaping bacterial and fungal communities ranked at first and fifth, respectively. Compared with the low sulfur group, the abundance of sulfur sensitive microorganisms Gemmatimonas , Pseudolabrys , MND1 , and Schizothecium were decreased by 68.79–97.22% (p < 0.01) at high sulfur one; the carbon fixation, nitrogen cycling, phosphorus cycling and resistance genes abundance were significantly lower (p < 0.01) at the latter. Such variations were strongly and closely correlated to the suppression of energy metabolism (M00009, M00011, M00086) and carbon fixation (M00173, M00376) functional module genes abundance in the high sulfur group. Collectively, high sulfur significantly suppressed the abundances of functional microorganisms and functional genes in slightly contaminated soil with Cd and Cr, possibly through inhibition of energy metabolism and carbon fixation of functional microorganisms. This study provided new insights into the environmental behavior of sulfur in slightly contaminated soil with Cd and Cr. [Display omitted] • Sulfur was a key factor affecting soil microbial community near mines. • High sulfur inhibited abundance of soil functional microbes. • The functional & resistance genes were suppressed by high sulfur. • Functional microbes were inhibited via energy metabolism and carbon fixation. [ABSTRACT FROM AUTHOR]

Siegesbeckia orientalis L. was identified as a novel Cd-hyperaccumulator and valuable phytoremediation material. However, the molecular mechanisms underlying Cd accumulation in S. orientalis are largely unknown. In this study, RNA-Seq analysis was performed to study the Cd-accumulating mechanisms in its roots with or without Cd treatment. The RNA-seq analysis generated 312 million pairs of clean reads and 78G sequencing data. De novo transcriptome assembly produced 355,070 transcripts with an average length of 823.59 bp and 194,207 unigenes with an average length of 605.68 bp. Comparative transcriptome analyses identified a large number of differentially expressed genes in roots under Cd stress, and functional annotation suggested that S. orientalis utilizes various biological pathways involving many gene networks working simultaneously to cope with the stress. This study revealed that four biological pathways were mainly involved in S. orientalis tolerance to Cd stress, including reactive oxygen species scavenging, phenylpropanoid biosynthesis pathway, Cd absorption and transport, and ABA signaling pathway. The genes related to photosynthesis and heavy metal transport are likely the potential candidates and could be further investigated to determine their roles in Cd tolerance in S. orientalis roots. These findings will be useful to understand the Cd accumulation mechanisms in S. orientalis and facilitate the study of phytoremediation at the molecular level in plants. [ABSTRACT FROM AUTHOR]

Soil washing with natural chelators to remediate metal-contaminated soils has been gained attention by researchers. However, the abilities of the chelators to remediate the multiple metal polluted soils are less effective. This study employed zero-valent iron nanoparticle (nZVI) to enhance the removal efficiencies of citric (CA), tartaric (TA) and oxalic acids (OA), and evaluate their feasibility. Results showed that metal removal efficiencies increased with the increasing concentration of nZVI and soil-liquid ratio, decreased with the increasing solution pH. The kinetic simulation indicated that pseudo-first-order and pseudo-second-order models could be used for describing the washing processes. Additionally, metal removals were significantly improved by addition of nZVI ( p  < 0.05). The highest enhancements of soil Cd, Pb and Zn removals under solution pH of 4.0, soil-liquid ratio of 1:20 and washing time of 120 min reached 12.83% (OA- nZVI), 24.92% (CA-nZVI) and 11.64% (OA- nZVI) for mine soil, and 19.24% (TA- nZVI), 18.16% (CA-nZVI) and 8.93% (OA- nZVI) for farmland soil, respectively. After soil washing, the exchangeable forms and the environmental risks of residual metals were markedly diminished in soils. Therefore, the combinations of the organic acids and nZVI are the feasible practices to repair the soils contaminated by heavy metals. [ABSTRACT FROM AUTHOR]

Toxic metal contamination causes a great threat to soil ecosystem and human health. Soil washing is a fast practice for removing metals, but its influences on microbial diversity and the stability of soil ecosystem remain unknown. In this study, ethylenediaminetetraacetic acid (EDTA), citric acid (CA), and fermented pineapple peel residue (FPP) were used as representatives of chelates, low molecular organic acids and biological materials to wash Pb-polluted soils, and their impacts on microbial community were investigated. Washing with these agents effectively removed Pb, but altered microbial community structure. After washing with EDTA, CA, and FPP, 3–8 bacterial phyla and 1 fungal phylum greatly increased, while 7–20 bacterial and 0–6 fungal phyla severely decreased or even disappeared. The alterations of different microbiomes were closely related to soil metal fractions. The labile metal fraction had negative effects on most bacteria and fungi, but also showed positive influences on Actinobacteria , Patescibacteria , and Fusobacteria. The moderately stable and stable fractions were nontoxic to the most microbes, but still harmful to Patescibacteria and Deinococcus-Thermus. These findings provide new insights for the effects of soil washing remediation and toxicity of metal fractions on the microbiomes with different abundance. [Display omitted] • Soil washing altered the diversity and abundance of microbial community. • The rare microbiome was sensitive to removal of metals by washing. • Toxic metal fractions showed diverse effects on different microbes. • The stable fractions were also harmful to some phyla such as Patescibacteria. • The fermented pineapple peel may be as a cleaner and sustainable washing agent. [ABSTRACT FROM AUTHOR]

Chemical washing is considered an effective technique for removing heavy metals (HMs) from industrial sludge. However, traditional washing methods have the potential to cause secondary environmental pollution. In this study, a new chemical washing strategy that circumvents the risk of secondary contamination by using two organic acid polymers—Caboxyethylthiosuccinic acid (CETSA) and itaconic-acrylic acid copolymer (IA-AA) were introduced to remove Pb, Zn, Ni and Cr from industrial sludge. The quantity of HMs removed from the sludge increases as a function of increasing agent concentration, Solid-to-liquid ratio, and washing time, while various trends were observed in response to increasing pH. In addition, response surface analysis showed that CETSA concentration significantly affected HM removal; and IA-AA concentration, pH, and washing time showed evident impacts on washing efficiency. Optimal washing specifications using CETSA, with respect to agent concentration, pH, and washing time, were 66.76 g/L, 2.76, and 248 min, respectively; while those of IA-AA were 100 g/L, 2, and 360 min, respectively. CETSA and IA-AA removed 69.04% and 98.31% of total HMs, respectively, and decreased the labile fractions of Zn and Ni. Fourier transform infrared spectroscopy analysis suggested that the hydroxyl, carboxyl, carbonyl might contribute to the heavy metal extraction. Overall, CETSA and IA-AA should be seriously considered as reliable washing agents for use in HM removal from sludge. [Display omitted] • CETSA and IA-AA can effectively remove Pb, Zn, Ni and Cr from industrial sludge. • Optimal washing specifications were obtained using Response surface methodology. • CTESA and IA-AA washing decreased the labile fraction concentration of heavy metals. [ABSTRACT FROM AUTHOR]

Soil heavy metal speciation has received much attention for their different ecological and environmental effects. However, the effects of climate and soil geochemical properties on them in uncontaminated soils at macroscale were still unclear. Therefore, a transect more than 4000 km was chosen to study the effects of these factors on soil Cd, Pb and Cr forms. The results revealed that mean annual temperature and precipitation showed significant positive relations with the exchangeable and Fe-Mn oxide bound states of Cd, Pb and Cr, and residual Cr. And humidity and drought indexes were significantly positively correlated with their organic and carbonate bound forms, respectively. As for soil geochemical properties, pH displayed significant negative relationships with exchangeable, Fe-Mn oxide and organic bound Pb and Cr, and exchangeable Cd. Fe 2 O 3 was significantly positively with the exchangeable and Fe-Mn oxide bound Cd, Pb and Cr, and residual Cr. And soil organic matter showed positive relations with organic bound Pb and Cr, and residual Cd and Cr, displayed negative relationships with carbonated bound Pb and Cr. Overall, climate and soil geochemical properties together affect the transformation and transport of heavy metals between different forms in uncontaminated soils. [Display omitted] • MAT and MAP positively relate with exchangeable and Fe-Mn oxide bound metals. • HI and DI positively relate with organic and carbonate bound metals respectively. • pH displayed significant negative relationships with Fe-Mn oxide bound Pb and Cr. • Soil organic matter showed negative relationship with carbonated bound Pb and Cr. [ABSTRACT FROM AUTHOR]