Search

There is a long-standing debate over the effectiveness of chemical extraction methods in assessing soil metal phytoavailability. This study addresses the limitations of widely-used chemical extraction methods and presents the water-extractable pool as a more reliable indicator based on wheat pot experiments using homogenized agricultural soil amended with lime materials, phosphate, and biochar. Over 120 days' pot experiments, Cd accumulation in whole wheat plants and tissues exhibited positive relationships with water-extractable Cd concentrations at heading and maturity stage (Spearman's rho: 0.521–0.851; P < 0.05), revealing that the water-extractable pool instead of other pools better indicates wheat metal accumulation. Water-extractable metal concentrations are effective in assessing phytoavailability of metals primarily in ionic forms in soil solution (e.g, Zn, Cd), but less reliable for metals strongly complexed with dissolved organic matter (DOM) or sensitive to redox conditions. It demonstrated that water-extractable metal concentrations and chemical forms are key factors, fundamentally determined by metal properties and impacted by environmental factors. This study clarifies a more direct link between chemical extraction and plant metal uptake mechanisms. Given the extensive application of chemical extraction methods over several decades, this study will help advance soil metal risk assessment and remediation practices. [Display omitted] • The water-extractable pool is more reliable for metal phytoavailability assessment. • Water-extractable Cd concentrations at heading and maturity stages significantly correlated with wheat accumulation. • Water-extractable metal concentrations and forms are key factors determining phytoavailability. [ABSTRACT FROM AUTHOR]

The application time and soil pH are key to manganese (Mn) bioavailability, which may influence Mn effects on cadmium (Cd) accumulation in rice. Accordingly, this study investigated the effects of Mn application at different stages, alone or with basal liming, on Cd accumulation in rice through pot and field experiments. The results showed that basal Mn application maximally elevated soil dissolved Mn, and increasing Mn accumulation in rice by 140%−367% compared to the control. Additionally, basal or tillering applications had better effects on enhancing iron manganese plaque (IMP) and inhibiting CaCl 2 -extractable Cd than later applications. Therefore, basal and tillering Mn reduced brown rice Cd by 24.6% and 18.9% compared to the control, respectively. Liming reduced CaCl 2 -extractable Cd by 83.3% compared to the control but inhibited soil dissolved Mn (25.8%−76.6%) and IMP (28.9%−29.7%), resulting in only a 41.7% reduction in brown rice Cd. Liming combined with tillering Mn maximally reduced brown rice Cd by 67.4%, structural equation modeling revealed CaCl 2 -extractable Cd and manganese plaque played the greatest positive and negative roles, respectively. Therefore, basal liming and tillering application of Mn is most effective at reducing rice Cd through inhibition of Cd bioavailability and alleviation of IMP reduction. [Display omitted] • Basal Mn alone induced higher Mn and lower Cd levels in rice than later application. • Soil liming inhibited iron manganese plaque and enhanced Cd transport in rice. • Tillering Mn greatly alleviated liming effects on Mn plaque and Cd transport. • Liming coupled with tillering Mn caused the highest reduction in brown rice Cd. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this study was to evaluate the combined effects of liming and behaviour of Sarcocornia fruticosa as a strategy of phytomanagement of metal polluted salt marsh soils. Soils were taken from two polluted salt marshes (one with fine texture and pH∼6.4 and the other one with sandy texture and pH∼3.1). A lime amendment derived from the marble industry was added to each soil at a rate of 20gkg−1, giving four treatments: neutral soil with/without liming and acidic soil with/without liming. Cuttings of S. fruticosa were planted in pots filled with these substrates and grown for 10 months. The pots were irrigated with eutrophicated water. As expected, lime amendment decreased the soluble metal concentrations. In both soils, liming favoured the growth of S. fruticosa and enhanced the capacity of the plants to phytostabilise metals in roots. [Copyright &y& Elsevier]

Abstract: Pure CaCO3 in ascending quantities was added to a soil to study the effect of liming after contamination by an acidic solution from the oxidation of pyrite tailings. The samples were placed in percolation columns, and soils and leachates were monitored. In the soil samples, the mineralogy, pH, CaCO3, iron, and total content in Cu, Zn, As, Cd, and Pb were determined. The presence of CaCO3 in the soils considerably limited their acidification, favouring the precipitation of Cu, Zn, and Cd, and promoting precipitation of iron and SO4 2− ions in the form of iron hydroxysulphates and gypsum. The iron hydroxysulphates tended to retain the less mobile elements (As, and Pb) near the top of the soil. The more mobile elements (Zn, Cd and Cu) precipitated in deeper layers, directly related mainly to the CaCO3 added and to pH. The CaCO3 clearly did not reduce Zn and Cd toxicity effectively enough, given that the concentrations of both elements were above the toxic level in all leachates. The amounts of liming needs to be properly controlled, as excessively high pH limits As fixing, at the same time as the effectiveness of CaCO3 is limited by coating precipitation, reducing its capacity to react with the acidic solution. [Copyright &y& Elsevier]

Abstract: This field study evaluated the effectiveness of three best management practices (BMPs) in reducing the weathering of Pb-bullets in a shooting range. The BMPs included replacing soil berm with sand berm, liming sand berm, and removing Pb-bullets from soil berm. Berm samples were collected before and after implementing BMPs and analyzed for total Pb and/or water-soluble Pb. After 11 months of operation, the total Pb concentrations in the sand berm (57mgkg−1) were significantly lower than that in the soil berm (277mgkg−1). The reduced weathering of Pb-bullets in the sand berm was attributed to its lower moisture content and organic matter as both water and CO2 are critical in chemical weathering. Though liming reduced total Pb concentrations in the sand berm from 497–777 to 302–362mgkg−1 after 15 months of application, it increased water-soluble Pb in some cases. While removal of Pb-bullets removed the sources of Pb, X-ray diffraction analysis indicated that its abrasive action transferred metallic Pb to the soil fraction (<2mm), with total Pb in soil berm increasing from 4,694 to 11,479mgkg−1. While all BMPs can be applied to mange Pb in shooting ranges, cautions need to be excised to minimize the adverse impacts. [Copyright &y& Elsevier]

Abstract: The effects of different concentrations of soil cadmium (0, 1, 3, 5, 10, and 20mgkg−1) on growth, structural changes and cadmium cellular localization in leaves of maize plants (Zea mays L.) were investigated in a pot experiment. The results showed that the structural changes observed in maize leaves were not only a response to the Cd-induced stress but also a cellular mechanism to reduce the free Cd+2 in the cytoplasm. However, this mechanism seems to be efficient only up to a Cd concentration in leaves between 27 and 35mgkg−1 for soils without and with liming, respectively. The cellular response varied with both the Cd concentration in soil and liming. For limed soil, Cd was preferentially accumulated in the apoplast while for unlimed soils Cd was more evenly distributed into the cells. The ability of Cd accumulation depended on the leaf tissue considered. The apoplast collenchyma presented the highest Cd concentration followed by the endodermis, perycicle, xylem, and epidermis. On the other hand, symplast Cd accumulated mainly in the endodermis, bundle sheath cells, parenchyma, and phloem. Based on the structural changes and growth reduction, the critical toxic concentration of soil Cd to maize plants is between 5 and 10mgkg−1. [Copyright &y& Elsevier]

Manganese (Mn) has the potential to reduce cadmium (Cd) uptake by rice; however, the efficiency depends on its soil availability. Therefore, this study designed a slow-release Mn fertilizer by employing a polyacrylate coating. Pot trials were conducted to study the effects of coated-Mn and uncoated-Mn alone or in combination with lime on the dynamics of soil dissolved-Mn and available Cd, and the transportation of Mn and Cd within rice. The results showed that coated-Mn declined the release of Mn until the 7th day of application; however, it consistently supplied more dissolved-Mn than uncoated-Mn. As a result, coated-Mn induced a greater Cd reduction (45.8%) in brown rice than uncoated-Mn (9.7%). The total Cd of rice and its proportion in brown rice were greatly reduced by coated-Mn, indicating the inhibition of root uptake and interior transport of Cd. Additionally, lime addition prominently increased the soil pH and decreased the CaCl 2 -extractable Cd (90.1–93.9%). However, since lime reduced the soil dissolved-Mn, downregulated the OsHMA3 expression and upregulated the OsNramp5 expression, brown rice Cd was reduced by only 43.0%. The combined addition of lime and coated-Mn alleviated the liming effect on soil Mn and gene expression in roots, thereby reducing brown rice Cd by 71.5%. [Display omitted] • Polymer coated-Mn (CMn) constantly supplied dissolved-Mn during rice growth period. • CMn also improved Mn accumulation in rice tissues, while reduced Cd in brown rice. • CMn along with lime was more effective to reduce Cd in whole plant and brown rice. • CMn alleviated the liming effects on soil available Mn and Cd-related transporters. [ABSTRACT FROM AUTHOR]