•Humic substances (HS) from compost showed good surfactant properties.•Soil aging changed the distribution of Zn, Ni and Cu but not that of Pb and Cd.•Cu, Ni and Zn removal with HS was greater in ...soils that had been aged less.•Pb and Cd removal with HS was not affected by soil aging.
There is a need for inexpensive, readily-available and environmentally-friendly soil washing agents to remediate polluted soils. Thus, batch washing experiments were performed to evaluate the feasibility of using a solution of humic substances (HS) extracted from compost as a washing agent for simultaneous removal of Cu, Cd, Zn, Pb and Ni from artificially contaminated soils aged for 1 month, 12 months and 24 months. The efficiency of metal removal in single and multiple washings and kinetic constants (equilibrium metal concentration qe and rate constant k from the second-order kinetic equation) were determined. On average, triple washing removed twice as much metal as that removed with a single washing. At pH 7 and a HS concentration of 2.2gCL−1, metal removal from all soils decreased in this order: Cd (79.1–82.6%)>Cu (51.5–71.8%)>Pb (44.8–47.6%)>Ni (35.4–46.1%)>Zn (27.9–35.8%). However, based on qe (mgkg−1), metal removal was in this order: Pb>Zn≈Cu>Ni>Cd. This difference was due to different concentrations of metals, which is typical for multi-metal contaminated soils. Regardless of washing mode, removal of Cd and Pb was not affected by soil age, whereas removal of Cu, Ni and Zn was higher in soils that had been aged for a shorter time. These results indicate that HS are suitable for remediating soil contaminated with multiple heavy metals in extremely high concentrations.
Dynamic behaviors of the newly deposited atmospheric heavy metals in the soil-pak choi (Brassica chinensis L.) system are investigated by a fully factorial atmospheric exposure experiment using soils ...exposed to 0.5-year and 1.5-year atmospheric depositions. The results showed approximately 17–87%, 19–64%, and 43–84% of the Cu, Cd, and Pb in pak choi edible parts were contributed from the new depositions, respectively. For the newly deposited metals, foliar uptake was the key pathway of shoot bioaccumulation rather than from root uptake of the deposited metals in soils, resulting in no significant soil contribution differences between pak chois growing in 0.5-year and 1.5-year exposed soils. Indeed, highly bioavailable metals in atmospheric deposition significantly increased the soil plant-bioavailable Cu, Cd, and Pb fractions; however, soil aging resulted in similar percentages of the plant-bioavailable fractions in 0.5-year and 1.5-year exposed soils, which indicated the bioavailability of metals deposited into soils rapidly decreased with aging. The soil aging process of the deposited metals was well fitted with the first-order exponential decay model, and soil organic matter and clay were the major driving factors. Our findings highlight high plant bioaccumulation rates and the rapid soil aging process of newly deposited metals during the plant growth period.
A thorough understanding of the geochemical behavior of W in soils is crucial for environmental risk assessment. Soil pH is known as master variable of element solubility and bioavailability in ...soils. Here we report on effects of soil pH (modified by liming and acid – base additions) and soil aging on the environmental availability of W in soil using W solubility and chemical fractionation as indicators. Experimental soils included two naturally acidic soils with contrasting soil texture (SAND, CLAY), at native pH or limed with 2.5% CaCO3, and spiked with increasing concentration of W.
Our results showed that W was significantly more labile in alkaline compared to acidic soils, confirming the validity of results of pure-mineral studies for more heterogeneously composed soils. While labile W was generally greater in the SAND compared to the CLAY soil, the reverse trend was observed in the limed soils at the highest W addition (5000 mg kg−1). Combining our results with previous mechanistic reports suggests that clay edge sorption sites significantly contributed to W retention in treatments with low to medium W additions, resulting in lower environmental availability for W in the CLAY soil. At high W concentrations and high pH, the stronger W retention in the SAND was attributed to continuous formation of W surface polymers on the more abundant metal (oxyhydr)oxides, a process that has been previously reported to occur even under alkaline conditions. A first comparison of various soil chemical methods (Bray & AB-DTPA extractions, soil solution centrifugation CL, diffusion-based DGT) to predict W phytoavailability in soil also revealed a strong pH dependency challenging the identification of a suitable method. This study is one of the first demonstrating the pH dependence of W in natural soils and delivers evidence for increased risk of W mobilization in W polluted, alkaline soil environments.
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•Soil pH and time (aging) are master variables governing bioavailability of tungsten (W) in soil.•W is significantly more labile in alkaline soils.•W polymerization plays a crucial role in determining W solubility in soils.•In acidic, high W soils, W polymer formation in the soil solution reduces W sorption.•Surface polymerization of W on (oxyhydr)oxide surfaces increases W sorption even at high pH.
Artificially contaminated soil is often used in laboratory experiments as a substitute for actual field contaminated soils. In the preparation and use of laboratory contaminated soils, questions ...remain as to how much and how long metals remain in labile form and in their oxidation state during the contamination process. Therefore, the objectives of this study were to determine if the speciation of added contaminants can be retained in the original form and to observe the change in lability of each element with aging time. In this study, natural soil was artificially polluted with five redox-sensitive toxic elements in their oxidized or reduced forms, i.e., As(III)/As(V), Sb(III)/Sb(V), Cr(III)/Cr(VI), Mo(VI), and W(V). Metal distribution was measured in progressive chemical fractionation using sequential extraction methods in contaminated soils after 3, 100, and 300 days of aging. The results indicated that the more strongly bound fraction of metals increased by day 100; whereas the fractions were not significantly different from those in the 300-day-aged soil. Among five metals, the ratio of weakly-bound fractions remained highest in As- and lowest in Cr-contaminated soils. The W(VI)-contaminated soil showed strong sorption without changes in speciation during aging. The oxidized or reduced metal species converged to occur as a single species under given soil conditions, regardless of the initial form of metal used to spike the soil. Both As and Sb existed as their oxidized form while Cr existed as its reduced form. The results of this study may provide a useful and practical guideline for artificial soil contamination.
•As and Mo were relatively more mobile than Sb, Cr, and W.•Tungsten fraction did not significantly change with soil aging.•Soil aging process is closely related to Fe–Mn oxides and soil organic matter.•The oxidation state of spiked metals converged to the one dominant oxidation state in soil.
The effects of wheat root exudates and the aging interactions between biochar and soil on atrazine desorption from biochar-amended soil were carefully examined. Compared with CaCl2 solution, wheat ...root exudates significantly increase the desorption of atrazine from biochar, mainly by promoting the desorption of atrazine adsorbed on biochar with specific forces. Wheat root exudates were effectively separated into three components with different electrical properties, namely, anionic, neutral, and cationic components. Mainly due to the carboxyl-containing compounds, the anionic component was the main active component in the wheat root exudates that enhances the desorption of atrazine from the biochar. Additionally, wheat root exudates can increase the desorption of atrazine from biochar-amended soil. The promotion of atrazine desorption by root exudates was more obvious in soils with low organic matter contents, where atrazine was mainly adsorbed by biochar. The aging interaction between the biochar and soil increased the total desorption rate and rapid desorbing fraction of the atrazine in the soil, most likely due to the reduction of the biochar sorption capacity in the aged biochar-amended soil.
•Root exudates released atrazine that was sorbed on biochar with specific forces.•Root exudates were divided into three components by electrodialysis.•Anionic component was the active component that released atrazine from biochar.•Aging interaction between biochar and soil increased atrazine desorption from soil.
Hydrochar, recognized as a green and sustainable soil amendment, has garnered significant attention. However, information on the aging process in soil and the temporal variability of hydrochar ...remains limited. This study delves deeper into the interaction between hydrochar and soil, focusing on primary factors influencing hydrochar aging during a 30-month rice–wheat rotation system. The results showed that the initial aging of hydrochar (0–16 months) is accompanied by the development of specific surface area and leaching of hydrochar-derived dissolved organic matter (HDOM), resulting in a smaller particle size and reduced carbon content. The initial aging also features a mineral shield, while the later aging (16 to 30 months) involves surface oxidation. These processes collectively alter the surface charge, hydrophilicity, and composition of aged hydrochar. Furthermore, this study reveals a dynamic interaction between the HDOM and DOM derived from soil, plants, and microbes at different aging stages. Initially, there is a preference for decomposing labile carbon, whereas later stages involve the formation of components with higher aromaticity and molecular weight. These insights are crucial for understanding the soil aging effects on hydrochar and HDOM as well as evaluating the interfacial behavior of hydrochar as a sustainable soil amendment.
EDTA-based remediation is reaching maturity but little information is available on the state of chelant in remediated soil. EDTA soil retention was examined after extracting 20 soil samples from Pb ...contaminated areas in Slovenia, Austria, Czech Republic and USA with 120 mM kg−1 Na2H2EDTA, CaNa2EDTA and H4EDTA for 2 and 24 h. On average, 73% of Pb was removed from acidic and 71% from calcareous soils (24 h extractions). On average, 15% and up to 64% of applied EDTA was after remediation retained in acidic soils. Much less; in average 1% and up to the 22% of EDTA was retained in calcareous soils. The secondary emissions of EDTA retained in selected remediated soil increased with the acidity of the media: the TCLP (Toxicity Characteristic Leaching Procedure) solution (average pH end point 3.6) released up to 36% of EDTA applied in the soil (28.1 mmol kg−1). Extraction with deionised water (pH > 6.0) did not produce measurable EDTA emissions. Exposing soil to model abiotic (thawing/freezing cycles) and biotic (ingestion by earthworms Lumbricus rubellus) ageing factors did not induce additional secondary emissions of EDTA retained in remediated soil.
•Chelant emissions are negative side-effect of EDTA-based soil remediation.•Less EDTA was retained in remediated calcareous compared to acidic soils.•Secondary emission of retained EDTA into acidic solutions were extensive.•Artificial soil ageing did not promote secondary emissions of EDTA.•Ca-salt of EDTA represents environmentally the safest choice of chelant.
•Pig glue, egg and milk all experienced deterioration due to the primary and secondary structure changes.•Pig glue owned better aging resistance because of the less changes in hydrophobic amino ...acids, FTIR spectrum and minimum secondary structure variations.•Ultramarine accelerated the soil aging process but did not bring extra influences on the primary structure.
Soil aging was the major aging form that affected great numbers of unearthed Chinese ancient artworks and would fundamentally influence the deterioration processes of the proteinaceous binders applied in polychromy artworks. The three main categories of the proteinaceous binders, pig glue, egg and milk, would present various stabilities towards soil aging due to their different characteristics, the study of which was of high importance for exploring the degradation mechanisms of polychromy artworks. In this paper, GC-MS and FTIR were applied to study the changes of the primary structure (amino acids) and secondary structure of pure pig glue, egg, milk and binder with ultramarine in a simulated anoxic, dark, microthermal, compacted stable burial environment for one year. Results illustrated that all binders experienced deterioration due to the changes in individual, different groups of amino acids and the broadening of Amide A. Comparatively, pig glue owned better aging resistance because of the less changes in hydrophobic amino acids, FTIR spectrum and minimum secondary structure variations. Moreover, ultramarine accelerated the soil aging process but did not bring extra influences on the primary structure.
This study examines the influence of soil aging on Standard Penetration Test (SPT) N-Vs correlations, and seismic site classification. Energy-corrected SPT-Vs correlations are developed for two ...regions where subsurface layering consists of soil deposits with very young geotechnical ages according to the last critical soil disturbance that occurred in the study areas. It is observed that the uncorrected correlations of the current study fall into the lower bound of the uncorrected SPT-Vs correlations existing in the literature due to soil aging effects. To better illustrate the effects of soil aging on SPT-Vs correlations, the uncorrected correlations from the literature and this study are divided into two age categories of Holocene and Pleistocene according to their geological age. Using the two age categories, the boundaries proposed in the NEHRP for different seismic site classes are divided into three zones according to their uncertainty level regarding seismic site classification. The results clearly indicate the need to consider the age of soil deposits for seismic site classification when using the SPT method to avoid incorrect seismic site classification. Additionally, it is found that the use of raw (uncorrected) SPT N values can lead to incorrect seismic site classification, with either conservative or unconservative results depending on the Energy Transfer Ratio (ETR) of the SPT hammer used for the seismic site class determination.
•Two new age categories of Holocene and Pleistocene are defined for the uncorrected SPTVs correlations for sandy soils.•Energy-corrected SPT-Vs correlation should be used to avoid inconsistency between different studies caused by hammer ETR.•In the SPT method, the use of uncorrected SPT N values can lead to incorrect seismic site classification.•The age of soil needs to be considered for seismic site classification when using the SPT method.
To investigate the change in biochar’s ability to directly immobilize Cd in soil, a successive wheat cultivation experiment was conducted. Three biochars with different Cd adsorption mechanisms were ...added to the soils, and a mesh bag was used to separate the soil particles (> 1 μm) from the biochar. The results showed that the ash contents and anionic contents (CO
3
2−
and PO
4
3−
) of the biochar decreased with the cultivation time, while the oxygen-containing functional group content and CEC of the biochar increased. As a result, the Cd concentration on biochar decreased, by 68.9% for WBC300, while unstable Cd species (acid soluble and reducible fraction of Cd) on biochar increased with successive cultivation, increasing from 3 to 17% for WBC300 in FS. Correspondingly, the ability of biochar to inhibit Cd accumulation in wheat decreased. The results of this study illustrated that the ability of biochar to directly immobilize Cd in soil is not permanent; it gradually decreases with aging in soil. The adsorption mechanism of Cd on biochar changed from precipitation to complexation, and ion exchange processes could be the main reason.
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