Effect of freeze-thaw manipulation on phytostabilization of industrially contaminated soil with halloysite nanotubes.

The latest trends in improving the performance properties of soils contaminated with potentially toxic elements (PTEs) relate to the possibility of using raw additives, including halloysite nanotubes (HNTs) due to eco-friendliness, and inexpensiveness. Lolium perenne L. was cultivated for 52 days in a greenhouse and then moved to a freezing-thawing chamber for 64 days. HNT addition into PTE-contaminated soil cultivated with grass under freezing-thawing conditions (FTC) was tested to demonstrate PTE immobilization during phytostabilization. The relative yields increased by 47% in HNT-enriched soil in a greenhouse, while under FTC decreased by 17% compared to the adequate greenhouse series. The higher PTE accumulation in roots in HNT presence was evident both in greenhouse and chamber conditions. (Cr/Cd and Cu)-relative contents were reduced in soil HNT-enriched-not-FTC-exposed, while (Cr and Cu) in HNT-enriched-FTC-exposed. PTE-immobilization was discernible by (Cd/Cr/Pb and Zn)-redistribution into the reducible fraction and (Cu/Ni and Zn) into the residual fraction in soil HNT-enriched-not-FTC-exposed. FTC and HNT facilitated transformation to the residual fraction mainly for Pb. Based on PTE-distribution patterns and redistribution indexes, HNT's role in increasing PTE stability in soils not-FTC-exposed is more pronounced than in FTC-exposed compared to the adequate series. Sphingomonas, Acidobacterium, and Mycobacterium appeared in all soils. HNTs mitigated FTC's negative effect on microbial diversity and increased Planctomycetia abundance.

Does biochar in combination with compost effectively promote phytostabilization of heavy metals in soil under different temperature regimes?

The article presents the effect of a combined amendment, i.e., biochar+compost (BC), on the process of Cd, Cu, Ni, Pb and Zn immobilization in soil cultivated with L. perenne under freezing and thawing conditions (FTC). In particular, the speciation analysis of the examined elements in phytostabilized soils based on their response using the sequential extraction, and the variability of the soil microbiome using 16S rRNA gene amplicon sequencing were systematically assessed. Metal stability in soils was evaluated by the reduced distribution index (Ir). Plants were grown in pots for 52 days under greenhouse conditions. After termination, phytostabilization was continued in a temperature chamber for 64 days to provide FTC. As a result, it was noted that biomass yield of L. perenne was promoted by BC (39 % higher than in the control pots) and reduced by FTC (45 % lower than in the BC-enriched soil not exposed to FTC). An efficacious level of phytostabilization, i.e., higher content of heavy metals in plant roots, was found in the BC-enriched soil, regardless of the changes in soil temperature conditions. BC improved soil pH before applying FTC more than after applying FTC. BC had the greatest impact on increasing Cu stability by redistributing it from the F1 and F2 fractions to the F3 and F4 fractions. For most metals, phytostabilization under FTC resulted in an increase in the proportion of the F1 fraction and a decrease in its stability. Only for Pb and Zn, FTC had greater impact on their stability than BC addition. In all soil samples, the core genera with about 2-3 % abundances were Sphingomonas sp. and Mycobacterium sp. FTC favored the growth of Bacteroidetes and Proteobacteria in soil. Microbial taxa that coped well with FTC but only in the absence of BC were Rhodococcus, Alkanindiges sp., Flavobacterium sp., Williamsia sp. Thermomonas sp.

New approach strategy for heavy metals immobilization and microbiome structure long-term industrially contaminated soils.

The progress of engineering technologies highly influences the development of methods that lead to the condition improvement of areas contaminated with heavy metals (HMs). The aided phytostabilization fits into this trend, and was used to evaluate HM-immobilization effectiveness in phytostabilized soils under variable temperatures by applying 16 freezing-thawing cycles (FTC). Diatomite amendment and Lolium perenne L., also were applied. Cd/Ni/Cu/Pb/Zn each total content in phytostabilized soils were determined, along with the verification for each metal of its distribution in four extracted fractions (F1 ÷ F4) from soils. Based on changes in HM distribution, each metal's stability was estimated. Moreover, HM accumulation in plant roots and stems and soil microbial composition were investigated. Independently of the experimental variant (no-FTC-exposure or FTC-exposure), the above-ground biomass yields in the diatomite-amended series were higher as compared to the corresponding control series. The evident changes in Pb/Zn-bioavailability were observed. The metal stability increase was mainly attributed to metal concentration decreasing in the F1 fraction and increasing in the F4 fraction, respectively. Diatomite increased Cd/Zn-stability in not-FTC-exposed-phytostabilized soils. FTC-exposure favorably influenced Pb/Zn stability. Diatomite increased soil pH values and Cd/Ni/Cu/Zn-bioaccumulation (except Pb) in roots than in stems (in both experimental variants). FTC-exposure influenced soil microbial composition, increasing bacteria abundance belonging to Actinobacteria, Gammaproteobacteria, and Sphingobacteria. At the genus level, FTC exposure significantly increased the abundances of Limnobacter sp., Tetrasphaera sp., Flavobacterium sp., and Dyella sp. Independently of the experimental variant, Sphingomonas sp. and Mycobacterium sp., which have a tolerance to HM contamination, were core bacterial groups, comprising about 6 ÷ 7% of all soil bacteria.

Effect of Biochar on Metal Distribution and Microbiome Dynamic of a Phytostabilized Metalloid-Contaminated Soil Following Freeze-Thaw Cycles.

In the present paper the effectiveness of biochar-aided phytostabilization of metal/metalloid-contaminated soil under freezing-thawing conditions and using the metal tolerating test plant Lolium perenne L. is comprehensively studied. The vegetative experiment consisted of plants cultivated for over 52 days with no exposure to freezing-thawing in a glass greenhouse, followed by 64 days under freezing-thawing in a temperature-controlled apparatus and was carried out in initial soil derived from a post-industrial urban area, characterized by the higher total content of Zn, Pb, Cu, Cr, As and Hg than the limit values included in the classification provided by the Regulation of the Polish Ministry of Environment. According to the substance priority list published by the Toxic Substances and Disease Registry Agency, As, Pb, and Hg are also indicated as being among the top three most hazardous substances. The initial soil was modified by biochar obtained from willow chips. The freeze-thaw effect on the total content of metals/metalloids (metal(-loid)s) in plant materials (roots and above-ground parts) and in phytostabilized soils (non- and biochar-amended) as well as on metal(-loid) concentration distribution/redistribution between four BCR (community bureau of reference) fractions extracted from phytostabilized soils was determined. Based on metal(-loid)s redistribution in phytostabilized soils, their stability was evaluated using the reduced partition index (Ir). Special attention was paid to investigating soil microbial composition. In both cases, before and after freezing-thawing, biochar increased plant biomass, soil pH value, and metal(-loid)s accumulation in roots, and decreased metal(-loid)s accumulation in stems and total content in the soil, respectively, as compared to the corresponding non-amended series (before and after freezing-thawing, respectively). In particular, in the phytostabilized biochar-amended series after freezing-thawing, the recorded total content of Zn, Cu, Pb, and As in roots substantially increased as well as the Hg, Cu, Cr, and Zn in the soil was significantly reduced as compared to the corresponding non-amended series after freezing-thawing. Moreover, exposure to freezing-thawing itself caused redistribution of examined metal(-loid)s from mobile and/or potentially mobile into the most stable fraction, but this transformation was favored by biochar presence, especially for Cu, Pb, Cr, and Hg. While freezing-thawing greatly affected soil microbiome composition, biochar reduced the freeze-thaw adverse effect on bacterial diversity and helped preserve bacterial groups important for efficient soil nutrient conversion. In biochar-amended soil exposed to freezing-thawing, psychrotolerant and trace element-resistant genera such as Rhodococcus sp. or Williamsia sp. were most abundant.

Change in Conductive-Radiative Heat Transfer Mechanism Forced by Graphite Microfiller in Expanded Polystyrene Thermal Insulation-Experimental and Simulated Investigations.

This article introduces an innovative approach to the investigation of the conductive-radiative heat transfer mechanism in expanded polystyrene (EPS) thermal insulation at negligible convection. Closed-cell EPS foam (bulk density 14-17 kg·m-3) in the form of panels (of thickness 0.02-0.18 m) was tested with 1-15 µm graphite microparticles (GMP) at two different industrial concentrations (up to 4.3% of the EPS mass). A heat flow meter (HFM) was found to be precise enough to observe all thermal effects under study: the dependence of the total thermal conductivity on thickness, density, and GMP content, as well as the thermal resistance relative gain. An alternative explanation of the total thermal conductivity "thickness effect" is proposed. The conductive-radiative components of the total thermal conductivity were separated, by comparing measured (with and without Al-foil) and simulated (i.e., calculated based on data reported in the literature) results. This helps to elucidate why a small addition of GMP (below 4.3%) forces such an evident drop in total thermal conductivity, down to 0.03 W·m-1·K-1. As proposed, a physical cause is related to the change in mechanism of the heat transfer by conduction and radiation. The main accomplishment is discovering that the change forced by GMP in the polymer matrix thermal conduction may dominate the radiation change. Hence, the matrix conduction component change is considered to be the major cause of the observed drop in total thermal conductivity of EPS insulation. At the microscopic level of the molecules or chains (e.g., in polymers), significant differences observed in the intensity of Raman spectra and in the glass transition temperature increase on differential scanning calorimetry(DSC) thermograms, when comparing EPS foam with and without GMP, complementarily support the above statement. An additional practical achievement is finding the maximum thickness at which one may reduce the "grey" EPS insulating layer, with respect to "dotted" EPS at a required level of thermal resistance. In the case of the thickest (0.30 m) panels for a passive building, above 18% of thickness reduction is found to be possible.

Morphometric Analysis of One-Component Polyurethane Foams Applicable in the Building Sector via X-ray Computed Microtomography.

A detailed morphometric analysis of one-component polyurethane (PU) expanding foams, with densities of 26 and 28 kg/m³ ('SUMMER' and 'WINTER' product versions), was conducted to evaluate the topology of the foam cells and to discover processing-to-structure relationships. The microstructural analysis of the heterogeneously distributed pores revealed tight relationships between the foam morphology and the cell topology, depending on the growth rate and local environmental conditions, governed by the properties of the blowing gas used. The most significant morphometric output included the following: open/closed porosity and (heterogeneous) pore distribution, relative density and (homogeneous) strut distribution, and total solid matrix surface and closed pore surface area-at the macroscopic level of the foam. While, at the microscopic level of the cells, the results embraced the following: the size of every detected strut and pore, identified two-dimensional (2D) shapes of the cell faces, and proposed three-dimensional (3D) topologies modelling the PU foam cells. The foam microstructure could be then related with macroscopic features, significant in building applications. Our protocol outlines the common procedures that are currently used for the sample preparation, X-ray scanning, 3D image reconstruction and dataset analysis in the frame of the X-ray computed microtomography (µ-CT) testing of the one-component PU foams, followed by a statistical (multiple Gaussian) analysis and conceptual considerations of the results in comparison with thematic literature.