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Despite notable achievements in the development and application of the remediation of metal-contaminated soils, the search for and study of promising immobilizing agents continues. This article presents a new approach to using brown coal and activated carbon and their application for metal stabilization. An experiment was conducted to test Medicago falcata L. on soils from industrial areas contaminated with varying levels of lead (Pb), cadmium (Cd), chromium (Cr), zinc (Zn), copper (Cu), and nickel (Ni) with the addition of carbons. This plant is a stress-tolerant leguminous species. In this study, the total content of metals in soil and the available forms to plants (single extractions with 0.02 M ethylenediaminetetraacetic acid, EDTA) were determined, along with metal contents in the plant. The use of carbons lowered the phytoavailable forms of metals for plants and thus, resulted in a reduction in the phytotoxicity of the soils. The contents of the tested metals in the roots and shoots were lower than in the combinations of soils with no carbon added. The activated carbon had a stronger effect on limiting the availability of metals than brown coal in relation to plants growing on soils without added carbon; the percentage of reduction for the shoots was Cr (18.2%) > Zn (11.5%) > Ni (10.7%) > Cu (10.3%) > Cd (8.9%) > Pb (2.4%) and Cu (13.3%) > Cr (12.5%) > Zn (10.5%) > Pb (9.0%) > Ni (5.7%) > Cd (4.6%) for roots. Metals reduced the growth of Medicago falcata L. roots from 44 to 21%, while the growth of shoots was reduced from 25 to 2%. Adding carbons to soils in all combinations resulted in a decrease in the following pollution indices: pollution index (PI), pollution load index (PLI), and non-carcinogenic (HQ) and carcinogenic risk factors (ILCR). [ABSTRACT FROM AUTHOR]

The contamination of soils with metals applies, in particular, to areas related to industry, the mining of raw materials and ores, transport, and agriculture. Unlike organic materials, metals cannot degrade over time and need to be reduced, removed, or immobilized in soil. One of the remediation methods for soils contaminated with metals is phytoextraction, which uses plants' ability to accumulate metals in their own tissues. Metals enter the plant organism through the roots and are transported to the aboveground parts, where they are accumulated. In this study, we evaluated the phytoaccumulative abilities of two plant species tested on soils from industrial areas contaminated with metals to different extents (Zn, Cd, Ni, Pb, Cr, and Cu). The research was conducted for three years under the conditions of a pot experiment. In order to obtain four soils with varying degrees of metal contamination, two soils from industrial areas, G1 (contaminated) and G2 (uncontaminated), were mixed in the following ratios: 1:1, 1:3, 1:7, and 1:9. In the phytoremediation process, Festuca rubra L. and Alyssum saxatile L. were tested. After analyzing the results of the bioconcentration factor (BCF) for the tested plants, it was noted that both of the tested plants accumulated Cd and Zn more easily, followed by Cu, Ni, and Cr, and then Pb to a lesser extent. The values of factors for Cd and Zn were correlated with the high mobility of these elements compared to other metals and their relatively easy uptake by plants. Alyssum saxatile L. has an ability to accumulate Cd compared to Festuca rubra L., which is confirmed by the BCF (0.764) and transfer factor (TF) (3.5) (for 1:7 combination) values. The calculated results for the BCFs for Alyssum saxatile L. are less than one for all tested metals, which allows us to state that Alyssum saxatile L. is not an accumulator. [ABSTRACT FROM AUTHOR]

Various factors can lead to the transformation of metal forms and to an increase in their solubility and, consequently, their mobility. One solution to the problem of increased solubility is the use of carbons as additives to soil in order to limit the potential migration of contaminants. The aim of this study was to determine the effect of using brown coal and activated carbon on metal forms that are available to plants. The mineral composition of the coals used in a pot experiment was analyzed. Observations were carried out with a JJSM-6380 LA scanning electron microscope (SEM) connected to an EDS electron micro-probe. The total contents of Zn, Cd, Pb and Cu in the assessed soils as well as the content of available metal forms were determined after single extractions with different reagents, namely 1 M NH4NO3, DTPA and 1 M HCl. Generalized linear models (GLMs) were used to evaluate the effectiveness of the stabilization methods in a long-term pot experiment. The carbons reduced the percentage of these forms relative to the total metal content in the soil. After adding brown coal, Zn, Cd, Pb and Cu forms were reduced by up to 32%, 30%, 33% and 43%, respectively. After adding activated carbon, the metal forms of Zn, Cd, Pb and Cu were reduced by up to 47%, 44%, 40% and 50%, respectively. The following order of extracted metal forms with different solutions was found: HCl: Zn > Pb > Cu > Cd; DTPA: Pb > Zn > Cu > Cd; NH4NO3: Zn > Cu > Pb > Cd. Eight years after setting up the pot experiment, the contents of humic substances in soils with the addition of both tested carbons were compared, and the soils with added carbons were found to have a stable content of humic fractions. The costs of remediation through the stabilization method using the tested brown coal and activated carbons do not exceed USD 75/t (taking into account the double doses of both carbons). [ABSTRACT FROM AUTHOR]