Thallium uptake by white mustard (Sinapis alba L.) grown on moderately contaminated soils--agro-environmental implications

The work focused on Tl uptake by white mustard (Sinapis alba L.) grown on moderately contaminated soils with different characteristics. The data presented here clearly demonstrate the ability of white mustard to (hyper)accumulate Tl. Substantially higher Tl levels were was found in mustard grown on the Arenosol as compared to the carbonate-rich Leptosol; a relationship between the content of labile Tl (adsorbed, bound to carbonates etc.) in soil and its uptake by the plant is suggested. Approximately 3-fold lower concentrations of Tl in roots and stems of the mature mustard (compared to the young plant) indicate a decreasing trend of Tl uptake with the age of the plant. The exchangeable/acid-extractable and reducible Tl fractions were evaluated as the dominant fractions controlling Tl transfer from both contrasting soils. Thallium associated with the residual fraction (e.g., incorporated into silicates) was rather stable in the rhizosphere, proving a negligible influence of root exudates on Tl release from such an operationally defined fraction, despite the anthropogenic origin of Tl. Regarding our results, when mustard is cultivated for nutrition purposes and/or as green manure, it may pose an important source of Tl introduction into the food chain.

Potential and drawbacks of EDDS-enhanced phytoextraction of copper from contaminated soils

Incubation and pot experiments using poplar (Populus nigra L. cv. Wolterson) were performed in order to evaluate the questionable efficiency of EDDS-enhanced phytoextraction of Cu from contaminated soils. Despite the promising conditions of the experiment (low contamination of soils with a single metal with a high affinity for EDDS, metal tolerant poplar species capable of producing high biomass yields, root colonization by mycorrhizal fungi), the phytoextraction efficiency was not sufficient. The EDDS concentrations used in this study (3 and 6 mmol kg(-1)) enhanced the mobility (up to a 100-fold increase) and plant uptake of Cu (up to a 65-fold increase). However, despite EDDS degradation and the competition of Fe and Al for the chelant, Cu leaching cannot be omitted during the process. Due to the low efficiency, further research should be focused on other environment-friendly methods of soil remediation.

Assessment of the BCR sequential extraction procedure for thallium fractionation using synthetic mineral mixtures

This work focused on the specific behavior of Tl-bearing phases in the BCR (Community Bureau of Reference) sequential extraction (SE) scheme, namely Tl-bearing ferrihydrite, goethite, birnessite, calcite, illite, sphalerite and feldspar in their simple model mixtures with quartz. Several significant discrepancies between the obtained and expected behaviors of these phases in the BCR SE were observed. The amount of Tl released as the exchangeable/acid-extractable fraction (55-82% of the total Tl content) showed a substantial H(+)-promoted dissolution of all Fe(III) and Mn(III, IV) oxides (corresponding to up to 61% of solid Fe dissolved) and incongruent (increased) extraction of Tl from ferrihydrite and goethite. Reductive conditions of the second SE step were insufficient to complete goethite dissolution with corresponding Tl amount retained in the solid phase. Similarly, insufficient oxidation of sphalerite and lower Tl recovery of the oxidisable fraction was identified. In contrast, the BCR SE seems to produce well predictable results of Tl leaching from Tl-bearing calcite and feldspar. Only 70% of total Tl content was extracted from Tl-modified illite in the exchangeable/acid-extractable step, while 30% was associated with the reducible and residual fractions, i.e., Tl was strongly fixed to the illite matrix.

Thallium dynamics in contrasting light sandy soils--soil vulnerability assessment to anthropogenic contamination

The influence of different soil conditions and the presence of LMWOA (Low Molecular Weight Organic Acids) on anthropogenic Tl dynamics were discussed in this study. A shift from the "labile" to the residual fraction during the ageing was identified, indicating Tl incorporation into stable phases (e.g., illite and/or amorphous silicates). The increased water-soluble Tl concentration (1.8-fold, in maximum) after the split application of LMWOA (simulating root exudation) was observed in all soils; partial dissolution of relatively "insoluble" Tl-bearing phases (silicates and eventually oxides) in the presence of LMWOA is suggested. Thermodynamic modeling showed that Tl mobilization in the presence of citric and oxalic acids was indirect and could be attributed to complexation of major elements (Ca, Mg, Al) originating from the dissolution of various soil phases. On the contrary, H(+)-promoted dissolution by acetic acid was assumed as the predominant mechanism of Tl mobilization. Manganese(III,IV) oxides, illite and probably amorphous silicates were evaluated as the dominant phases responsible for Tl retention in the soils. In carbonate-rich soils, Tl coprecipitation with the newly formed carbonates seems to be an important factor influencing Tl release. Therefore, we suggest data on CEC, pH(ZPC) and soil mineralogy to be critical for assessment of Tl behavior in soil systems.

Interactions of EDDS with Fe- and Al-(hydr)oxides

The efficiency of EDDS ([S,S]-ethylenediaminedisuccinate) in metal (phyto) extraction has been discussed in many recent papers. This study demonstrated that the presence of Fe- and Al-(hydr)oxides in soils influences the speciation of EDDS and thus can decrease the extraction of the targeted metallic contaminants (e.g., Pb, Cu, Zn). Above all, amorphous and poorly crystalline oxides (e.g., ferrihydrite) seem to significantly control dissolved Fe and Al concentrations in soils in the presence of metal-EDDS complexes and especially uncomplexed EDDS. Metals released from these minerals compete for the chelating agent and the extraction efficiency of the targeted metals is lowered. The formation of stable Cu-EDDS complexes, which are preferentially formed in soils with high Cu concentrations, results into a lower dissolution of ferrihydrite and goethite compared to free EDDS and Al-EDDS. Information about the contents of amorphous and poorly crystalline oxides in the treated soils would thus be beneficial for choosing efficient EDDS dosages.

Retention of copper originating from different fungicides in contrasting soil types

This work described the retention of Cu from two different commonly used pesticides, the Bordeaux mixture (CuSO(4)+Ca(OH)(2)) and Cu-oxychloride (3Cu(OH)(2).CuCl(2)), and from Cu(NO(3))(2) in contrasting soil types (Leptosol, Chernozem, Cambisol). Thermodynamic modeling showed that Cu speciation was similar in all fungicide solutions. However, the retention of Cu differed with the fungicide used (maximum retention from the Bordeaux mixture) which indicates that different retention processes occurred in the studied soils. The suggested mechanisms include: specific and non-specific adsorption (especially on soil organic matter), precipitation of newly formed phases, such as CuO, Cu(OH)(2), Cu(2)(OH)(3)NO(3), CuCO(3)/Cu(2)(OH)(2)CO(3) and in the case of the Bordeaux mixture, precipitation of various Cu-hydroxysulfates. These phases were identified by the speciation model. The retention of fungicide-derived Cu in the studied soil types followed well the Freundlich isotherm and was directly controlled by the chemical form of Cu. This fact should be taken into account for both environmental and practical applications.

Contrasting lead speciation in forest and tilled soils heavily polluted by lead metallurgy

The concentration trends and chemical fractionation of Pb was studied in eight tilled and forest soil profiles heavily polluted by Pb metallurgy in the Pribram district, Czech Republic. The highest Pb concentrations were observed in surface and subsurface horizons attaining 35,300 mg kg-1 in forest soils and 1233 mg kg-1 in tilled soils. Total Pb concentrations were one order of magnitude lower in tilled soil due to intensive ploughing and annual crop off-take. The results of the Tessier sequential extraction procedure showed the preferential binding of Pb in forest soils to operationally-defined exchangeable positions and soil organic matter (oxidisable fraction). The Pb exchangeable fraction is thought to correspond to weak electrostatic binding on the functional groups of organic matter. In tilled soil, Pb is predominantly bound to operationally-defined Fe and Mn oxides (reducible fraction). A comparison with the background Pb concentration values showed a strong contamination even in mineral horizons IIC and confirmed a strong vertical mobility of Pb within the soil profiles. The calculated mobility factors (MF) showed that up to 72% of Pb is mobile and bioavailable in forest soils. In contrast, the bioavailability of Pb in tilled soils was significantly lower as the MF accounted for up to 30%. In the most polluted horizon of forest soil profile, the X-ray powder diffraction (XRPD) analysis confirmed the presence of anglesite (PbSO4), derived likely from the smelter emissions.