Galina Vasilyeva

Dynamics of PCB removal and detoxification in historically contaminated soils amended with activated carbon.

Activated carbon (AC) can help overcome toxicity of pollutants to microbes and facilitate soil bioremediation. We used this approach to treat a Histosol and an Alluvial soil historically contaminated with PCB (4190 and 1585 mg kg(-1), respectively; primarily tri-, tetra- and pentachlorinated congeners). Results confirmed PCB persistence; reductions in PCB extractable from control and AC-amended soils were mostly due to a decrease in tri- and to some extent tetrachlorinated congeners as well as formation of a bound fraction. Mechanisms of PCB binding by soil and AC were different. In addition to microbial degradation of less chlorinated congeners, we postulate AC catalyzed dechlorination of higher chlorinated congeners. A large decrease in bioavailable PCB in AC-amended soils was demonstrated by greater clover germination and biomass. Phytotoxicity was low in treated soils but remained high in untreated soils for the duration of a 39-month experiment. These observations indicate the utility of AC for remediation of soils historically contaminated with PCB.

Catalytic oxidation of TNT by activated carbon

Activated carbon can remove 2,4,6-trinitrotoluene (TNT) and 1,3,5-trinitrobenzene (TNB) from aqueous solution and promote oxidation of TNT. After equilibrating a 0.35 mM TNT solution with activated carbon (0.2-1% w/v), HPLC and GC/MS analysis confirmed the presence of 2,4,6-trinitrobenzaldehyde (TNBAld) and 2,4,6-trinitrobenzene (TNB), and provided strong evidence supporting 2,4,6-trinitrobenzyl alcohol (TNBAlc) as an intermediate of TNT oxidation. After 6 d, TNT and its oxidation products were strongly bound to the activated carbon, while TNB was extractable with acetonitrile. Observations indicate that activated carbon catalyzes TNT oxidation to TNBAlc, which is readily oxidized to TNBAld and TNB in the absence of activated carbon under dark conditions. While adsorbed TNB was extractable with acetonitrile, activated carbon promoted rapid TNT oxidation and formation of unextractable residues. Strong binding is attributed to catalyzed oxidation of the TNT methyl group, probably through a free radical mechanism, and subsequent chemisorption of oligomers and polymerized products that are not desorbed from micropores. Our observations indicate TNT oxidation and bound residue formation after sorption by activated carbon increases the effectiveness of activated carbon to decontaminate water.

Accelerated Transformation and Binding of 2,4,6-Trinitrotoluene in Rhizosphere Soil

Enhanced microbial activity and xenobiotic transformations take place in the rhizosphere. Degradation and binding of 2,4,6-trinitrotoluene (TNT) were determined in two rhizosphere soils (RS) and compared to respective unplanted control soils (CS). The rhizosphere soils were obtained after growing corn for 70 d in soils containing 2.8% (Soil A) or 5.9% (Soil B) organic matter. Aerobically agitated soil slurries (3:1, solution/soil) were prepared from RS and CS and amended with 75 mg TNT L−1 (14C-labeled). TNT degraded more rapidly and formed more un-extractable bound residue in RS than in CS. In Soil A, total extractable TNT decreased from 225 to 1.0 mg kg−1 in RS, whereas 11 mg kg−1 remained in CS after 15 d. Unextractable bound 14C residues accounted for 40% of the added 14C-TNT in RS and 28% in CS. The smaller differences in Soil B were attributed partially to the higher organic matter content. The predominant TNT degradation products were monoaminodinitrotoluenes (ADNT), which accumulated and disappear...

Aerobic TNT reduction via 2-hydroxylamino-4,6-dinitrotoluene by Pseudomonas aeruginosa strain MX isolated from munitions-contaminated soil

Bioremediation of munitions-contaminated soil requires effective transformation and detoxification of high concentrations of 2,4,6-trinitrotoluene (TNT). Pseudomonas aeruginosa strain MX, isolated from munitions-contaminated soil, aerobically transformed TNT (100 mg/L) in culture medium within 15 h, causing transient accumulation of hydroxylaminodinitrotoluenes (HADNTs). The predominance of 2-hydroxylamino-4,6-dinitrotoluene (2HADNT), as well as 2-amino-4,6-dinitrotoluene (2ADNT) and 4,4′,6,6′ -tetranitro-2,2′ -azoxytoluene (2,2′AZT), indicated preferential reduction of the TNT ortho nitro group. While only 12% of the TNT was transformed to 2ADNT, up to 65% was transformed to tetranitroazoxytoluenes (AZTs), which accumulated as a precipitate. The precipitate was formed by microscopic particles adhering to bacterial cells, which subsequently formed clusters containing lysed cells. Toxicity toward bacteria was primarily attributed to 2ADNT, because pure AZTs preincubated with sterile medium had little effect on the strain. While the culture medium containing TNT exhibited toxicity toward corn (Zea mays L.) and witchgrass (Panicum capillare L.), little phytotoxicity was observed after incubating with P. aeruginosa strain MX for 4 d. Strong binding of HADNTs to soil and low AZT bioavailability may further promote the detoxification of TNT in soil.

USE OF ACTIVATED CARBON FOR SOIL BIOREMEDIATION

The use of activated carbon may help overcome the toxicity of organic pollutants to microbes and plants during soil bioremediation. Experiments were conducted with 3,4-dichloroaniline (DCA), 2,4,6-trinitrotoluene (TNT), and polychlorinated biphenyls (PCB) to demonstrate that activated carbon (AC) can reduce the toxicity of readily available chemicals in soil by transferring them to a less toxic soil fraction. This process results in accelerated biodegradation of DCA by inoculated chloroaniline-degrading strains. In the case of TNT, the AC promotes strong binding through accelerated microbial reduction of its nitro groups and catalytic chemical oxidation of the methyl group and polymerization or binding of the products formed. Degradation of PCB in soil is rather slow. However, amendment with AC leads to a sharp reduction of extractable PCB, mostly due to strong binding to the adsorbent. The introduced AC was shown to maintain a low content of toxicants in soil solution, creating favorable conditions for plant growth, while in the unamended soils plants die or are highly inhibited. Biotests with Daphnia magna also demonstrated a sharp reduction of the toxicity of these contaminated soils in the presence of AC.

Using Plants to Remove Foreign Compounds from Contaminated Water and Soil

Depending on the physico-chemical properties of the organic pollutant to be removed or detoxified, as well as on the specific plant physiology and biochemistry, different phytotreatments are available to decontaminate water and soils. For example, aquatic macrophytes or even terrestrial plants can be grown under hydroponic conditions or in constructed wetlands to remove many xenobiotic compounds, e.g. sulphonated anthraquinones and azo dyes present in wastewater from the dye and textile industries.

Witches’ broom and normal crown clones from the same trees of Pinus sibirica: a comparative morphological study

Key messageMutational witches’ broom clones show a growth redistribution compared with normal clones. The main factor affecting the variations in mutant clone morphology is the strength of the mutation.AbstractMutational witches’ broom is a fragment of the tree crown with abnormally dense branching and slower shoot growth, compared with those of a normal crown. Thousands of dwarf ornamental cultivars widely used in landscape design have been developed from mutational witches’ broom. In this study, crown morphology was compared between grafted clones of witches’ broom and normal clones from the same trees. The results quantify variations in crown structure between the mutants and normal clones. The sample materials were 10 pairs of grafted witches’ broom and normal crown clones of Pinus sibirica. The mutant and normal clones were discrete sets. Many morphological traits were affected in the mutants. Compared with the normal-crown clones, the mutants showed male sterility, decreased apical dominance, reduced shoot and needle length, and increased branching and seed cone bearing. In terms of morphogenic changes induced by the mutation, the shoots of the witches’ broom clones were bicyclic, generated seed cones that were much shorter than those of normal clones, and had acquired the ability to form lateral buds. The extent of interclonal variation was significantly greater among witches’ broom clones than among normal clones. Compared with the morphological traits of normal clones, those of the mutants were shifted in the same direction but to different extents. Therefore, mutational witches’ broom is the expression of a mutation that can be weak, medium, or strong. These results will be useful for unraveling the genetic basis of witches’ broom in conifers and for breeding new dwarf cultivars.

Benzo[a]pyrene degradation and bioaccumulation in soil-plant system under artificial contamination

The involvement of benzo[a]pyrene (BaP) one of the most toxic polycyclic aromatic hydrocarbons (PAHs) in the soil-plant system causes its potential carcinogenicity and mutagenicity for human health. The aim of this article is benzo[a]pyrene (BaP) degradation and bioaccumulation in soil-plant system under artificial contamination in model experiment with Haplic Chernozem and that spiked with various doses of BaP (20, 200, 400 and 800μgkg-1) equivalent to 1, 10, 20 and 40 levels of maximal permissible concentrations (MPC) planted with spring barley (Hordeum sativum distichum). The experimental soil samples were planted every spring and incubated outdoor during 4years. The express-method of subcritical water extraction was used for BaP extraction from samples. It was established the values of BaP period of semi-degradation in soil (T50, y) contaminated with 10, 20 and 40MPC deviated from 1.4 to 1.8years, while these values in low contaminated soils deviated from 2.9 to 5.4years. It was found the BaP concentrations in plants depended on initial BaP contamination and reduced simultaneously with diminish of BaP concentration in the related spiked samples. Growing of spring barley in the BaP spiked soils lead to BaP accumulation in plants. The bioaccumulation factors for BaP in roots and vegetative part of barley plants (BAFr and BAFv respectively) fluctuated within 0.035-0.065 and 0.015-0.025 respectively at the 1st season and then reduced about twice to the 4th season. Meantime those values in control soils vice-versa increased twice from 0.03 and 0.01 respectively.

Phytoaccumulation of Benzo[a]pyrene by the Barley in Artificially Contaminated Soil

ABSTRACT The assessment of toxic effects of polycyclic aromatic hydrocarbons (PAHs) on Haplic chernozems soil was developed by using spring barley (Hordeum sativum distichum) bioaccumulation tendencies. Spring barley was used to estimate the negative effect of chernozemic soil contamination with benzo[a]pyrene (BaP), one the most carcinogenic and mutagenic PAHs compounds. The bioaccumulation tendencies were studied in soil spiking with BaP. Spiked doses were close to technogenic pressure level in studied area, 0–800 µg/kg of BaP. Condition and doses of BaP during 4 years of model experiment influenced morphometric characteristics of spring barley and rates of BaP uptake by plants. Exposure to the growth characteristics containing at least 20 µg/kg BaP promoted absorbing BaP by plants root system as well as increased roots length. Tendencies of phytotoxicity parameters inhibition were observed for all morphometric characteristics of spring barley as energy of germination, length of vegetation part, plant weight and ear height. Quantifiable levels of BaP uptake by spring barley roots exceeded vegetative part more than 2.5 times in all polluted variants. The constant of BaP semi-degradation in artificially polluted Haplic chernozems for 48 months of model experiment T50 reached 1.2–3.4 years. Thus, the BaP uptake by spring barley from chernozem soil contributes to the bioindication responses during environmental monitoring to assess the impact of BaP pollution.