C - Lublin
C - Lublin
C - Lublin
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Only minor amounts of 14 C-TNT (1-2%) were mineralized to 14 CO 2 in both<br />
treatments. Almost all the disappeared extractable 14 C-TNT was detected as bound<br />
14 C. However, the process of TNT binding occurred much faster and was more<br />
extensive in the AC-amended soil compared to the control. The bound 14 C-<br />
products were very resistant to solvent extraction. Practically no 14 C-products were<br />
released from the amended soil after 3 or 4 sequential extractions with acetonitrile.<br />
Plant tissues contained no more than 0.5% of the initially added<br />
14 C,<br />
demonstrating low accumulation of TNT and its products in corn plants growing<br />
in contaminated soil amended with AC.<br />
Microbial toxicity of TNT was indicated by a greater than 50% decrease in<br />
platable heterotrophic microorganisms in soils containing 1000 or 2000 mg<br />
TNT/kg. Similarly, the activated carbon reduced the phytotoxicity of TNT in the<br />
soil. While corn plant growth was severely inhibited in TNT-contaminated soil,<br />
their growth characteristics in AC-amended soil (TNT contaminated or<br />
uncontaminated) were similar to the uncontaminated control. The results<br />
corresponded to minimal phytotoxic concentration of TNT in solution in<br />
experiments with corn and tall fescue seedlings growing in hydroponics culture at<br />
presence of TNT. Their growth began to decline negligibly at 5 mg TNT/l while<br />
growth was inhibited or the seedling died at a higher concentration [3].<br />
The next mechanism of accelerated detoxification of TNT in the AC-amended<br />
soil was suggested. The activated carbon promoted strong binding of TNT to soil<br />
matrix in two steps. First, some of the adsorbed TNT was quickly bound to AC<br />
through catalytic oxidation and polymerization of the oxidized products. Then the<br />
remaining TNT that was reversibly adsorbed to AC was microbially (and<br />
chemically) transformed to reduction products, which were bound to soil humus<br />
and likely polymerized with the TNT oxidation products. TNT oxidation in the<br />
amended soil presents evidences of strong oxidative properties of AC. It probably<br />
plays the role of catalyst that promotes formation of active oxygen containing<br />
species (OH-radical and others) on the AC surface including its intraporous spaces.<br />
The suggested mechanism of TNT binding in AC-amended soil is presented in [4].<br />
The bound TNT products were shown to be nontoxic to heterotrophic soil<br />
microorganisms and plants.<br />
Detoxification of PCB. First positive results have been received when<br />
adsorptive bioremediation was applied for soils highly contaminated with<br />
polychlorinated byphenils (PCB) (C 0 =200-4000 mg/kg). Amendment of PCB<br />
contaminated soil with activated carbon sharply decreased their concentration and<br />
soil toxicity. Bio- and phytotoxicity of the treated soil reduced to minimal levels<br />
after 2 month’ incubation, while low reduction of PCB concentration and toxicity<br />
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