Sterilizing soils

Sterilized soils did not show evidence of carbofuran degradation (Felsot et al. 1981)... 

Comparison of evolved 14CO from four sterile and non-sterile soils 60 days after treatment with MSMA-l2tC showed that from 1.7 to 10.0% of the MSMA-14C was degraded in non-sterile soil, as compared with 0.7% in steam-sterilized controls. Four soil micro-organisms isolated in pure culture degraded... 

The proposal was fatally flawed by failing to address some of the most critical elements of soil washing. Soil washing is essentially a hydraulic flotation process which removes the fines from the soil. Depending upon the soil, that can account for between 5% and 15% of the volume processed. The process is strictly one of density settling and stokes law is followed in the separation process. What you wind up with is a clean and sterile soil because the organic materials in the soil have a density of between 1.2 and about 2.0 and the clays, and some of the silts, because of their particle size are removed from the soil. In the case of Belarus soils, this also removed about 60%-80% of the fine radioactive materials, but that was not the problem. The problem was one of scale and residuals. 

Soil A reversible equilibrium is quickly established when aniline covalently bonds with humates in soils forming imine linkages. These quinoidal structures may oxidize to give nitrogen-substituted quinoid rings. The average second-order rate constant for this reaction in a pH 7 buffer at 30 °C is 9.47 x 10 L/g-h (Parris, 1980). In sterile soil, aniline partially degraded to azobenzene, phenazine, formanilide, and acetanilide and the tentatively identified compounds nitrobenzene and jD-benzoquinone (Pillai et ah, 1982). 

Biological. It was suggested that the rapid disappearance of methylhydrazine in sterile and nonsterile soil (Arrendondo fine sand) under aerobic conditions was due to chemical oxidation. Although the oxidation product was not identified, it biodegraded to carbon dioxide in the nonsterile soil. The oxidation product did not degrade in the sterile soil (Ou and Street, 1988). 

Ismail and Lee (1995) studied the persistence of metsulfuron-methyl in a sandy loam (pH 5.1) and clay soil (3.1) under laboratory conditions. Degradation was more rapid in nonsterilized than in sterilized soil. In nonsterilized soil, the rate of degradation increased with increasing soil moisture content. When the moisture level in the sandy loam and clay soil was increased from 20 to 80% of field capacity at 35 °C, the half-lives were reduced from 9.0 to 5.7 and 11.2 to 4.6 d, respectively. The investigators concluded that the disappearance of metsulfuron-methyl in soil resulted from microbial degradation and chemical hydrolysis. 

Figure 12.8 shows an example of parathion distribution in sterilized and natural, biologically active Gilat soil columns. We see that, at relatively early times, when the effect of decomposition is minimal, the parathion distribution is similar to that in the sterile soil. After four days, the effect of microbial activity on decomposition is evident, and the distribution pattern is significantly different. After seven days, the parathion is almost completely decomposed. This example emphasizes the necessity to consider additional processes, snch as degradation, in analyses of pollutant transport. 

Table 16.4 Percent of remaining parathion and of incubation, in 14 sterile soils with different chemical...

Spore forming microorganisms can be preserved by isolation of spores and storing dried spores in sterile soil or on carrier beads. 

Lorenz, M. G., Reipschlager, K. Wackernagel, W. (1992). Plasmid transformation of naturally competent Acinetobacter calcoaceticus in non-sterile soil extract and groundwater. Archives of Microbiology, 157, 355-60. 

A residual CP concentration is often observed after soil bioremediation. The leveling-off of degradation is not due to decreased microbial activity, since freshly added CPs are rapidly degraded (Harmsen, 1993 Salkinoja-Salonen et al., 1989). The residual concentrations are explained by the gradual diffusion of pollutants deep into micropores, as well as by their adsorption onto soil organic matter (Harmsen, 1993). Lagas (1988) observed that the nonextractable fraction of CPs in sterile soil increased according to the square root of time as a consequence of diffusion into humic material. 

Lamar, R.T., Glaser, J. A. Kirk, T. K. (1990b). Fate of pentachlorophenol (PCP) in sterile soils inoculated with the white-rot basidiomycete Phanerochaete chrysosporium. mineralization, volatilization and depletion of PCP. Soil Biology and Biochemistry, 4, 433-40. 

Fungal Decay of Woods. Blocks of sweet gum and southern pine sapwood were inoculated with test fungi by the standard soil-block method (7). The test fungi were the brown rots Poria monticolla and Lentinus lepidius and the white rot Polyporus versicolor. As a control, one block of pine and one block of gum were left in the sterilized soil-block chambers in which the fungus had been started on feeder blocks and then sterilized. 

One of the most effective fumigants is methyl bromide. It essentially sterilizes soil when applied under a ground covering, because it kills insects, nematodes, and weed seed but also is used to fumigate warehouses. Overexposure to this compound causes respiratory distress, cardiac arrest, and central nervous effects. The inhalation LC50 is 0.06 mg/L (15 min) of air (rat) and 7900 ppm (1.5 h) (human). Methyl bromide has been classified as an ozone depleter under the Clean Air Act and is due to be phased out of use by 2005. 

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