Soil degradation mineralization

During decomposition of plant remains, many phenolic compounds are released by leaching, microbial degradation or are synthesized by microbial activity. In forestry, problems of natural regeneration and reforestation are connected to the presence of phenolic substances deposited in the soil. Methods for extrachon and identification of toxic substances from different soil types (mineral or organic) are described. The method for extracting of soil phytotoxins is based on the use of ethylacetate and methanol (free phenolics) and alkaline hydrolysis (bound phenolics). 

Biological. Bis(2-ethylhexyl) phthalate degraded in both amended and unamended calcareous soils from New Mexico. After 146 d, 76 to 93% degraded (mineralized) to carbon dioxide. No other metabolites were detected (Fairbanks et al, 1985). In a 56-d experiment, [ C]bis(2-ethylhexyl) phthalate applied to soil-water suspensions under aerobic and anaerobic conditions gave CO2 yields of 11.6 and 8.1%, respectively (Scheunert et al, 1987). 

Work at the EPA Gulf Breeze Laboratory has demonstrated the potential usefulness of encapsulation in the bioremediation of PAHs. A model system has been developed in which a pure culture capable of degrading fluoranthene (strain EPA505) has been successfully encapsulated in polyurethane foam and polyvinyl alcohol (Baker et al., 1988). The capsules can be stored for several months at 4 °C with only minimal loss of viability. Upon addition of the capsules to moist soil, fluoranthene mineralization commenced in approximately the same way as observed when fresh bacterial cells were added to the soil. These results are shown in Figure 5.7a. Since the same inoculation size was used in all flasks during this experiment, the results suggest that the immobilization process does not significantly affect microbial activity. 

Several pure cultures isolated from soils degraded nitrophenols (EPA 1985). As in the case of water, adaptation of soil to 4-nitrophenol was a prerequisite for biodegradation the presence of a critical number of degrader microorganisms was necessary for the initiation of biodegradation However, unlike in natural water, the mineralization of low concentrations of 4-nitrophenol proceeds with little or no initial acclimation period (Scow et al. 1986). Addition of specific nutrients from pristine aquifer also resulted in more rapid adaptation (Aelion et al. 1987 Swindoll et al. 1988), and the rate of biodegradation was concentration-dependent (Scow et al. 1986). The biodegradation of... 

Soil. Degradation proceeds via hydrolysis and microbial degradation, with final mineralization to COr Isoxaflutole and its major metabolites are nonmobile under field conditions... 

Soil. Undergoes rapid degradation to the free acid (DT50 <2 hr) and then further to phenyl and pyridine moieties which are bound to the soil and mineralized. The free acid is mobile in soil, but is further degraded with DT50 5-20 days negligible leaching potential... 

Soil. Degradation via hydrolysis and microbial degradation with final mineralization to C02. Mobile under simulated conditions. However, under field conditions, residues remain in the surface horizons... 

Baker, W.E., 1973. The role of humic acids from Tasmanian podzolic soils in mineral degradation and metal mobilization. Geochim. Cosmochim. Acta, 37 269—281. 

Once in the soil environment organic contaminants may move in, or interact with, the soil atmosphere, soil water, mineral fractions and organic matter. Ultimately, however, the organic contaminants will either dissipate or persist (Fig. 4.27). Compounds persist if they are of low volatility, low solubility (Box 4.14) or have a molecular structure that resists degradation. Conversely, if compounds are highly volatile, highly soluble or are easily degraded, they will be... 

Baker, W. E. (1973). Role of humic acids from Tasmanian podzolic soils in mineral degradation and metal mobilization. Geochim. Cosmochim. Acta 37, 269-281. Bamhisel, R. I. (1977). Chlorites and hydroxy interlayered vermiculite and smectite. In "Minerals in Soil Environments" (J. B. Dixon and S. B. Weed, eds.), pp. 331-356. Soil Science Society of America, Madison, Wisconsin. 

Soil acidification affects extensive areas in many countries of the region, caused by both natural factors and human interventions. Assessment of natural aspects of soil acidification was shown in Section 2. The anthropogenic problems of soil degradation due to acidification are related to acid rains (mainly forest soils, see more details in Chapter 4) and application of mineral fertilizers, most of which are physiologically acid and increase the soil acidity during perennial application, especially application of nitrogen and phosphorus fertilizers. 

Within the last decade applications of new cidture-independent molecular tools based on PCR analysis of soil-extracted nucleic acids have provided unique insights into the conqiosition, richness and structure of microbial communities (58-61). Quantitative PCR methods will be used to estimate the abundance in soils of genes that encode atrazine-degradation enzymes, and by quantifying mRNA, their expression. Magnetic capture hybridization (MCH) followed by nested PCR could predict die potential of a soil to mineralize atrazine (62). In diis study, atzA gene copy number was quantified and found to be correlated... 

Soil composition (mineral) Determines the cation exchange capacity (CEC) Contact between polymer and clayey soils can be difficult. Clay could have a catalytic role in polymer degradation. High CEC assures higher levels of mineral nutrients (NH4, K, Mg % Ca ) which can otherwise become limiting factors. 

Soil ppm MADS 95% Primary degradation Mineralization after 85 days... 

CDU in pure form is a white powder. It is made slowly available to the soil solution by nature of its limited solubihty in water. Once in the soil solution, nitrogen from CDU is made available to the plant through a combination of hydrolysis and microbial decomposition. As with any CRE which is dependent on microbial action, the mineralization of CDU is temperature dependent. Product particle size has a significant effect on CDU nitrogen release rate. Smaller particles mineralize more rapidly because of the larger surface contact with the soil solution and the microbial environment. The rate of nitrogen release is also affected by pH because CDU degrades more rapidly in acidic soils. 

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