Phenol, aerobic degradation

Since the aerobic degradation of halogenated phenols takes place by monooxygenation and is discussed in Part 2 of this chapter, it is not discussed here except to note the production of chlorocat-echols from chlorophenols and chloroanilines. Emphasis is placed on chlorinated substrates, and reference may be made to a review (Allard and Neilson 2003) for details of their brominated and iodinated analogs. The degradation of aromatic fluorinated compounds is discussed in Part 3 of this chapter. 

The aerobic degradation of phenols is initiated by monooxidation with the production of catechols that undergo ring fission. A nnmber of stndies have used various strains of Rhodococcus sp. and Mycobacterium sp. to examine the metabolism of fluorinated phenols, and have illustrated important alternatives ... 

Cultures are being found that can degrade both polychlorinated biphenyls and petroleum hydrocarbons. There is also interest in the role of rhizosphere organisms in polychlorinated biphenyl degradation, particularly since some plants exude phenolic compounds into the rhizosphere that can stimulate the aerobic degradation of the less chlorinated biphenyls. 

Phenols derived from lignin degradation were used as markers to determine the origin of waters of the Seine estuary in France. Thus, fluvial run-off contains syringic, hydroxyben-zoic and vanillic phenols, whereas upstream penetrating marine waters contain cinnamic phenols derived from the estuarine herbs. In the maximum turbidity zone the vanillic acid (38) to vanillin (39) ratio increases due to aerobic degradation of lignin . ... 

Aerobic biodegradation of trichloroethylene occurs by cometabolism with aromatie eompounds (Ensley 1991) and thus requires a cosubstrate such as phenol (Nelson et al. 1987, 1988) or toluene (Fan and Scow 1993). Trichloroethylene degradation by toluene-degrading baeteria has been demonstrated in the presence, but not absence, of toluene (Mu and Scow 1994). Isoprene, a structural analog of trichloroethylene, has also been used as a cosubstrate for triehloroethylene oxidation by some bacteria (Ewers et al. 1990). One source of inhibition of degradation in the absence of cosubstrate may be the toxieity of triehloroethylene itself to indigenous bacteria. 

In some cases, microorganisms can transform a contaminant, but they are not able to use this compound as a source of energy or carbon. This biotransformation is often called co-metabolism. In co-metabolism, the transformation of the compound is an incidental reaction catalyzed by enzymes, which are involved in the normal microbial metabolism.33 A well-known example of co-metabolism is the degradation of (TCE) by methanotrophic bacteria, a group of bacteria that use methane as their source of carbon and energy. When metabolizing methane, methanotrophs produce the enzyme methane monooxygenase, which catalyzes the oxidation of TCE and other chlorinated aliphatics under aerobic conditions.34 In addition to methane, toluene and phenol have been used as primary substrates to stimulate the aerobic co-metabolism of chlorinated solvents. 

TCE is the other major contaminant at the site and is a common groundwater contaminant in aquifers throughout the United States [425]. Since TCE is a suspected carcinogen, the fate and transport of TCE in the environment and its microbial degradation have been extensively studied [25,63, 95,268,426,427]. Reductive dechlorination under anaerobic conditions and aerobic co-metabolic processes are the predominant pathways for TCE transformation. In aerobic co-metabolic processes, oxidation of TCE is catalyzed by the enzymes induced and expressed for the initial oxidation of the growth substrates [25, 63, 268, 426]. Several growth substrates such as methane, propane, butane, phenol, and toluene have been shown to induce oxygenase enzymes which co-metabolize TCE [428]. 

Available data indicate that phenol biodegrades in soil under both aerobic and anaerobic soil conditions. The half-life of phenol in soil is generally less than 5 days (Baker and Mayfield 1980 HSDB 1997), but acidic soils and some surface soils may have half-lives of between 20 and 25 days (HSDB 1997). Mineralization in an alkaline, para-brown soil under aerobic conditions was 45.5, 48, and 65% after 3, 7, and 70 days, respectively (Haider et al. 1974). Half-lives for degradation of low concentrations of phenol in two silt loam soils were 2.70 and 3.51 hours (Scott et al. 1983). Plants have been shown to be capable of metabolizing phenol readily (Cataldo et al. 1987). 

While degradation is slower under anaerobic conditions, evidence presented in the literature suggests that phenol can be rapidly and virtually completely degraded in soil under both aerobic and anaerobic conditions (HSDB 1997). 

Haider K, Jagnow G, Kohnen R, et al. 1974. [Degradation of chlorinated benzol, phenol and cyclohexane derivatives by soil bacteria that utilize benzol and phenol under aerobic conditions.] Arch Microbiol 96 183-200. (German)... 

Soil. Loehr and Matthews (1992) studied the degradation of phenol in different soils under aerobic conditions. In a slightly basic sandy loam (3.25% organic matter) and in acidic clay soil (<1.0% organic matter), the resultant degradation half-lives were 4.1 and 23 d, respectively. 

Soil Under aerobic conditions, diclofop-methyl decomposes in soil forming diclofop-acid (Smith, 1977, 1979a Hartley and Kidd, 1987 Humburg et al., 1989) which degraded to 4-(l4-di-chlorophenoxy)phenol (Smith, 1979), 4-(2,4-dichlorophenoxy)ethoxybenzene (Smith, 1977, 1979a), and hydroxylated free acids (Hartley and Kidd, 1987 Humburg et al, 1989). The half-lives in sandy soils and sandy clay soils were reported to be 10 and 30 d, respectively (Ashton and Monaco, 1991). 

Haider, K.,Jagnow, G., Kohnen, R.. and Lim, S.U. Degradation of chlorinated benzenes, phenols, and cyclohexane derivatives by benzene- and phenol-utilizing bacteria under aerobic conditions, in Decomposition of Toxic and Nontoxic Organic Compounds in Soil Overcash. V.R., Ed. (Ann Arbor. MI Ann Arbor Science Publishers, 1981), pp. 207-223. 

The lab half-life of carbofuran In six soils (each under 4 different levels of moisture and 2-3 different temperatures) was In the range of 5-261 days. After 28 days of aerobic Incubation In two of the six soils, parent carbofuran was the major extractable compound degradation products comprised <5% of the extractable material (65). However, under anaerobic (flooded soil) conditions, the degradation product carbofuran phenol was found to be the principal product and to persist (66). 

The biodegradation of 1,3-DNB in water requires the presence of microorganisms that are acclimated to 1,3-DNB (ERA 1991b). Therefore, biodegradation of 1,3-DNB is not likely to occur in pristine waters. A mixed bacterial culture, with Pseudomonas predominating, adapted to metabolize phenol as the sole source of carbon had the ability to degrade 100 mg/L 1,3-DNB and 1,3,5-TNB under aerobic conditions (Chambers et al. 1963). Both compounds were slowly oxidized, and... 

Since these reactions are relatively rapid, i.e., phenolic acids are rapidly degraded aerobically, their presence in the soil under these conditions appears transitory. It has been difficult to detect unbound phenolic acids in the soil solution and the compounds do not appear to accumulate in appreciable amounts under aerobic conditions. However, the soil is a heterogeneous medium consisting of loci or microenvironments that are at times completely opposite in character, i.e., anerobic microsites in a well-aerated soil (57). The phytotoxicity problem should be viewed in the context of a specially variable environment. 

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