Degradation, aerobic analysis

For aerobic degradation, uptake of oxygen or the evolution of carbon dioxide is most widely used. Use of the concentration of dissolved organic carbon may present technical problems when particulate matter is present, though analysis of dissolved inorganic carbon in a closed system has been advocated (Birch and Fletcher 1991), and may simultaneously overcome problems with poorly soluble or volatile compounds. 

Analysis of chlorobenzoates in sediments, which had been contaminated with PCBs, was used to demonstrate that the lower PCB congeners that had initially been produced by anaerobic dechlorination were subsequently degraded under aerobic conditions. The chlorobenzoates were transient metabolites and their concentrations were extremely low since bacteria that could successfully degrade them were present in the sediment samples (Elanagan and May 1993). 

The bacterial aerobic degradation of pyrene is initiated by the formation of cfi-pyrene-4,5-dihydrodiol. Analysis for this metabolite was used to demonstrate the biodegradability of pyrene in an environment in which there was continuous input of the substrate, when it was not possible to use any diminution in its concentration as evidence for biodegradation (Li et al. 1996). The corresponding metabolite from naphthalene—cfi-naphthalene-1,2-dihydrodiol—has been used to demonstrate biodegradation of naphthalene both in site-derived enrichment cultures and in leachate from the contaminated site (Wilson and Madsen 1996). 

Another preservative used in the analysis of non-ionic surfactants is sodium azide (NaNs), normally used at a concentration of 100 mg L-1. Kiewiet et al. [11] tested much higher concentrations and found that 0.01 M (650 mg LT1) sodium azide could not prevent substantial losses of the alcohol ethoxylates, probably due to the fact that sodium azide is only an inhibitor for aerobic degradation. However, in closed bottles, anaerobic degradation processes could play an important role as well. They observed substantial losses (17-81%) of non-ionic surfactants during transport and seven days storage of the wastewater samples. 

It would be helpful to develop data determining the accuracy of PBDE determinations (e.g., percent recovery) in environmental samples. Methods for determining degradation products and metabolites of PBDE are needed. There is no information in the literature of detectable biodegradation of PBDEs in the environment under aerobic or anaerobic conditions. The analysis of PBDE pyrolysis degradation products, such as polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs), is often disturbed by the presence of PBDEs. Ebert et al. (1999) demonstrated that by using a Florisil column ina sample clean-up process, almost complete separation of PBDEs and PBDD/Fs is achieved before analysis by GC-MS. 

Eckart and co-workers have published a series of papers on laboratory studies of biodesulfurization of petroleum and petroleum fractions. The ability of various aerobic mixed cultures to desulfurize Romashkino crude oil (1.69 wt.% S) was addressed by Eckart et al. (21). After 5 days of incubation at 30°C in sulfur-free mineral medium with oil as sole source of carbon and sulfur, approximately 55% of the total sulfur was recovered in the aqueous phase from two of the most active cultures. In another study, gas oil (1.2 to 2 wt.% S), vacuum distillates (1.8 to 2 wt.% S) and fuel oil (up to 4 wt.% S) were used as sole carbon and sulfur sources for the oil-degrading microorganisms (36). The addition of an emulsifying agent was required to enhance desulfurization. Sulfur removals of up to 20% from the gas oil, 5% from the vacuum distillates, and 25% from the fuel oil were observed after 5 to 7 days of incubation. In a later study (37). approximately 30% of the sulfur was removed from fuel-D-oil by a mixed population of bacteria. The removal of benzothiophene, dibenzothiophene and naphthobenzothiophene was shown by high resolution MS analysis. Hydrocarbon degradation was observed in each of these studies. For example, in the latter study with fuel-D-oil, the decreases in the n-alkane and aromatic content were 59% and 14%, respectively. 

Cysteine ligands have also been reported in the synthesis of intricate copper nanoparticles following a literature modified reduction procedure. The Cu° nanoclusters revealed a plasmon resonance band at 398 nm and an average size distribution of 3.5 0.8nm by TEM. Infrared analysis of the stabilized nanoparticles showed a weakened S-H stretch at 2598 cm suggesting uncoordinated cysteine thiols, supporting the possible involvement of the amine functional group from the cysteine alpha carbon in particle stabilization. These particles displayed extreme O2 sensitivity, degrading under aerobic conditions to Cu (I) and then Cu (II) cysteine complexes. Additionally, this sensitivity precluded the convenient determination of nanoparticle crystallinity. ... 

Formation of zero-valent copper clusters with glutathione has been studied anaerobically. The ligand has been reported to provide a snbstantial degree of surface passivation. Rednction of a Cu(II)-GSH complex prodnced nanoparticles with a plasmon resonance band at 363 nm. These nanoparticles possessed a diameter of 9.7 4.3nm as demonstrated by TEM analysis. Under aerobic conditions, the nanoparticles oxidatively degrade as evinced by the loss of the plasmon absorption band over time. 

Oxidation reactions are dramatically enhanced by US energy, as discussed in detail in Chapter 7. Analytically, US-assisted oxidation reactions are of enormous interest. Two cases in point are the determination of the oxidative stability of edible oils [35], where the analysis time is reduced from 129 h to only 50.5 min, and the degradation of highly contaminated organic compounds, which is typically 10000 times faster than natural aerobic degradation [36]. 

Raghavan D, Wagner GC,Wool RP (1993) Aerobic biometer analysis of glucose and starch biodegradation. J Environ Polym Degrad 1 203-211... 

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