Tests Under Aerobic Conditions

Studies of intrinsic biodegradation can be performed using samples from different sites tested under aerobic conditions. 

Endosulfan in aqueous solutions is also expected to undergo biodegradation. In laboratory tests at pH 7 and 20 , Pseudomonas bacteria degraded endosulfan (isomers not specified) under aerobic conditions with a half-life of about 1 week (Greve and Wit 1971). Biotic and abiotic transformations of endosulfan in seawater/sediment microcosms have been reported (Gotham and Bidleman 1989). In biotic tests, half-lives for the a- and P-isomers in seawater-only microcosms (pH 8) were about 5 and 2 days, respectively. In seawater-only microcosms under sterile conditions at a pH of 8 or higher, the half-life for the a-isomer was 2-3 days, whereas the half-life for the p-isomer was 1-2 days. Half-lives were longer in seawater/sediment microcosms, possibly because of the lower pHs (7.3-7.7) in these test systems half-lives were 22 and 8.3 days for the a- and P-isomers, respectively. Endosulfan diol was the main metabolite identified. 

In a very recent work, the Pd-catalysed cross-coupling reactions with arenediazonium salts under aerobic conditions in the presence of a chiral monothiourea ligand were reported (Scheme 25) [106]. Even if this Hgand bears four chiral centres, no test in asymmetric Heck-type reaction has been described so far. 

Ready biodegradability refers to the situation in which the test compound is totally degraded (under aerobic conditions to COj, HjO, etc.) within the time span of a standardized test usually lasting 5, 7, or 28 d. 

Production. Xanthan gum is produced by the microorganism X. campestris, originally isolated from the mtabaga plant. The gum is produced commercially by culturing X. campestris purely under aerobic conditions in a medium containing commercial glucose, a suitable nitrogen source, dipotassium phosphate, and appropriate essential elements. When the fermentation is complete, the gum is recovered from the fermentation broth by precipitation with isopropyl alcohol, and dried, milled, tested, and packed. 

Thus, the rates of biodegradation are likely to vary considerably, depending on the environment to which a chemical is released, as tests from various media have demonstrated (Boethling et al., 1995 Federle et al., 1997). Also, the rates under different conditions may vary depending upon the type of chemical structure. For example, nitro aromatic compounds are usually fairly resistant to biodegradation under aerobic conditions but are reduced rapidly to amines under anaerobic conditions. 

It is visualized that the proposed coal slurry pipelines could be used as biological plug flow reactors under aerobic conditions. The laboratory corrosion studies under dynamic test conditions show that use of a corrosion inhibitor will limit the pipeline corrosion rate to acceptable levels. 

Sediment estimated first-order t,/2 = 23-69.3 d from biodegradation rate constant k = 0.01-0.03 d 1 at 9-21°C by river die-away test in slurry sediment of aquatic systems (Lee Ryan 1979 quoted, Scow 1982) t,/2 = 27 d for sediment-water microcosm under aerobic conditions (quoted, Muir 1991). 

Biodegradation aqueous aerobic t,2 = 168-672 h, based on unacclimated aqueous aerobic screening test data (Gummer 1979 Kanazawa 1987 quoted, Howard et al. 1991) aqueous anaerobic t,/2 = 672-2688 h, based on estimated unacclimated aqueous aerobic biodegradation half-life (Howard et al. 1991) t, 2 = 44 d under aerobic conditions and t,/2 = 59 d under anaerobic conditions in water used a combination of activated sludge, silt loam soil and sediment as an inoculum t,/2 = 78 d under aerobic conditions and t, 2 = 125 d under anaerobic conditions at pH 6.9 (Howard 1991). 

Biodegradation degradation complete in 20 h under aerobic conditions and 48 h under anaerobic conditions in a die-away test using water from a stagnant lake (Howard 1989)... 

Because of the central role that estimates of biodegradability play in environmental impact assessments, a great deal of effort has been devoted to developing standardized test procedures (Gerike and Fischer 1981). In spite of this, conventional tests for biodegradability under aerobic conditions retain some questionable, or even undesirable, features from an environmental point of view. Attention is therefore drawn to two valuable critiques of widely used procedures (Howard and Banerjee 1984 Battersby 1990). Some of the important issues in the design of such tests are therefore only briefly summarized here. 

ISO 11266 1994 Soil quality - Guidance on laboratory testing for biodegradation of organic chemicals in soil under aerobic conditions. 

The spray formulation appears to be nontoxic because both fish and algae grow readily in the ponds. The pH level of the water in the ponds has remained constant, which indicates that bacteria are not converting sulfur to sulfuric acid. Samples of the formulation were exposed to bacterial attack in a controlled environmental chamber maintained at a high moisture level to accelerate the rate of attack. No evidence of bacterial attack on the samples has been detected after 1 yr of exposure under aerobic conditions. Initial corrosion tests showed that samples of the formulation did not lose weight after exposure in 1 and 5% sulfuric acid solutions for 4 months. 

---