Biodegradation natural conditions

Secondary alkanesulfonates are easily biodegradable under aerobic conditions but are less so in an anaerobic environment, a feature common to all sulfonates with the stable carbon-sulfur bond. The recent discussions on anaerobic biodegradation [103] should be put into perspective since in the sewage or deposition path a temporary anaerobic step quickly gives way to a stage where natural conditions, which are aerobic, prevail. Thus, anaerobic biodegradation... 

Although research on the biodegradation of MTBE under natural conditions is limited, the potential for significant in situ aerobic... 

Physical parameters such as temperature, salinity, pH, and oxygen concentration may critically determine the persistence or otherwise of a xenobiotic under natural conditions and these should therefore be critically evaluated. Experiments can be carried out under any of the conditions that simulate the natural environment, and these can be imposed both during isolation of the organisms by enrichment and incorporated into the design of subsequent experiments on biodegradation and biotransformation. In practice, most experiments are carried out with mesophiles and at pH values in the vicinity of pH 7, presumably motivated by the fact that these are — or are assumed to be — prevalent in natural ecosystems. It should also be emphasized that water temperatures during the winter in high latitudes in both the Northern and Southern Hemispheres are low — probably well under 10°C, so that... 

In summary, there seems to be a wide variation in the intrinsic potential for MTBE biodegradation depending on time and degree of the MTBE contamination, availability of electron acceptors, concentrations and types of co-contaminants as well on the geological and hydrogeological site conditions [11-14]. These very different natural conditions have to be taken into account if ENA measures are being considered. 

PROBABLE FATE photolysis-, aqueous photolysis is not expected to be important, reaction with photochemically produced hydroxyl radicals has a half-life of 13.44 hr, direct photolysis is not expected to be important since it should not adsorb wavelengths >290 nm oxidation photooxidation is not expected to be important, photooxidation only in atmosphere, photooxidation half-life in air 9.65 hrs-4.02 days hydrolysis very slow, maybe significant, hydrolysis of carbon-chloride bonds, release to water results in hydrolysis with a half-life of 40 days when released to soil, it may hydrolyze hydrolyzed slowly in aqueous dimethylformamide at pH 7, first-order hydrolytic half-life 22yrs volatilization expected to volatilize if released to water, volatilization half-lives from lakes, rivers, and streams 3.5, 4.4, and 180.5 days respectively sorption not an important process biological processes biodegrades in water after several weeks of acclimation, biodegradation not important under natural conditions, no bioaccumulation noted... 

PROBABLE FATE photolysis, no direct photolysis, indirect photolysis is too slow to be important, the vapor is expected to react with photochemically produced hydroxyl radicals, with an estimated half-life of 22.2 hrs oxidation not an important process, photooxidation half-life in water 2.4-12.2 yrs, photooxidation half-life in air 21 hrs-8.8 days hydrolysis expected to be too slow to be important under natural conditions, first-order hydrolytic half-life 8.8 yrs volatilization not considered as important as sorption, however, there is very little data, volatilizes from dry soil surfaces, volatilization may be important in shallow rivers sorption adsorption onto solids and particles and complexation with humic material (flilvic acid) are the principal transport mechanisms biological processes bioaccumulation, biodegradation, and biotransformation by many organisms (including humans) are very significant fates... 

PROBABLE FATE photolysis slow photolysis in aqueous solution, but fast in atmosphere is the principle fate, atmospheric and aqueous photolytic half-lives 0.5-1 hr oxidation not an important process, photooxidation half-life in air 25.4 hrs-10.6 days hydrolysis does not occur under natural conditions, relatively resistant to hydrolysis, one study reports a half-life of 3 weeks in aerobic soils under laboratory conditions volatilization too slow to be an important process, if released to the surface of warm, wet soils, it will quickly volatilize sorption does not occur biological processes no bioaccumulation, resistant to biodegradation under natural conditions... 

PROBABLE FATE photolysis slow photolysis very likely to occur, if released to water, will be lost to photolysis oxidation oxidation by hydroxy radical attack, half-life 14 hr, photooxidation half-life in air 7-71 hrs hydrolysis slight potential for hydrolysis after adsorption by clay materials volatilization not an important process, if released to water will volatilize, half-life 12 days in a model river sorption adsorbed to a moderate degree by clay materials, adsorption to sediment is minor biological processes no bioaeeumulation very resistant to biodegradation under natural conditions... 

PROBABLE FATE photolysis-, slow process, but might be only degradation process that occurs, atmospheric and aqueous photolytic half-life 13.7 days, in clear surface waters, half-life 2-14 days and faster if the water is acidic or contains nitrate or nitrite ions oxidation-. attack by hydroxyl radicals at C-2 and C-4 positions occurs, half-life 14 hrs, photooxidation half-life in water 21 days-5.6 yrs, photooxidation half-life in air 6 days hydrolysis slight possibility of hydrolysis to 1,4-benzoquinone after sorption by clay minerals volatilization not an important process sorption slight potential for irreversible sorption by clay minerals biological processes no bioaccumulation, resists biodegradation under natural conditions and inhibits microbial growth... 

Simple to carry out, this technique is however dependent on the enzyme chosen and does not conclude whether there is definite biodegradation of the sample tested when placed under natural conditions. Most authors remain cautious and speak only of degradation. 

As biodegradation test we predominantly used the polyester hydrolysis with lipases. The free acids built during the ester cleavage were monitored via an automatic and improved titration system. Beside the enzyme test we also performed soil burial tests, compost simulations and tests with isolated microorganisms to check whether the results obtained with the lipase can be transferred to natural conditions. 

Comparison of the results obtained with the enzymatic tests with biodegr ation in natural environments proved that the conclusions drawn from the enzyme tests have also relevance for biodegradation under natural conditions. ... 

Before the start of biodegradation, a period of acclimatization may be required. Acclimatization (natural conditions) and acclimation (laboratory conditions) are the adjustment process of an organism or a colony to an environmental change, normally occurring in short periods of time (days or weeks). 

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