Abiotic sterile control

Optionally, one additional flask is used containing a reference compound for procedure control and another containing the test substance and a sterilizing agent, e.g., mercury chloride, for abiotic sterile control. As reference compoimds, sodium benzoate, sodium acetate or aniline may be used. 

It was shown, however, that these were formed even in sterile controls by undetermined abiotic reactions. 

Whereas plausible fungal metabolites from anthracene, acenaphthylene, fluorene, and benz[fl]anthracene—anthracene-9,10-quinone, acenaphthene-9,10-dione, fluorene-9-one, and benz[fl]anthracene-7,12-quinone—were found transiently in compost-amended soil, these were formed even in sterile controls by abiotic reactions (Wischmann and Steinhart 1997). 

In addition, although most abiotic processes are nonenantioselective, not aU are indeed the case. Nucleophilic 5 jv2-substitution reactions at a chiral center will result in chiral inversion to the antipodal enantiomer. While such processes are often biologically mediated, as for the nonsteroidal anti-inflammatory drugs [328], they can also be abiotic. Appropriate sterile controls should be used for experiments with such compounds, as was done in the demonstration of microbial chiral inversion of ibuprofen in Swiss lake water [329]. Photolysis of a-HCH [114], /3-PCCH [114], and chlordane compounds [116] was demonstrated not to be enantioselective, as expected for an abiotic process. However, this may not be the case for some pyrethroids, known to isomerize photolytically. 

Over the initial incubation period, for all the sources of sediment and soil, toluene was the only alkylbenzene in the mixture that was completely metabolized. Some abiotic loss of benzene and xylenes occurred gradually over the 120-day incubation period. Utilization and degradation, however, was noted only for toluene. No loss of toluene was noted in sterile control cultures. Partial loss, but not biodegradation, of o-xylene was observed, whereas no activity was noted on any of the other compounds (Figure 4). 

Micro-organisms may not always enhance corrosion. The same bacterial species may show both corrosive and protective effects. For example, Hernandez et al. [56] reported the corrosive effects of two microbial species, one of which was Pseudomonas sp. By changing certain conditions, the very same micro-organisms were showing protective effects and slowing down corrosion. Those researchers also reported that in the presence of bacteria such as aerobic pseudomonades sp. and facultative anaerobic serratia marcescens in synthetic seawater, corrosion of mild steel is inhibited. The effect seemed to disappear with time in natural seawater. Jack et al. [57] reported monocultures of an aerobic Bacillus sp. that induced greater corrosion than that of an abiotic environment, but the rate of this corrosion decreased to that of a sterile control after 17 days. 

The ammonium dynamics showed that the initial concentrations of N were reduced after the first 3 days, and after that, a release of the mineral occurred from day 3 up to day 14. Later still, the concentration of ammonium decreased by up to < 14 mg N kg 1 dry soil for all the treatments in both the Otumba and Texcoco soils, and the ammonium concentration decreased by up to < 2 mg N kg 1 dry soil for all treatments, except for the soil treated with sterilized sludge, < 31 mg N kg 1 dry soil. The contour of the ammonium dynamics was similar in both the Otumba and Texcoco soils. Many abiotic and biotic processes might affect the concentration of NH4+ in soil, such as NH4+ fixation in the soil matrix, volatilisation of NH3, and immobilization or oxidation of NH4+. Some soil processes were occurring at too low a level to be detectable, such as NH4+ fixation and the volatilisation of NH3. The nitrate dynamics were similar in both soils. The concentration of N03 was 120 mg N kg 1 dry soil in the control treatment in both soils. The ammonium concentration was similar in both soils, > 200 mg N kg 1 dry soil, treatments with sludge reached > 255 mg N kg 1 dry soil and > 300 mg N kg 1 dry soil in the Texcoco and Otumba soils respectively, and soils treated with sterilized sludge increased the concentration... 

Benoit and Barriuso (1997) carried out experiments to study the transformation of C-ring-labeled 2,4-D, 4-chlorophenol (4-CP) and 2,4-dichlorophenol (4-DCP) during straw composting under controlled laboratory conditions. Incubation under sterile and nonsterile conditions was done to evaluate the relative importance of the biotic and abiotic processes. Precomposted straw was treated with three chemicals and the availability of the different chemicals was monitored during incubations as well as their degradation. Under nonsterile conditions, Benoit and Barriuso (1997) observed that the mineralization of both chlorophenols reached 20% of the applied... 

Abiotic control can be used as a negative control using sterile soil. This was obtained by heating up to 500 g of soil in an oven at 125 C for six hours. Then the water lost during sterilisation was restored by using a 0.02 wt% aqueous solution of sodium azide (NaNj) and thoroughly mixing [63]. 

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