Microbial processes weight loss

Oxidation of testosterone to oestradiol was again shown to involve the loss of the lj8- and 2/5-hydrogen atoms. Microbial degradation of the steroid nucleus includes cleavage of ring B followed by ring a. The enzyme for the latter process has been purified and shown to have a molecular weight of about 280 000 and to contain one iron atom. ... 

The degradation pathways of higher molecular weight PAHs—such as pyrene, benzo(e)pyrene, and benzo(a)pyrene—are less well understood (Neilson and Allard, 1998). Because these compounds are more resistant to microbial degradation processes, they tend to persist longer in contaminated environments (Van Bmmmelen et al., 1998 Neilson and Allard, 1998 Bosma et al., 2001). However, the degradation of fluoranthene, pyrene, benz(a)anthracene, benzo(a)-pyrene, benzo(b)fluorene, chrysene, and benzo(b)fluoranthene has been reported in laboratory conditions (Barnsley, 1975 Mueller et al., 1988,1990 Schneider a/., 1996 Ye etal., 1996 Neilson and Allard, 1998). Elevated temperatures increase the rate of biotransformation reactions in vitro. For example, laboratory studies have shown a 50% loss of phenanthrene after 180 d at 8 °C in water compared to 75% loss in 28 d at 25 °C (Sherrill and Sayler, 1981 Lee etal., 1981). It is widely believed that PAHs with three or more condensed rings tend not to act as sole... 

Consequently, microbial attack occurs by a process of bioerosion from the surface of the polymer with loss of weight but without significant reduction in molar mass of the polymer bulk. 

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