Figure 3 Cell viability expressed as the number of live cells per milliliter (×1000) over a 120-h observation period: control (+); cholesterol (); cholesterol oxide (*); 7-ketocholesterol (∆); 5α,6α-epoxide (▲); β-sitosterol (x); β-sitosterol oxides (○). Lines followed by A–D were significantly different at p<0.05. (From Ref. 27. Figure reproduced with permission of the Journal of Agricultural and Food Chemistry).

The degradation products of phytosterol oxides can also have negative biological effects. Female mosquito fish (Gambusia affinis) were found to develop anal fins that were elongated like those of male fish when inhabiting a stream polluted by paper mill waste (29). Although they displayed typical male reproductive behavior, the female fish still possessed reproductive capabilities slightly less than those of normal female fish. The abnormality was apparently only external. The males in the stream were normal. Paper mill effluents from facilities pulping pinewood chips contained tall oil, which is known to contain up to 3% phytosterols, of which 85% is sitosterol and campesterol (30). Degradation of these compounds by certain species of Mycobacterium results in C19 steroids, which were thought to have induced the masculinization of the female fish (31). Figure 4 shows the structure of one such compound, androstenedione, that was identified in river water containing paper mill effluent where deformed fish were also found (32). This compound shows the characteristic four-ring structure of sterols and is believed to be a bacterial metabolite of plant sterols. Such compounds have been reported to be produced by Mycobacterium strains through an oxidation mechanism in culture (33).