Investigations of cholesterol transformation during sewage treatment: relevance to estrogen formation pathways?

There is currently a great deal of concern over the observation of so-calle d estrogenic effects (specifically increases in the concentrations of the e gg yolk precursor, vitellogenin) in mate fish living in some UK rivers. The effects have been attributed to chemicals, including estrogenic steroids, which enter the rivers via sewage effluents. The origins of these estrogeni c steroids in sewage may include contributions from the influents and possi bly in situ transformation processes of other steroids occurring during sew age treatment. The present study examined the latter possibility. The bacte rial metabolism of radiolabelled cholesterol during laboratory-simulated ae robic sewage treatment was studied by reverse phase radio-high performance liquid chromatography (rHPLC) and radio-gas chromatography (rGC) to examine the hypothesis that cholesterol could undergo A-ring aromatisation to form first, 19-norcholest-1,3,5(10)-trien-3-ol (NCT) and hence, by known bacter ial pathways, the estrogenic steroid, estrone. The results showed that, to the contrary, much of the cholesterol (approx. 50% in 96 h) underwent rapid mineralisation to carbon dioxide., consistent with A-ring rupture (rather than aromatisation) and P-oxidation of the alkyl side chain as major transf ormation routes. Some polar (early-eluting) rHPLC products were observed, p ossibly steroidal conjugates and/or fatty acids. Among the minor metabolite s detected by rGC and GC-mass spectrometry (GC-MS) were cholest-3,5-diene a nd a second cholestadiene isomer. However, since alkenes were unexpected in this rHPLC fraction, they may arise as artefacts from thermal decompositio n of cholesteryl esters, indicating that some cholesterol esterification ha d also occurred. In the alcohol rHPLC fractions. cholestadienol was identif ied by GC and GC-MS but neither NCT or estrone were detected. This suggests that, at least under these simulated conditions, in situ aromatisation of cholesterol to NCT and formation of estrone from NCT were not major process es. (C) 2001 Elsevier Science B.V. All rights reserved.