Fundamentals of Biological Intervention 57polar and easily cleared from the blood by the kidneys. It is in this modified
and inactive form that it is excreted into the sewage. However, bacteria present
in the aerobic secondary treatment in sewage treatment plants, have the enzyme,
β-glucuronidase, which removes this modification thus reactivating the hormone.
As an aside, glucuronidation is not confined to hormones but is a process used
to detoxify a number of drugs, toxins and carcinogens in the liver. The enzyme
catalysing this process is induced in response to prolonged exposure to the toxin
thus imparting increased tolerance or even resistance to the chemical.
Returning to the problem of elevated levels of active hormones in the water-
ways, another aspect is that steroids do not occur in bacteria, although they are
present in fungi, and so bacteria lack the necessary pathways to allow com-
plete degradation of these hormones at a rate compatible with the dwell time in
sewage treatment plants. The consequence has been raised levels of reactivated
oestrogen and 17α-ethinyloestradiol in the waterways leading to disturbances
of the endocrine, or hormonal, system in fauna downstream from sewage treat-
ment plants. Such disturbances have been monitored by measuring the presence
of the protein vitellogenin (Soleet al. 2001) which is a precursor to egg yolk
protein, the results of which have indicated feminisation of male fish in many
species including minnows, trout and flounders. The source of environmental
oestrogens is not confined to outfall from sewage treatment plants, however,
the fate of endocrine disrupters, examples of which are given in Figure 3.2,
in sewage treatment plants is the subject of much research (Byrns 2001). Many
other chemicals, including polyaromatic hydrocarbons (PAHs), dichlorodiphenyl-
trichloroethane (DDT), alkyl phenols and some detergents may also mimic the
activity of oestrogen. There is general concern as to the ability of some organisms
to accumulate these endocrine disrupters in addition to the alarm being raised as
to the accumulative effects on humans of oestrogen-like activity from a number
of xenobiotic sources.
To date there is no absolute evidence of risk to human health but the Environ-
mental Agency and Water UK are recommending the monitoring of environmen-
tal oestrogens in sewage treatment outfall. Assays are being developed further to
make these assessments (Gutendorf and Westendorf 2001) and to predict poten-
tial endocrine disrupter activity of suspected compounds (Takeyoshiet al2002).
Oestrogen and progesterone are both heat labile. In addition, oestrogen appears
to be susceptible to treatment with ultra-violet light, the effects of which are
augmented by titanium dioxide (Eggins 1999). The oestrogen is degraded com-
pletely to carbon dioxide and water thus presenting a plausible method for water
polishing prior to consumption.
Another method for the removal of oestrogens from water, in this case involv-
ingAspergillus, has also been proposed (Ridgeway and Wiseman 1998). Sulpha-
tion of the molecule by isolated mammalian enzymes, as a means of hormone
inactivation is also being investigated (Suiko 2000). Taken overall, it seems
unlikely that elevated levels of oestrogen in the waterways will pose a problem