Views & Reviews Outside the Box

The feminisation of nature

BMJ 2011; 343 doi: (Published 30 December 2011) Cite this as: BMJ 2011;343:d8348
  1. Trisha Greenhalgh, professor of primary health care, Barts and the London School of Medicine and Dentistry, London
  1. p.greenhalgh{at}

This year marks the 25th anniversary of the start of a scientific survey of the feminisation of fish in the River Lea in southeast England, which took several years formally to confirm what local anglers had been describing since the late 1970s: that roach living downstream of sewage effluent showed a high prevalence of intersex.

Can you recall the biochemical pathway that begins with cholesterol and progresses through progesterone and various hydroxylations to oestrogen, testosterone, and cortisol (summarised on the “steroid hormones” page on Wikipedia, Whether you can or not, you will be able to spot androgenising syndromes in women (from virilising tumours to the hirsute teenager whom you’re not sure whether to reassure or refer) and feminising syndromes in men (from the testosterone insensitive XY female to Homer Simpson’s cushingoid man boobs). Most are subfertile.

I cannot recall a general practice surgery when I did not prescribe the oral contraceptive pill, hormone replacement therapy, or a short course of progesterone to delay menstruation for a honeymoon. Metabolites of such drugs appear in the urine and then in our rivers and lakes.

Intersex is not a natural state in fish, particularly in roach, because the species has only one gonad. But the male roach exposed to high oestrogen concentrations produces the female hormone vitellogenin, leading first to growth of oocytes within the testis and then (at higher concentrations) to sex reversal. Subfertile and transgender fish mean fewer offspring and declining fish stocks, not to mention the reverberations throughout the ecosystem. In the past 25 years, dozens of papers have appeared describing similar syndromes in other species of fish.

As in any problem of an ecological nature, the solution is not simple, and we can’t just stop prescribing steroid hormones. Rather, doctors must engage with the interdisciplinary work being undertaken between ecologists, geographers, industrial chemists, and mathematical modellers to better understand the delicate equilibrium of the freshwater ecosystem and how pharmaceuticals in human waste contribute to its imperilment. We might, for example, note the research on the widely differing potency of different steroids in the chain of causation of the feminisation of nature and try to ease back on anti-androgens, which are particularly potent in rocking the ecological boat. If you want more on the as yet unanswered research questions, see this review: Journal of Environmental Monitoring 2008;10:1476-85, doi:10.1039/B815741N.


Cite this as: BMJ 2011;343:d8348


  • I thank Rob Macfarlane for alerting me to this matter.

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