PITY male fish swimming in oestrogen-laced water. As if smaller testes weren鈥檛 bad enough, some will even become 鈥渋ntersex鈥� and be unable to breed, with disastrous effects on the population鈥檚 future.
The effect of continuous, low-level exposure to oestrogen from waste water on wild fish populations has never been fully explored before. Karen Kidd, an ecotoxicologist now at the Canadian Rivers Institute at the University of New Brunswick in Saint John, and colleagues tested what the hormone did to wild minnows in a 34-hectare lake in Ontario, far from directly polluted watercourses.
Kidd鈥檚 team first surveyed the minnows for two years. Then for three years they added the oestrogen used in birth-control pills 鈥� 17 alpha-ethinyloestradiol 鈥� to the water, keeping the concentration at around 5 to 6 nanograms per litre, similar to that observed in some rivers downstream of sewage plants.
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Within a year male minnows had delayed sperm development and smaller testes, and were producing egg proteins. In some cases the male fish were found to be 鈥渋ntersex鈥�, having both male and female gonadal tissues. In females egg development was delayed.
鈥淲ithin a year males had delayed sperm development and smaller testes, and were producing egg proteins鈥�
Two years after Kidd鈥檚 team stopped putting oestrogen in the water, there had been a 2000-fold decrease in the size of the minnow population (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.0609568104).
鈥淲e expected the minnows to be more resilient. It shows that this is a very potent compound,鈥� says Kidd. The minnows may have been hit particularly hard because of their short four-year lifespan.
The experiment is interesting because it is on a large scale, says John Sumpter at the Institute for the Environment at Brunel University in London, UK. He points out that in the real world fish are exposed to complex mixtures of many oestrogenic compounds that may each be at low levels but together can have a detrimental effect.
As well as chemicals such as mercury and PCBs, says Kidd, 鈥渨e also need to look at the chemicals that aren鈥檛 as persistent because, like the oestrogens, they may also have dramatic effects鈥�.
