The study is published in the journal Environmental Science and Technology. The fish in the study were exposed to treated waste water from three sewage treatment works in Stockholm, Umeå and Gothenburg. The study shows that levonorgestrel - which is found in many contraceptive pills, including the morning-after pill - can impact on the environment and constitutes a risk factor for the ability of fish to reproduce. Levonogestrel is designed to mimic the female sex hormone progesterone and is produced synthetically.
A study from Germany showed very recently that less than a billionth of a gram of levonorgestrel per litre inhibited the reproduction of fish in aquarium-based trials.
"We are finding these levels in treated waste water in Sweden," explains Jerker Fick at the Department of Chemistry at Umeå University.
For around ten years it has been known that synthetic oestrogen from contraceptive pills can affect fish that live downstream from sewage treatment works. The new study shows that synthetic progesterone-like hormones in contraceptive pills also carry risks.
The fish in the study were exposed to undiluted waste water, whilst in the natural environment there tends to be a degree of dilution in watercourses. But the study pointed out that there are also watercourses with very little dilution, and probably treatment plants that filter out the hormone less effectively than those included in the study. These findings will help to improve our understanding of which substances need to be removed from waste water.
"If we know how our medicines affect the environment, we will be in a better position to choose environmentally friendly alternatives, though we must always put the health of patients first," says Joakim Larsson at the Sahlgrenska Academy, one of the researchers behind the study.
Combined contraceptive pills contain synthetic forms of female sex hormones, such as synthetic oestrogen and progesterone-like hormones. The hormones that go into the pills vary between products, but levonorgestrel is a progesterone-like hormone that is used in many contraceptive pills, hormone implants and morning-after pills. It is thought that around 80-90 million women use the contraceptive pill worldwide, and that around 400,000 of them are Swedish.