London: Chemicals flushed down household drains have caused around 20 per cent of male river fish to have female characteristics, according to research.

Males are displaying feminised traits and even producing eggs, a study by Professor Charles Tyler of the University of Exeter has found.

A Common Roach Credit:Viridiflavus/Commons

Some have reduced sperm quality and display less aggressive and competitive behaviour, which makes them less likely to breed successfully.

The chemicals causing these effects include ingredients in the contraceptive pill, by-products of cleaning agents, plastics and cosmetics, according to the findings.