Fracking may increase health risks from hormone-disrupting chemicals released into the environment, say researchers.

Scientists sounded the warning after studying water pollution at sites in the US where the controversial natural gas drilling technique is used.

The team looked at 12 suspected or known "endocrine disrupting chemicals" used in fracking operations and measured their ability to mimic or block the effects of reproductive hormones.

Water samples from drilling sites with a record of spillages had levels of the chemicals high enough to interfere with the body's responses to male hormones, as well as oestrogen. Little endocrine disrupter activity was found in water samples from sites where little drilling was taking place.

The study published was in the journal Endocrinology."