Small traces of the world’s most widely used insecticides have been detected in tap water for the first time.
Samples taken by scientists in the US state of Iowa showed that levels of neonicotinoid chemicals remained constant despite treatment.
However drinking water treated using a different method of filtration showed big reductions in neonic levels.
Scientists say they cannot draw any conclusions relating to human health but argue that further study is needed.
The use of neonicotinoids has increased rapidly since their introduction in the early 1990s.
These systemic chemicals were seen as an advance because they are usually applied as a seed coating and are lethal to insects but not to other species.
See further information: