Prototypes built by researchers at the Naval Research Laboratory, Stanford University and Philips, a Dutch electrical-goods firm, can detect a substance that is present at a concentration of less than one part in a million billion.

ECONOMIST: Labs on a chip

One million people took part in BBC Domesday, sending in photographs and articles about where they lived.

BBC: Revisit the BBC's 1986 Domesday project

"What we found for our 124 sharks that we sampled was that about one-third of them came in with mercury levels that were over the Food and Drug Administration's action level of one part per million, " said Hueter.

CNN: Beware of shark meat, FDA warns