Scientists at a mid Wales university believe they can use shellfish to accurately measure water pollution.
Dr Perkins with some of the oldest creatures on Earth... clams
Researchers at the University of Wales in Aberystwyth have come up with a way of unlocking the secrets held in the shells of cockles and mussels.
The molluscs are made up of calcium carbonate which grows in layers, forming a pattern like rings in a tree.
Pollutants become trapped between the layers, providing a chemical trace which can be followed back decades.
The Aberystwyth team, led by Dr Bill Perkins of the Centre for Research in Environment and Health at the Institute of Geography and Earth Sciences, have been working on a laser-based technique to extract samples from the individual layers on a shell in minute quantities.
According to Dr Perkins the sea has been the ultimate "sink" for waste since man started mining and processing metals.
One clam, Arcitca islandica, found in Cardigan Bay on the west Wales coast, has become known as the tree of the sea because it is the longest living creature on Earth, living for anything from 150 to 225 years.
He said: "The oceans have been used to wash away man's dirt for thousands of years and there are many techniques that allow scientists to monitor the levels of pollution and to look at long term changes in concentrations.
"However, there is an increasing need to pinpoint when a pollution incident takes place and the likely source of the contamination, as people become more aware of the effects of pollution on the environment and their lives.
"The technique we have developed, coupled with our increased understanding of how shells are formed, means that we will soon be able to pinpoint a pollution incident to a particular day and even identify the source."
He added that the work would enable scientists to be much more accurate in the increasingly important field of environmental forensics, where there is a need to prove who is responsible for a particular incident.