The living sensors can detect some metals at levels as low as 10 thousandths of a gram per litre. The molluscs are not quite as sensitive as hi-tech chemical instruments but the information they convey is much more valuable. Meanwhile, Dr Markich and colleague Dr Ross Jeffree have worked out how to read records of past pollution levels written in mussel shells. Mussel shells grow by about a millionth of a metre in diameter each day. Toxins are incorporated in the shell so chemical analysis of the growth bands reveals the pollution history of the environment.
Scientists can detect changes over weeks, months, years or even decades.
Mussels have very long natural lifespans - up to 60 years in the southern hemisphere. Ultimately, these secondary ions pass through a mass spectrometer which sorts them according to their mass, enabling the identification of the elements in the sample. The scientists have used the technique to build up a pollution history of the water around the abandoned uranium and copper minesite at Rum Jungle in the Northern Territory. The Rum Jungle project ran in the 1950s and early 1960s. The site was remediated in the early 1980s.