Researchers have developed a new way to use mussel shells to diagnose a sick environment.
While alive, mussels incorporate metals from the environment into their shells, which can then serve as enduring chemical snapshots of environmental conditions.
To see whether mussel shells tell an accurate ecological story, Megan E. Brown of Virginia Tech in Blacksburg and her colleagues focused on a well-documented case of environmental contamination.
They collected 366 mussel shells from five sites along the North Fork Holston River in Virginia. Three sites were downstream and two were upstream of a factory that emitted mercury into the river between 1950 and 1972. As early as 1957, mussel populations in the river began dying out.
In shells that the USGS team harvested just downstream of the factory, mercury concentrations ranged up to 4,637 micrograms per kilogram (µg/kg). The upper reading for shells upstream was 31 µg/kg. Shells farther downstream from the plant topped out at 115 µg/kg. Museum specimens of shells collected from the river before the factory existed showed mercury concentrations of about 6 µg/kg.
Although river currents often damage or move shells, mussel remains can reveal the history of local environmental contamination, the researchers conclude in an upcoming Environmental Science & Technology.