Application of 137Cs and 210Pb in tracing the fate of mercury in a river-reservoir system

The vertical distribution of 137Cs and 210Pb in sediment cores from the Tennessee River-Reservoir System (USA) was used to trace the fate of Hg discharged from two upstream facilities and to resolve the relative contribution from each facility. Discharges since 1943 at the Oak Ridge nuclear facilities left a clear record of releases for Hg and 137Cs in undisturbed downstream sediments. High releases in the 1950s are reflected in well-defined peaks, located 30 cm or more below the sediment-water interface, which can now be used to accurately date sediment layers. Chronologies based on 210Pb gave sediment ages concordant with those based on the release histories and helped to resolve mercury contributions from a chloralkali plant located 150 km downstream of the Oak Ridge facilities