Monitoring anthropogenic radioactivity in salt marsh environments through in situ gamma-ray spectrometry

Radionuclide bearing effluents discharged into the Irish Sea have resulted in the accumulation of radionuclides in salt marsh environments which can contribute to critical group exposures. Recent developments in in situ gamma-ray spectrometry provide a novel and effective method for monitoring anthropogenic radionuclide concentrations and distributions within these coastal environments. This paper presents the results from an in situ survey at Caerlaverock salt marsh, Dumfries, Scotland. An in situ n-type HPGe detector was used to estimate: i) a spectrally derived calibration coefficient (QCs) to map changes in 137Cs activity (kBq m-2) and its vertical activity distribution β (g cm-2); ii) sediment accretion rates (g cm-2 a-1); and iii) surface 241Am activities (Bq kg-1) across the salt marsh. The in situ results compared favourably with sediment core derived estimates, indicating that 137Cs activities were consistently within 10–15% and 241Am was within 25% of core sample estimates, accuracies comparable with sampling errors. The vertical activity distribution β and sediment accretion rates were also mapped directly through in situ measurements. The technique is sufficiently sensitive to monitor changes in β over a 5 year interval and provides a rapid and cost-effective technique for monitoring and mapping of anthropogenic activity and sediment accretion in salt marsh environments.