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 c ontribute to critical group exposures. Recent developments in in situ gamma -ray spectrometry provide a novel and effective method for monitoring anthr opogenic radionuclide concentrations and distributions within these coastal environments. This paper presents the results from an in situ survey at Ca erlaverock salt marsh, Dumfries, Scotland. An in situ n-type HPGe detector was used to estimate: i) a spectrally derived calibration coefficient (Q(Cs )) to map changes in Cs-137 activity (kBq m(-2)) and its vertical activity distribution beta (g cm(-2)); ii) sediment accretion rates (g cm(-2) a(-1)) ; and iii) surface Am-241 activities (Bq kg(-1)) across the salt marsh. The in situ results compared favourably with sediment core derived estimates, indicating that Cs-137 activities were consistently within 10-15% and Am-24 1 was within 25% of core sample estimates, accuracies comparable with sampl ing errors. The vertical activity distribution beta and sediment accretion rates were also mapped directly through in situ measurements. The technique is sufficiently sensitive to monitor changes in beta over a 5 year interva l and provides a rapid and cost-effective technique for monitoring and mapp ing of anthropogenic activity and sediment accretion in salt marsh environm ents. (C) 1999 Elsevier Science Ltd. All rights reserved.