Enhancement of tritium concentrations on uptake by marine biota: experience from UK coastal waters

Concentrations of tritium in sea water and marine biota as reported over the last approximately 10 years from monitoring programmes carried out by this laboratory under contract to the UK Food Standards Agency are reviewed from three areas: near Cardiff; Sellafield; and Hartlepool. Near Cardiff, enhancement of concentration factors (CFs) above an a priori value of approximately 1 have already been studied, and attributed to compounds containing organically bound tritium in local radioactive waste discharges. Further data for Cardiff up to 2006 are reported in this note. Up to 2001, CFs increased to values of more than approximately 7000 in flounders and approximately 4000 in mussels, but have subsequently reduced; this variability could be due to changes in the organic constitution of compounds discharged. Near Sellafield and Hartlepool, enhancements to the tritium concentration factor are observed but they are relatively small compared with those near Cardiff. Near Sellafield, plaice and mussels appear to have a CF for tritium of approximately 10; in some cases concentrations of tritium in winkles are below detection limits and positively measured values indicate a CF of approximately 3. The variation could be due to mechanisms of uptake by the different organisms. Near Hartlepool there were only a few cases where tritium was positively measured. These data give a value of approximately 5 for the CF in plaice (on the basis of two samples); approximately 15 in winkles (eight samples); and > 45 in mussels (two samples). Any differences between the behaviours at Sellafield and Hartlepool would need to be confirmed by improved measurements. Possible causes are the organic composition of the effluent and differences in environmental behaviour and uptake by organisms near the two sites. These potential causes need further investigation. It is emphasised that results from tritium analyses are heavily method dependent; thus comparison with results from other programmes needs to take this into account. Further, the results for enhancement of CF will also depend on the definition of CF itself.