Incorporation of organic tritium (H-3) by marine organisms and sediment inthe Severn estuary/Bristol Channel (UK)

Discharges of tritium (H-3) into the Severn estuary/Bristol Channel (UK) ar ise from the authorized release of wastes from nuclear power plants at Hink ley Point and Berkley/Oldbury and from the Nycomed-Amersham radiochemical p lant, via the sewer system, at Cardiff. The wastes from the nuclear power p lants probably consist almost entirely of (H2O)-H-3, whereas those from the radiochemical plant also include uncharacterized 3H labelled organic compo unds. The total 3H concentrations in demersal fish and other benthic organi sms in the vicinity of the Cardiff Eastern sewer outfall are significantly elevated compared to those observed around other UK nuclear establishments. Concentrations in filtered seawater were approximately 10 Bq kg(-1) whilst levels in surface sediment, seaweed (Fucus vesiculosis) and mussels (Mytil us edulis)/flounder (Platichthys flesus) were in the order of 6 x 10(2), 2 x 10(3), and 10(5) Bq kg(-1) (dry weight), respectively. Almost all the H-3 found in sediment and biota were organically bound tritium (OBT). The high concentration in these materials, relative to that in seawater, is due to the presence of bioavailable organic H-3 labelled compounds in the radioche mical waste. It is suggested that bioaccumulation of H-3 by benthic organis ms and demersal fish occurs primarily via a pathway of physico-chemical sor ption/bacterial transformation of dissolved H-3 labelled organic compounds into particulate organic matter, and subsequent transfer up a web of sedime nt dwelling microbes and meiofauna. Variations in H-3 accumulation between individual organisms have been interpreted in terms of their different feed ing behaviour. Relatively low concentrations were observed in the herbivoro us winkle (Littorina littorea) and the pelagic Sprat (Spratus spratus) comp ared with other benthic organisms and demersal fish. The elevated H-3 conce ntrations in seafood, due to bioaccumulation of OBT, have low radiological significance even for the local critical group of seafood consumers. Crown Copyright (C) 2001 Published by Elsevier Science Ltd. All rights reserved.