Temporal and spatial responses of the bioindicator Fucus to discharges of 99Tc in the eastern Irish Sea

Technetium-99 is a radioactive isotope discharged under authorisation to the Irish Sea from the British Nuclear Fuels plc Sellafield reprocessing plant in Cumbria via a marine pipeline. An increase in 99Tc discharges from Sellafield in recent years has provided an ideal opportunity to undertake a more detailed investigation of its environmental behaviour. Here, the temporal and spatial response of Fucus sp. to the increased discharges has been investigated and its role as a bioindicator assessed. Initial investigations in 1995, have confirmed the expectation that Fucus does act as an effective bioindicator of 99Tc, with easily detectable 99Tc concentrations (1 - 15 kBq kg-1 wet weight) being encountered, providing a time integrated signal of 99Tc discharges. Analysis of subsequent samples collected during 1996, however, have shown significant short-term peaks in Fucus 99Tc concentrations close to Sellafield (up to 90 kBq kg-1 wet weight) and this can be related to peaks in 99Tc seawater concentrations. This type of response suggests that Fucus has a means of rapidly accumulating 99Tc, although the rate at which this accumulated component may be eliminated remains unclear. This effect was only observed at sites close to Sellafield (within 15 km). Relatively constant 99Tc concentrations in Fucus were found at more distant sites (50 - 150 km). (author)