The behaviour of 210Pb and 226Ra in the Eastern Irish Sea

The sedimentary inventory of excess 210Pb in the eastern Irish Sea is higher than can be supported by atmospheric deposition plus its in-situ production from 226Ra in the overlying water column. The depositional fluxes (30-500 Bq m-2 y-1) necessary to maintain the inventories increase towards the coast. Enhanced concentrations of dissolved 226Ra found in this area cannot account for the excess 210Pb production but evidence suggests that both these nuclides may have a common local source. Similarly, very high concentrations of unsupported 230Th are found in the surface sediments (1-60 Bq kg-1, the distribution of which mirrors that of 210Pb. The source of these natural radionuclides appears to be liquid waste discharged from a chemical factory involved in phosphate production. Annual variations of 226Ra and unsupported 210Pb concentrations in sediments over the period 1959-1986 were derived from cores, of known chronology, collected from a nearby harbour (Maryport). The temporal records of these nuclides correlate well with discharge data provided by the chemical plant. (author)