Temporal and spatial survey of dissolved 226Ra in coastal waters of the eastern Irish Sea

Phosphogypsum waste has been discharged from the Albright and Wilson Whitehaven phosphoric acid production plant, under authorisation, into the eastern Irish Sea since 1954. The operators changed their working practices in June 1992, i.e. started importing phosphoric acid rather than phosphate ore, and these resulted in a large reduction in 226Ra and other radionuclides discharged. In the 6 months immediately following the changes at the plant, the concentration of 226Ra in filtered seawater fell by 91% at the discharge pipeline. A further reduction in concentration of 27% took place between December 1992 and May 1993. Background concentrations of 226Ra in areas of the Irish Sea unaffected by industrial inputs of 226Ra average 2.0 mBq l−1. Ninety-eight percent of the survey arca had 226Ra concentrations > 3 mBq l−1 prior to June 1992; this had fallen to 12% in December 1992 and then to < 1% by May 1993, although concentrations throughout most (96%) of the survey area remained above the natural background level. The background corrected inventory of 226Ra in the surface waters of the survey area fell exponentially from a maximum value of 1.46 GBq prior to June 1992 to a value of 0.06 GBq in December 1993, yielding an effective half time of 70 days. The variable concentration of 226Ra in the surface waters of the survey area resulted from dispersion away from the outfall and the survey area in the year following cessation of large discharges of 226Ra. The estimated enhancement of 226Ra in excess of background levels, and resulting from discharges from the Albright and Wilson plant, were 7% of estimated background levels by December 1993. It is possible that this excess is a consequence of continued, much reduced discharges, that were equivalent to 6% of the background water column inventory in the survey area during 1993.