TEMPORAL AND SPATIAL SURVEY OF DISSOLVED RA-226 IN COASTAL WATERS OF THE EASTERN IRISH SEA

Phosphogypsum waste has been discharged from the Albright and Wilson W hitehaven 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 Ra-226 and other radionuclides discharged. In the 6 months immediately follow ing the changes at the plant, the concentration of Ra-226 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. B ackground concentrations of Ra-226 in areas of the Irish Sea unaffecte d by industrial inputs of Ra-226 average 2.0 mBq 1(-1). Ninety-eight p ercent of the survey area had Ra-226 concentrations > 3 mBq 1(-1) prio r 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 s urvey area remained above the natural background level. The background corrected inventory of Ra-226 in the surface waters of the survey are a fell exponentially from a maximum value of 1.46 GBq prior to June 19 92 to a value of 0.06 GBq in December 1993, yielding an effective half time of 70 days. The variable concentration of Ra-226 in the surface waters of the survey area resulted from dispersion away from the outfa ll and the survey area in the year following cessation of large discha rges of Ra-226. The estimated enhancement of Ra-226 in excess of backg round levels, and resulting from discharges from the Albright and Wils on plant, were 7% of estimated background levels by December 1993. It is possible that this excess is a consequence of continued, much reduc ed discharges, that were equivalent to 6% of the background water colu mn inventory in the survey area during 1993.