Water from the separation plant at Sullom Voe is discharged into the sea under agreed conditions from a diffuser situated to the north of Calback Ness, close to natural scallop (Pecten maximus) beds.

As part of the arrangements to monitor potential effects of the discharge, Torry Research Station was asked to assess, for petroleum taint, shellfish which would be sampled at intervals from Sullom Voe. To avoid depletion of the natural shellfish beds, queen scallops (Chlamys opercularis) or scallops, whichever were available from other areas, were set out in cages suspended (or on the bottom) 100–1250 m eastwards of the outfall for a period, and then recovered, frozen, and assessed subsequently at the laboratory by a trained taste panel, and compared with the same species unexposed.

The cages were laid on 10 occasions from March 1980 to February 1987. Initially, no petroleum taint was detected. In August 1980 and May 1981, a different flavour, but not recognisable as a petroleum taint, was detected at 800–1000 m from the outfall after three days exposure. In May 1982, 33% of the queen scallops in the cage on the bottom, 100 m south east of the diffuser, were dead after six days exposure, and taint was detected at the threshold level in shellfish in the cage at 300 m. In May 1983, taint and petroleum derived hydrocarbons were detected in the sample from the cage on the bottom, 100 m south east of the diffuser, after seven days exposure. In May 1984, taint was again detected at the bottom, 200 m south east of the outfall, after 10 days exposure.

Enquiries established that the diffuser was not operating with maximum efficiency. Subsequently, monitoring revealed an improvement. Taint assessment proved to be a sensitive detector of petroleum contamination.