Brigitta Montanari

The Italian chemical tanker Brigitta Montanari, transporting more than 1,300 tonnes of vinyl chloride monomer (VCM), sank in the Adriatic Sea on 16 November 1984, to a depth of 82 m, near the city of Sibenik (Yugoslavia).

The solution chosen to deal with the wreck was to refloat it, then to pump out the chemicals. This decision was made based on ecological considerations, but also technical feasability, safety and economic viability.

Rescue operations began in August 1987, on the assumption that the vinyl chloride monomer tanks had not been damaged. However a leak of VCM estimated at 1 kg/day was detected at the beginning of the operation. The leak was thought to be situated between the left side of the wreck and the deck (the wreck was lying on the right side).

Operations began by positioning the wreck on its keel. This operation is often the first step in raising procedures, however it could have been dangerous because of the risk of a sudden spill of a large quantity of vinyl chloride. To release this chemical, a 5 mm hole was drilled in the deck. An significant leak of VCM began (estimated at 3 tonnes/day). A concentration of vinyl chloride greater than 5 µg/L was observed in the water column, 300 m from the wreck.

After the chemicals had been leaking for several days, divers connected PVC piping to the holes which had been drilled. The vinyl chloride was piped to the suface where it dispersed into the atmosphere or was burned.

The operations were stopped in winter 1987, then resumed in spring 1988. The wreck was raised to a depth of 55 m to be towed underwater to a small sheltered bay near the island of Kaprije, where it grounded. It was then raised to a depth of 30 m, while insuring that the hydrostatic pressure was higher outside the tanks. This precautionary measure was taken to avoid vinyl chloride being released from the corroded tanks. 700 tonnes of vinyl chloride were then pump tranferred into another boat.

Biological monitoring began in 1987 on bottom-dwelling populations, including histopathological exams and biochemical testing. Organism samples were taken from the wreck and the surrounding area, as well as from a non-polluted control site. The results showed that the vinyl chloride leak had not resulted in any acute toxic effect on the organisms studied. The wreck was covered in marine organisms, despite the fact that the vinyl chloride concentration in the immediate surroundings was often relatively high (over 10 mg/L).

In light of the biochemical and histopathological results, it appears that sublethal effects could take place on sedentary bottom-dwelling fish, however these results were not confirmed.

Source:

- The sinking and fate of the chemical tanker Brigitta Montanari, M.AHEL. Centre of Marine Research Zagreb, Rudjer Boskovic Institute, Zagreb Yougoslavia