1973 - Viggo Hinrichsen

On September 29, 1973, the dry cargo ship Viggo Hinrichsen of German flag encountered machinery failure during bad weather whilst en route from Rotterdam to Rönnskär, Sweden (see Figure 1). The ship, whilst on tow, listed and sank in 17 metres of water with a cargo of 234 tons of chromium trioxide packaged in 1100 drums and 180 tons of sodium dichromate in 700 drums. All drums had removable heads (see Figure 2 for typical closures, for metal drums with removal heads). The cargo was stowed in the holds except for 27 drums stowed on deck.

On September 29, 1973, the dry cargo ship Viggo Hinrichsen of German flag encountered machinery failure during bad weather whilst en route from Rotterdam to Rönnskär, Sweden (see Figure 1). The ship, whilst on tow, listed and sank in 17 metres of water with a cargo of 234 tons of chromium trioxide packaged in 1100 drums and 180 tons of sodium dichromate in 700 drums. All drums had removable heads (see Figure 2 for typical closures, for metal drums with removal heads). The cargo was stowed in the holds except for 27 drums stowed on deck.

Chemical analysis of water samples taken around the wreck showed the presence of dissolved chromium (1g/l close to the vessel; few mg/l 100 metres away from the wreck) which indicated that the chromium had begun to leak.

Like all transition metals, chromium exhibits two or more oxidation states. Chromium trioxide (CrO3) and sodium dichromate (Na2Cr2O7) have an oxidation state of six (Cr6+). Both of these compounds are very soluble in water and dissociate in water to form "chromic acid".

When informed of the leakage, the Swedish authorities decided that the ship should be salvaged. Three days after the accident, the site was treated with 11 tons of ferrosulphate which was added from sacks which were cut open prior to the addition.

Ferrous sulphate is a reducing agent which lowers the oxidation state of the chromium (Cr6+ to Cr3+), reducing its toxicity and solubility and therefore rendering the chromium less harmful to the environment. Some scientists did claim after the accident that the addition of ferrosulphate was irrelevant (did not do any good or any harm).

Before sinking, 10 drums had fallen overboard during towage of the ship. Eight of these were located by sonar equipment using a naval submarine. Some of the drums were found damaged and empty.

Six days after the accident, pontoon cranes lifted the ship to the surface and towed her, hanging in the cranes, to a nearby port where the rest of the cargo was offloaded. The total loss of chromium to the environment was estimated at 1 - 2 tons.