Because it is such a convenient hiding place for wastes, the sea has long been a receptacle for obsolete weaponry. After World War II more than thirty thousand bombs and canisters containing poison gases - along with other unwanted munitions, mostly German - were dumped into the southern Baltic Sea . In 1969 these rusting canisters came back to haunt Baltic shorelines; leaking mustard gas injured fishermen and panicked bathers. Danish fishermen caught at least sixteen mustard-gas bombs in their nets and suspected contamination from these materials caused the boycotting of thousands of tons of fish. In 1976, mustard-gas bombs washed ashore along the Welsh coast, the debris from the dumping of British chemical munitions off the coasts of Scotland and Ireland between 1945 and 1956. The USA has disposed of obsolete chemical warfare agents in the sea on at least three known occasions, in 1967, 1968 and 1970. The materials were embedded in concrete within steel vaults and carried several hundred miles out to sea aboard obsolete ships, which were scuttled. The effects these agents might have on the sea is not known.