Preliminary analysis was said to have indicated very low levels of the toxic liquid chlorobutadiene, a ton and a quarter of which was discharged into the lough on Tuesday. But government sources said no all- clear could be given until full results were available.
The authorities are to investigate why the spillage, which took place on Tuesday, was not reported by Du Pont until Friday. Du Pont said it knew there had been a leak, but did not immediately appreciate its size.
The Northern Ireland minister responsible for the environment, Michael Mates, told journalists yesterday that while the Government was concerned about the spillage, 'there is no cause for anyone to have any alarm at all, except perhaps those who have been fishing . . . (and) who may have caught fish'. People have been advised to stop eating fish and shellfish from Lough Foyle until further notice.
Dr Cecil McMurray, chief scientific officer at the Northern Ireland department of agriculture, said initial testing had shown the presence of very low levels of chlorobutadiene, at a rate of one tenth of a part per million. Du Pont's normal safety level for the chemical is ten parts per million.
Chlorobutadiene is said to be not particularly toxic, not soluble in water and prone to evaporation. The hope therefore is that the spillage has been spread over a wide area and has broken up and evaporated.
Mr Mates added: 'The testing will go on so that we can reassure the public, just as soon as we can, that there has been no lasting damage done and there is no damage to anybody.'