SYDNEY (CP) - Faulty equipment caused elevated readings of a dangerous chemical in Sydney's air, government officials said Friday.

High readings of toluene were appearing and disappearing around the Cape Breton city earlier this summer. The high levels of the chemical dissipated, only to reappear four more times in July and in August at different sites.

But on Friday, a release from the Sydney Tar Ponds cleanup project ruled out the presence of elevated levels of toluene.

"The problem seems to lie with one set of sampling equipment," said Walter van Veen, a consultant to the cleanup.

Officials had said from the outset that they doubted the readings were coming from Sydney's notorious tar ponds.

Toluene is a clear liquid with a distinctive smell that occurs naturally in crude oil, coal and certain trees. Gasoline, which contains five to seven per cent toluene, is the largest source of toluene released to the atmosphere.

Breathing toluene in at low levels can cause tiredness, nausea and a loss of appetite, but symptoms usually disappear when exposure is stopped.

Tests carried out last week paired sampling air canisters from a new supplier with instruments from the original supplier. The new units showed normal toluene readings, while the old ones still produced false readings.

Project managers have ordered an additional round of testing to recheck the findings.