Xstrata has been cleared of releasing high levels of lead into the air at the Queensland mining town of Mount Isa.

Tests at the rural mining town, however, showed activities by other miners could be responsible for what appears to be reasonably high levels of lead in the air.

Earlier samples collected at the end of last year showed lead concentration levels of 2.1 micrograms per cubic metre from Xstrata’s operations, up by 0.6 micrograms from the permitted health limit, according to ABC News.

Re-testing of the original samples by two nationally accredited laboratories, one of them owned by the Queensland Government, found lead levels to be within acceptable limits.

It also found, however, that one in five air sampling stations in Mount Isa exceeded 1.5 microgram per cubic metre of lead allowed into the atmosphere.

In an attempt to continue monitoring lead levels 150 children, aged between one and four, will be examined over the next five months as part of a survey on lead exposure in Mount Isa.

The survey follows up a 2008 Queensland Health investigation which found 11% of children tested in the city had unsafe levels of lead in their blood.

A number of Mount Isa families are also suing Xstrata after seven of their children were found to have elevated lead levels in their blood.