A government-appointed team of experts has completed a report on acid mine drainage, but the document will not be made public yet, officials said on Friday.

The team met the ministers of water and environmental affairs, Buyelwa Sonjica, and her mineral resources counterpart Susan Shabangu on Thursday, their departments said in a joint statement.

The ministers sit on an interministerial committee on mine drainage, which has been described as the single biggest threat to the environment in South Africa.

The experts were appointed at the beginning of September, following a Cabinet mandate to Sonjica.

Friday's statement said that following a presentation and discussions, the ministers had asked the team to look at more options to resolve the matter, as well as their cost implications.

The ministers would then meet the experts again "and look at [a] way to take the matter forward".

"Further correspondence and the release of the report will follow the second meeting of the [committee] and experts," the statement read.

Acid mine drainage affects the Gauteng, Mpumalanga, North West and Free State provinces. It results from the oxidation of sulphide minerals which are exposed in a mine or are present in dust in underground shafts and tunnels. As a result of its acidity, the water dissolves rock material and may contain a range of toxic metals.

Concern has been expressed over the rising level of acid mine water under Johannesburg.