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White mildew appearing on surfaces in some South Dunedin homes following recent flooding may be harmless, a contamination specialist says.
But residents are being urged to perform a simple home test to ensure the residue is not a harmful mould or fungus.
The Otago Daily Times understands South Dunedin residents whose homes were affected by flooding are concerned the white deposits may carry a health risk.
The deposits could, in fact, be crystallised salt left from the water table high tide.
Specialist Jason Pickering, of Christchurch-based company Decontamination Medix, said recently if the deposit was growing on timber, such as floor joists, it was probably a fungus, which could pose a health risk.
''The easiest way to tell would be just to grab hold of some and try to dissolve it with your fingers in some water.
''If it dissolves, it's a mineral; if it flakes apart in chunks, it's [mould].''
Mr Pickering said it was possible the deposits were crystallised salt.
They could appear slimy and grow ''like cauliflower'', but they were not harmful.
However, that did not mean there was nothing to worry about, he said.
''It is still caused by moisture coming from underneath [the house].''
Mr Pickering said the best way to counter any deposits in the home was to lay black polythene on the ground under the floor.