''The reason why we have recommended off-site sampling is to reassure the public that our findings are correct and it is the only way of adequately alleviating community concerns about potential mercury contamination,'' said CDM Smith senior environmental scientist Loek Munnichs.

The report revealed that historic mercury emissions in the air ''may have exceeded international standards for long-term exposure'' in close proximity (500 metres) of the former plant and needed further investigation.

The move is being hailed as a win by the community angry that the EPA kept fobbing them off without conducting testing on any homes.

Resident Len Mahoney said it was ''unacceptable'' that they had to battle the EPA and had to bring in their own experts before they were taken seriously. In 2012, residents had commissioned a proposal from Hg Recoveries to test for mercury but they say Orica argued against it partly because it was worried mercury from dental fillings and broken thermometers might skew the results.

Mr Mahoney said residents had been critical of the conflict of interest created by the EPA allowing the polluter of the site, Orica, to commission and set the scope of previous public health assessment reports, which found no unacceptable public health risk but did not consider any off-site contamination. The EPA said the previous reports were only to ''assess risks from the known on-site contamination''.