NSW's environmental regulator has defended not releasing a study reportedly showing mercury was leaking from a Sydney chemical plant.
Fairfax Media says the report, conducted by two University of Sydney professors in 1991, found the toxic metal was going down the drain from Orica's former chlor-alkali plant in Botany, in Sydney's south-east.
The Orica-commissioned study is now with the NSW Environment Protection Authority (EPA), which has itself commissioned an investigation into the plant.
NSW EPA chief Barry Buffier says the report was given to the authority on the condition it not be publicly released.
He says there was no public interest to justify its release.
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"There is nothing in the document regarding impacts to human health or the environment which would require its immediate release into the public arena," Mr Buffier told AAP on Monday.
The EPA has commissioned consultancy firm CDM Smith to look at whether there was likely to be any contamination from the Botany plant.
Its initial report is expected to be released by the end of the year.
The 1991 study is one of 200 other reports being looked at by CDM Smith, Mr Buffier said.
Comment is being sought from Orica.
Orica says it has and will continue to provide access to all relevant documents relating to mercury issues at Botany to the EPA.
"Community representatives on the steering panel for that review have access to the report in question and other documents," a company spokesman told AAP.
"The process ensures that all available information is considered in context."
