An investigation by Fairfax Media has discovered mercury was found in very high concentrations in the sediment within a nearby estuary and in low levels along the shoreline near the port's container facilities.

There are also suspicions that tonnes of highly toxic mercury-contaminated sludge may have been dumped, decades ago, on land near Orica's former Chlor Alkai plant in Matraville.

Reports commissioned by Orica on potential health risks have ignored off-site soil contamination, which could affect more than 1500 homes.

Angry resident Sharon Price, a mother of two, said she only became aware of the potential risks because of other residents.

''When you start taking an interest, it is frightening what you find,'' Ms Price said.

The revelations come as an Australian expert in mercury recovery, Andrew Helps, warned that tonnes of accumulated toxic waste from the plant, as well as gas emissions into the atmosphere over its 57-year life, remain unaccounted for and ignored in Orica's reports.

''Despite 10 years and millions of dollars of consultant reports totally focused on the issues with this plant site, Orica has never investigated or quantified the mercury vapour and mercury absorbed on to particulates that have travelled offsite into surrounding residential properties or those that have directly entered Botany Bay,'' Mr Helps said.

Orica made headlines in August 2011 when its chemical plant at Kooragang Island released a cloud of cancer-causing chemicals over a Newcastle suburb. There have also been numerous leaks at its Port Kembla plant and at the Botany site.

Orica has been told by the Environmental Protection Authority to clean up the mercury contamination at Port Botany but reports, which Orica has been allowed to commission itself, are confined only to the site and the groundwater underneath it.

Orica has never done any offsite soil testing in the adjoining residential areas, some of which are just 100 metres away.

Resident Sherry Butt said a review of Orica's official Human Health and Environmental Risk Assessment Report and a proposal for testing that residents requested from Mr Helps were met with derision by Orica officials at a community meeting last month.

Mr Helps, whose company Hg Recoveries specialises in remediating mercury contaminated sites, and who is a member of the United Nations Environmental Program Global Mercury Partnership, said that soil samples and air quality surrounding about 1590 houses and apartments in a 1.25-kilometre radius of the site should be tested.

Mercury readily bioaccumulates throughout the food chain including in plants, fish and crustaceans. It can be taken up by vegetable gardens and fruit trees and people who eat this produce can then be at risk.

In a letter to Mr Helps dated January 11, Orica's executive global head of corporate affairs and social responsibility, Gavin Jackman, said Orica ''is satisfied with the results of these investigations and there is no unacceptable risk to community health''.

The Greens MP Cate Faehrmann said if Orica was reluctant to fund an investigation into its offsite mercury pollution the Environmental Protection Authority or the state Environment Minister, Robyn Parker, must force it.

''The last time Orica didn't respond swiftly to a pollution crisis, it was a PR disaster for the company and the minister. If there is mercury contamination in the neighbourhood it has potential to be more serious than the Kooragang Island debacle.''

An Orica spokesman said on Friday it was not opposed to further testing and would consider requests if it was supported by all stakeholders, conducted using internationally accepted standards and was the subject of a robust tender and evaluation process.

The spokesman said the company had found a document trail back to the 1990s that showed that sludge from the site was disposed of in licensed landfill sites approved by the EPA.

A spokesman for the Minister for Roads and Ports, Duncan Gay, has confirmed that low levels of mercury have been found on the Port Botany shoreline.

However, a report prepared for the ports in 2003 in anticipation of an expansion warned that there were exceptionally high levels of mercury found in the Penrhyn estuary sediment, which have most likely accumulated from water and effluent flowing from the Chlor Alkai site into Botany Bay.

smh.com.au