But those plans hit a snag when the government was forced to admit that because the company no longer existed, it could not be pursued for remediation.

Brisbane City Council and a private developer are planning to remediate their own portions of a large section of West End's Riverside Drive, where toxins have leached into the soil due to years of chemical processing.

A Department of Environment spokesman said on Monday the department was aware of the planned remediation works on the privately owned and council-owned land.

Part of the contaminated site now belongs to the state government, which is not participating in a large-scale excavation of the area planned by the council.

"The state government is still pursuing options to ensure the parties responsible for the pollution of the land remediate the site," the department spokesman said.

However on Tuesday, when asked who was responsible for the contamination, the department spokesman said the company responsible for the historical contamination "no longer exists and cannot be pursued for remediation".

"The Department of Environment and Science’s investigation into parties responsible for the contamination commenced in 2016," he said.

"The department is now working with the owners of impacted land regarding remediation."

A coal tar processing plant was on the site from the 1920s until its closure in 1986, but it was not clear who owned the site during that time.

Toxins from the contaminated land leaching into the water sparked warnings last February not to swim or go near the river for fear of skin rashes and reactions. The land is deemed relatively safe for walking and riding through.

The contaminants include heavy metals, hydrocarbons and polycyclic aromatic hydrocarbons.

A council spokeswoman said last week that the council estimated potentially 13,500 square metres of soil would have to be removed from the riverbank and taken to a licensed facility for treatment.

"Council will continue to work with the adjoining private property owner and the state government to ensure the land is remediated and trees retained where possible," she said.

"The remediation works are proposed to be co-ordinated with the adjacent development, however these works do not prevent the developer from remediating and developing their property at any stage."

The council projected the total cost of the remediation works as just more than $15 million between 2018 and 2020, according to its 2018 budget.

The state-owned contaminated land is about 600 square metres but the department spokesman said more surveying was needed to define the total underground sub-surface contamination.

The development on the corner of Donkin Street and Buchanan Street runs parallel with the contaminated land.