Officials have been surprised to discover stores of firefighting foams containing a long-banned chemical at six airports and other sites across New Zealand.

Products containing perfluorooctane sulfonate, or PFOS, had been used in firefighting foams since the 1960s before it was banned in 2011 because of the potential harm it posed to the environment and human health.

Strict controls were also set that year to manage its storage and disposal.

An investigation by the Environmental Protection Authority (EPA), covering 166 sites around the country, sought to check whether PFOS-containing foams had been imported, manufactured, used, stored or disposed of illegally.

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Of the 14 airports approached initially, four - Gisborne, Nelson, Palmerston North and Hawke's Bay - confirmed they held non-compliant firefighting foam.

EPA investigators physically inspected these airports, and equipment was examined and samples taken.

Later testing showed PFOS contamination in foams at three further airports: Queenstown, New Plymouth and Auckland.

Two had low levels of contamination in foam in two fire trucks each; the other had a low level of contamination in redundant foam in storage.

Of the remaining 19 airports investigated, Kapiti Coast and the Chatham Islands confirmed they held redundant non-compliant firefighting foam.

Of 92 ports, refineries, bulk-fuel storage and petrochemicals sites investigated, three, all controlled by Shell Taranaki Ltd in New Plymouth, also held PFOS firefighting foam.

A third stage of the investigation, checking ships and shipping companies, revealed two ships - the vessels MV Maui 1 and MV Purau - had non-compliant foam onboard.

"We were very surprised to find the banned foams at six airports; in equipment owned by two companies that service airports; at three sites controlled by a major oil company; in two tug boats; and at a tyre company," EPA chief executive Dr Allan Freeth said.

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But Freeth added that, in all cases, operators have taken the EPA's direction and complied with storage and labelling laws, and any ongoing risks to the environment had been mitigated.

There was no risk to workers or the public.

"In all instances, our aim was to secure the best outcome by working with parties, either on a voluntary basis or via a compliance order, to ensure they took the necessary steps to decontaminate or dispose of the foam in line with technical standards," he said.

"I want to stress that we found no intentional non-compliance.

"We concluded it was highly likely that all the banned foam we identified had been imported before 2006, when it was legal.

"There is, however, no excuse when businesses that are part of the professional firefighting sector do not keep up to date with law changes in their industry."

Three compliance orders were issued early in the investigation to reflect "the seriousness of the public and environmental issues arising from use of these foams", he said.

A later compliance order was served on an operator in response to its reluctance to take action.

"We consider that we have met the objectives of our investigation. While no prosecutions were undertaken, enforcement and compliance action has been successful.

"We remain vigilant and will take very seriously any circumstances where we might find banned foam being used or stored illegally in the future."

The investigation was a first for the EPA, which had been given new enforcement powers under the Hazardous Substances and New Organisms (HSNO) Act.

PFOS

• From the 1960s to the 1990s, firefighting foams containing PFOS were widely used internationally, including for firefighting training. They were the most effective means of extinguishing highly volatile, liquid fuel fires. So they were often deployed at airports, oil facilities and military bases.

• They have a narrow and specific use, and would not be present in home fire extinguishers, for example. PFOS is classified as a Persistent Organic Pollutant (POP) under the Stockholm Convention, an international agreement on managing POPs to protect the environment and human health. New Zealand became a signatory to the Convention in May 2001.

• POPs are stable compounds that do not readily break down through chemical or biological processes. They persist for a long time, both in the environment and the human body, with potential health effects.