Australasian Science: Australia's authority on science since 1938

Cleaning Up the Toxins After the Fire

Firefighting

The South Carolina Fire Academy goes through its paces. Credit: Ryan Adrian King

By Venkata Kambala

Toxic chemicals in firefighting foam accumulate in animal and human tissue, causing cancer and neonatal mortality. New technology is now keeping it from accumulating in the environment.

Perfluorochemicals (PFCs) have long been used in fire-fighting foam because they improve the effectiveness of the surfactants that enable the foam to smother fire. PFCs are also widely used in the treatment of fabrics and leather, in paper products, food packaging and insecticides. They are relatively inert and heat-stable, which has made them attractive to manufacturers.

However, evidence has also been accumulating about the toxicity of PFCs, and how these chemicals move into ecosystems and up food chains to accumulate in animal tissue. For example, the commonly used PFC perfluorooctane sulfonate (PFOS) accumulates in the liver and blood, and has been linked to bladder cancer, liver cancer, and developmental and reproductive toxicity, including neonatal mortality. There is a growing global concern over the risks to human health and the environment from its use on fires at tens of thousands of emergency and training sites worldwide over the past half century.

Threat to People and Wildlife
Similar effects have been noted in animals, with PFOS suspected of causing cancer, physical development delays, endocrine disruption and neonatal mortality. In 2006, Olivero-Verbel and colleagues at the University of Cartagena, Columbia, examined the tissue of pelicans living in Cartagena Bay, Colombia, an area that receives both industrial and urban sewage discharges from the city of Cartagena (population 925,000). Even though the amounts involved were tiny, the research was able to show how PFCs were distributed throughout the bodies of the birds feeding in a PFC-contaminated food chain.

In one study of Canadian wildlife, PFOS levels were measured in egg, liver, kidney, serum and plasma samples. Some of the highest recorded values as of January 2006 reported by researchers at University of Guelph, Canada are listed in Table 1.

Humans are also accumulating different types of PFCs in body tissue. PFOS has been widely detected in the blood serum of Americans, although concentrations appear to be decreasing. By contrast, blood levels of PFOS are rising in China.

Separate North American studies have found an association between PFOS levels in pregnant women and pre-eclampsia; with altered thyroid hormone values; and also a link with attention deficit hyperactivity disorder for children aged 12–15.

Research in the USA has focused on several sites where PFCs were manufactured or disposed of over a period of decades, including the 3M plant in Washington County, Minnesota. In response, Minnesota authorities have set the acceptable maximum levels for drinking water at 7 ppb for perfluorobutanoic acid (PFBA) and 0.3 ppb for both perfluoro-octanoic acid (PFOA) and PFOS. For soil in residential areas, the limit was set at 77 ppm for PFBA and 2 ppm for both PFOA and PFOS.

Although they are being phased out of modern foams, PFOS and PFOA dominate residual contaminants at many sites around the world. Many, if not most, of the world’s 49,000 airports, including 450 civilian and military airports in Australia, have regularly used foam in fire-fighting exercises for years, as well as in actual aircraft fires, and the chemicals have been subsequently detected in nearby groundwater and streams.

Although various types of fire-fighting foams are available, those containing PFOS and PFOA have been used almost exclusively by some of the largest users. Foams are also deployed on a range of other fires too, including traffic, truck and railway accidents and even fires in buildings, where the foam can escape into the surrounding urban or rural environment and contaminate local creeks and water supplies.

Munching at a Molecular Level
Even though at some locations the mixture of foam and water might be carefully contained and collected, treatment of the wastewater has remained expensive and difficult. For example, older clean-up techniques based on carbon filters are relatively ineffective, as well as being much more expensive.

Our work on this problem began when the Department of Defence was looking for a clean-up solution to the PFC-contamination problems at the RAAF base at Edinburgh, South Australia. From the outset we were fairly confident that clay-based materials offered the most promise, given their excellent adsorption properties and the chemistry of the PFCs involved. The plate structure of clays in particular presents a very high surface area per unit of material available for adsorption. Furthermore, the capacity of such materials for the removal of contaminants can be greatly improved by mineral tailoring. This offers several advantages, including the low cost of abundant natural sources and versatility in the preparation of selective and modified materials for target contaminants.

This hunch was confirmed by initial testing, which led to a search for local materials to keep costs low. After testing seven local possibilities, we settled on one clay type that we proceeded to modify in response to a series of experiments. Scaling up to column studies in the laboratory using 100 litres of contaminated water at a time, promising results encouraged us to run a large 10 kL trial. Again the results were excellent, with full recovery of the PFCs and none of the wastewater breaking through the clean-up medium.

Having determined an ideal formula for the adsorbent material, which we named MatCARE, we then turned to a local Adelaide business, Soil and Groundwater Consulting Pty Ltd, to build the first prototype for field trials. With the support of the Department of Defence, and in a stroke of economic ingenuity, the company constructed the first fully portable working plant in a shipping container to enable mobility in the field.

In further laboratory trials MatCARETM has removed PFOS, PFOA and other fluorinated surfactants to below detection limits. Amounts exceeding 10,000 ppb have been removed from wastewater, and in contaminated soil it can immobilise fluoro-surfactants of concentrations greater than 50 ppm. More recently a field trial was successfully conducted at a site in Darwin to treat 7.5 tonnes of PFOS- and PFOA-contaminated soil.

While no national or state jurisdiction has yet legislated for maximum levels of PFCs allowed in soil or water, the Stockholm Convention on Persistent Organic Pollutants (2004) listed PFCs as chemicals of concern to human health. As research reveals more about the long-term effects of minute amounts of PFCs on people and animals, governments and communities are likely to demand increasing restrictions on their use and tolerate lower levels of environmental contamination. If that eventuates, this new Australian technology could suddenly be in international demand.

The Australian Department of Defence has now requested for this clean-up capacity to be available to four more of its sites where fire-fighting foam has a history of use. In the meantime, interest in MatCARETM has now been expressed from US, Canada, the UK, New Zealand, India, Russia and Japan, and we anticipate that international interest in this Australian solution to a global problem will continue to grow.

Venkata Kambala is a research fellow with CRC CARE and the Centre for Environmental Risk Assessment and Remediation (CERAR) at the University of South Australia.