Aquatic toxicity of firefighting foams
Published: 01 January, 2006
In a newsletter published in October 2006 from an American special interest group of foam manufacturers, the aquatic toxicity of firefighting foams is discussed.
The only thing of actual interest in this newsletter is the ingenuity used to deflect the reader from the facts regarding the subject of ‘Aquatic Toxicity’.
The intention of the ‘Special Edition’ of this newsletter is to try and indicate to the reader that foams described as ‘fluoro-free’ or ‘environmentally-friendly’ have a higher aquatic toxicity than products containing fluorosurfactants such as AFFF, AFFF-AR, FFFP, FFFP-AR and Fluoroprotein foams.
Black or white?
The newsletter accurately describes the terminology of aquatic toxicity values as ‘an indicator of the relative toxicity of a chemical or compound in water’. This is how foam is used, a concentrated compound blended or mixed with water.
However, this newsletter then proceeds to publish test results of the aquatic toxicity of both fluorosurfactant-based foams and fluoro-free foams as concentrates.
So why would foam manufacturers, represented by the writers of this newsletter, publish data in this way? Is it to make the reader believe that the published figures and graphs are an indication of toxicity of the foams as they are actually used - which they are not? Or is it to deflect the reader from the fact that foams containing fluorosufactants have long-term detrimental impact on the environment and that fluoro-free foams do not?
Aquatic toxicity
The technical information on a foam is, of course, essential data. It details the products’ physical properties, performance and approvals. Equally important are the ecotoxicological data, which are not always supplied by the manufacturer.
This information should include biodegradability and aquatic toxicity, and should state whether the information is provided by an independent source or by the manufacturer.
In Europe, the toxicity of a product is determined by a standard provided by the ‘Organisation for Economic Co-operation and Development (OECD) (Fig i). In the United States, it is the ‘Fish and Wildlife Services’ (FWS) that provide a scale of toxicity (Fig ii).
You will note that the OECD scale is simplified and based on three levels of toxicity. A compound determined on this scale is either Highly Toxic, Toxic or Harmful, whilst the FWS scale is determined a further two levels above and below the OECD scale.
If a compound is determined to be ‘Highly Toxic’ on either scale, its dispersive use would never be allowed, so there seems little value in classing a product as ‘Super Toxic’. This phrase is not found on the OECD scale.
Aquatic toxicity is determined by the effect a compound will have on specific waterborne lifeforms, such as very young fish and shrimp (Leuciscus and Daphnia). The concentration is measured in mg/L.
A given amount of the compound is added to water until 50% of the fish die and this concentration is the LC50. This means that the toxicity level is counterintuitive - higher LC50s mean that the material is less toxic. Levels above 100mg/L are not classified as harmful on the OECD scale.
Deflection from persistence
Let us not be deflected from the real environmental concerns of fluorinated firefighting foams. In terms of ‘Aquatic Toxicity’ all foams, when used at the manufacturers recommended concen-trations with water, would not cause concerns of toxic overload for aquatic life as the finished foams would be all classed as non-toxic on the OECD scale.
The concern has always been the persistence of fluorinated compounds which have long-term environmental implications because this type of molecule cannot be destroyed once released into the environment.
Persistence is associated with all fluorosurfactants, not just those that are PFOS-based, this includes fluoro-telomer surfactants (which degrade to H-PFOS also known as 6:2 FtS).
The scale and graph here have been provided by Bio-Ex. It shows the LC50 figures for a typical Class A foam, AFFF-AR, AFFF and a Fluoro-free Class B foam. The Fluoro-free foams are indicated in green, the foams containing fluorosufactants are in red. The two graphs indicate LC50 figures for both the concentrate and the finished foam.
You will note that the LC50s for all four of the finished foams, fluorinated and fluoro-free, are between 5,600 and 85,000 mg/L, many times higher than 100mg/L.
However, the foams indicated in green have no fluorosurfactants and will completely biodegrade with no long term implications. The foams indicated as red will need to be contained and treated following use, as their release into the environment could lead to the contamination of ground water as was the case following the Buncefield fire at Hemel Hempstead in December 2005.
Conclusions
As I have written in previous articles, using the appropriate foams for the appropriate fuel risks is part of the answer. This surely means that we have assessed and understand that risk, which also includes the potential environmental impact?
Film forming foams are extremely efficient fire extinguishing products and for the forseeable future will be used in specific applications and when they can be contained and treated to remove fluorinated material post-fire.
In a vast number of cases, however, film forming-foams are not appropriate and foams such as BIO FOR N and ECOPOL can and should be used.
The Fire Service is a classic case where fluoro-free foams and and development of foam delivery systems such as CAF and Hydroflow induction equipment are begining to have a significant impact on the type of foam we use.
In a short period of time, it has become clear that fluorosurfactant free foams used for the appropriate risk, are becoming established as a safe alternative in terms of both performance and the environment.
