PERFLUORINATED COMPOUNDS ( PFC )
As a result of the growth of the synthetic chemical industry over the last 50 years , many thousands of new fluorinated molecules have been synthesised and through various mechanisms , have become almost ubiquitous in the environment . A multitude of poly- and perfluoroalkyl substances ( PFAS ), valued for their ability to repel both water and oils , have been used for decades for diverse applications such as water repellent “ outdoor ” fabrics , stain resistant carpets , non-stick frying pans and firefighting foams .
PFOS ( perfluorooctane sulphonate ) and PFOA ( perfluorooctanoate ) are the best known examples of PFAS . Their potential impact on human health has already been recognized internationally as they are extremely persistent , bioaccumulative and toxic .
As a result , PFOS is restricted under the Stockholm Convention and classed as a persistent organic pollutant ( POP ), with PFOA being actively considered for inclusion .
PFOS is also listed in the European Union Priority Substances Directive ( 2013 / 39 / EU ) with Environmental Quality Standards ( EQSs ) in fresh , surface water , coastal waters and biota .
However , more recently , regulators ’ in differing countries interest and concern has expanded to take in a much wider number of the PFAS now known to be present in the environment such as perfluorinated or polyfluorinated alkyl substances compounds ( PFAS ) which have entered the environment from aqueous film forming foam ( AFFF ) and multiple other products . Perfluorinated compounds do not break down or biotransform under natural conditions in the environment . Whereas , the polyfluorinated compounds are sometimes termed “ precursors ” as they can biotransform to form more simple Perfluorinated alkyl acids such as PFOA .
As a result , there are significant analytical challenges to overcome when considering how to assess soil and groundwater contaminated with PFAS as there are multiple analytes to consider , not just PFOS and PFOA , with many of the perfluorinated compounds being of unknown composition .
Routine analysis of these compounds is undertaken by Liquid Chromatography - Triple Quadrupole Mass Spectrometry ( LC-QQQ ). This analytical technique is very selective and sensitive , allowing for compounds which have been calibrated for to be detected at low concentrations , typically around 1 ng / l or less in water and 1 ug / Kg in soil . However LC- QQQ does not measure compounds which have not be calibrated for and there could be many thousands of these in the PFAS category .
To allow assessment of the polyfluorinated “ precursors ” of unknown composition , which are not in the standard analytical suites , the Total Oxidisable Precursor ( TOP ) Assay has been developed .
The TOP assay has four steps
• Analyse the routine analysis list of PFAS ( pre-oxidised sample )
• Oxidise a portion of the sample to convert polyfluorinated precursors to target perfluorinated compounds
• Analyse the oxidised sample for routine list of PFAS ( post-oxidised sample )
• Compare pre-oxidised sample results to post-oxidised sample results . The difference is the polyfluorinated “ pre-cursor ” concentration of the sample which may biotransform to the measured perfluorinated compounds over time in the natural environment .
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