TOP – Total Oxidizable Precursors - English
Today thousands of PFAS compounds exist and it is not analytically possible to determine all. In current risk assessment of PFAS it has become accepted that a wider evaluation including also so called precursors is necessary. Precursors are compounds, both known and unknown, which have the potential to form PFCA (perflourinated carboxylic acids) and PFSA (perflourinated sulphonic acids) at degradation. Thus these substances are of interest both for present and future exposure for humans and biota. Besides risks and toxicological effects it may also be important to know about their presence at remedial actions. Among the “known” precursors, those forming PFOS (so called PreFOS) and a wide range of fluorotelomers e.g. FTS (fluorotelomer sulphonates) producing a different PFCAs can be mentioned. Moreover, numerous “unknowns”, not included in conventional analyses or potentially not identified may be present. To cover these, fully or to a great extent, other methods are needed such as the TOP assay.
It is known that precursors can be chemically oxidized to corresponding perflourinated substances. TOP is based on oxidation using hot persulphate in an alkaline solution. Under these conditions hydroxyl radicals are formed reacting with both telomers and sulfonamide precursors. The parameters are selected in a way so PFCA and PFSA initially present should not be affected. In comparison to naturally occurring biodegradation in the TOP assay sulfonamide containing precursors form a corresponding Cn PFCA e.g. in the case of PreFOS, PFOA is the resulting product. As in the environment telomer (n:2) oxidation is more complex and a series of PFCAs are produced, which includes the Cn+1, Cn, Cn-1 etc down to the C4 acid.
Eurofins SE can know offer TOP analysis of water samples. There is a number of TOP packages PFOS+PFOA (PLW6T), SLV 11 (Swe Food Agency 11 PFAS; PLWS6), PFAS 22-pack (PLWHM) and PFAS 30-pack (PLWLU). These match our regular PFAS “non-oxidised” packs. Preferred sample volume is 500ml and minimum 200ml. TOP can be performed without any accompanying regular PFAS analysis, but this is not recommended since your possibility to evaluate known and unknown precursors is lost. Limit of quantification is similar to the regular analysis i.e. 0.3 ng/l for most compounds, with the exception of PFBA (5 ng/l). If also a “non-oxidised” determination is to be performed additional bottles are required (2x500ml, min 1x200ml). Please use PE bottles delivered by Eurofins. If expected levels are very high (>10 000 ng/l) please mention this on the order form.
Further information (e.g. characteristics, concentrations, biodegradation and sorption) on the TOP analysis and various precursors are given in the “short facts” mini-review.
During the summer our capacity will be very limited and delivery time extended. Please contact us before any sample submission! From 21 Aug (week 34) we will offer a regular delivery time of 10 working days.
More information on PFAS analyses can be found in our search engine.
Contact Eurofins experts!
Questions on PFAS can be answered by Patrick van Hees: tel +46 (0)10-490 8151, e-mail: patrickvanhees@eurofins.se or Needa Shaheen: tel +46 (0)10-490 8150, e-mail Needashaheen@eurofins.se