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A matrix effect-free method for reliable quantification of perfluoroalkyl carboxylic acids and perfluoroalkane sulfonic acids at low parts per trillion levels in dietary samples
Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
(English)Manuscript (preprint) (Other academic)
Abstract [en]

In recent exposure modeling studies diet has been identified as the dominant pathway of human exposure to perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS). However, the paucity of highly sensitive and accurate analytical data to support these studies means that their conclusions are open to question. Here a novel matrix effect-free method is described for ultra-trace analysis of perfluoroalkyl carboxylic acids (PFCAs, all homologues from perfluorohexanoic acid to perfluorododecanoic acid) and perfluoroalkane sulfonic acids (PFSAs, perfluorohexane and perfluorooctane sulfonic acid) in dietary samples of varied composition. The method employs ion pair extraction of the analytes into methyl

tert-butyl ether and subsequent solid phase extraction clean-up on Florisil and graphitized carbon. Instrumental analysis was undertaken using ultra performance liquid chromatography coupled to tandem mass spectrometry. Special care was taken to avoid procedural blank contamination and potential contamination sources were elucidated. The performance of the method was evaluated for five different food test matrices including a duplicate diet sample. Method detection limits in the low to sub pg g-1 range were obtained for all target analytes, which are 5-100 times more sensitive than previously reported for duplicate diet samples. The method provided recoveries consistently between 50 and 80% for all analytes in the food matrices tested and effects of co-extracted matrix constituents on ionization were found to be negligible. Acceptable precision, defined as percentage relative standard deviation <30%, was achieved for all analytes. Accurate quantification at ultra-trace levels was demonstrated by a method intercomparison study with an independent recently developed method. For the first time the presence of long-chain PFCAs in duplicate diet samples is reported. The method presented here can thus support an improved assessment of dietary exposure to PFCAs and PFSAs. Re-analysis of duplicate diet samples, which had been previously analyzed using another older analytical methodology, indicated that human exposure to PFOA and PFOS from dietary sources may previously have been overestimated

Keyword [en]
food, diet, human exposure, perfluoroalkyl acids, PFOA, PFOS
National Category
Environmental Sciences
Research subject
Applied Environmental Science
Identifiers
URN: urn:nbn:se:su:diva-63653OAI: oai:DiVA.org:su-63653DiVA: diva2:451614
Available from: 2011-10-26 Created: 2011-10-26 Last updated: 2011-10-27Bibliographically approved
In thesis
1. Human exposure to perfluoroalkyl acids
Open this publication in new window or tab >>Human exposure to perfluoroalkyl acids
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkane sulfonic acids (PFSAs) are persistent organic contaminants which have been globally measured in human serum samples at low μg L-1 concentrations. One hypothesis, the so-called "indirect hypothesis", postulates that exposure to precursor compounds is responsible for the presence of PFCAs and PFSAs in human serum. The main purpose of this thesis was to test an alternative hypothesis that direct intake of PFCAs and PFSAs via the diet is the dominant ongoing pathway of exposure. Exposure modeling results in paper I and II demonstrate that dietary intake is the major exposure pathway of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), while known precursors account for only a few percent of the total exposure. To address the uncertainties related to dietary intake pathways, highly sensitive analytical methods for a range of PFCAs and PFSAs are developed, validated and applied in paper III and IV. By the development of a novel analytical technique in paper III, detection limits in the pg g-1 range are achieved for a wide range of analytes in different food categories. Analysis of a large set of food basket samples from the Swedish market in paper IV shows that the concentrations in many dietary samples are lower than those used to estimate exposure to PFOA and PFOS in paper I and II. However, an updated dietary intake estimate in paper IV supports the conclusion of paper I and II that dietary intake is the major ongoing human exposure pathway for the general population. Pharmacokinetic modeling undertaken in paper II was reevaluated in this thesis and back-calculated daily intakes from serum concentrations of PFOA and PFOS are shown to be in agreement with the estimated dietary intakes from paper IV. However, due to uncertainties and simplifying assumptions in the pharmacokinetic model, it is possible that there are additional pathways of human exposure contributing to human serum levels.

Place, publisher, year, edition, pages
Stockholm: Department of Applied Environmental Science (ITM), Stockholm University, 2011. 46 p.
National Category
Environmental Sciences
Research subject
Applied Environmental Science
Identifiers
urn:nbn:se:su:diva-63685 (URN)978-91-7447-391-9 (ISBN)
Public defence
2011-12-02, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 4: Manuscript.Available from: 2011-11-10 Created: 2011-10-26 Last updated: 2011-10-31Bibliographically approved

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