Contribution of Direct and Indirect Exposure to Human Serum Concentrations of Perfluorooctanoic Acid in an Occupationally Exposed Group of Ski Waxers

Abstract

The contribution of direct (i.e., uptake of perfluorooctanoic acid (PFOA) itself) and indirect (i.e., uptake of 8:2 fluorotelomer alcohol (FTOH) and metabolism to PFOA) exposure to PFOA serum concentrations was investigated using a dynamic one-compartment pharmacokinetic (PK) model. The PK model was applied to six occupationally exposed ski waxers for whom direct and indirect exposures via inhalation were characterized using multiple measurements with personal air sampling devices. The model was able to predict the diverging individual temporal trends of PFOA in serum with correlation coefficients of 0.82-0.94. For the four technicians with high initial concentrations of PFOA in serum (250-1050 ng/mL), the ongoing occupational exposure (both direct and indirect) was of minor importance and net depuration of PFOA was observed throughout the ski season. An estimated average intrinsic elimination half-life of 2.4 years (1.8-3.1 years accounting for variation between technicians and model uncertainty) was derived for these technicians. The remaining two technicians, who had much lower initial serum concentrations (10-17 ng/mL), were strongly influenced by exposure during the ski season with indirect exposure contributing to 45% of PFOA serum concentrations. On the basis of these model simulations, an average metabolism yield of 0.003 (molar concentration basis; uncertainty range of 0.0006-0.01) was derived for transformation of 8:2 FTOH to PFOA. An uncertainty analysis was performed, and it was determined that the input parameters quantifying the intake of PFOA were mainly responsible for the uncertainty of the metabolism yield and the initial concentration of PFOA in serum was mainly contributing to the uncertainty of estimated serum half-lives.

Half-lives of PFOS, PFHxS and PFOA after end of exposure to contaminated drinking water

“…Our estimate of apparent half-life for PFOA is in the range of values reported from five studies with averages ranging from 2.3 to 3.94 years, observed in fluorocarbon workers 4 ; studies in populations living in PFOA-polluted areas around production plants, followed for 1–2 years after provision of clean drinking water 5 12 ; occupationally exposed ski waxers 13 ; and a study in a community exposed residentially to PFAS. 11 For PFOS, the population half-life has been estimated to be 4.3 years from studies in US blood donors reflecting general population reduction in exposure.…”

Children's exposure to perfluoroalkyl acids – a modelling approach

“…Current estimations for the half-life and volume of distribution used in several model approaches seem to be accurate, as indicated by successful model results in other studies. 18,34 In the presented model, the values of the serum elimination halflife and of the volume of distribution of PFOA, PFOS and PFHxS were taken from a study that successfully estimated serum concentration trends of PFOA and PFOS in adults. 35 Verner et al (2016) used slightly different values for the half-life and volume of distribution of PFOA and PFOS compared to the present work.…”

Perfluoroalkyl substances with isomer analysis in umbilical cord serum in China

“…Beesoon et al (2011) analyzed 20 cord samples from manufacturing method for PFOA today, resulting in almost pure linear isomer. In addition to the environmental PFOA direct exposure, it has been hypothesized that the indirect exposure, such as the exposure of PFOA precursor, might be another important exposure route for the body burden of POFA (Gomis et al 2016). Experimental studies showed that precursor compounds uptake, like polyfluoroalkyl phosphate esters, a common food-contact paper packaging material, might be metabolized into PFOA in the body after uptake (D'eon and Mabury 2011; Vestergren et al 2008).…”