(2008)), and iv) different exposure pathways are included in the various studies. As for PFOS, our initial hypothesis, that reexamination of total PFOA exposure with up-to-date data would result in lower calculated daily exposures, is verified. This change in total PFOA exposures is in line with changes observed

in temporal trend monitoring studies. The hypothesis that precursors play a more important role compared to earlier estimations is accepted for all exposure scenarios. The scarcity of data on uptake and biotransformation factors for individual PFCAs and their precursors create uncertainties in the estimations of total human exposure to PFCAs as well as precursor PR-171 in vivo contribution to this exposure. Addressing these knowledge gaps should be a key priority in future research on human exposure to PFCAs. Concentrations of PFDA and PFDoDA in human serum cannot be modelled based on the estimated exposures as serum elimination half-lives and volumes of distribution for these PFAAs are currently not available. On the other hand, these parameters are available

for PFBA, PFHxA, PFOA, and PFOS learn more (see Section 2.4). Based on the estimated daily exposure, the modelled PFBA and PFHxA concentrations in serum are 0.0039 and 0.014 ng/g, respectively (Fig. 5). Literature data on PFBA and PFHxA in human serum from European and North American countries is extremely limited. In human serum from the USA, PFBA and PFHxA concentrations are higher compared to the modelled serum concentrations, Myosin which could be due to local high exposure to PFBA and PFHxA in the USA study, or incorrect model parameterization for these substances. The modelled PFOA concentration in serum based on total daily PFOA exposure ranges between 1.9 and 3.2 ng/g, which is in good agreement with concentrations reported in serum samples, although there were some studies reporting on higher PFOA concentrations

(Fig. 5). Based on the estimated total daily PFOS exposure, the modelled concentration ranges between 4.0 and 5.1 ng/g. This is generally lower compared to the measured concentrations in serum samples collected during and after 2007 in North America, Europe and Asia (Fig. 5). The reported higher PFOS levels in serum samples relative to the modelled concentrations can be explained by the long elimination half-lives of PFOS in humans (i.e., serum contains PFOS derived from historic exposure) (Section 2.4) together with the decreasing temporal trends in exposure media such as food items (Johansson et al., 2014) and in human serum (e.g., Glynn et al., 2012). Other factors could be that uptake and biotransformation factors are underestimated or that certain populations are (locally) more exposed to PFAAs and precursors than was estimated using the available literature data.