Time Trends in Human Milk Derived from WHO- and UNEP-Coordinated Exposure Studies, Chapter 3: Perfluoroalkyl Substances (PFAS)

Abstract Temporal trends of perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA), and perfluorohexane sulfonic acid (PFHxS) were assessed using 86 pooled human milk samples from 59 countries from all United Nations Regional Groups collected between 2008 and 2019 as part of the WHO/UNEP-coordinated exposure studies. The primary objective of these temporal studies is to provide monitoring data for the effectiveness evaluation of the Stockholm Convention on Persistent Organic Pollutants (POPs). General temporal trends were estimated using data from all participating countries by grouping into three equal four-year periods (2008–2011, 2012–2015, and 2016–2019) reflecting the performance of three rounds of the studies. A more precise approach is the use of data from 24 countries with repeated participation in the WHO/UNEP-coordinated exposure studies, 22 of them in different periods and two in the same period. However, there were no Western European countries with multiple participation, and only two countries from the Asia-Pacific Region with one country submitting two samples in the same period. The country-specific PFOS data showed decreasing tendencies in 19 of the 22 countries with participation in different periods, quite constant levels in two countries and increasing tendencies in one country (from its first participation in 2010 to the second participation in 2015). For the two countries with repeated participation in the same period, it does not seem appropriate to derive country-specific temporal tendencies. An overall decrease of PFOS concentrations over 10 years of 48% and 52%, respectively, was calculated by the Theil–Sen method (1) using all samples and (2) using samples from countries with repeated participation. PFOA concentrations showed decreasing tendencies in 17 countries of the 22 countries with participation in different periods, quite constant levels in two countries and increasing tendencies in three countries (from their first participation between 2009 and 2011 to the second participation in 2015). An overall decrease over 10 years for PFOA concentrations of 42% and 47%, respectively, was calculated by the Theil–Sen method (1) using all samples and (2) using samples from countries with repeated participation. The estimation of general temporal trends for PFHxS was not possible, as in 84% of the samples PFHxS concentrations were below the limit of quantification (5.7 ng/L).