Estimation of per- and poly-fluoroalkyl substances mass loads in the Danube River using passive sampling

As Europe's second longest river, the Danube is an important water source for drinking water and irrigation for many countries, before discharging into the Black Sea in the East. Per- and poly-fluoroalkyl substances (PFAS) have been observed over the last two decades in concentrations exceeding the European Union's drinking water guidelines for total sum of 20 select PFAS of 0.1 μg L^-1. Their presence is a result of current and historical use and high environmental persistence, necessitating their monitoring for human risk assessments. The aim of this study is to use recently developed passive sampling technology to calculate time-integrated water concentrations and mass loads of 11 select PFAS at 9 sites along the Danube River. Results indicate ∑₁₁ PFAS concentrations in the range of 9.3-29.6 ng L^-1 were not in exceedance of EU drinking water guidelines, but perfluorooctanesulfonic acid (PFOS) was in exceedance of the environmental quality standard (0.65 ng L^-1) at all sampling locations. The highest ∑₁₁ PFAS mass loads were observed at Ruse (9.5 kg day^-1) and Budapest (6.3 kg day^-1), believed to be driven by proximity to industrial facilities and large populations (urban runoff). Finally, we estimate 4.9 kg of total PFAS (∑₁₁ PFAS) were delivered to the Black Sea daily over Summer 2019.