Modelling the fate of per- and polyfluoroalkyl substances in the North- and Baltic Sea
Authors: Simon Pascal , Bieser Johannes , Schrum Corinna 
Published: March 2022

&lt;p&gt;&lt;span&gt;Per- and polyfluoroalkyl substances (PFASs) present themselves as a large self-imposed risk to human health and the environment as a whole. This risk is amplified by the high persistence and long-range transport in oceans. Therefore, this study considers the marine transport of the most widely used PFAS: Perfluorooctanoic acid (PFOA) in the North- and Baltic-Sea, &lt;/span&gt;&lt;span&gt;to determine and quantify the relationship between the physico-chemical properties and the potential for long range transport, &lt;/span&gt;&lt;span&gt;temporary storage&lt;/span&gt; &lt;span&gt;and permanent degradation&lt;/span&gt; &lt;span&gt;respectively&lt;/span&gt;&lt;span&gt;.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;For this purpose, an extensive model chain was established. It contains &lt;/span&gt;&lt;span&gt;a newly developed emission model for PFOA&lt;/span&gt;&lt;span&gt; approximating global emissions &lt;/span&gt;&lt;span&gt;centred around the year 2001&lt;/span&gt;&lt;span&gt; by combining specific point sources (e.g., PTFE production sites) and diffuse emissions by population, from which total &lt;/span&gt;&lt;span&gt;PFOA- &lt;/span&gt;&lt;span&gt;oads &lt;/span&gt;&lt;span&gt;of &lt;/span&gt;&lt;span&gt;European&lt;/span&gt;&lt;span&gt; river&lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt; are obtained by a&lt;/span&gt;&lt;span&gt; hydrological-discharge-model (HDM). &lt;/span&gt;&lt;span&gt;This discharge as well as approximations of the air sea exchange based on observed atmospheric concentrations &lt;/span&gt;&lt;span&gt;form the input for&lt;/span&gt;&lt;span&gt; the Hamburg Shelf Ocean Model (HAMSOM) &lt;/span&gt;&lt;span&gt;which is combined with&lt;/span&gt; &lt;span&gt;the&lt;/span&gt;&lt;span&gt; ecosystem-model ECOSMO. &lt;/span&gt;&lt;span&gt;These models are complemented by several &lt;/span&gt;&lt;span&gt;newly implemented, &lt;/span&gt;&lt;span&gt;locally resolved mechanisms, including photolytic and &lt;/span&gt;&lt;span&gt;bio-chemical&lt;/span&gt;&lt;span&gt; degradation, adhesion to dissolved and particulate organic matter as well as sedimentation.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;To relate &lt;/span&gt;&lt;span&gt;the&lt;/span&gt;&lt;span&gt; properties of PFOA to its environmental fate, this novel&lt;/span&gt; &lt;span&gt;system has been used to consider the &lt;/span&gt;&lt;span&gt;PFOA&lt;/span&gt;&lt;span&gt; budgets of the major input and output pathways and the exchange between the &lt;/span&gt;&lt;span&gt;N&lt;/span&gt;&lt;span&gt;orth and &lt;/span&gt;&lt;span&gt;B&lt;/span&gt;&lt;span&gt;altic &lt;/span&gt;&lt;span&gt;S&lt;/span&gt;&lt;span&gt;ea&lt;/span&gt;&lt;span&gt;.&lt;/span&gt; &lt;span&gt;In multiple simulations&lt;/span&gt; &lt;span&gt;these&lt;/span&gt;&lt;span&gt; uncertain physico-chemical properties, as well as boundary conditions for input and output &lt;/span&gt;&lt;span&gt;were varied and the simulation was run over multiple years&lt;/span&gt; &lt;span&gt;until a quasi-equilibria state was reached&lt;/span&gt;&lt;span&gt;.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;The simulated budgets show that degradation plays in general a minor role for the North- and Baltic-Sea while the ratio of PFOA stored in sediments compared to the amount lost to the Arctic- and Atlantic Ocean strongly depends on the chosen partitioning coefficients. Furthermore, the comparison of simulated concentrations to actual marine measurements allowed to narrow the plausible range of these uncertain physico-chemical properties, based on marine conditions in contrast to lab measurements.&lt;/p&gt;&lt;p&gt;Understanding the sensitivity of the transport and long-term fate of PFOA depending on its properties may point to simpler approaches to assess the fate of other PFASs where, due to their limited use, less data is available.&lt;/p&gt;