Exposure pathways for PFASs and other persistent chemicals in biota

The presence of organic contaminants in the environment has been of concern due to the potential for ecological and human exposure. Traditionally, there has been a focus on aquatic foodwebs which often possess many trophic levels, leading to strong bioaccumulation and biomagnification for persistent, bioaccumulative and toxic (PBT) compounds. There is ample evidence for the strong biomagnification of several key classes of hydrophobic organic contaminants (HOCs), including PCBs, dioxins/furans and DDTs, resulting in enhanced exposure of top predators, including humans. The more recent focus on per- and polyfluorinated alkyl substances (PFASs) has brought some of the same concerns for legacy compounds, such as PFOS, PFHxS and PFOA. These again show strong bioaccumulation in aquatic foodwebs, leading to their listing or consideration as persistent organic pollutants under the Stockholm Convention. Yet there are important differences for the class of PFASs relative to HOCs. First, as PFASs contain a hydrophilic functional group the compounds are more water-soluble, leading to different exposure pathways from drinking contaminated water to their enrichment in plants. Second, there are polyfluorinated precursor compounds that can be transformed into the persistent perfluorinated compounds, meaning that a wider group of compounds has to be observed and targeted for elimination. (author)