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Evidence of aerobic biotransformation is provided from studies of PFAS composition throughout the continuum of wastewater treatments<ref name="Arvaniti2015">Arvaniti, O.S. and Stasinakis, A.S., 2015. Review on the occurrence, fate and removal of perfluorinated compounds during wastewater treatment. Science of the Total Environment, 524, pp. 81-92.  [https://doi.org/10.1016/j.scitotenv.2015.04.023 DOI: 10.1016/j.scitotenv.2015.04.023]</ref>, from field studies at AFFF-impacted sites<ref name="Houtz2013" /><ref name="McGuire2014" /><ref name="Anderson2016" /><ref name="Weber2017" />, and from microcosm experiments. In general, the literature on aerobic biotransformation collectively demonstrates or indirectly supports the following conclusions as summarized in ITRC 2020<ref name="ITRC2020" />:

Evidence of aerobic biotransformation is provided from studies of PFAS composition throughout the continuum of wastewater treatments<ref name="Arvaniti2015">Arvaniti, O.S. and Stasinakis, A.S., 2015. Review on the occurrence, fate and removal of perfluorinated compounds during wastewater treatment. Science of the Total Environment, 524, pp. 81-92.  [https://doi.org/10.1016/j.scitotenv.2015.04.023 DOI: 10.1016/j.scitotenv.2015.04.023]</ref>, from field studies at AFFF-impacted sites<ref name="Houtz2013" /><ref name="McGuire2014" /><ref name="Anderson2016" /><ref name="Weber2017" />, and from microcosm experiments. In general, the literature on aerobic biotransformation collectively demonstrates or indirectly supports the following conclusions as summarized in ITRC 2020<ref name="ITRC2020" />:

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[[File:Fate-and-transport_v3.mp4|thumb|500px|left|Figure 4. PFAS Fate and Transport.]] 

*Numerous aerobic biotransformation pathways exist with relatively rapid kinetics

*Numerous aerobic biotransformation pathways exist with relatively rapid kinetics

*All polyfluorinated precursors studied to date have the potential to aerobically biotransform to PFAAs

*All polyfluorinated precursors studied to date have the potential to aerobically biotransform to PFAAs

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Precursor transformation can complicate CSMs (and risk assessments) and should be considered during comprehensive site investigations.  For example, atmospheric emissions of volatile precursors can result in long-range transport where subsequent transformation and deposition can result in detectable levels of PFAAs in environmental media independent of obvious point-sources<ref name="Vedagiri2018">Vedagiri, U.K., Anderson, R.H., Loso, H.M. and Schwach, C.M., 2018. Ambient levels of PFOS and PFOA in multiple environmental media. Remediation Journal, 28(2), pp. 9-51.  [https://doi.org/10.1002/rem.21548 DOI: 10.1002/rem.21548]</ref>.  With respect to site-related precursors, transformation of otherwise unmeasured PFAS into detectable PFAAs is obviously relevant to site investigations to the extent transformation occurs after initial site characterization efforts or if past remedial efforts have accelerated ''in situ'' transformation rates<ref name="McGuire2014" />.  Additionally, differential transport rates between precursor PFAS and the corresponding terminal PFAA could also confound CSMs if transformation rates are slower than transport rates as has been suggested<ref name="Weber2017" />.    

Precursor transformation can complicate CSMs (and risk assessments) and should be considered during comprehensive site investigations.  For example, atmospheric emissions of volatile precursors can result in long-range transport where subsequent transformation and deposition can result in detectable levels of PFAAs in environmental media independent of obvious point-sources<ref name="Vedagiri2018">Vedagiri, U.K., Anderson, R.H., Loso, H.M. and Schwach, C.M., 2018. Ambient levels of PFOS and PFOA in multiple environmental media. Remediation Journal, 28(2), pp. 9-51.  [https://doi.org/10.1002/rem.21548 DOI: 10.1002/rem.21548]</ref>.  With respect to site-related precursors, transformation of otherwise unmeasured PFAS into detectable PFAAs is obviously relevant to site investigations to the extent transformation occurs after initial site characterization efforts or if past remedial efforts have accelerated ''in situ'' transformation rates<ref name="McGuire2014" />.  Additionally, differential transport rates between precursor PFAS and the corresponding terminal PFAA could also confound CSMs if transformation rates are slower than transport rates as has been suggested<ref name="Weber2017" />.    

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To account for otherwise unmeasurable precursors, several surrogate analytical methods have been developed.  

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To account for otherwise unmeasurable precursors, several surrogate analytical methods have been developed.

==References==

==References==

Enviro Wiki - Recent changes [en]

PFAS Transport and Fate

File:Fate-and-transport v3.mp4