In addition to accounting for environmental
conditions ( 67 ), another complicating factor is
that contaminants commonly exist as compo-
nents in complex mixtures. One common pre-
cursor source is aqueous-film-forming foam
(AFFF), formulations of which contain mix-
tures of PFAS, and co-contaminants such as
nonfluorinated surfactants. High concentra-
tions of organic solvents have been shown to
inhibit PFOA degradation under in situ re-
medial chemical oxidation studies, suggest-
ingthatinteractionsofPFASwithother
non-PFAS co-contaminants can alter PFAS
transformation ( 40 ). Additionally, the pres-
ence of different PFAS has resulted in chang-
ing compositions of microbial communitieswhen comparing cultures spiked with PFOA or
PFOS against microbial compositions without
PFAS ( 46 ). Considering that PFAS environ-
mental transformation is mediated primarily
by microbes, data suggest that the presence of
complex mixtures could indirectly alter bio-
degradation and that the presence of one PFAS
may affect the transformation rate of another,Evichet al.,Science 375 , eabg9065 (2022) 4 February 2022 5 of 14
Fig. 3. Breakdown pathways of classes of PFAS.Shown are reaction schemes for 8:2 FTOH ( 47 , 53 , 63 )(A) andN-EtFOSE ( 65 , 66 )(B). Transformation products
proposed by the original investigators are shown with brackets.
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