most PFAS do not naturally degrade to non-
fluorinated chemical species, these long-term
sinks are time-delayed sources. For example,
landfills are recognized PFAS sources through
PFAS-enriched landfill gas and liquid leachates
( 71 ). The only permanent solution to PFAS is
the destructive remineralization of the under-
lying fluorine, whether directly acting on con-
taminated media or from treatment of residual
streams of other treatment techniques, such as
spent sorbents or regenerant solutions.
Thermal treatment is a destructive approach
that can achieve PFAS mineralization. Incin-
eration by itself has been shown to at least par-
tially destroy even highly fluorinated wastes
( 143 ), and advanced thermal oxidation can be
used on solid, liquid, and gas samples to con-
vert PFAS to constituent gases with an acid-
scrubber cleanup ( 152 ). Ideally, this process
yields HF, NOx, SOx, and CO 2 gases that are
handled by traditional air pollution control
technologies. However, thermal treatment re-
quires substantial temperatures (>700°C) for
a sufficient period to convert PFAS into HF
and nonfluorinated products, with more highly
fluorinated species requiring more time and
higher temperature ( 153 , 154 ). Catalytic oxida-
tion at lower temperatures (e.g., 400°C) has
been demonstrated for some PFAS ( 155 ). Ther-
mal processes, however, have not been dem-
onstrated at scale, where inefficiencies can
reduce performance. Atmospheric emission
of products of incomplete destruction or the
air pollution control technologies associated
with thermal treatment processes, including
the regeneration of spent GAC, can become
additional PFAS sources. Capture or destruc-
tion of these products in the exhaust of ther-
mal processes also is an area of active research,
although forefront technologies are like those
applied for other media, namely scrubbers,
activated-carbon adsorption, and thermal
oxidation.
Other destructive treatments for aqueous
streams include electrochemical degradation,
sonolysis, nonthermal plasma, advanced oxi-
dation (e.g., sulfate radicals) and reduction
(solvated electrons), biodegradation (Feammox),
zero-valent iron, hydrothermal, and supercrit-
ical water oxidation ( 149 , 156 ). Although many
of these technologies have shown the ability to
destroy select PFAS, none have demonstrated
long-term performance approaching mineral-
ization at full scale with natural and industrial
water matrices for a wide assortment of PFAS.
Also, the energy costs of many of these tech-
nologies limit their sustainability and desira-
bility, and the formation of harmful by-products
(e.g., bromate, perchlorate) remains a concern
( 144 ). The lack of widespread testing and lim-
ited field usage has led to a reluctance in using
these technologies because additional manage-
ment of the waste or residual streams will be
needed. These unknowns, among others, fur-
ther demonstrate the need to minimize use of
PFAS and find a total waste-management ap-
proach in which complete destruction of PFAS
is ensured.Conclusions
The pool of new PFAS, for which physical,
chemical, and toxicological data remain un-
determined, is expanding rapidly and now
includes untold numbers of compounds having
widely varying chemical structures, volatilities,
and solubilities, as well as uncertain potential
exposure consequences. Early studies on struc-
turally similar PFAS suggest that behavioral
trends gleaned from legacy PFAS studies can
be useful as a basis to predict fate, toxicity, and
remediation strategies for emerging com-
pounds. Recently, an internationally authored
paper called for PFAS to be managed as a class
based upon widespread use in commerce, shared
inclusion of strongly bonded perfluorocarbon
moiety, and the resulting environmental per-
sistence of common terminal products ( 157 ).
Current international reporting practices
used to document PFAS synthesis, production
volumes, and potential releases vary among
countries and are not always tailored to pro-
vide the knowledge necessary to adequately
track and understand the movement of these
compounds in the environment. These efforts
typically serve as a critical first step in de-
veloping knowledge to be used in future as-
sessment and potential regulation of PFAS.
In the United States, expansion of the Toxic
Release Inventory will include ~172 long-chain
PFAS starting in 2021, providing limited but
valuable information in the form of sources,
compositions, and quantities released for these
compounds. However, under regulatory frame-
works around the world, information on many
PFAS is protected as confidential business
information and will not be disclosed pub-
licly ( 16 ), thereby necessitating substantial
continued discovery and forensic identifica-
tion efforts around the world. Other PFAS,
such as many of those classified as chemical
substances of unknown or variable compo-
sition, by-products, or biological materials and
polymers, may be too complex to fully charac-
terize and can challenge scientific investigation.
There is an ongoing need to advance re-
sponsive PFAS science, particularly regard-
ing investigating environmental sources and
sinks, toxicity, and remediation technologies,
but evidence suggests that preventative up-
stream actions are critical to facilitating the
transition to safer alternatives and minimizing
the impact of PFAS on human health and the
environment. Examples of these upstream ac-
tions include the EPAÕs Stewardship Program
( 158 ), the Amendment to the Polymer Exemp-
tion Rule removing side-chain fluorotelomer
polymers from the Exemption Rule ( 159 ), the
Significant New Use Rule removing an ex-emption for a set of PFAS used as coatings
( 160 ), the recently announced Comprehensive
National Strategy to confront PFAS pollution
( 161 ),andabanonPFASinfoodcontactpaper
in Denmark ( 162 ). Regardless of the regula-
tory approach implemented, collaborative ef-
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