Per- and polyfluoroalkyl
substances (PFASs) are important environmental
contaminants, yet relatively few analytical reference standards exist
for this class. Nontarget analyses performed by means of high-resolution
mass spectrometry (HRMS) are increasingly common for the discovery
and identification of PFASs in environmental and biological samples.
The certainty of PFAS identifications made via HRMS must be communicated
through a reliable and harmonized approach. Here, we present a confidence
scale along with identification criteria specific to suspect or nontarget
analysis of PFASs by means of nontarget HRMS. Confidence levels range
from level 1a—“Confirmed by Reference Standard,”
and level 1b—“Indistinguishable from Reference Standard,”
to level 5—“Exact Masses of Interest,” which
are identified by suspect screening or data filtering, two common
forms of feature prioritization. This confidence scale is consistent
with general criteria for communicating confidence in the identification
of small organic molecules by HRMS (e.g., through a match to analytical
reference standards, library MS/MS, and/or retention times) but incorporates
the specific conventions and tools used in PFAS classification and
analysis (e.g., detection of homologous series and specific ranges
of mass defects). Our scale clarifies the level of certainty in PFAS
identification and, in doing so, facilitates more efficient identification.
The source tracking of per- and polyfluoroalkyl
substances (PFASs)
is a new and increasingly necessary subfield within environmental
forensics. We define PFAS source tracking as the accurate characterization
and differentiation of multiple sources contributing to PFAS contamination
in the environment. PFAS source tracking should employ analytical
measurements, multivariate analyses, and an understanding of PFAS
fate and transport within the framework of a conceptual site model.
Converging lines of evidence used to differentiate PFAS sources include:
identification of PFASs strongly associated with unique sources; the
ratios of PFAS homologues, classes, and isomers at a contaminated
site; and a site’s hydrogeochemical conditions. As the field
of PFAS source tracking progresses, the development of new PFAS analytical
standards and the wider availability of high-resolution mass spectral
data will enhance currently available analytical capabilities. In
addition, multivariate computational tools, including unsupervised
(i.e., exploratory) and supervised (i.e., predictive) machine learning
techniques, may lead to novel insights that define a targeted list
of PFASs that will be useful for environmental PFAS source tracking.
In this Perspective, we identify the current tools available and principal
developments necessary to enable greater confidence in environmental
source tracking to identify and apportion PFAS sources.
Urban stormwater, municipal wastewater effluent, and agricultural runoff contain trace amounts of organic contaminants that can compromise water quality. To provide a passive, low-cost means of oxidizing substituted phenols, aromatic amines, and other electron-rich organic compounds during infiltration of contaminated waters, we coated sand with manganese oxide using a new approach involving the room-temperature oxidation of Mn with permanganate. Manganese oxide-coated sand effectively oxidized bisphenol A under typical infiltration conditions and sustained reactivity longer than previously described geomedia. Because geomedia reactivity decreased after extended operation, chlorine was evaluated for use as an in situ geomedia regenerant. Geomedia regenerated by HOCl demonstrated similar reactivity and longevity to that of virgin geomedia. Chemical analyses indicated that the average manganese oxidation state of the coatings decreased as the geomedia passivated. X-ray absorption spectroscopy and X-ray diffraction showed that the reactive virgin and regenerated geomedia coatings had nanocrystalline manganese oxide structures, whereas the failed geomedia coating exhibited greater crystallinity and resembled cryptomelane. These results suggest that it is possible to regenerate the oxidative capacity of manganese oxide-coated sands without excavating stormwater infiltration systems. These results also suggest that manganese oxide geomedia may be a cost-effective means of treating urban stormwater and other contaminated waters.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.