key: cord-0963916-m6nvoecy
authors: Hammel, Emily; Webster, Thomas F.; Gurney, Rich; Heiger-Bernays, Wendy
title: Implications of PFAS definitions using fluorinated pharmaceuticals
date: 2022-03-02
journal: iScience
DOI: 10.1016/j.isci.2022.104020
sha: 3488d2d0c1973a45e3a0c40a18b6223b29791654
doc_id: 963916
cord_uid: m6nvoecy

There are 9,000+ per- and polyfluoroalkyl substances (PFAS) in existence, which makes studying and regulating PFAS individually, or even as small mixtures, infeasible. Multiple PFAS definitions based on structure have been proposed, yet these definitions do not consider the implications for the full suite of organofluorine chemicals. For example, organofluorine pharmaceuticals, whose use may be essential and are found in human serum and wastewater, are not uniformly identified across all definitions. Using nine definitions prepared by various stakeholders, we screened the 360 organofluorine pharmaceuticals approved and used globally between 1954 and 2021. Definitions ranged in their inclusion of organofluorine pharmaceuticals (1%–100%). The most inclusive definitions include several top prescribed pharmaceuticals, e.g., Prozac and Lipitor. This analysis provides a framework against which organizations can make decisions about how best to proceed when defining PFAS.

Since manufacturing began in the 1940s, per-and poly-fluoroalkyl substances (PFAS) have been widely used in textile manufacturing, food packaging, cookware, pesticide applicators, medical equipment, and other commercial products . To date, upward of 9,000 PFAS have been identified (USEPA, 2021a) . Many are toxic, persistent, and widely detected in the environment and human serum, prompting global discussion around their cost and benefits (Cordner et al., 2021) , essential uses (Cousins et al., 2019) , and effective strategies for regulation.

The large number of PFAS and the substitution of legacy compounds such as PFOA and PFOS by newer compounds-about which less is known although they may turn out to be just as problematic-has prompted movement away from the traditional chemical-by-chemical regulation toward regulation of these compounds as a class in both the U.S. (116th Congress, 2019; Kwiatkowski et al., 2020; B alan et al., 2021) and Europe (ECHA, 2021) . Several agencies, non-governmental organizations, and other groups have adopted class-based PFAS definitions for regulatory and non-regulatory purposes (Tables 1 and 2) . Notably, the U.S. National Defense Authorization Act (NDAA) includes the PFAS Act of 2019, which adopts a structural definition classifying PFAS as any compound with at least ''one fully fluorinated carbon'' (116th Congress, 2019) . The act authorizes funding for Department of Defense (DoD) initiatives related to PFAS remediation in areas impacted by military activities and sets restrictions on the use of PFAS in firefighting foam, personal protective equipment for firefighters, and food packaging used in military meals. Importantly, the act also sets requirements for environmental monitoring for PFAS in surface and groundwater and biomonitoring for PFAS among military personnel.

Recent work describes the advantages and disadvantages of different grouping strategies of PFAS based on their persistence and toxicity Wallington et al., 2021) , yet relatively little work has been done to understand the differences between specific PFAS definitions and what set of compounds they will include. We focus here on organofluorine pharmaceuticals: they present an opportunity to assess the implications of PFAS definitions for a diverse but well-defined set of chemicals used globally. Organic fluorine was first introduced to the pharmaceutical industry in 1954 and is useful in altering the physiochemical properties of a drug to achieve a desired pharmacological effect (Inoue et tl., 2020) . Pharmaceuticals represent a class of regulated chemicals whose use might be deemed at least partially ''essential'' for medical purposes. They are also of interest to environmental scientists for a number of reasons. For example, pharmaceutical waste enters the wastewater treatment systems (Kolpin et al., 2002) , where metabolites are either discharged back into the receiving waters, or are found in the biosolids after treatment (Massey and Waldron, 2011) . While the degradation products of many pharmaceuticals remain unknown, active pharmaceutical ingredients and their metabolites are measurable in wastewater effluent (Yu et al., 2006) . Models to predict biodegradability suggest some organofluorine pharmaceuticals may degrade into metabolites with trifluoromethyl groups and thus are likely to persist in the environment given the strength and durability of the CF 3 -R functional group (Neuwoehner et al., 2009 ).

Definitions of PFAS are developed for multiple purposes, also referred to as ''working scopes'' (OECD, 2021) , and can be both regulatory and non-regulatory. Regardless of its intended purpose, a useful definition requires clear, unambiguous language that is interpretable by stakeholders. In this analysis, we describe nine definitions of PFAS and examine some potential ambiguities in their language. We use each definition to screen a comprehensive list of organofluorine pharmaceuticals to determine which pharmaceuticals are included. Finally, we discuss some implications of these definitions given their intended purpose for use in regulatory or non-regulatory initiatives. Similar analyses could be performed for other groups of compounds. Tables 1 and 2 show the nine PFAS definitions and their intended purpose. These include definitions developed by Buck et al. (2011) , the Organisation for Economic Co-operation and Development (OECD), Glü ge et al. (2020) , the Toxic Use Reduction Act (TURA) Program of Massachusetts, U.S. EPA Office of Pollution Prevention and Toxics (U.S. EPA OPPT) (USEPA, 2021b), the NDAA (116th Congress, 2019) and laws from the states of Washington (2021) , Vermont (2021) , Maine (2021) , and California (2020) , and several non-governmental environmental advocacy organizations (e.g., Sierra Club of Massachusetts) TURA (2021a) ''Those PFAS that contain a perfluoroalkyl moiety with three or more carbons (e.g., -C n F 2n -, n R 3; or CF 3 -C n F 2n -, n R 2) or a perfluoroalkylether moiety with two or more carbons (e.g., -C n F 2n OC m F 2m À or -C n F 2n OC m F m -, n and m R 1).'' Key to this definition is that the compound must contain a string of at least three carbon atoms, each containing two or more fluorine atoms.

Perfluoroalkylethers are compounds that contain two -CF 2 -groups connected by an oxygen. Includes linear, branched, cyclic compounds and aromatic rings TURA (2021b) ''Certain PFAS not otherwise listed includes those PFAS that contain a perfluoroalkyl moiety with three or more carbons (e.g., -C n F 2n -, n R 3; or CF 3 -C n F 2n -, n R 2) or a perfluoroalkylether moiety with two or more carbons (e.g., -C n F 2n OC m F 2m À or -C n F 2n OC m F m , n and m R 1), wherein for the example structures shown the dash (À) is not a bond to a hydrogen and may represent a straight or branched structure, that are not otherwise listed.''

Clarifies that in TURA 2021a the (À) does not include a 

Using the publicly available KEGG drug database (KEGG, 2021), 363 pharmaceuticals approved in the U.S., Japan, and Europe are identified including two over-the-counter drugs. Three compounds were excluded from analysis: the insecticide novaluron, the veterinary pharmaceutical dirlotapide, and sulfur hexafluoride (Lumason) which does not contain organically bound fluorine. The remaining 360 pharmaceuticals were included in the analysis: the complete list of chemical structures, therapeutic use areas, chemical identifiers, and numbers of prescriptions (where available) are provided in the supplemental information (Data S1).

Organofluorine pharmaceuticals can be organized by substructures within the compound. Figure 1 presents the frequency of substructures identified among the 360 fluorinated pharmaceuticals; 50% of organofluorine pharmaceuticals contain a single fluorine; 35% contain a single aromatic fluorine; 10% contain more than three fluorine atoms. Only four pharmaceuticals were fully or nearly fully fluorinated aliphatic compounds. There were 88 compounds containing at least one trifluoromethyl moiety (R-CF 3 ) where R is not hydrogen, 15 of which contained two trifluoromethyl moieties. Table 3 summarizes the proportion of organofluorine pharmaceuticals that meet each of the nine structural definitions, disregarding for now their intended applications. The most inclusive is the ''all-organofluorine'' definition, including 100% of organofluorine pharmaceuticals. The revised TURA 2021b definition is least inclusive and captures the fewest (1.1%). We will now discuss each PFAS definition in roughly in the order in which they were proposed.

PFAS identified by Buck et al. Buck et al. (2011) provided one of the earliest and most widely used of the PFAS definitions, replacing earlier terminology. According to Buck et al., PFAS are ''aliphatic substances containing one or more C atoms on which all the H substituents present in the nonfluorinated analogs from which they are notionally derived have been replaced by F atoms, in such a manner that PFASs contain the perfluoroalkyl moiety C n F 2n+1 -.'' A restatement in less technical language is given in Any compound whose structure contains a carbon attached to a fluorine atom a Authorities whose legislation defines PFAS as a class of fluorinated organic chemicals containing at least one fully fluorinated carbon atom (WA, VT, ME, CA, NDAA Table 2 

The TURA Program originally defined PFAS as a compound containing ''a perfluoroalkyl moiety with three or more carbons (e.g., -C n F 2n -, n R 3; or CF 3 -C n F 2n -, n R 2) or a perfluoroalkylether moiety with two or more carbons (e.g., -C n F 2n OC m F 2m À or -C n F 2n OC m F m -, n and m R 1)'' (Administrative Council on Toxics Use Reduction, 2021a). The slightly revised definition (Table 2) clarifies that the ''-'' excludes bonding to hydrogen. The original definition was ambiguous about this point and could be interpreted to include enflurane ( Figure 2B ) while the revised definition would not. Both would include perflexane ( Figure 2E ). The TURA 2021a definition includes six (1.7%) organofluorine pharmaceuticals while the revised definition includes four (1.1%).

The U.S. EPA OPPT defines PFAS as ''. a structure that contains the unit R-CF 2 -CF(R 0 ) (R 00 ), where R, R 0 , and R 00 do not equal ''H'' and the carbon-carbon bond is saturated'' (USEPA, 2021b). It also indicates that branched structures, heteroatoms, and cyclic structures are included. This definition is unambiguous, recognizing five (1.4%) organofluorine pharmaceuticals as PFAS. There were no compounds included 

The U.S. NDAA defines PFAS as any substance containing ''at least one fully fluorinated carbon'' as do certain laws of the states of Washington, Vermont, Maine, and California (specific applications are discussed below). The NDAA defines a fully fluorinated carbon as ''a carbon atom on which all of the hydrogen substituents have been replaced by fluorine'' (116th Congress, 2019) . However, the definition does not specify whether the fully fluorinated carbon is saturated or unsaturated (saturated compounds only contain single bonds). We therefore interpreted it to mean that the carbon could have single, double, or even triple bonds. This interpretation includes compounds containing a single fluorine atom attached to a benzene ring. As written, this definition captures 337 (94%) organofluorine pharmaceuticals. It includes the cholesterol-lowering medication atorvastatin (Lipitor), the top prescribed drug in the U.S. ( Figure 2H ) with 112,104,359 annual prescriptions (Table 4) , as well as ciprofloxacin, a critical antibiotic (See Data S1). The ambiguity of the term ''fully fluorinated carbon'' is worth further consideration. If it had instead been interpreted to mean a trifluoromethyl group (R-CF 3 ) where R is not hydrogen, similar to Buck et al. (but without the latter definition's restriction to aliphatic compounds), neither Lipitor nor ciprofloxacin would be included, but Prozac ( Figure 2G ) would.

Some NGOs (Table 1) advocate for a broader definition of PFAS as any substance containing organofluorine. This definition is unambiguous and includes all 360 (100%) organofluorine pharmaceuticals, including widely used cancer chemotherapy drugs as well as Prozac and Lipitor discussed earlier.

The large number of PFAS listed by U.S. EPA and OECD suggests that research and regulation on a compound-by-compound basis is not practical. Multiple groups have devised definitions of PFAS to facilitate research into the prevalence, usage, and health effects of these substances, as well as serve as the basis for regulatory actions. Our analysis shows that the definitions have a very large range in the percent of organofluorine pharmaceuticals included. For this group of compounds, the definitions offer different and often conflicting views of what is and is not ''PFAS''. The framework we used is consistent with the systematic approach described in the OECD report (OECD, 2021) that provides practical guidance on characterizing PFAS based on molecular structure, and is similarly in line with the strategies described by (Wang et al., 2021) to facilitate unambiguous communication around PFAS. The cited examples serve to illustrate why PFAS definitions must be clear and that seemingly straightforward language-e.g., ''fully fluorinated carbon''-can have multiple interpretations. Without specifying saturation (i.e., saturated compounds contain only single bonds), the fully fluorinated carbon definition can be interpreted to include any compound with iScience Article a single aromatic fluorine, as well as other cases. While the definition was presumably intended to be clear and easy to interpret by stakeholders, it illustrates the importance of using specific and non-ambiguous language and being explicit in describing the context for which a definition shall be used. detection limits, etc. Biomonitoring programs may not be interested in organofluorine pharmaceuticals (e.g., the widely used Lipitor) themselves, except perhaps to try to close some of the gap between currently measured PFAS in serum vs. extractable organic fluorine (Yeung et al., 2008) . Instead, biomonitoring programs would be more likely to examine the trends of known PFAS and add emerging compounds as they are discovered. California Biomonitoring currently uses the Buck et al. definition of PFAS (which would include very few organofluorine pharmaceuticals) (OEHHA, 2021). As discussed earlier, the PFAS definition included in the NDAA-which requires biomonitoring for PFAS among all military firefighters during their annual exam-uses the very broad and ambiguous ''fully fluorinated carbon'' definition, which includes over 90% of organofluorine drugs. Both of these applications may consider exempting such compounds.

On the other hand, monitoring of surface water, wastewater, biosolids, and other environmental media may be more interested in organofluorine pharmaceuticals as well as more traditional PFAS. Here, the definition of PFAS could well have regulatory implications and the choice of definition and possible exceptions would need to be carefully considered. For example, the NDAA applies the ''fully fluorinated carbon'' definition to environmental monitoring of PFAS in surface and groundwater by the United States Geological Survey (116th Congress, 2019) . Recent efforts to measure total organic fluorine (TOF) in surface water (Ruyle et al., 2021) and in animal serum (Yeung et al., 2009) show that only a fraction of extractable organic fluorine (EOF) can be explained by known (targeted) PFAS, leaving a substantial portion of unidentified fluorine from other sources. Given the fate of organofluorine pharmaceuticals in wastewater, it is likely that these compounds would contribute to EOF measured in wastewater, and authorities that use the ''fully fluorinated carbon'' definition to measure or regulate PFAS will need to consider the implications for organofluorine pharmaceuticals. Alternatively, if the U.S. EPA OPPT definition were used, only a handful of organofluorine pharmaceuticals would be included. As a result, most pharmaceutical compounds, for which very little is understood on the biodegradability and recombination of breakdown products, would not be measured. Legislation in Washington, Vermont, California, and Maine (as well as the NDAA discussed above) each define PFAS as any compound containing at least one fully fluorinated carbon, but the applications differ. In California, the fully fluorinated carbon definition applies specifically to PFAS used in firefighting equipment and aqueous film forming foam (AFFF) (California, 2020) . In Washington, this definition is applied to AFFF and food contact materials (Washington, 2021) . Vermont applies the definition to AFFF as well as products added to rugs, food packaging, and ski wax (Vermont, 2021) . When applied in these cases, the definition would not include organofluorine pharmaceuticals. Maine applies the fully fluorinated carbon definition in its legislation banning the selling or importing of any product containing intentionally added PFAS (Maine, 2021) . The language of this legislation recognizes product categories in which the use of PFAS is currently unavoidable, which may include pharmaceuticals. Without this recognition, this law would include 94% of organofluorine pharmaceuticals.

The Massachusetts Toxic Use Reduction legislation provides an interesting example of exceptions. Certain industrial sectors are exempt from reporting toxic substances (MassDEP, 2018) , including hospitals that may generate waste containing fluorinated contrast agents or other organofluorine pharmaceuticals used during hospital-based activities (e.g., surgical procedures, ventilation, etc.). Another approach to exceptions relevant to organofluorine pharmaceuticals is whether such products are deemed essential (Cousins et al., 2019) .

Importantly, the list of organofluorine pharmaceuticals is dynamic and new drugs containing fluorine are developed each year. In fact, five organofluorine pharmaceuticals were approved during the final months of 2021, including Pfizer's new drug Paxlovid, the first protease inhibitor for treatment of SARS-CoV-2 ll OPEN ACCESS iScience 25, 104020, April 15, 2022 iScience Article (Pfizer, 2021) . Pfizer signed a licensing agreement in November 2021 that will enable qualified manufacturers to produce and distribute the drug globally in order to reach a wider range of the global population (Pfizer, 2021) . Paxlovid is an organofluorine pharmaceutical that meets the criteria of the revised OECD definition, the all-organofluorine definition, as well as the fully fluorinated carbon definition.

The definitions may be characterized by three attributes: clarity, inclusion, and specificity. Clarity may be interpreted as the degree to which a particular definition is open to conflicting decisions on whether a given PFAS structure meets the stated definition. Next, inclusion may be interpreted as the extent to which a definition would label any organofluorine compound as ''PFAS'', which we have illustrated here with pharmaceuticals. By specificity, we mean usefulness for its intended purpose. Specificity may be of particular importance to monitoring and regulatory bodies, which may need to consider exemptions for certain types of organofluorines if broad PFAS definitions are used. While consideration of these factors is important as we move forward, the real danger is not adopting any definition, for fear of not having a perfect definition, and the consequential delay in decision making.

This analysis considers nine available definitions of PFAS, yet new definitions may be developed for unique purposes, and previously established definitions may be revised in the future. Only those definitions available in the public space were included in this analysis. We include a comprehensive list of organofluorine pharmaceuticals approved between 1954 through June 1, 2021, including compounds that have been withdrawn. New therapeutics containing organofluorine approved after June 1, 2021 are not included. Our analysis is limited to human pharmaceuticals and does not include pharmaceuticals used in animals. Finally, available data on annual prescriptions are limited to the most widely prescribed drugs.

Detailed methods are provided in the online version of this paper and include the following:

d KEY RESOURCES TABLE

Aliphatic: saturated organic compounds in which the carbon atoms may form an open chain or closed rings Alkyl group: a portion of a compound made up by carbon and hydrogen atoms arranged in a chain and whose structure follows the formula C n H 2n+1 Aromatic: organic compounds containing a planar unsaturated ring of atoms that is stabilized by an interaction of the bonds forming the ring. Such compounds are typified by benzene and its derivatives Ether: organic functional group typified by an oxygen atom connected to two carbon atoms, which may be aliphatic, olefinic, or aromatic.

Methyl group: a small molecule consisting of one carbon and three hydrogen atoms -CH3 

One or more of the authors of this paper self-identifies as a member of the LGBTQ+ community. One or more of the authors of this paper received support from a program designed to increase minority representation in science. iScience 25, 104020, April 15, 2022 iScience Article representative survey of households and medical care providers across the U.S. and includes information on household-reported prescription drug use.

We also compile data on global sales and revenues from PharmaCompass, where available, on the organofluorine pharmaceuticals that rank in the top 500 prescribed drugs (PharmaCompass, 2021). ''Blockbuster'' drugs are defined as those whose global sales exceed $1B annually. Revenues can change from year to year based on whether a drug's patent is expired, and the availability of generics. It is more useful and consistent with the available data to compare the total number of prescriptions in a calendar year as a measure of how widely a drug is used. The pharmaceutical name and CAS registry number refers to the non-ionic form of the drug, unless the ionic equivalent is necessary for identification in which case both forms are included. Ionic equivalents are presented primarily for corticosteroids in which case multiple ionic forms of the compounds have distinct clinical uses. For example, fluoxetine hydrochloride is presented simply as fluoxetine whereas fluticasone propionate and fluticasone furoate are presented separately since they are different drugs with unique pharmacological activity.

Each of the identified organofluorine pharmaceutical structures were reviewed against the nine definitions. The definitions were ranked from most to least inclusive with the most inclusive definition containing the largest number of compounds. We describe ambiguities in some definitions with examples.

iScience 25, 104020, April 15, 2022 15 iScience Article

Text -S.1790 -116th Congress (2019-2020): National Defense Authorization Act for Fiscal Year 2020

TURA program administrative council meeting

December 7, 2021 meeting of the TURA program administrative council

Medical expenditure panel survey household component

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Perfluoroalkyl and polyfluoroalkyl substances in the environment: terminology, classification, and origins

Bill text -SB-1044 firefighting equipment and foam: PFAS chemicals

The true cost of PFAS and the benefits of acting now

The concept of essential use for determining when uses of PFASs can be phased out

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Commission staff working document: poly-and perfluoroalkyl substances (PFAS)

An overview of the uses of perand polyfluoroalkyl substances (PFAS)

Contribution of organofluorine compounds to pharmaceuticals

KEGG drug database, new drug approvals in the

PubChem in 2021: new data content and improved web interfaces

Pharmaceuticals, hormones, and other organic wastewater contaminants in U.S. streams, 1999-2000: a national reconnaissance

Scientific basis for managing PFAS as a chemical class

LD 1503, HP 1113, text and status, an act to stop perfluoroalkyl and polyfluoroalkyl substances pollution

Response to comments 301 CMR 41.00 toxic or hazardous substance list

Pharmaceutical Compounds in Merrimack River Water Used for Public Supply

Physiological modes of action of fluoxetine and its human metabolites in algae

Toward a new comprehensive global database of per-and polyfluoroalkyl substances (PFASs)

Reconciling terminology of the universe of per-and polyfluoroalkyl substances: recommendations and practical guidance

Biomonitoring california priority chemicals

Pfizer and the medicines patent pool (MPP) sign licensing agreement for COVID-19 oral antiviral treatment candidate to expand access in low-and middle-income countries

PharmaCompass database

Isolating the AFFF signature in coastal watersheds using oxidizable PFAS precursors and unexplained organofluorine

CompTox chemicals dashboard

Toxic substances control act reporting and recordkeeping requirements for perfluoroalkyl and polyfluoroalkyl substances

Bill status S

The case for a more precise definition of regulated PFAS

A new OECD definition for per-and polyfluoroalkyl substances

RCW 70A.222.010: definitions

Perfluorinated compounds and total and extractable organic fluorine in human blood samples from

Comparison of total fluorine, extractable organic fluorine and perfluorinated compounds in the blood of wild and pefluorooctanoate (PFOA)-exposed rats: evidence for the presence of other organofluorine compounds

Occurrence and biodegradability studies of selected pharmaceuticals and personal care products in sewage effluent

Further information and requests for resources should be directed to and will be fulfilled by the lead contact, Emily Hammel (eghammel@bu.edu).

This study did not generate new materials.

This paper analyzes existing, publicly available data. The data generated in this manuscript are supplied in a supplemental table. Any additional information required to reanalyze the data reported in this paper is available from the lead contact upon request. This paper does not report original code.

We selected and reviewed nine adopted definitions of PFAS that were available at the time of writing developed by both regulatory and non-regulatory organizations, presented in Table 1 . Selection was based on the availability of a PFAS definition and a traceable description of the purpose for the development of the definition as it fits into the organizations' mandates or working scope. We present the organizations chronologically based on when the definition of PFAS was developed. For the purposes of direct comparison, we present the updated definitions for two of the organizations together with the originally developed definition.

To establish a comprehensive list of organofluorine pharmaceuticals registered globally to date, we extended the work by Inoue et al. (2020) , which included pharmaceuticals approved between 1954 and 2019, by querying the KEGG Drug database (Release version 99.1) for new organofluorine drugs approved between January 1, 2020 and June 1, 2021 (KEGG, 2021). KEGG Drug Database is a publicly available repository of approved drugs in the U.S., Europe and Japan, their chemical properties, and molecular structure, and other identifiers for prescription and over-the-counter (OTC) pharmaceuticals, including organofluorine pharmaceuticals that have been withdrawn either due to lack of demand or risk to patients.The organofluorine pharmaceuticals identified from the KEGG Drug Database were queried using PubChem for the drug names, available synonyms, CAS registry number, molecular structure, chemical formula, InChI key, and therapeutic use area (Kim et al., 2019) . Drug name refers to the generic pharmaceutical name; available brand names the pharmaceutical is sold under are listed separately as synonyms. Where available, the most recently collected data from 2019 on the number of U.S. prescriptions and the rank order by frequency prescribed within a calendar year were compiled from the ClinCalc DrugStats database (ClinCalc DrugStats Database, 2019) and are presented in Table 4 in addition to being made available in an Excel worksheet (Data S1). Drug utilization data from ClinCalc DrugStats was generated via the Agency