Perspectives on the Inclusion ofPerfluorooctane Sulfonate into theStockholm Convention on PersistentOrganic Pollutants1

T H A N H W A N GY A W E I W A N GC H U N Y A N G L I A OY A Q I C A IG U I B I N J I A N G *

State Key Laboratory of Environmental Chemistry andEcotoxicology, Research Center for Eco-EnvironmentalSciences, Chinese Academy of Sciences, Beijing

Reflections on the inclusion of perfluorooctane sulfonate intothe Stockholm Convention on Persistent Organic Pollutants.

Persistent organic pollutants (POPs) have been of consider-able public health and environmental concern for severaldecades. These are organic substances that persist in theenvironment, can undergo long distance transportation, areable to bioaccumulate, and pose a risk of causing adverseeffects to animals and human health. As a measure to controland mitigate the threats of POPs, an international treaty wassigned in 2001 and came into force on May 2004 for itssignatories (1). The treaty, called the Stockholm Conventionon Persistent Organic Pollutants (SC), initially listed twelvechemicals, the so-called “Dirty Dozen” for final elimination(Annex A), or restricted use (Annex B), and/or reducedreleases of unintentional production (Annex C). The SC alsoincluded a section stating that additional chemicals can benominated by its member parties, after which the candidatechemical would undergo several screening and evaluationrounds before it could be voted for inclusion into theConvention (Figure 1).

The (possible) inclusion of one of these suspected POPs,perfluorooctane sulfonate (PFOS), is currently a controversialissue and we provide some of our viewpoints below, mainlyconcerning the current production pattern, adverse healtheffects, and economical issues. Review documents weremainly cited due to limitations on article length, andinterested readers are advised to consult relevant articlescited within these reviews.

Environmental Concerns of PFOS

Perfluorinated compounds (PFCs) exhibit unique propertiessuch as high surface activity, thermal and acid resistance,are both hydro- and lipophobic, and have therefore beenfound very useful in a wide range of applications: in industryas polymers, surfactants, lubricants, and pesticides; and inconsumer products as textile coatings, nonstick coatings,stain repellent, food packaging, firefighting foams, and more(2). Unfortunately, the very properties that make thesechemicals valuable also render some PFCs extremely resistantto environmental and biological breakdown. These chemicalswere long assumed to be inert and thus safe, but it was foundin recent years that PFCs can be released during certainindustrial applications and during the lifetime of commercialproducts containing them (3). Among these, the eight carbonchained PFOS (Figure 2) and perfluorooctanoic acid (PFOA)were found to be environmentally persistent and globallyprevalent even in remote areas such as the Arctic and havebeen detected in wildlife and humans, typically with PFOSat higher concentrations than PFOA (4). Therefore, thesetwo compounds have lately drawn considerable scientificand public interest. Consequently, regulators have also begunto take action, and in the advent of increasing environmentaland health concerns, Sweden proposed in 2005 to list PFOSand 96 so-called precursors, which contain the PFOS moiety(C8F17SO3

-) and are suspected to be degradable to PFOS, inthe SC for ultimate elimination.

Once released into the environment, PFOS behaves verydifferently from what is usually expected for a POP. Thesedifferences include intrinsic properties such as the surfaceactivity, water solubility, nonmeasurable octanol/water

1 Editor’s Note: This manuscript was accepted for publication onApril 24, 2009. On May 9, 2009, the Conference of the Parties 4 of theStockholm Convention (COP-4) in Geneva placed perfluorooctanesulfonate and perfluorooctane sulfonyl fluoride (PFOS and PFOSF)in Annex B (see below for other included substances). Due to ourproduction timelines, it was impossible to have this article appearprior to the COP-4 meeting (began May 4, 2009). Therefore theconditional/future tensing within this article, now made moot bythe COP-4 decision, has been edited into parentheses. Much of thispaper describes the toxicological considerations of PFOS/PFOSF thatled to its inclusion. Taking the information in this Viewpoint article,readers may wish to consider the placement of PFOS/PFOSF as arguedby the authors. According to the press release of the (COP-4) May9, 2009 resolution (http://chm.pops.int/Convention/Pressrelease/COP4Geneva9May2009/tabid/542/language/en-US/Default.aspx), thecompounds listed in this paper were assigned as follows: PFOS, itssalts, and PFOSF - Annex B, pentabromodiphenyl ether - Annex A,hexabromobiphenyl - Annex A, chlordecone - Annex A, pentachlo-robenzene - Annex A and Annex C, lindane - Annex A, R- and�-hexachlorocyclohexane - Annex A.

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Published on Web 06/08/2009

coefficient (Kow) values, and relatively low bioaccumulationpotential (2). Despite these differences, the StockholmConvention POPs Review Committee (POPRC) consideredPFOS to meet the criteria of a POP after assessing itsenvironmental properties during the initial screening stage(Annex D, (5)), the risk profile (Annex E, (6)), and riskmanagement evaluation (Annex F, (7)), whereby the com-mittee recommended that perfluorooctane sulfonic acid(PFOSH), its salts and the main production intermediate,perfluorooctane sulfonyl fluoride (PFOSF), be listed in theSC. The choice of PFOSH was mainly due to the lack ofdesignated CAS number for the PFOS anion, and it wasthought that inclusion of PFOSF would incorporate most ofthe precursors as PFOSF is used as starting chemical forsynthesizing PFOS chemicals. The inclusion of PFOS will beup for vote at the fourth meeting of the Conference of Partiesin May 2009 (see link in Editor’s Note above).

Production ConsiderationProduction volume and use profiles are important assessmentcriteria for a suspected POP; high production volume of apersistent industrial chemical that can be readily releasedinto the environment will ultimately lead to widespread globaldistribution at high concentrations, while low productionvolume is likely to have a lesser global impact. The actualproduction of PFOS chemicals is still unclear due to anabsence of proper registration of current PFOS stockpilesand production in many countries. There is also confusionas to whether some of the reported amounts relate to PFOSalone, to PFOSF, or to combined PFOS-related substances.A standardization of terminology for reporting PFOS andrelated substances is therefore warranted. The commercialproduction of PFOS chemicals began over half a centuryago, and total production (mainly as PFOSF) from 1970 to2002 was estimated to be ∼100,000 t (3). By 2003, PFOSchemicals were no longer manufactured by 3M, the mainU.S. producer. However, due to important uses in specializedindustrial processes without suitable replacementsssemiconductors, medical devices, aviation, metal plating,pest control, and photographic processessproduction ofPFOS is still ongoing in other countries, though to a muchsmaller extent than previous to 2003 (7). Interestingly, aslegislation has become stricter for PFOS products in devel-oped countries, there has been a production shift to othercountries with less robust environmental regulations. For

example, companies in China fittingly began large scaleproduction in 2003 at the advent of 3M’s phase out, havingan annual production in 2004 of <50 t, but have increaseddrastically in recent years: estimated >200 t in 2006, of which100 t was designated for export (8).

Stricter regulations within countries with historical pro-duction or use of PFOS and PFOA (which is also facing asimilar phase out process) cause companies to take pre-cautionary steps in assessing cost benefit against potentialpublic risks. These kinds of regulatory environment andprecautious reasoning have, largely, still not reached de-veloping or transition countries as the majority are stilladopting the “grow first, clean up later” principle for thesake of domestic economic growth. The economic lossesfollowing a ban on PFOS would probably be large to affectedindustries, not to mention the extensive investment and time-consuming efforts that might be needed for current producersand downstream users to develop and implement substitu-tions. However, an economic argument is likely to be viewedas unacceptable by many regulatory bodies of developedcountries due to the environmental concerns of PFOS. Manyof those principal companies with phased out PFOS or PFOAproduction have more or less already developed and startedcommercializing alternative chemicals and are also employ-ing new PFC emission reduction technologies in theirfactories (9). One of the problems to tackle with an (eventual)inclusion of PFOS in the SC, is(/would be) how to formulate

FIGURE 1. General overview of the processes for adding new POPs into the Stockholm Convention on POPs and the interactionsbetween the convention secretariat, the persistent organic pollutants review committee (POPRC), and the parties of the convention.Adapted from (44). Time frame from nomination to final submission of proposal to the Conference of Parties for decision is estimatedto be minimum three and a half years.

FIGURE 2. Chemical structure of relevant PFCs: (a) potassium saltof perfluorooctane sulfonate (PFOS); (b) perfluorooctylsulfonylfluoride (POSF); (c) N-ethyl perfluorooctanesulfonamide (sulfur-amid); (d) perfluorobutane sulfonate (PFBuS), (e) perfluorooctanoicacid (PFOA).

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appropriate support on capacity building to those affecteddeveloping countries in transition to suitable alternatives,and how willing the leading PFC industries are to share theirknowledge.

Toxicity and Human Risk AssessmentPFOS is well absorbed orally with relatively slow elimination.It mainly distributes in the blood serum and the liver andbinds to proteins rather than to fatty lipids unlike other POPs(4). Ecotoxicological studies have shown that PFOS exhibitslow to moderate acute toxicity to aquatic life forms (2). Someof the observed adverse end points on laboratory animalsfollowing PFOS exposure include decreased body weight,enlarged liver, hepatotoxicity, decreased serum cholesterollevels, teratogenicity, neurotoxicity, induced peroxisomeproliferation, and endocrine disruption, but no direct geno-toxicity was found (4, 10). Recent findings suggest thatenvironmentally relevant levels can also affect immunefunctions in animals (11). Furthermore, PFOS might alsointeract with other molecules in chemical mixtures. Forexample, although PFOS is mostly found in extracellularspaces, its amphiphilic properties might facilitate the cellmembrane permeability of other pollutants and therebyindirectly induce adverse effects caused by these chemicals(12, 13). Although toxicological research on PFOS has beenexpanded in recent years, the potential toxic end points fromchronic exposure at environmentally relevant levels andmodes of action are still insufficiently explored.

Translating results from animal studies on PFOS to humanhealth risk is an intricate task, further complicated bydiscrepancies in results obtained among different laboratoryanimals (4). Evidently harmful effects from laboratory studiesoften occur at levels that largely exceed environmentallyrelevant concentrations, except for accidental industrial oroccupational spills that might cause locally high levels.Worldwide patterns for human blood serum suggest higherlevels in developed countries and those with past and presentPFOS industries (4). Serum PFOS levels have been found todecline in recent years for the general U.S. population(currently at lower parts-per-billion levels), suggesting thatthe phase-out of PFOS chemicals by 3M has been effective(14, 15). So far, there has been no clear evidence thatoccupational exposures of PFOS lead to adverse health effectsdespite relatively high individual serum levels of 3M workersreaching parts-per-million concentrations (13, 16-19). Aconfounding animal study that received notable attentionconcerned the developmental effects of PFOS: the reproduc-tive functions of parental rats were largely unaffected at thehighest exposure group (receiving a daily dose of 3.2 mg/kgbody weight), but all first generation offspring died within2 d of birth, and about one-third of offspring died within 4 dof birth at half the dose (20). However, clinical and epide-miological studies on the general human population have sofar given inconclusive results. While some studies foundcorrelation between PFOS levels and natal factors such asbirth weight, others did not find corresponding associations(16). A recently published pilot study found that the decreasein sperm quality for a small cohort of young men wascorrelated with higher serum levels of PFOS and PFOA, butthe results would have to be further confirmed by studyinga larger cohort (21). Human elimination half-life has beenestimated to be approximately 5 yr, which is much slowerthan the 100 d for laboratory rats and 100-200 d forcynomolgus monkeys, further pointing out the difficulties inextrapolating results from animal studies to humans (4, 22).

Model estimations, based on published data, indicate thathuman exposure of PFOS mainly derives from food consump-tion and ingestion/inhalation of dust containing PFOS releasedfrom treated or contaminated products (23). Preliminary

assessments estimated the human exposure doses to be in therange 3.9-520 ng/(kg ·d) for different age and gender groupsin a generalized western population, although the intermediatedoses were ∼15-33 ng/(kg ·d) (24). However, limited availabledata and large uncertainty in the calculations involving sources,environmental fate, degradation mechanisms, pharmacoki-netics, and exposure patterns of the general population anddifferent subgroups (especially children) (25), makes it pre-mature to properly assess the risks, and hinders the installmentof proper governmental regulations.

Based on available research, we view that the currentinformation on toxicity and adverse health effects in humansis largely incomplete and too inconclusive to warrant animmediate global action against PFOS. However, the currenthealth concern was deemed by the POPRC to be sufficient tojustify listing of PFOS, partly in reference to the precautionaryapproach as stated in principle 15 in the Rio Declaration:“[w]here there are threats of serious or irreversible damage,lack of full scientific certainty shall not be used as a reason forpostponing cost-effective measures to prevent environmentaldegradation” (26). The inclusion of the precautionary principlein an operational manner is one of the most significant aspectsof the SC and provides a relatively solid foundation for thePOPRC when assessing nominated substances (27). One ofthe disagreements within the scientific community and amongthe stakeholders is to what extent PFOS can cause threats ofserious or irreversible damage.

Regulatory Frameworks and GuidelinesThe EPA has included PFOS into its significant new use rule(SNUR, (28)) to regulate its usage. The EU has already imposedsevere restrictions and banned the marketing and use (withcertain exemptions) of products that exceed 0.005-0.1%PFOS by mass under its directives (29). Canada has includedPFOS in their “virtual elimination” list (30). These regulationswill probably have minor impact on the market withincountries with discontinued production and phased outusage of PFOS chemicals, but would impact regions withrecently developed production and downstream usage, suchas the textile industry in China (31).

There are currently no existing national regulationsconcerning PFOS in drinking water or foodstuffs, althougha few agencies have issued guidelines on recommendedmaximum allowable levels. The Minnesota Department ofHealth issued a health risk limit value of 0.3 µg PFOS/L indrinking water (32), whereas in Germany, the Drinking WaterCommission of the Ministry of Health deduced a tentativeTolerable Daily Intake (TDI) of 100 ng/kg body weight (25).The European Food Safety Authority (EFSA) proposed a TDIof 150 ng/kg body weight, and it is noted that the currentexposure of PFOS to the general population is well below theTDIs and not likely to promote adverse effects (25, 33).

Further PerspectivesThe negotiations leading to the original framework of the SCwere lively, with debates concerning the adoption of theprecautionary principle, financial mechanisms, and futureaddition of suspected POPs into the Convention, all of whichculminated in compromising resolutions between opposingviews (27, 34). During COP-4, PFOS was(/will be) reviewedtogether with a handful of other suspected POPs: commercialmixtures of penta- and octabrominated diphenyl ethers(PBDEs), hexabromobiphenyl, chlordecone, pentachloroben-zene, lindane, and alpha- and beta-hexachlorocyclohexane(see Editor’s Note at beginning). These chemicals will be thefirst batch to be considered for inclusion since the original“Dirty Dozen”, and will be a test of the process of addingnew POPs to the SC. The practice of the precautionaryprinciple during the screening processes is not unique to

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PFOS; the POPRC considered that lack of conclusive infor-mation on the long-range transportation properties ofchlordecone, a pesticide, should not prevent its inclusion.However, a distinction is that all known production ofchlordecone has been ceased for several years (35).

Although it is apparent that global large-scale productionof PFOS products is no longer a feasible option, many of thecurrent replacements are just shorter chained PFCs (9).Substitutes, such as perfluorobutane sulfonate (PFBuS), areconsidered less bioaccumulative (36, 37) and preliminarilyfound to be less adverse than PFOS, but research regardingtheir potential toxicity is still limited (38, 39), and the modeof (bio)action might be different from that of PFOS. Para-doxically, PFOS-based firefighting foams were one of thealternative replacements to halon-based fire extinguishersthat were phased out following the Montreal Protocol onSubstances that Deplete the Ozone Layer. Sulfuramid, whichcan degrade to PFOS, is used as an alternative to chlordaneand mirex (both listed in the SC) for ant and termite control,especially in severely affected countries such as China andBrazil (40, 41). The lack of sufficient resources to enactenvironmental laws and regulations in these countries alreadyrepresents a major obstacle, and these recurring bans mightintimidate domestic industry stakeholders to hesitate beforeinvesting or acquiring licenses for new replacements oralternative technologies.

It is also perceived that some parties without a currenteconomic stake seem to readily approve inclusion, whereasother parties with production uses may be more cautiousabout restrictive measures (42). (Although it is currentlyunclear) how PFOS is(/would be) listed in the SC, (whether)in Annex (A or) B, several options have been discussed andexplored (43). (Upon assessing the inclusion of PFOS into[Annex B of] the SC), we advise the parties to take into accountthe current relatively low production amount and highimportance of PFOS in certain specialized industrial ap-plications, where no suitable replacements are available inthe foreseeable future. We further recommend that the partiesof the SC actively communicate in finding a coherent solution.The fundamental principle of the Stockholm Convention isto protect the environment and human health, but the finalfate of PFOS is also likely to be the subject of political andeconomical debates (40).

Thanh Wang is a Ph.D. candidate at the State Key Laboratory ofEnvironmental Chemistry and Ecotoxicology, Research Center forEco-Environmental Sciences, part of the Chinese Academy ofSciences. Yawei Wang is an associate professor in the same laboratoryand works on the environmental fate and bioaccumulation ofemerging organic chemicals such as PBDEs and PFOS. ChunyangLiao is currently an associate professor at the Yantai Institute ofCoastal Zone Research for Sustainable Development, ChineseAcademy of Sciences. His research focuses on the in vivo and in vitroecotoxicological effects of environmental pollutants such as PFOS.Yaqi Cai is a professor at the State Key Laboratory of EnvironmentalChemistry and Ecotoxicology, and his field of research includesanalytical method development and environmental monitoring ofemerging pollutants. Professor Guibin Jiang is the Director of theState Key Laboratory of Environmental Chemistry and Ecotoxicology.His broad research areas include analytical methodology and theenvironmental fate and toxicological effects of persistent organicchemicals, organometallic compounds, and nanomaterials. Addresscorrespondence about this article to gbjiang@rcees.ac.cn.

AcknowledgmentsAll authors declare they have no potential competing financialinterest. The views expressed in this paper are those of theauthors and do not necessarily reflect the views or policiesof any stakeholders or funding agencies.

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