Urgent research needs for better understanding the toxicity of PFASs

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1 Urgent research needs for better understanding the toxicity of PFASs Jamie DeWitt Department of Pharmacology & Toxicology Brody School of Medicine East Carolina University Greenville, NC Presented for: Northeast Superfund Research Program Meeting April 5, 2017

2 Site-specific studies of PFAS serum concentrations and human health effects in the U.S. Sources: Vieira et al., 2013, Environmental Health Perspectives, 121: ATSDR Public Health Assessment for PFC Contamination in Lake Elmo and Oakdale, Washington County, Minnesota, 2008.

3 (Some) Associations reported between serum PFAS concentrations and human health outcomes Immune suppression reduced responses to vaccinations High cholesterol Cancer - kidney and testicular Pregnancy and development complications (ADHD/behavioral) Autoimmune-related diseases Thyroid Disease These findings are diverse. Are there underlying modes or mechanisms common to these findings? Do we need mechanism of action to make decisions about these compounds?

4 PFOA and PFOS??

5 Activation of the peroxisome proliferator activated receptor alpha (PPARα) Activity for mouse and human PPARα in transfected COS-1 cells: PFOA > PFOS (Wolf et al., 2008). Alteration of in vitro cytokine release is PPARα-dependent for PFOA but not for PFOS (Corsini et al., 2011), but some PFOS in vitro cytokine release is PPARαdependent (Mollenhauer, 2008). PFOA is dependent on PPARα for developmental toxicity in 129S1 mice (Abbott et al., 2007), PFOS is not (Abbott et al., 2009). Antigen-specific antibody production is PPARαindependent in C57BL/6 mice (DeWitt et al, 2016). Is PPARα a sufficient and consistent mechanism for all toxicities? All PFASs?

6 PPARα activation is not the only mode/mechanism Endocrine disruption, especially modulation of reproductive hormone pathways and thyroid hormones. Direct cytotoxicity. Oxidative stress and damage, leading to cytotoxicity. Can mechanism be used as the basis of comparison? For screening? For prioritization? Will it pay off to spend time and effort identifying a common mechanism? Is one necessary?

7 PFASs are themselves diverse with diverse uses. Can we use chemistry to understand toxicity? By class? By chain length? By functional group? By chemical constituent? Other factors? Do these impact mechanism? Source of figure: Buck et al., 2011, Integrated Environmental Assessment and Management, 7:

8 Some of the non-polymer PFASs Class Perfluoroalkyl substances Polyfluoroalkyl substances Examples PFAAs: Perfluoroalkyl carboxylic acids and perfluoroalkyl carboxylates (PFCAs) Perfluoralkane sulfonic acids and perfluoroalkane sulfonates (PFSAs); PASFs: Perfluoroalkane sulfonyl fluorides; FASAs: Perfluoroalkane sulfonamides; PAFs: Perfluoroalkanoyl fluorides; PFAIs: Perfluoroalkyl iodides; PFALs: Perfluoroalkyl aldehydes FASEs, FASAAs, MeFASA/E/As, EtFASA/E/As, BuFASA/E/As: Perfluoroalkane sulfonamido substances; Fluorotelomer substances: Numerous compounds, including flurotelomer iodides, olefins, alcohols, acrylates, aldehydes, carboxylic acids, and sulfonic acids; Miscellaneous: Polyfluoroalkyl ether carboxylic acids Surfactants Raw materials for surfactants and surface protection products Raw material for PFOA (PAFs) as well as for surfactants and surface protection products Surfactant and surface protection products (specific fluorotelomer substances) Ski wax and medical applications (semifluorinated n-alkanes and alkenes) Intermediate environmental transformation products (various) Source: Buck et al., 2011, Integrated Environmental Assessment and Management, 7:

9 Polymer PFASs side-chain fluorinated polymers -C n F 2n+1 side chains Fluorinated acrylate and methacrylate polymers Fluorinated urethane polymers Fluorinated oxetane polymers Surfactant and surface protection products Synthesis of these agents involves incorporation of one or more PFASs as monomers, which creates the potential for degradation of the polymer during or after its useful lifetime (Buck et al., 2011). Manufacture of polymer PFASs requires a PFAS as a processing aid. Environmental PFAS release therefore is possible during processing and during or after their lifetimes. How should these substances be evaluated toxicologically? As the parent or as the (potential) contaminants/breakdown product(s)? Source: Buck et al., 2011, Integrated Environmental Assessment and Management, 7:

10 PFOA and PFOS, the legacy PFAAs (C8s) Perfluorooctanoic acid (PFOA) Cancer, immunotoxicity, and behavioral changes reported in epidemiological studies. Reported toxicities in animal models = cancer (liver, pancreatic, and testicular), developmental effects, immunotoxicity, liver, and kidney toxicity. Perfluorooctane sulfonate (PFOS) Reported toxicities in animal models = developmental effects, liver toxicity, and serum lipid alterations, and neurotoxicity. Human studies support associations between serum levels and serum lipids and possibly developmental effects, endocrine disruption, and immunotoxicity. Source of images: ChemSpider.com

11 Are differences in functional group sufficient to explain differences in toxicity?

12 Short(er) chain length PFASs Perfluorobutane sulfonate (PFBS; C4) Estimates of serum half-lives: < 5 hours in rats; ~4 days in monkeys; ~28 days in humans. Faster than PFOA and PFOS. Ability to activate mouse PPARα < PFOA and PFOS. Ability to activate human PPARα < PFOA and > PFOS. Perfluorohexane sulfonate (PFHxS; C6) Estimates of serum half-lives: ~20-30 days in rats and mice; ~100 days in monkeys; 8.5 years in humans. May be a sex difference in rodents and monkeys. About the same or slower than PFOA and PFOS. Ability to activate mouse PPARα < PFOA and > PFOS. Ability to activate human PPARα < PFOA and > PFOS. Source of images: ChemSpider.com. Source of data: C. Lau Perfluoroalkyl Acids & Wolf et al., 2008, Toxicol Sciences, 106:

13 Are differences in chain length sufficient to explain differences in toxicity? While persistent in the environment, PFCA chemicals with fewer than eight carbons, such as pefluorohexanoic acid (PFHxA), and PFSA chemicals with fewer than six carbons, such as perfluorobutane sulfonic acid (PFBS), are generally less toxic and less bioaccumulative in wildlife and humans.

14 2,3,3,3-tetrafluoro-2- (heptafluoropropoxy)- propanoate (polyfluorinated) Polyfluorinated PFASs Perfluorooctanoic acid (PFOA, perfluorinated) Polyfluorinated compound used to replace PFOA in some applications. Differences in accumulation and excretion may exist between male and female animals, notably mice and possibly in monkeys. Multi-system toxicant with health effects reported in myriad species, including humans. May induce some toxicities through activation of PPARα; other toxicities induced via other putative mechanisms. Classified as a 2B (possibly carcinogenic to humans) carcinogen by the IARC. Source of images: ChemSpider.com. Source of data: Rae et al., 2015, Toxicol Rep, 2: ; Gannon et al., 2016, Toxicol, 340:1-9; Rushing et al., 2008, Toxicol Sciences, epub.

15 2,3,3,3-tetrafluoro-2- (heptafluoropropoxy)-propanoate Appear to be sex differences in accumulation and elimination when given orally to experimental animal models: ½ life of about 70 hours in male and female rats (beta phase) ½ life of 37 hours in male mice & 24 hours in female mice (beta phase) [½ life of about 64 hours in male cynomologus monkeys & 80 hours in female cynomologus monkeys when given IV] Are differences in fluorine substitution sufficient to explain differences in toxicity? Source of data: Gannon et al., 2016, Toxicol, 340:1-9.

16 Polymer versus non-polymer PFASs Fluorotelomer-based polymers (FTPs) >80% of all fluorotelomerbased raw materials worldwide. May be precursors to PFAAs, especially carboxylate PFAAs such as PFOA. In rats, a flurotelomer-based urethane polymeric product induced hepatotoxicity in a 90-day oral study and reduced thyroid weights in F1 offspring in a developmental study. Perfluorooctanoic acid (PFOA) Multi-system toxicant with health effects reported in myriad species, including humans. May induce some toxicities through activation of PPARα; other toxicities induced via other putative mechanisms. Classified as a 2B (possibly carcinogenic to humans) carcinogen by the IARC. Source of images: ChemSpider.com. Source of FTP data: Rankin et al., 2011, ES&T, 48: ; Stadler et al., 2008, Drug & Chemical Toxicol, 31:

17 Are differences in chemical substituent sufficient to explain differences in toxicity? Weight-of-evidence is sufficient for PFOA and PFOS, but insufficient for nearly all other PFASs. What is the best research path forward for these diverse and numerous compounds?

18 What do independent research scientists need?c Use and production data from industry. o Most data on environmental occurrence comes from time-consuming and labor-intensive surveys of environmental media. Standards, analytical methods, and other existing information and knowledge to accelerate research by other stakeholders. o A principle behind the REACH approach in Europe. Researchers across disciplines MUST work together. o PFASs present a challenging multidisciplinary problem that requires cooperation and collaboration of many parties. Studies of mechanism and mode. o o Adverse outcome pathways to better predict non-tested PFASs. But for what compounds? Source Wang et al., 2017, ES&T.

19 What does the future hold? The future will likely result in a greater number and diversity of PFASs and fewer resources for regulatory oversight. Reliance on toxicological data specific to PFOA and PFOS may underestimate site-specific public health risks due to the chemical diversity of these compounds. Areas highlighted in blue indicate zip codes where PFASs were detected in one or more water samples from that were at or above minimum reporting levels required by the EPA. From Hu et al., We need to find a way to prioritize compounds, sites, and toxicities and decide on mechanistic approaches.

20 Thank you! Current PFAS collaborators: Dr. Mark Strynar and Dr. Andy Lindstrom at the U.S. EPA Dr. Chris Higgins at the Colorado School of Mines Dr. Nicole Reisdorph at the University of Colorado Anschutz Medical Campus Dr. Sarah Blossom at the Arkansas Children s Research Institute