Widespread exposure to several per/polyfluorinated alkyl substances (PFAS) is associated with a wide array of toxicities. The National Toxicology Program (NTP) conducted 28-day toxicity studies in male and female Sprague Dawley (Hsd:Sprague Dawley SD) rats (n = 10/dose; five doses) to compare the toxicities of seven PFAS chemicals (three sulfonic acids or salt: perfluorobutane sulfonic acid, perfluorohexane sulfonate potassium salt, and perfluorooctane sulfonic acid; and four carboxylates: perfluorohexanoic acid [PFHxA], perfluorooctanoic acid [PFOA], perfluorononanoic acid [PFNA], and perfluorodecanoic acid [PFDA]) via gavage in deionized water with 2% Tween 80. This report describes the studies of the four carboxylates (PFHxA, PFOA, PFNA, and PFDA); a companion report (NTP Toxicity Study Report 96) describes the studies of the three PFAS sulfonates. Doses were 0 to 1,000 mg/kg/day for PFHxA, 0 to 10 mg/kg/day for PFOA males, 0 to 100 mg/kg/day for PFOA females, 0 to 10 mg/kg/day for PFNA males, 0 to 25 mg/kg/day for PFNA females, and 0 to 2.5 mg/kg/day for PFDA.
A peroxisome proliferator-activated receptor alpha (PPARα) agonist (Wyeth-14,643) was used at a dose of 0 to 25 mg/kg/day for qualitative comparison to the PFAS evaluated. These studies evaluated clinical pathology, thyroid hormones, liver expression of PPARα- (Cyp4a1, Acox1) and constitutive androstane receptor (CAR) related genes (Cyp2b1, Cyp2b2), liver acyl-CoA oxidase enzyme activity (males only), plasma and liver (males only) concentrations, and histopathology.
There was no effect on survival in animals administered PFHxA, PFOA, or PFDA, but treatment-related reduced survival was observed in males and females administered PFNA. Lower body weights were observed in male rats treated with PFHxA, PFOA, PFNA, and PFDA; lower body weights were also observed in females administered PFNA and PFDA. Plasma and liver concentrations normalized to dose were generally higher in animals administered the longer-chain PFAS. PFHxA and PFOA females had lower plasma concentrations than did males when normalized to dose. Common findings across two or more of the PFAS presented in this report included increased liver weights (absolute and relative to body weight); increased Acox1, Cyp4a1, Cyp2b1, and Cyp2b2 expression; and increased acyl-CoA oxidase activity. Clinical chemistry endpoints were altered in several PFAS, including increased liver enzyme activities (aspartate aminotransferase, alkaline phosphatase, alanine aminotransferase, and sorbitol dehydrogenase); decreased globulin and cholesterol concentrations; and increased total bile acids and direct bilirubin concentrations. PFHxA male and female rats had a dose-dependent hypochromic, macrocytic, regenerative decrease in the red blood cell mass characterized by a decrease in erythrocyte count, hemoglobin concentration, and hematocrit with an increase in reticulocyte counts. In most PFAS, total thyroxine (T4) and free T4 were decreased with no compensatory increase in thyroid stimulating hormone. Histopathologic findings observed in more than one PFAS were in the liver (hepatocyte hypertrophy, hepatocyte cytoplasmic alteration, and hepatocyte necrosis), nose (olfactory epithelium degeneration and hyperplasia), bone marrow (hypocellularity), thymus (atrophy), testes (germinal epithelium degeneration, interstitial cell atrophy, and spermatid retention), and epididymis (exfoliated germ cell).
PFHxA, PFNA, and PFDA were negative in bacterial mutagenicity tests; PFOA was equivocal in bacterial mutagenicity tests. In vivo, no increases in micronucleated reticulocytes were seen in male or female rats exposed to PFHxA, PFNA, or PFDA; a small increase in micronucleated reticulocytes was observed in male rats exposed to PFOA.
In general, the effects in male and female rats administered PFHxA were of lower magnitude (e.g., liver or clinical pathology findings) or not apparent compared to the effects in animals exposed to PFNA or PFDA. Several of the effects observed in the liver were also observed in Wyeth-14,643 animals, but some extrahepatic effects were not observed with Wyeth-14,643, suggesting that PFAS chemicals induce toxicity by a variety of pathways apart from PPARα. These data provide a basis for comparisons across the PFAS class, either using external (e.g., mol/kg/day) or internal (e.g., plasma µM) dose.
National Toxicology Program (NTP). 2022. NTP technical report on the toxicity studies of perfluoroalkyl carboxylates (perfluorohexanoic acid, perfluorooctanoic acid, perfluorononanoic acid, and perfluorodecanoic acid) administered by gavage to Sprague Dawley (Hsd:Sprague Dawley SD) rats (revised). Research Triangle Park, NC: National Toxicology Program. Toxicity Report 97. https://doi.org/10.22427/NTP-TOX-97