Gerald L. Kennedy

The toxicology of perfluorooctanoate.

ABSTRACT PFOA is a peroxisome proliferator (PPAR agonist) and exerts morphological and biochemical effects characteristic of PPAR agonists. These effects include increased β-oxidation of fatty acids, increases in several cytochrome P-450 (CYP450)-mediated reactions, and inhibition of the secretion of very low-density lipoproteins and cholesterol from the liver. These effects on lipid metabolism and transport result in a reduction of cholesterol and triglycerides in serum and an accumulation of lipids in the liver. The triad of tumors observed (liver, Leydig cell, and pancreatic acinar-cell) is typical of many PPAR agonists and is believed to involve nongenotoxic mechanisms. The hepatocellular tumors observed in rats are likely to have been the result of the activation of the peroxisome proliferator activated receptor α (PPARα). The tumors observed in the testis (Leydig-cell) have been hypothesized to be associated with an increased level of serum estradiol in concert with testicular growth factors. The mechanism responsible for the acinarcell tumors of the pancreas in rats remains the subject of active investigation. The mechanism resulting in the hepatocellular tumors in rats (PPARα activation) is not likely to be relevant to humans. Similarly, the proposed mechanism for Leydig-cell tumor formation is of questionable relevance to humans. Acinar tumors of the pancreas are rare in humans, and the relevance of the these tumors, as found in rats, to humans is uncertain. Epidemiological investigations and medical surveillance of occupationally exposed workers have not found consistent associations between PFOA exposure and adverse health effects.

Absorption, distribution, and excretion of ammonium perfluorooctanoate (APFO) after oral administration to various species.

Male and female mice, rats, hamsters, and rabbits were treated with a single oral dose of 14C-ammonium perfluorooctanoate (APFO), and the excretion and tissue distributions were followed for 120 h (168 h in the rabbit). Substantial sex and species differences in the excretion and disposition of 14C-radioactivity derived from 14C-labeled APFO were observed in this study. The female rat and the male hamster excreted more than 99% of the original 14C activity by 120 h after dosing; conversely, the male rat and the female hamster excreted only 39% and 60% of the original 14C activity, respectively, by 120 h postdosing. The male and female rabbits excreted the 14C activity as rapidly and completely as the female rat and the male hamster, whereas male and female mice excreted only 21% of the original 14C activity by 120 h postdosing. The rapid excretors (female rat, male hamster, and male and female rabbits) contained negligible amounts of 14C in organs and tissues at sacrifice. The slow excretors exhibited the highest 14C concentrations in the blood and liver followed by the kidneys, lungs, and skin.

Biological Effects of Acetamide, Formamide, and Their Monomethyl and Dimethyl Derivatives

The industrial use of certain acetamides and formamides (particularly DMAC and DMF) for their solvent properties has resulted in rather extensive examination of their biological properties. Both DMAC and DMF are rapidly absorbed through biological membranes and are metabolized by demethylation first to monomethyl derivatives and then to the parent acetamide or formamide. Relatively high single doses to various species following oral, dermal, i.p., i.v., or inhalation exposures generally are required to produce mortality. The liver is the primary target following acute high level exposure, but massive doses can also produce damage to other organs and tissues. Repeated sublethal treatment by various routes also shows the liver to be the target organ with the degree of damage being proportional to the amount absorbed. With MMF, the potential usefulness as a cancer chemotherapeutic agent needs to be measured against the hepatotoxic effects produced in man. Acetamides and formamides are generally inactive in mutagenicity tests. Mammalian test systems do not appear to be genetically sensitive and DMF has been recommended for use as the vehicle in microbial assays designed to test for genetic activity of hard-to-dissolve chemicals. Embryotoxicity can be demonstrated at high doses; doses which generally show toxicity to the maternal animals. Structural abnormalities in sensitive species such as the rabbit are produced following exposure at near-lethal levels. The spectrum of abnormalities seen is broad and fails to show any time or site specificity in terms of developing organs/organ systems. Inhalation exposures to DMAC and DMF at levels producing some maternal toxicity in rats have produced no teratogenic response and only slight evidence of embryotoxicity. Long-term feeding of relatively high levels of acetamide produces liver cancer in rats. DMAC and DMF appear to be noncarcinogenic. The environmental toxicity of these chemicals is low. Liver damage can be produced by overexposure to these chemicals in man. Airborne concentrations need to be controlled and care should be taken to avoid excessive liquid contact as the chemicals are absorbed through the skin. A relationship exists between the amount of DMAC or DMF absorbed and the amount of MMAC or MMF excreted in the urine so that biomonitoring of the urinary metabolites can indicate situations in which total exposures, both dermal and inhalation, are excessive. An interaction between DMF and ethanol occurs such that signs, including severe facial flushing, appear when DMF-exposed individuals consume alcoholic beverages.

Establishing aerosol exposure concentrations for inhalation toxicity studies

Criteria for the selection of aerosol concentrations to be used in inhalation studies assessing the toxicity and carcinogenicity of chemical substances were discussed by the authors in a meeting sponsored by the National Toxicology Program. Concepts in the design of aerosol inhalation studies emerged from that meeting and are being communicated through this publication. Inhalation studies assessing the toxicity and carcinogenicity of aerosols have often used maximum exposure levels on the basis of technological feasibility. Evidence has now accumulated that the amount of pulmonary burden of deposited particles impacts on particle clearance above some as yet not well-defined exposure concentration. The sequelae are such that lung clearance decreases with increased particulate burden to the point of approaching complete cessation. This paper focuses on the major determinants in establishing maximal aerosol concentrations for use in inhalation toxicity studies with special emphasis on experimental design features to assess lung retention. The subject matter of this paper is a rapidly developing area in terms of knowledge. Accordingly, the contents of this article are intended as guidelines and not as absolute rules for the conduct and interpretation of inhalation exposure studies.

Inhalation toxicity of ammonium perfluorooctanoate

Ammonium perfluorooctanoate (CAS Registry No. 3825-26-1) is a fine white powder which can become airborne; hence its inhalation toxicity was studied in the male rat. The compound was found to be moderately toxic following single 4-hr exposures, with an LC50 of 980 mg/m3. This concentration produced both an increase in liver size and corneal opacity. Both findings diminished with increasing time after exposure. Subchronic head-only inhalation exposures (6 hr/day on 5 days/wk for 2 wk to 0, 1, 8 or 84 mg/m3) suppressed body-weight gain at 84 mg/m3. Reversible liver-weight increases, reversible increases in serum enzyme activities, and microscopic liver pathology, including necrosis, occurred at exposure of 8 and 84 mg/m3. No ocular changes were produced. Concentrations of organofluoride in the blood showed a dose relationship with initial levels of 108 ppm in rats treated at 84 mg/m3 falling to 0.84 ppm after 84 days with a blood half-life of 5-7 days. The no-observed-effect level was 1 mg/m3 and a mean organofluoride blood level of 13 ppm was detected in rats immediately after the tenth exposure to an atmospheric level of 1 mg ammonium perfluorooctanoate/m3.

An investigation of the teratogenic potential of captan, folpet, and Difolatan

Abstract Three fungicides, captan, folpet, and Difolatan, were found to be nonteratogenic in two strains of rabbits that were particularly sensitive to the embryotoxic effects of thalidomide. Two metabolic products, phthalimide and tetrahydrophthalimide were also found to be nonteratogenic in the Dutch Belted rabbit. Offspring of albino rats, given the fungicides either during gestation only or over three consecutive generations, were free of abnormalities. Captan administered to the hamster throughout gestation did not produce abnormal young.

1-methyl-2-pyrrolidone (nmp): reproductive and developmental toxicity study by inhalation in the rat

A two-generation reproduction study with a developmental toxicity component was conducted. For the reproduction phase, male and female rats inhaled 0, 10, 51, or 116 ppm NMP daily for 6 hr/day, 7 days/week from 34 days of age to the end of the mating period for the males (100 exposure days) and till weaning for the females (about 143 exposure days, but interrupted from Day 20 of gestation to Day 4 Postpartum). On Day 70 postpartum, one male and one female selected from each litter later mated with newly obtained, nonexposed adults of the opposite sex to produce an F2 generation. For the developmental phase, rats of both sexes inhaled 0 or 116 ppm NMP as outlined above, but euthanization of the females occurred on Day 21 of gestation followed by fetal examination for structural alterations. The indices of reproductive performance for the NMP-exposed rats did not differ significantly from those obtained for the control rats. Rats exposed to 116 ppm had a detectable decrease in response to sound. No other signs of NMP-related toxicity were detected among the parental rats. An exposure-related but slight decrease in fetal weight was detected only among the F1 offspring whose parents both inhaled NMP at 116 ppm. This slight effect also appeared at birth among the pups of the reproductive phase where it persisted till 21 days after birth when NMP inhalation by the mother ceased. Thereafter, the body weight of the offspring was comparable to the control values. No detectable or developmental effects appeared in the 10 or 51 ppm groups.

Toxicology of Fluorine-Containing Monomers

Fluorine-containing monomers form the basis for production of a large number of commercially important polymers. Most of the polymerization occurs as gas-phase reactions, hence the hazards associated with the monomers arises primarily from inhalation. The chemicals covered in this review include bromotrifluoroethylene (BTFE), chlorotrifluoroethylene (CTFE), hexafluoroacetone (HFA), hexafluoroisobutylene (HFIB), hexafluoropropylene (HFP), perfluorobutylene (PFBE), tetrafluoroethylene (TFE), trichloropropene (TFP), vinyl fluoride (VF), and vinylidene fluoride (VF2). The amount of toxicologic information available on the compounds is relatively small and for certain of these the information consists is short-term or acute, hence the current need to make predictions of biologic activity based on analogy or chemical reactivity is great. In animal models and in man, these monomers may be absorbed into the body at varying rates and the metabolism ranges from extensive to little in a species, dose, and chemical specific fashion. The major toxicologic target of these materials is the kidney, and the degree of involvement depends greatly on the excretion patterns and metabolic profiles of the monomers. However, other target sites exist, such as the reproductive system for HFA, making the use of structure-activity relationships difficult.

Pulmonary response to inhaled Kevlar aramid synthetic fibers in rats

Groups of male rats were exposed to specially prepared ultrafine Kevlar pulp fibers (du Ponts registered trademark for certain aramid fibers) at atmospheric concentrations of either 0.1, 0.5, 3.0, or 18 mg/m3 for 2 weeks. Rats were killed at 0 and 2 weeks and 3 and 6 months postexposure (PE) except the rats exposed to 18 mg/m3, which were killed 0, 4, and 14 days and 1, 3, and 6 months PE. Another group of male rats was exposed to 18 mg/m3 (respirable dust approximately 2.5 mg/m3) of commercial Kevlar fibers for 2 weeks and were killed at 0 and 2 weeks and 3 and 6 months PE. Inhaled ultrafine Kevlar fibers were mostly phagocytized by alveolar macrophages (dust cells) in the alveolar ducts and adjoining alveoli after exposure to either 0.1 or 0.5 micrograms/m3. Most dust cells had disappeared and lungs showed a normal appearance throughout 6 months PE. The pulmonary response almost satisfied the biological criteria for a nuisance dust. Rats exposed to 3 mg/m3 ultrafine Kevlar fibers revealed occasional patchy thickening of alveolar ducts with dust cells and inflammatory cells but with no collagen fibers deposited throughout 6 months PE. After exposure to 18 mg/m3 ultrafine Kevlar, the respiratory bronchioles, alveolar ducts, and adjoining alveoli showed granulomatous lesions with dust cells by 2 weeks PE. The granulomatous lesions converted to patchy fibrotic thickening with dust cells after 1 month PE. The fibrotic lesions were markedly reduced in cellularity, size, and numbers from 3 to 6 months PE but revealed networks of reticulum fibers with slight collagen fiber deposition.

Penetration of ammonium perfluorooctanoate through rat and human skin in vitro.

Rat and human epidermal membranes were mounted onto in vitro diffusion cells with an exposure area of 0.64 cm2, and skin integrity was confirmed using electrical impedance. Following membrane selection, Fluorad FC-118, a 20% aqueous solution of ammonium perfluorooctanoate (AFPO), was applied to the epidermal surface of each skin replicate at approximately 150 µL/cm2 and the donor chamber opening occluded with Parafilm. Serial receptor fluid samples were collected hourly from 1 to 6 h and at 12, 24, 30, and 48 h and analyzed by liquid chromatography–mass spectrometry (LC-MS) for APFO anion (PFO−). For rat skin, the time to steady-state penetration (6500 ± 3000 ng APFO · cm− 2· h− 1) occurred in less than 12 h, which was sustained until termination (48 h). Based on the concentration of the applied test material, the permeability coefficient (Kp) for APFO in rat skin was calculated to be 3.25 ± 1.51 × 10− 5 cm/h. By end of the 48-h exposure period, only a small portion of the total APFO applied (1.44 ± 1.13%) had penetrated through rat skin. For human skin, steady-state penetration of APFO (190 ± 57 ng APFO · cm− 2· h− 1) was reached by 12 h. Based on the concentration of the applied test material, the permeability coefficient for APFO in human skin was calculated to be 9.49 ± 2.86 × 10− 7 cm/h. By the end of the 48-h exposure period, only a negligible amount of the total APFO applied (0.048 ± 0.01%) had penetrated through human skin. Thus, under infinite dose and occlusive conditions, the steady-state penetration of APFO from a 20% solution was approximately 34-fold faster through rat skin than human skin.