Two-generation reproductive toxicity study of inhaled acrylonitrile vapors in Crl:CD(SD) rats

Acrylonitrile induction of rodent neoplasia: Potential mechanism of action and relevance to humans

Acrylonitrile, an industrial chemical, is a multisite carcinogen in rats and mice, producing tumors in four tissues with barrier function, that is, brain, forestomach, Zymbal’s gland, and Harderian gland. To assess mechanism(s) of action (MoA) for induction of neoplasia and to evaluate whether the findings in rodents are indicative of human hazard, data on the potential key effects produced by acrylonitrile in the four rodent target tissues of carcinogenicity were evaluated. A notable finding was depletion of glutathione in various organs, including two target tissues, the brain, and forestomach, suggesting that this effect could be a critical initiating event. An additional combination of oxidative DNA damage and cytotoxic effects of acrylonitrile and its metabolites, cyanide, and 2-cyanoethylene oxide, could initiate pro-inflammatory signaling and sustained cell and tissue injury, leading to compensatory cell proliferation and neoplastic development. The in vivo DNA-binding and genotoxicity of acrylonitrile has been studied in several target tissues with no compelling positive results. Thus, while some mutagenic effects were reported in acrylonitrile-exposed rodents, data to determine whether this mutagenicity stems from direct DNA reactivity of acrylonitrile are insufficient. Accordingly, the induction of tumors in rodents is consistent primarily with a non-genotoxic MoA, although a contribution from weak mutagenicity cannot be ruled out. Mechanistic data to support conclusions regarding human hazard from acrylonitrile exposure is weak. Comparison of metabolism of acrylonitrile between rodents and humans provide little support for human hazard. Three of the tissues affected in bioassays (forestomach, Zymbal’s gland, and Harderian gland) are present only in rodents, while the brain is anatomically different between rodents and humans, diminishing relevance of tumor induction in these tissues to human hazard. Extensive epidemiological data has not revealed causation of human cancer by acrylonitrile.

Facing the key workplace challenge: assessing and preventing exposure to nanoparticles at source

Nanomaterials present new challenges to understanding, predicting, and managing potential health risks in occupational environments. In this study, we characterize the key physical processes related to formation and growth of nanoparticles. The main focus is on various occupational environments, as these are known to be major environments with nanoparticles in indoor air. The protection of people potentially to be exposed to nanoparticles is one of the key issues in terms of risk assessment and prevention. Two of the main protection techniques that are discussed and characterized are ventilation and filtration, which are widely used in practical applications.

Weight-of-the-evidence review of acrylonitrile reproductive and developmental toxicity studies

Risk assessment of acrylonitrile (AN) toxicity to humans has focused on potential carcinogenicity and acute toxicity. Epidemiological studies from China reported reproductive and developmental effects in AN workers, including infertility, birth defects, and spontaneous abortions. A weight-of-the-evidence (WoE) evaluation of the AN database assessed study strength, characterized toxicity, and identified no-observed-adverse-effect levels (NOAELs). The epidemiological studies do not demonstrate causality and are not sufficiently robust to be used for risk assessment. Rodent developmental studies showed fetotoxicity and malformations at maternally toxic levels; there was no unique developmental susceptibility. NOAELs for oral and inhalation exposures were 10 mg/kg/day and 12 ppm (6 h/day), respectively. Drinking-water and inhalation reproductive toxicity studies showed no clear effects on reproductive performance or fertility. Maternally toxic concentrations caused decreased pup growth. The drinking-water reproductive NOAEL was 100 ppm (moderate confidence due to study limitations). The inhalation exposure reproductive and neonatal toxicity high confidence NOAEL was 45 ppm (first generation 90 ppm) (6 h/day). The inhalation reproductive toxicity study provides the most robust data for risk assessment. Based on the WoE evaluation, AN is not expected to be a developmental or reproductive toxicant in the absence of significant maternal toxicity.

Derivation of noncancer reference values for acrylonitrile

Dose-response assessments were conducted for the noncancer effects of acrylonitrile (AN) for the purposes of deriving subchronic and chronic oral reference dose (RfD) and inhalation reference concentration (RfC) values. Based upon an evaluation of available toxicity data, the irritation and neurological effects of AN were determined to be appropriate bases for deriving reference values. A PBPK model, which describes the toxicokinetics of AN and its metabolite 2-cyanoethylene oxide (CEO) in both rats and humans, was used to assess the dose-response data in terms of an internal dose measure for the oral RfD values, but could not be used in deriving the inhalation RfC values. Benchmark dose (BMD) methods were used to derive all reference values. Where sufficient information was available, data-derived uncertainty factors were applied to the points of departure determined by BMD methods. From this assessment, subchronic and chronic oral RfD values of 0.5 and 0.05 mg/kg/day, respectively, were derived. Similarly, subchronic and chronic inhalation RfC values of 0.1 and 0.06 mg/m(3), respectively, were derived. Confidence in the reference values derived for AN was considered to be medium to high, based upon a consideration of the confidence in the key studies, the toxicity database, dosimetry, and dose-response modeling.