title: Inhalation cancer risk assessment of cobalt metal.
abstract: Cobalt compounds (metal, salts, hard metals, oxides, and alloys) are used widely in various industrial, medical and military applications. Chronic inhalation exposure to cobalt metal and cobalt sulfate has caused lung cancer in rats and mice, as well as systemic tumors in rats. Cobalt compounds are listed as probable or possible human carcinogens by some agencies, and there is a need for quantitative cancer toxicity criteria. The U.S. Environmental Protection Agency has derived a provisional inhalation unit risk (IUR) of 0.009 per μg/m(3) based on a chronic inhalation study of soluble cobalt sulfate heptahydrate; however, a recent 2-year cancer bioassay affords the opportunity to derive IURs specifically for cobalt metal. The mechanistic data support that the carcinogenic mode of action (MOA) is likely to involve oxidative stress, and thus, non-linear/threshold mechanisms. However, the lack of a detailed MOA and use of high, toxic exposure concentrations in the bioassay (≥1.25 mg/m(3)) preclude derivation of a reference concentration (RfC) protective of cancer. Several analyses resulted in an IUR of 0.003 per μg/m(3) for cobalt metal, which is ∼3-fold less potent than the provisional IUR. Future research should focus on establishing the exposure-response for key precursor events to improve cobalt metal risk assessment.
authors.affiliation: ToxStrategies, Inc., Mission Viejo, CA, United States.
authors.forename: Mina
authors.initials: M
authors.lastname: Suh
authors.affiliation: ToxStrategies, Inc., Katy, TX, United States.
authors.forename: Chad M
authors.initials: CM
authors.lastname: Thompson
authors.affiliation: ToxStrategies, Inc., Richmond, CA, United States.
authors.forename: Gregory P
authors.initials: GP
authors.lastname: Brorby
authors.affiliation: ToxStrategies, Inc., Katy, TX, United States.
authors.forename: Liz
authors.initials: L
authors.lastname: Mittal
authors.affiliation: ToxStrategies, Inc., Mission Viejo, CA, United States. Electronic address: dproctor@toxstrategies.com.
authors.forename: Deborah M
authors.initials: DM
authors.lastname: Proctor
mesh_terms: D000818:Animals; D019985:Benchmarking; D015197:Carcinogenicity Tests / Q000379:methods* / Q000592:standards; D003035:Cobalt / Q000633:toxicity*; D004305:Dose-Response Relationship, Drug; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D019570:Inhalation Exposure / Q000009:adverse effects*; D023421:Models, Animal; D009152:Mutagenicity Tests; D009369:Neoplasms / Q000139:chemically induced* / Q000235:genetics / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects; D018570:Risk Assessment; D013045:Species Specificity; D013997:Time Factors
chemical_list: D003035:Cobalt
keywords: Benchmark dose (BMD) modeling; Cobalt metal; Inhalation unit risk (IUR); Risk assessment