Reference concentration , inhalation

Inhalation Reference Concentration (RfC) An estimate (with an uncertainty spanning perhaps an order of magnitude) of the daily exposure of the human population to a chemical, through inhalation, that is likely to be without risk of deleterious effects during a lifetime. 

EPA. 1989c. Interim methods for development of inhalation reference concentrations. Washington,... 

EPA. 1990b. Interim methods for development of inhalation reference concentrations. Washington, DC U.S, Environmental Protection Agency, Office of Health and Environmental Assessment, Office of Research and Development, Environmental Criteria and Assessment Office. EPA600/8-90/066. 

The oral reference dose (RfD) for trichloroethylene is currently imder review by an EPA workgroup (IRIS 1996). No inhalation reference concentration (RfC) has been derived (IRIS 1996). The National Center for Environmental Assessment, EPA has begun an effort to reassess the health risks associated with trichloroethylene. 

EPA has derived both an oral reference dose (RfD) and an inhalation reference concentration (RfC) for chronic exposure to hydrogen sulfide. The RfD of 0.003 mg/kg/day is based on the NOAEL of 3.1 mg/kg/day for gastrointestinal disturbance in pigs in a study by Wetterau et al. (1964) (IRIS 1998). The NOAEL value of 3.1 mg/kg/day was divided by an uncertainty factor of 1,000 to account for interspecies extrapolation (10), sensitive individuals (10), and subchronic exposure (10) (IRIS 1998). 

EPA. 1994b. Methods for derivation of inhalation reference concentrations and application of inhalation dosimetry. EPA/600/8-90/066F October 1994. 

The Environmental Protection Agency (EPA) inhalation reference concentration (RfC) for -hexane is 0.2 mg/m3 (0.06 ppm by volume). No reference dose (RfD) has been derived for this compound (IRIS 1998). 

Reference Concentration (RfC)—An estimate (with uncertainty spanning perhaps an order of magnitude) of a continuous inhalation exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious noncancer health effects during a lifetime. The inhalation reference concentration is for continuous inhalation exposures and is appropriately expressed in units of mg/m3 or ppm. The RfC is operationally derived from the No-Observed-Adverse-Effect Level (NOAEL- from animal and human studies) by a consistent application of uncertainty factors that reflect various types of data used to estimate RfCs and an additional modifying factor, which is based on a professional judgment of the entire database on the chemical. The RfCs are not applicable to nonthreshold effects such as cancer. 

The MRL was based on a hepatic NOAEL of 3 ppm chloroform administered for 6 hours a day for 7 consecutive days to mice (Larson et al. 1994c). Female mice exposed to 100 or 300 ppm exhibited centrilobular hepatocyte necrosis and severe diffuse vacuolar degeneration of midzonal and periportal hepatocytes, while exposure to 10 or 30 ppm resulted in mild-to-moderate vacuolar changes in centrilobular hepatocytes. Decreased eosinophilia of the centrilobular and midzonal hepatocyte cytoplasm relative to periportal hepatocytes was observed at 30 ppm. Livers of mice in the 1 and 3 ppm groups did not differ significantly from control animals and were considered to be NOAELs for liver effects. The NOAEL of 3 ppm was converted to the Human Equivalent Concentration (HEC) as described in Equation 4-10 in Interim Methods for Development of Inhalation Reference Concentrations (ERA 1990b). This calculation resulted in a NOAEL hec] of 3 ppm. An uncertainty factor of 30 (3 for extrapolation from animals to humans and 10 for human variability) was applied to the NOAEL hec] value, which resulted in an MRL of 0.1 ppm. 

The EPA has no oral reference dose (RfD) or inhalation reference concentration (RfC) for any of the fuel oils. 

Oral reference doses and inhalation reference concentrations (RfDs and RfCs, respectively) for chronic noncarcinogenic health effects... 

OSHA = Occupational Safety and Health Administration PEL = permissible exposure limit ppm = parts per million REL = recommended exposure limit RfC = inhalation reference concentration RfD = oral reference dose STEL = short-term exposure limit TLV = threshold limit value TWA = time-weighted average... 

HDl has not been evaluated by the EPA for evidence of human carcinogenic potential (IRIS 1997). However, the EPA has established an inhalation reference concentration (RfC) of 1x10 mg/m for HDl (IRIS 1997). 

Foureman GL, Greenberg MM, Sangha GK, et al. 1994. Evaluation of nasal tract lesions in derivation of the inhalation reference concentration for hexamethylene diisocyanate. Inhalation Toxicology 6 341-355. 

Using Equation 4-7 and 0.0076 for RDDRi r in Table H-l (MMAD = 0.1, Sigma g = 1.4) in EPA (1990 -Interim Methods for Development of Inhalation Reference Concentrations), and correcting by the body weight ratios, the NOAEL q is calculated ... 

RfC = inhalation reference concentration RfD = oral reference dose STEL = short-term exposure limit ... 

Malsch PA, Proctor DM, Finley BL. 1994. Estimation of chromium inhalation reference concentration using the benchmark dose method a case study. Regul Toxicol Pharmacol 20 58-82. 

The human equivalent concentration (HEC) was calculated using Formula 4-11, from Interim Methods for Development of Inhalation Reference Concentrations, EPA 1990h ... 

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