Abstract  This document presents background information and justification for the Integrated Risk Information System (IRIS) Summary of the hazard and dose-response assessment of carbon tetrachloride. IRIS Summaries may include oral reference dose (RfD) and inhalation reference concentration (RfC) values for chronic and other exposure durations, and a carcinogenicity assessment. The RfD and RfC, if derived, provide quantitative information for use in risk assessments for health effects known or assumed to be produced through a nonlinear (presumed threshold) mode of action. The RfD (expressed in units of mg/kg-day) is defined as an estimate (with uncertainty spanning perhaps an order of magnitude) of a daily exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. The inhalation RfC (expressed in units of mg/m3) is analogous to the oral RfD, but provides a continuous inhalation exposure estimate. The inhalation RfC considers toxic effects for both the respiratory system (portal of entry) and for effects peripheral to the respiratory system (extrarespiratory or systemic effects).

Abstract  To determine if there is an association between occupational exposure to external ionizing radiation and leukemia mortality among civilian Portsmouth Naval Shipyard workers after potential confounders and effect modifiers such as solvent exposure, and time since exposure are considered. This study employs a nested case-control design and includes 115 leukemia cases and 460 controls. Among the cases and controls, 201 (35%) were monitored for radiation exposure. Badge doses and exposures to work-required medical x-rays were included in the analysis. Benzene and carbon tetrachloride exposure was assessed using workers' job information and industrial hygiene records. Conditional logistic regression was used to analyze the exposure-response relationship between external ionizing radiation exposure and leukemia mortality. A significant positive association was found between leukemia mortality and external ionizing whole-body radiation exposure (OR= 1.08 at 10 mSv; 95% CI=1.01, 1.16) adjusting for gender, radiation worker status and solvent exposure duration.

Abstract  The neurotoxic effects of organic solvents are reviewed. Organic solvents have been used in extraction, dissolution or suspension of fats, waxes and resins. Studies have shown that acute neurotoxicity is similar for human and laboratory animal exposures and is characterized by narcosis, anesthesia, central nervous system depression, respiratory arrest, loss of consciousness and death. Chronic effects have been studied to a limited extent in animals and have been documented epidemiologically for workers and solvent abusers. Reported effects included peripheral neuropathy and mild toxic encephalopathy. Three severity levels were defined for chronic human exposures: minimal, organic affective syndrome; moderate, mild, chronic toxic encephalopathy; and pronounced, severe, chronic toxic encephalopathy. Neurophysiological effects (electromyogram or electroencephalogram abnormalities, decreased nerve conduction velocities) have also been reported in exposed workers. Neurobehavioral effects such as reversible subjective symptoms, prolonged personality or mood changes and intellectual impairment have been studied epidemiologically and in volunteers. Severe exposure has produced irreversible impairment of intellect and memory (dementia) and structural central nervous system damage. Metabolic aspects of organic solvent exposure were discussed. Guidelines for minimizing worker exposure are discussed in relation to exposure monitoring; control of exposure through contaminant control, worker isolation, use of personal protective equipment and worker education; and medical surveillance. A table containing a summary of NIOSH recommended exposure limits for organic solvents is presented. Examples of solvents neurotoxic to humans discussed include carbon-disulfide (75150), n-hexane (110543), methyl-n-butyl-ketone (591786), trichloroethylene (79016), perchloroethylene (127184) and toluene (108883)