Abstract  This document presents background information and justification for the Integrated Risk Information System (IRIS) Summary of the hazard and dose-response assessment of dichloromethane. 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). Reference values are generally derived for chronic exposures (up to a lifetime), but may also be derived for acute (.24 hours), short-term (>24 hours up to 30 days), and subchronic (>30 days up to 10% of lifetime) exposure durations, all of which are derived based on an assumption of continuous exposure throughout the duration specified. Unless specified otherwise, the RfD and RfC are derived for chronic exposure duration. The carcinogenicity assessment provides information on the carcinogenic hazard potential of the substance in question and quantitative estimates of risk from oral and inhalation exposure may be derived. The information includes a weight-of-evidence judgment of the likelihood that the agent is a human carcinogen and the conditions under which the carcinogenic effects may be expressed. Quantitative risk estimates may be derived from the application of a low-dose extrapolation procedure. If derived, the oral slope factor is a plausible upper bound on the estimate of risk per mg/kg-day of oral exposure.

Abstract  The purpose of this document is to establish the basis for a PHG for DCM in drinking water. DCM is a synthetic volatile chemical without known natural sources. The production of DCM exceeds 200 million pounds annually in the United States (U.S.) and it is used in more than ten industries. In 1993, the U.S. EPA characterized DCM as the third most commonly used halogenated solvent based on 1991 data. DCM is used principally as a solvent in the removal of paint and grease; as a propellant for aerosolizing paints, automotive products, and insect sprays; and as a process solvent in the manufacture of foam polymers, pharmaceuticals and photographic film coatings. Other major uses are as a cleaner in electronic manufacturing, a degreening agent for citrus fruits, and a blowing agent in the production of urethane foam. Sources of DCM contamination in drinking water are mainly discharges from pharmaceutical and chemical factories. DCM has been detected in finished and raw water supplies in the U.S., and in groundwater wells used as drinking water sources in California at median concentrations ranging from 0.7 to 10 mg/L ppb).

Abstract  In Canada, approximately 13.2 kilotonnes of dichloromethane are used annually, in such applications as paint removal, as a blowing agent in foam production, and as a component in aerosols. Due to its volatility and the dispersive nature of its uses, the majority of dichloromethane used may be released into the environment, primarily the atmosphere. Dichloromethane has been measured in indoor air, outdoor air, and surface waters across Canada. Based on these considerations, it has been concluded that dichloromethane occurs at concentrations that may be harmful to the environment, and that may constitute a danger in Canada to human life or health. It has been concluded that dichloromethane occurs at concentrations that do not constitute a danger to the environment on which human life depends. (Copyright (c) Minister of Supply and Services Canada 1993.)

Abstract  Acceptable exposure limits for methylene-chloride (75092) (MC) were investigated. Twenty human volunteers were exposed to 50, 100, 250, and 500 parts per million (ppm) MC vapor for 1, 3, and 7.5 hours per day, 5 days per week for up to 6 weeks. At various times before and after exposure, the subjects underwent complete medical examinations, including determinations of urinary urobilinogen, alveolar MC and carbon-monoxide (CO), blood carboxyhemoglobin (COHb), neurological function, pulmonary function, blood biochemistry, and cognitive testing. Alveolar MC concentrations correlated with duration and degree of exposure. The persistence of alveolar MC was also correlated to degree of exposure. No accumulation of MC with repeated exposure was evident. Results of alveolar CO measurements were not reported. MC caused significant, dose related increases in blood COHb. COHb continued to increase for up to 2 hours after exposure. The biological half life was twice as long as that reported for COHb produced by exposure to CO. MC exposure did not affect the functional integrity of the airways, alveolar capillary gas exchange, or pulmonary ventilation. Increases in hemoglobin affinity for oxygen were associated with the increased COHb values. No significant MC related changes in neurologic function or cognitive ability were recorded. The authors conclude that the threshold limit value for MC should be set at 50ppm to avoid excessive COHb body burdens. Breath analysis for MC or its metabolite, CO, provides an excellent test for determining the magnitude of exposure, and can be used as a Biological Threshold Limit measurement for exposed workers.

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)