Abstract  The Guidelines for Exposure Assessment describe the general concepts of exposure assessment including definitions and associated units, and by providing guidance on the planning and conducting of an exposure assessment. Guidance is also provided on presenting the results of the exposure assessment and characterizing uncertainty. Although these Guidelines focus on exposures of humans to chemical substances, much of the guidance also pertains to assessing wildlife exposure to chemicals, or human exposures to biological, noise, or radiological agents. The Guidelines include a glossary which helps standardize terminology used by the Agency in exposure assessment. They emphasize that exposure assessments done as part of a risk assessment need to consider the hazard identification and dose-response parts of the risk assessment in the planning stages of the exposure assessment so that these three parts can be smoothly integrated into the risk characterization. The Guidelines discuss and reference a number of approaches and tools for exposure assessment, along with discussion of their appropriate use. The Guidelines also stress that exposure estimates along with supporting information will be fully presented in Agency risk assessment documents, and that Agency scientists will identify the strengths and weaknesses of each assessment by describing uncertainties, assumptions, and limitations, as well as the scientific basis and rationale for each assessment.

Abstract  In response to a request from the owner, an investigation was begun into methylene-chloride (75092) (MeCl) exposures at Ackerman and Sons (SIC-7641), Littleton, Colorado. Work at the shop included paint stripping, furniture repair, refinishing, and recovering. Five refinishers were employed at the site, and usually spent only a few hours stripping per week, but occasionally stripped 3 to 4 hours in one day. Personal exposures to MeCl ranged from 83 to 523 parts per million (ppm) with a time weighted average figure of 2.4 to 177ppm. Exposures to methanol (67561) ranged from 39 to 95ppm. A significant lowering of airborne concentrations of stripping compounds was noted after the stripping booth was enclosed and ventilated. Personal MeCl exposures ranged from 10 to 110ppm and 8 hour time weighted averages ranged from 0.7 to 31ppm. The authors conclude that methylene-chloride exposures did not exceed the OSHA Permissible Exposure Limit of 500ppm; NIOSH recommends that exposures be maintained at the lowest feasible concentration. The authors recommend that worker exposures to methylene-chloride be lowered.

Abstract  Methylene chloride (dichloromethane) is a clear, highly volatile, non-flammable liquid with a penetrating ether-like odour. The pure dry compound is very stable. Methylene chloride hydrolyses slowly in the presence of moisture, producing small quantities of hydrogen chloride. Commercial methylene chloride normally contains small quantities of stabilizers to prevent decomposition. Analytical methods are available for the determination of methylene chloride in biological media and environmental samples. All methods involve gas chromatography in combination with a suitable detector. In this way, very low detection limits have been reached (e.g., in food: 7 ng/sample; water: 0.01 µg/litre; air: 1.76 µg/m3 (0.5 ppb); blood: 0.022 mg/litre).

Abstract  Mitochondrial reactive oxygen species (ROS) are widely implicated in physiological and pathological pathways. We propose that it is critical to understand the specific sites of mitochondrial ROS production and their mechanisms of action. Mitochondria possess at least eight distinct sites of ROS production in the electron transport chain and matrix compartment. In this chapter, we describe the nature of the mitochondrial ROS-producing machinery and the relative capacities of each site. We provide detailed methods for the measurement of H2O2 release and the conditions under which maximal rates from each site can be achieved in intact skeletal muscle mitochondria.

Abstract  This risk evaluation for methylene chloride was performed in accordance with the Frank R. Lautenberg Chemical Safety for the 21st Century Act and is being issued following public comment and peer review. The Frank R. Lautenberg Chemical Safety for the 21st Century Act amended the Toxic Substances Control Act (TSCA), the Nation’s primary chemicals management law, in June 2016. Under the amended statute, EPA is required, under TSCA § 6(b), to conduct risk evaluations to determine whether a chemical substance presents unreasonable risk of injury to health or the environment, under the conditions of use, without consideration of costs or other non-risk factors, including an unreasonable risk to potentially exposed or susceptible subpopulations, identified as relevant to the risk evaluation. Also, as required by TSCA § (6)(b), EPA established, by rule, a process to conduct these risk evaluations. Procedures for Chemical Risk Evaluation Under the Amended Toxic Substances Control Act (82 FR 33726). (Risk Evaluation Rule). This risk evaluation is in conformance with TSCA § 6(b), and the Risk Evaluation Rule, and is to be used to inform risk management decisions. In accordance with TSCA section 6(b), if EPA finds unreasonable risk from a chemical substance under its conditions of use in any final risk evaluation, the Agency will propose actions to address those risks within the timeframe required by TSCA. However, any proposed or final determination that a chemical substance presents unreasonable risk under TSCA section 6(b) is not the same as a finding that a chemical substance is “imminently hazardous” under TSCA section 7. The conclusions, findings, and determinations in this final risk evaluation are for the purpose of identifying whether the chemical substance presents unreasonable risk or no unreasonable risk under the conditions of use, in accordance with TSCA Section 6, and are not intended to represent any findings under TSCA Section 7.