Particulate matter: Fine and Ultrafine-How emerging data on engineered nanomaterials may change how we regulate worker exposures to dust

Currently in the United States, agencies responsible for regulations related to worker or public exposures to dust set rules based on a few general categories determined by gross particle size categories like PM10 (particles < 10 μm) and PM2.5 (particles < 2.5 μm) and the total mass of certain specific compounds (e.g., 3.5 mg/m3 of carbon black). Environmental health researchers however, have begun to focus on a new category of ultrafine particles (PM0.1; particles < 100 nm) as being more indicative of actual health risks in people. The emerging field of nanotoxicology meanwhile is providing new insights into how and why certain particles cause damage in the lungs by investigating the effects of exposure in animals to very well characterized engineered nanomaterials. Based on this recent research the National Institute of Occupational Safety and Health (NIOSH) has issued new recommended exposure limits (RELs) for carbon nanotubes (CNTs) and titanium dioxide nanoparticles that are 2-3 orders of magnitude more stringent than RELs for larger particles of the same or similar substance. It remains unclear at present how stringent future regulations may be for engineered and inadvertently created nanoparticles or ultrafine dusts. Nor is it clear whether verification methods to demonstrate compliance with these rules could or should be devised to differentiate between engineered and inadvertently created nanoparticles. This study presents a review of the history of dust regulation in the United States, how emerging data on the health risks of ultrafine particles and engineered nanoparticles is changing our understanding of the risks of inhaled dust, and how future rulemaking in regards to these and similar particulate materials may unfold. This review shows the extent to which rules on dust have become more stringent over time specifically in the case of diesel emissions and silica exposure, and indicates that new rules on worker exposure to ultrafine dusts or engineered nanomaterials may be expected in the United States within 5-10 years based on past experience on the time delay in connecting research on new hazards to regulatory intervention. Current research suggests there will be several challenges to compliance with these rules depending on the structure of the final rule and the development of detection technologies. Although the research on ultrafine dust control technologies appears to indicate that once rulemaking begins there may be no serious feasibility limits to controlling these exposures. Based on ongoing exposure studies, those industries likely to be most affected by a new rule on ultrafine dusts not specific to engineered nanomaterials will include transportation, mining, paper and wood products, construction, and manufacturing.