Hazard and risk assessment strategies for nanoparticle exposures: how far have we come in the past 10 years?

Nanotechnology is an emerging, cross-disciplinary technology designed to create and synthesize new materials at the nanoscale (generally defined as a particle size range of ≤10 meters) to generate innovative or altered material properties. The particle properties can be modified to promote different and more flexible applications, resulting in consumer benefits, particularly in medical, cosmetic, and industrial applications. As this applied science matures and flourishes, concerns have arisen regarding potential health effects of exposures to untested materials, as many newly developed products have not been adequately evaluated. Indeed, it is necessary to ensure that societal and commercial advantages are not outweighed by potential human health or environmental disadvantages. Therefore, a variety of international planning activities or research efforts have been proposed or implemented, particularly in the European Union and United States, with the expectation that significant advances will be made in understanding potential hazards related to exposures in the occupational and/or consumer environments. One of the first conclusions reached regarding hazardous effects of nanoparticles stemmed from the findings of early pulmonary toxicology studies, suggesting that lung exposures to ultrafine particles were more toxic than those to larger, fine-sized particles of similar chemistry. This review documents some of the conceptual planning efforts, implementation strategies/activities, and research accomplishments over the past 10 years or so. It also highlights (in this author's opinion) some shortcomings in the research efforts and accomplishments over the same duration. In general, much progress has been made in developing and implementing environmental, health, and safety research-based protocols for addressing nanosafety issues. However, challenges remain in adequately investigating health effects given 1) many different nanomaterial types, 2) various potential routes of exposure, 3) nanomaterial characterization issues, 4) limitations in research methodologies, such as time-course and dose-response issues, and 5) inadequate methodologies for standardized, guideline toxicity testing.