Review on Ultrafine Particle Health Effects

Abstract

Background: Due to their small size, inhaled ultrafine particles (UFPs) may enter into alveoli and are even capable of penetrating cell membranes. Toxicological studies suggest that UFPs contribute to the development and progression of various diseases. However, epidemiological evidence for health effects of UFPs is scarce. The aim of this project is to give an overview of the epidemiological literature on the effects of UFPs on health.Methods: We conducted a systematic literature review searching MEDLINE and LUDOK data bases (time period January 2011 - May 2017) as well as a by hand search for review articles and conference proceedings. We focused on epidemiologic studies that investigated health effects of UFPs, included quantitative effect measures and had a common UFPs-measure. Data extraction and quality assessment using standard instruments was conducted by two reviewers.Results: Overall, 85 unique references were included in the review. Most of these studies were conducted in North America (n=37) or Western Europe (n=27). The majority of the studies investigated short-term effects (n=75). Ten studies investigated long-term associations. Short-term studies were dominated by panel studies with repeated measures, scripted exposure studies and time-series studies. The investigation of health effects in epidemiological studies has substantially developed during the last 7 years. Specifically, the more recent studies have undertaken efforts to control for co-pollutants in order to identify independent effects of UFPs. Despite the advances in the field, the evidence on health effects remains inconclusive or insufficient for most of the studied outcomes.Conclusions: A future challenge is the development of enhanced spatiotemporal models that are able to contribute to a more precise exposure assessment across larger areas and incorporate multipollutant models to estimate independent UFP effects.