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Expert elicitation on ultrafine particles: likelihood of health effects and causal pathways

Anne B Knol1 email, Jeroen J de Hartog1,2 email, Hanna Boogaard2 email, Pauline Slottje1 email, Jeroen P van der Sluijs2,3 email, Erik Lebret1,2 email, Flemming R Cassee1 email, J Arjan Wardekker3 email, Jon G Ayres4 email, Paul J Borm5 email, Bert Brunekreef2,6 email, Kenneth Donaldson7 email, Francesco Forastiere8 email, Stephen T Holgate9 email, Wolfgang G Kreyling10 email, Benoit Nemery11 email, Juha Pekkanen12 email, Vicky Stone13 email, H-Erich Wichmann10 email and Gerard Hoek2 email

Dutch National Institute for Public Health and the Environment (RIVM), Bilthoven, the Netherlands

University of Utrecht, Institute for Risk Assessment Sciences, Utrecht, The Netherlands

University of Utrecht, Copernicus Institute, Utrecht, the Netherlands

Institute of Occupational & Environmental Medicine, University of Birmingham, Birmingham, UK

Centre of Expertise in Life Sciences, Hogeschool Zuyd, Heerlen, The Netherlands

Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Utrecht, The Netherlands

University of Edinburgh Centre for Inflammation Research, Edinburgh, UK

Department of Epidemiology, Health Authority Rome, Italy

University of Southampton, School of Medicine, UK

10  Institute of Lung Biology and Focus Network Nanoparticles and Health, Helmholtz Center Munich, Neuherberg/Munich, Germany

11  Lung Toxicology Research Unit, K.U. Leuven, Leuven, Belgium

12  National Public Health Institute, Unit of Environmental Epidemiology, Kuopio, Finland

13  School of Life Sciences, Napier University, Edinburgh, UK

author email corresponding author email

Particle and Fibre Toxicology 2009, 6:19doi:10.1186/1743-8977-6-19

Published: 24 July 2009

Abstract

Background

Exposure to fine ambient particulate matter (PM) has consistently been associated with increased morbidity and mortality. The relationship between exposure to ultrafine particles (UFP) and health effects is less firmly established. If UFP cause health effects independently from coarser fractions, this could affect health impact assessment of air pollution, which would possibly lead to alternative policy options to be considered to reduce the disease burden of PM. Therefore, we organized an expert elicitation workshop to assess the evidence for a causal relationship between exposure to UFP and health endpoints.

Methods

An expert elicitation on the health effects of ambient ultrafine particle exposure was carried out, focusing on: 1) the likelihood of causal relationships with key health endpoints, and 2) the likelihood of potential causal pathways for cardiac events. Based on a systematic peer-nomination procedure, fourteen European experts (epidemiologists, toxicologists and clinicians) were selected, of whom twelve attended. They were provided with a briefing book containing key literature. After a group discussion, individual expert judgments in the form of ratings of the likelihood of causal relationships and pathways were obtained using a confidence scheme adapted from the one used by the Intergovernmental Panel on Climate Change.

Results

The likelihood of an independent causal relationship between increased short-term UFP exposure and increased all-cause mortality, hospital admissions for cardiovascular and respiratory diseases, aggravation of asthma symptoms and lung function decrements was rated medium to high by most experts. The likelihood for long-term UFP exposure to be causally related to all cause mortality, cardiovascular and respiratory morbidity and lung cancer was rated slightly lower, mostly medium. The experts rated the likelihood of each of the six identified possible causal pathways separately. Out of these six, the highest likelihood was rated for the pathway involving respiratory inflammation and subsequent thrombotic effects.

Conclusion

The overall medium to high likelihood rating of causality of health effects of UFP exposure and the high likelihood rating of at least one of the proposed causal mechanisms explaining associations between UFP and cardiac events, stresses the importance of considering UFP in future health impact assessments of (transport-related) air pollution, and the need for further research on UFP exposure and health effects.


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