Health effects of coarse airborne particles

1. Health effects of coarse airborne particles Peter Baxter UK Natural Dust and Human Health Network Cambridge University 14 March 2008 29 May, January 2007

2. Crustal particles • Volcanic ash • Review: Horwell & Baxter, Bull. Volcanol 2006 • Soil-derived in urban air (“coarse fraction”) • Dust storms and wind-blown dust • Review: Brunekreef & Forsberg, Eur Respir J 2005

3. Mount St Helens volcano, USA. May 18, 1980 Massive disruption for 5 days TSP > 30 mg/m³ Loggers highest exposed group over next 3 months

4. Mount St Helens: acute and chronic health effects of ash ER visits May 18, May 25 and June 12 ash falls Acute respiratory effects – respirable particles Confusion over crystalline silica content (7 wt%, PM10) and silicosis risk in general population and outdoor workers Many businesses relocated

5. Montserrat eruption Unprecedented exposure to volcanic PM MVO MVO

6. Soufrière Hills volcano, Montserrat • Eruption July 1995 – present • Asthma studies in school children, 1998 and 2008 • Hazard of cristobalite in lava dome eruption identified and quantified 1999 • Cumulative exposure assessment 1996-2000 • Toxicological studies • Quantified risk assessment for silicosis • CXR and lung function studies in adults and children

7. Some factors affecting lung toxicity of silica particles • Freshly fractured v. aged surfaces • Particle - generated free radical activity • Iron ions as contaminants • Association with clay • Pure silica surface v. Al covered as • in silica sands • Hydrophobic v. hydrophilic surfaces • H-bonding to membranes • High peak exposures Montserrat – ash incorporated into soil

8. Respiratory health hazards of volcanic ash: a review (Horwell & Baxter, Bull Volcanol, 2006) • Few epidemiological or clinical studies of acute effects – most since Mount St Helens 1980 • Poor characterisation of ash samples • Inadequate exposure information • Only Mount St Helens 1980 and SHV Montserrat 1995-present where detailed studies undertaken • Variable findings - Pinatubo, 1991, no asthma/bronchitis (c.f. Mount St Helens, 1980) • Cerro Negro, 1992 – cinder cone, basaltic ash: asthma outbreak

9. Effects of coarse PM on short-term mortality • A number of time series studies found no effect • Arid Coachella Valley, CA: CVD only • Phoenix, Arizona: coarse and fine PM: CVD

10. Effects of coarse PM on long-term mortality • Six Cities study found an effect for fine but not coarse PM for total mortality (14 years follow up)

11. Effect of coarse particles on short-term morbidity • Effect on hospital admissions for respiratory and CVD (11 papers) and ER visits (3 papers) • In several studies, coarse fraction better predictor than fine fraction for daily numbers of asthma, COPD, all respiratory admissions • Coachella Valley, CA. Association of CP with heart-rate variability in CHD patients

12. Effects of dust storms and wind-blown dust • Spokane, WA (Schwartz et al.). Time series mortality – no effect (average PM10 = 263µm/m³) • Washington State – small increase in respiratory hospital admissions after dust storms where max. 24 hr PM10 > 1 mg/m³ • Anchorage, USA. PM10 dominated by crustal CP and effect on OP visits for asthma, bronchitis, URTIs • Asian dust events (Taipei): no consistent findings

13. Summary points… • Some evidence for an effect of coarse PM on mortality • COPD, asthma and respiratory admissions: coarse PM has a stronger or as strong short term effect as fine PM? • Few studies on long term effects of coarse PM on morbidity, e.g., lung growth • Many factors moderate silicosis risk (volcanic ash model) • Certain forms of crustal and volcanic PM more toxic than others - can these be detected by cell or in vitro screening tests? • Is volcanic ash a model for crustal particle toxicity – many different forms • Health risk assessment (volcanic ash) requires evidence-based expert judgement and should not be based on a single measure • COMEAP report on mortality & long term air pollution focused on PM2.5 • Co-factors, e.g., sulphate in PM2.5 ?