Woodsmoke and Human Health

Ryan W. Allen, PhD

Associate Professor

Faculty of Health Sciences

Simon Fraser University

Burnaby, BC, Canada

allenr@sfu.ca

National Educational Forum on the Residential Wood Heater NSPS

November 8, 2012

Minneapolis, MN
Presentation Overview

 What are the exposure/public health impacts 

of woodsmoke?

 At what levels and duration of time are there 

health impacts?

 Some general comments on air pollution and health

 How does woodsmoke differ from pollution 

generated by other sources?

 Woodsmoke and health

 What do we know? What don’t we know?

 Emphasis from studies in developed countries

 Range of health effects and exposure-effect time scales
Air Pollution Epidemiology 

Requires an Exposure Gradient

 Temporal or spatial (or both)

 Temporal gradients

 Hours to days

 Provide information on “acute” effects 

of air pollution

 Example: On days with more air 

pollution, more people die 

(“triggering”)

 Spatial gradients

 M to 1000s of KM

 Provide information on “chronic” 

effects of air pollution

 Example: People living in more 

polluted areas of a city die younger 

than those in less polluted areas 

(underlying disease?)
Air Pollution and Health

 Air pollution influences a wide 

range of health outcomes and 

severities

 Historical focus on respiratory 

effects

 Now also strong evidence of 

cardiovascular effects

 Growing evidence of other impacts 

(e.g. birth effects)

 Individual risks are small, but 

many are exposed, so 

population impacts can be 

substantial

 Example: air pollution vs. smoking
How is Woodsmoke Different?

mass emitted

massinhaled inhalation intake fraction 

Reis, Brauer et al., 2009

 Residential Woodsmoke Intake Fraction

 Vancouver study

 13 – 15 per million

 Similar to vehicle emissions

 ~7x higher than all-source PM
How is Woodsmoke Different?

Londahl et al., 2008, 2009

• Compared dose of deposited particles in airway for traffic exhaust 

and residential wood combustion particles.

• Subjects breathed concentrations of 100 μg/m3

• Traffic particle dose was 16x by number, and 3x by surface area.

WHY?

• Traffic particles have:

• Higher deposition probability

• Higher particle number and surface area per mass concentration

Particle toxicity influenced by size, composition, physical 

properties, etc.
• Epidemiologic Evidence:

“.....epidemiologic studies of indoor and community exposure 

to biomass smoke indicate a generally consistent relationship 

between exposure and increased respiratory symptoms, 

increased risk of respiratory illness, including hospital 

admissions and emergency room visits, and decreased 

lung function. Several studies suggest that asthmatics are 

a particularly susceptible subpopulation with respect to 

smoke exposure....”

Naeher et al., 2007

Woodsmoke and Health: Evidence
• General Conclusions

“...at the present time fine particles may represent 

the best metric to characterize exposures to smoke 

from residential wood combustion...”

“There is no persuasive evidence that woodsmoke

particles are significantly less dangerous for 

respiratory disease than other major categories of 

combustion-derived particles in the same size range.”

“There is too little evidence available today, 

however, to make a judgment about the relative toxicity 

of woodsmoke particles with respect to cardiovascular

or cancer outcomes.”

Naeher et al., 2007

Woodsmoke and Health: Evidence
Woodsmoke and Health: Evidence

 Constituents

 Toxicology

 Biomass burning in developing countries

 Forest fires

 Firefighters

 Impacted communities

 Communities impacted by agricultural burning

 Controlled human exposure studies

 Limitation: only acute, reversible effects

 Communities impacted by residential 

woodsmoke

 Challenge: often small communities 

(limited statistical power) Sarnat S. et al., JAWMA, 2006
Some Woodsmoke Constituents

*Indoor emissions from household combustion of biomass fuel (primarily

wood) are categorized as a Group 2A carcinogen (probably

carcinogenic to humans – limited human evidence with supporting

animal evidence) by the International Agency for Research on Cancer

(IARC).

Constituent Properties

Particulate Matter (PM2.5) Inflammation, oxidative stress

Carbon Monoxide Asphyxiant

Nitrogen Dioxide Irritant

Benzene Carcinogen*, mutagen

PAHs Carcinogen*, mutagen

Aldehydes Irritant, carcinogen*, mutagen

Phenols Irritant, carcinogen*, mutagen, teratogen

Adapted from Larson & Koenig, 1994; Naeher et al., 2007
Indoor Biomass Smoke

WHO, Fuel for Life, 2006

 Indoor biomass (wood, crops) and 

coal smoke:

 3 billion exposed

 1.6 million premature deaths

 2.7% of global burden of disease

 Strong evidence for:

 Respiratory infections

 Obstructive lung disease (women)

 Low birth weight

 Cataracts

 Limited evidence for:

 Tuberculosis

 Asthma

 Otitis media

 Lung cancer (biomass)

MUCH HIGHER 

EXPOSURES THAN IN 

DEVELOPED WORLD
Controlled Exposure Experiments

Barregard et al., 2006
Controlled Exposure Experiments

 13 subjects exposed 

to wood smoke and 

clean air

 240–280 μg/m3

 4-hour sessions, 1 

week apart

Barregard et al., 2006
Air Pollution and Hospital 

Admissions in Christchurch, NZ

 “Uniquely in Christchurch, more than 90% of particulate air 

pollution has been estimated to come from the city’s 47,000 

wood burners and open fires that are used during the cold 

winters months”

 McGowan et al., 2002:

 3.37% increase in respiratory admissions and 1.26% 

increase in cardiac admissions per 15 μg/m3 outdoor 

PM10

 Barnett et al., 2006:

 No significant effects of PM10 on cardiac admissions

Sarnat S. et al., JAWMA, 2006

McGowan et al., ANZJPH, 2002; Barnett et al., EHP, 2006
• 45 participants, 25 

homes in Smithers, BC

• Portable HEPA filters 

60%  in indoor PM2.5

• 11.2  4.6 ug/m3

• Increases in endothelial 

function and decreases 

in systemic inflammatory 

markers

Random

Selection

HEPA Filtration

“Placebo” Filtration

Day 0

Technician

Visit

Day 7

Technician 

Visit

Day 14

Technician

Visit

Health

Measurements

Health

Measurements

Monitoring Session 1 Monitoring Session 2

Monitoring Session 1 Monitoring Session 2

Allen et al., AJRCCM 2011

Intervention Studies
• ~30% reduction in winter PM2.5

•  in childhood wheeze, itchy eyes, sore throat, cold, bronchitis, 

influenza, throat infections

• School absence associations inconsistent

Libby Intervention , Montana stove exchange Studies

Noonan et al., HEI Report 162, December 2011
Mobile Monitoring on Cold, 

Clear Winter Evenings

Lowest third

Middle third

Highest third

Lowest third

Middle third

Highest third

(~ 12,000 points)

Larson et al. Environmental Science and Technology. 2007

Reis et al, Environmental Science and Technology. 2009 

Mapping Woodsmoke in Vancouver
Outcome Exposure

window

N

(n cases)

Design Mean 

Days 

exposed 

[IQR]

Adjusted# OR 

(95% CI)

SGA birth All pregnancy 70,249 

(6,939)

Cohort 65 [43] 1.00 (0.91 - 1.09)

Asthma3

(0 – 48 mos.)

All pregnancy

0 -12 months

37,401 

(3,482)

Nested 

C-C**

60 [33]

89 [17]

1.00 (0.94 - 1.07)

1.00 (0.98 - 1.02)

Bronchiolitis1 2 – 12 months 86,337

(10,485)

Nested 

C-C*

54 [45] 1.08 (1.04 - 1.11)

Otitis Media2

(1 – 24 mos.) 

1 month prediagnosis45,513 

(19,115)

Cohort 15 [16] 1.32 (1.27 - 1.36)

# per IQR increase, adjusted for covariates: Infant sex (SGA, B, OM) First Nations Status (SGA, B, OM), Parity (SGA, B, A), Maternal 

age (SGA, B, OM), Maternal smoking during pregnancy (SGA, B, OM), Month-year of birth (SGA), maternal initiation of breastfeeding 

at birth (B, OM, A), Income (SGA, B, OM, A), Maternal education (SGA, B, OM, A), older siblings (OM), birth season (OM), 

birthweight (OM, A), gestational duration (OM, A). *incidence-density matching (up to 1:10) on date of birth **matched 1:5 by 

sex, month-yr of birth 1Karr et al., AJRCCM 20009; 2 MacIntyre et al., Epidemiology 2011; 3Clark et al., EHP 

Vancouver Results
Summary

 Biomass smoke contains many pollutants with 

known adverse effects on health

 Woodsmoke is an important source of air pollution 

in many communities

 Emissions in populated areas  high “intake fraction”

 For respiratory outcomes, no evidence that 

woodsmoke particles are less dangerous than other, 

similarly-sized particles

 Short-term (≤24 hour) effects on symptoms, lung 

function, admissions, & ED visits

 Cardiovascular evidence is mixed (controlled 

exposure & in-home studies vs. population studies)

 Emerging evidence that spatio-temporal variations 

in woodsmoke relate to important effects in children
allenr@sfu.ca
Kocbach Bølling et al. 2009

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