The toxicology of inhaled woodsmoke

Abstract

In addition to developing nations relying almost exclusively upon biomass fuels, such as wood for cooking and home heating, North Americans, particularly in Canada and the northwestern and northeastern sections of the United States, have increasingly turned to woodburning as an alternate method for domestic heating because of increasing energy costs. As a result, the number of households using woodburning devices has increased dramatically. This has resulted in an increase in public exposure to indoor and outdoor woodsmoke-associated pollutants, which has prompted widespread concern about the adverse human health consequences that may be associated with prolonged woodsmoke exposure. This mini-review article brings together many of the human and animal studies performed over the last three decades in an attempt to better define the toxicological impact of inhaled woodsmoke on exposed children and adults; particular attention is given to effects upon the immune system. General information regarding occurrence and woodsmoke chemistry is provided so as to set the stage for a better understanding of the toxicological impact. It can be concluded from this review that exposure to woodsmoke, particularly for children, represents a potential health hazard. However, despite its widespread occurrence and apparent human health risks, relatively few studies have focused upon this particular area of research. More laboratory studies aimed at understanding the effects and underlying mechanisms of woodsmoke exposure, particularly on those individuals deemed to be at greatest risk, are badly needed, so that precise human health risks can be defined, appropriate regulatory standards can be set, and accurate decisions can be made concerning the use of current and new woodburning devices.

Full text

THE TOXICOLOGY OF INHALED WOODSMOKE
Judith T. Zelikoff, Lung Chi Chen, Mitchell D. Cohen,
Richard B. Schlesinger
New York University School of Medicine, Nelson Institute
of Environmental Medicine, Tuxedo, New York, USA
In addition to developing nations relying almost exclusively upon biomass fuels, such as
wood for cooking and home heating, North Americans, particularly in Canada and the
northwestern and northeastern sections of the United States, have increasingly turned to
woodburning as an alternate method for domestic heating because of increasing energy
costs. As a result, the number of households using woodburning devices has increased
dramatically. This has resulted in an increase in public exposure to indoor and outdoor
woodsmoke-associated pollutants, which has prompted widespread concern about the
adverse human health consequences that may be associated with prolonged woodsmoke
exposure. This mini-review article brings together many of the human and animal studies
performed over the last three decades in an attempt to better define the toxicological
impact of inhaled woodsmoke on exposed children and adults; particular attention is
given to effects upon the immune system. General information regarding occurrence and
woodsmoke chemistry is provided so as to set the stage for a better understanding of the
toxicological impact. It can be concluded from this review that exposure to woodsmoke,
particularly for children, represents a potential health hazard. However, despite its wide-
spread occurrence and apparent human health risks, relatively few studies have focused
upon this particular area of research. More laboratory studies aimed at understanding the
effects and underlying mechanisms of woodsmoke exposure, particularly on those individ-
uals deemed to be at greatest risk, are badly needed, so that precise human health risks
can be defined, appropriate regulatory standards can be set, and accurate decisions can
be made concerning the use of current and new woodburning devices.
BACKGROUND AND OCCURRENCE
In developing nations, biomass fuels such as wood, animal dung, and
crop residues are used extensively for home heating and cooking (Inter-
national Institute for Population Science
[
IIPS
]
, 1995; Smith, 2000). For
example, three-quarters of all households in India use unprocessed biomass
as their primary fuel for cooking, and among those homes, more than 90%
use either wood or animal dung (IIPS, 1995). In countries such as India,
daily air pollution exposures from cooking with biomass fuels typically
exceed relevant health-based guidelines by at least 20-fold (Smith & Liu,
1994; Smith, 2000). It has been estimated that indoor air pollution in
developing countries accounts for 2.2–2.5 million deaths annually (WHO,
1997). While biomass fuels are at the high end of the fuel ladder in terms of
269
Journal of Toxicology and Environmental Health, Part B, 5:269–282, 2002
Copyright© 2002 Taylor & Francis
1093-7404 /02 $12.00 + .00
DOI: 10.1080/1093740029007006 2
Support for studies performed in this laboratory was provided by the Center for Indoor Air
Research, contract 94-03C.
Address correspondence to Judith T. Zelikoff, New York University School of Medicine, 57 Old
Forge Road, Tuxedo, NY 10987, USA. E-mail: judyz@env.med.nyu.edu

pollution emissions, they score low for combustion efficiency. Thus, efflu-
ents from these sources contain numerous toxic/carcinogenic components,
such as formaldehyde and polyaromatic hydrocarbons (PAH), which at high
exposure concentrations can cause serious health problems (Smith, 1987,
1993; Larson & Koenig, 1994; Nolte et al., 2001). Among the major respi-
ratory illnesses, cooking smoke appears to increase the risk of chronic ob-
structive lung disease (Pandey, 1984; Malik, 1985; Perez-Padilla et al.,
1996), lung cancer (Sobue, 1990; Franco, 1998), and respiratory infections
(Pandey et al., 1989; Mishra & Retherferd, 1997; Kammen et al., 1998). In
fact, a recent study in northern India noted an association between the use
of wood and/or cow-dung cakes and an increased incidence of pulmonary
tuberculosis in children (Gupta et al., 1997).
In addition to domestic woodburning in developing countries, over the
past two decades, due to rising energy costs and the uncertain availability of
petroleum and natural gas, homeowners in the United States and Canada
have increasingly turned to the use of wood as an alternate heating fuel.
Interestingly, most of the residential woodburning in the United States is
done by people in the middle to upper-middle socioeconomic class. In-
creased usage of wood for home heating has been especially striking in the
northeastern and northwestern United States (National Research Council,
1981). For example, the Washington State Department of Ecology estimated
that during the 1980s wood was burned in 60% of all Washington house-
holds, with about 2.2 million cords consumed annually (Pierson et al.,
1989). In Massachusetts, studies during this same time frame showed that
65% of all households surveyed used woodburning devices, and of those,
68% were in use all day (Tuthill, 1984). Between 1972 and 1989, sales of
woodstoves increased 10-fold (by the late 1980s, the number of operating
woodstoves was thought to exceed 11 million), and it is estimated that
approximately 10% of the total space-heating input for the United States is
from firewood (Lipfert & Dungan, 1983; Samet et al., 1987). While usage of
wood for home heating and sales of woodburning devices declined after
1989, woodburning has resurged in the new millennium, again as a result of
increasing energy costs.
In Canada, it is estimated that about 400,000 homes use wood as the
primary heating fuel, and many others use fireplaces and woodstoves as sup-
plementary sources of heat or for aesthetics. While the Atlantic provinces
are more dependent upon wood for home heating than other locations, it
is in British Columbia that smoke from residential woodburning poses the
greatest threat to health (British Columbia Ministry of Environment, 1995).
Here, inversions in weather patterns frequently warm the air on mountain-
sides, trapping cooler air and smoke at ground level in valleys and allowing
the buildup of pollutants to high concentrations.
Increased usage of woodburning devices has resulted in greater public
exposure to smoke-associated pollutants generated during combustion and
an increased concern by local residents regarding the health effects associ-
270 J. T. ZELIKOFF ET AL.

ated with such exposure. Although legislative action mandating the reduc-
tion of residential woodsmoke levels is moving forward (Koenig et al.,
1988), only a few states are currently affected by regulations (i.e., Colo-
rado, Washington, Oregon), and legislation in other states will take several
years to enact. Meanwhile, those most vulnerable to health impairment due
to air pollutants, such as very young children, individuals with preexisting
cardiopulmonary disease, asthmatics, and the elderly, will continue to be
exposed both indoors and outdoors for prolonged periods of time to high
concentrations of woodsmoke-generated pollutants (Koenig & Pierson, 1991).
CHEMICAL CHARACTERIZATION AND POLLUTANT DISTRIBUTION
Woodsmoke is a complex mixture of numerous gases and respirable fine/
ultrafine particles of varying inorganic/organic composition and diameter
(Pierson et al., 1989; U.S. EPA, 1993; Nolte et al., 2001). Smoke generated
from burning wood is thought to consist of over 200 chemicals and com-
pound groups, which are contained in an effluent that is almost entirely in
the inhalable size range (Cooper, 1980; U.S. EPA, 1993). Woodburning
stoves, furnaces, and fireplaces emit significant quantities of toxic com-
pounds, including respirable particulate matter (PM) with diameters <10
µm (PM
10
), carbon monoxide (CO), nitrogen and sulfur oxides (NO
X
and
SO
X
), aldehydes, PAHs, volatile organic compounds (VOCs), chlorinated di-
oxins, and free radicals (Cooper, 1980; Dasch, 1982; Lao, 1983; Tuthill,
1984; Sexton et al., 1986; Traynor et al., 1987; Lachocki et al., 1989; Koenig
& Pierson, 1991; Hildemann et al., 1991; Koenig et al., 1993; U.S. EPA,
1993; Larson & Koenig, 1994; Nolte et al., 2001).
Under normal usage conditions, woodburning devices create indoor
pollution (Lao, 1983; Sexton et al., 1986; Traynor et al., 1987; Samet et al.,
1987, 1988). It has been reported that both airtight and non-airtight stoves
release fine/ultrafine-sized PM, CO, and PAHs directly within the indoor
environment (Traynor et al., 1987). Concentrations of PM as great as 820
µg/m
3
(U.S. EPA standard for PM
10
is 150 µg/m
3
for a 24-h period, not to be
exceeded >2% of the time) have been measured indoors from non-airtight
stoves over a 24-h period (Traynor et al., 1987). In addition to that amount
released directly inside the home, a large percentage (i.e., 70%) of outdoor
woodsmoke from chimneys actually reenters the house and permeates
neighboring dwellings (Pierson et al., 1989). Many circumstances, including
improper installation, negative indoor air pressure, and downdrafts, facilitate
entry of incomplete combustion products back into the home (Pierson et al.,
1989; U.S. EPA, 1994). Since individuals typically spend 60–70% of their
out-of-work time at home (Szalar, 1972; Chapin, 1974; Sexton et al., 1986),
indoor woodsmoke potentially represents a major source for human expo-
sure.
In addition to pollution created indoors, woodburning devices also con-
tribute to outdoor air pollution (Butcher & Sorenson, 1979; Cooper, 1980;
TOXICOLOGY OF WOODSMOKE 271

Koenig et al., 1988, 1993; Koenig & Pierson, 1991). For example, alde-
hydes released into the ambient environment from woodburning have been
measured at levels comparable to those emitted from power plants and
automobiles (Lipari et al., 1984). Moreover, studies have demonstrated that,
on a moderately cold winter day, 51% of the respirable air particulates in
the Portland, OR, area were from residential wood combustion sources
(Cooper, 1980). Investigations examining other parts of the northwest re-
ported that residential woodsmoke in the Olympia, WA, area accounted for
50% (on clear days) to 85% (on polluted days) of airborne PM (Koenig et
al., 1988). Additional studies in the same geographic area have demon-
strated that 80–90% of the PM measured in the ambient air was due to use
of woodburning devices during nighttime hours (Larson et al., 1992). Such
studies have led to the conclusion that woodsmoke represents a more sig-
nificant source of ambient PM, VOCs, and CO, than the sum total of all
industrial point sources in the state of Washington (Koenig et al., 1988).
While most residential woodburning is currently associated with wood-
stoves, burning in fireplaces also contribute to elevated concentrations (both
indoors and outdoors) of woodsmoke-associated pollutants. For example,
studies have demonstrated that the levels of PAH and PM in homes with
open fireplaces were approximately equal to those with non-airtight stoves,
and substantially greater than those with airtight woodstoves (Maschandreas
& Zabransky, 1980). Moreover, it has been reported that wood burned in an
open fireplace yielded indoor PAH concentrations comparable to those of
ambient urban air (Alfheim & Ramdahl, 1984). These same studies also
reported that the mutagenicity of air samples collected from burning fire-
places exceeded the activity from samples emitted from airtight stoves. On
the other hand, because airtight stoves burn wood in an oxygen-starved
environment, organic chemicals are produced in greater variety in a wood-
burning stove than in a fireplace.
HEALTH EFFECTS
Individually, many woodsmoke constituents have been shown to pro-
duce acute and chronic biologic effects and/or cause deleterious physiologic
responses in exposed humans (Anderson et al., 1973; Speizer et al., 1980;
Ramage et al., 1988; Koenig et al., 1988; Pierson et al., 1989; Koenig &
Pierson, 1991; Schwartz, 1993). For example, CO at levels measured in
homes using woodstoves (in the range of 1.2–43 ppm, compared to the
indoor level of 5 ppm recommended by the American Society for Heating,
Refrigeration, and Air Conditioning Engineers
[
ASHRAE
]
and the current
outdoor standard of 9 ppm for an 8-h period) has been shown to produce
carboxyhemoglobin and increase the incidence of angina among persons
with cardiac disease (Anderson et al., 1973). Nitrogen oxides (primarily
nitrogen dioxide and nitric oxide) bind to hemoglobin to produce methemo-
globin and hematologic aberrations, affect the activity of several enzyme
272 J. T. ZELIKOFF ET AL.

systems, cause vascular membrane injury and leakage leading to edema,
and may produce bronchoconstriction in asthmatics at low levels. The PAHs
that are released into the environment adsorbed onto emitted PM are im-
munosuppressive in laboratory animals (White et al., 1994), as well as car-
cinogenic in animals and possibly humans (Koenig et al., 1988; Pierson et
al., 1989). Aldehydes, mostly as formaldehyde and acrolein, measured
indoors during operation of a woodburning device at concentrations rang-
ing from 0.3 to 1 ppm (compared to ASHRAE recommended indoor levels
of 0.1 ppm), are associated with upper airway irritation, headaches and
other neurophysiologic dysfunctions, exacerbation of bronchial asthma, and
possibly cancer (Kerns et al., 1983). In addition to the effects previously
cited, other chronic health ailments have also been associated with expo-
sure of humans to individual woodsmoke constituents. These include in-
creased airway resistance, decreased vital capacity, increased respiratory
symptoms (i.e., cough, wheeze, dyspnea), and infections in children (Koenig
et al., 1988; Butterfield et al., 1989).
One of the most interesting components of woodsmoke pollution is PM
(Butcher & Sorenson, 1979; Hytönen et al., 1983; Sexton et al., 1986; Tray-
nor et al., 1987; Pierson et al., 1989; Hildemann et al., 1991; U.S. EPA,
2001). Woodsmoke-emitted respirable particulates (<3.5 µm), composed of
a relatively equal mixture of ultrafine/fine (0.02–2.5 µm) and coarse (2.5–3.5
µm) particles (Sexton et al., 1986; Traynor et al., 1987; Hildemann et al.,
1991) can penetrate into the deep lung, producing a variety of morphologi-
cal and biochemical changes. A considerable body of epidemiologic evi-
dence has associated short-term exposure to PM from a variety of sources
with respiratory symptoms, increased use of asthmatic medication, hospital
admissions, early mortality, exacerbation of preexisting medical conditions
including a reduced likelihood of recovering from infectious diseases such
as pneumonia, and an increased incidence and rate of infectious respiratory
diseases in children (Schwartz, 1991, 1993; Pope, 1991; Kammen et al.,
1998).
Although health effects associated with exposure to whole woodsmoke
emissions are not as well studied as its individual components, a number of
adverse health effects have been demonstrated. For example, exposure of
laboratory animals to woodsmoke effluents decreased ventilatory frequency
and ventilatory response to CO
2
(Wong et al., 1984), increased microvascu-
lar permeability and produced pulmonary edema (Nieman et al., 1988),
caused necrotizing tracheobronchial epithelial cell injury (Thorning et al.,
1982), possibly increased the lung cancer incidence in mice (Liang et al.,
1988), increased levels of angiotensin-1-converting enzyme in the lungs
(Brizio-Molteni et al., 1984), and compromised pulmonary macrophage-
mediated immune mechanisms important in antimicrobial defense (Zelikoff
et al., 1995a, 1995b), most likely via alterations in the integrity of the
macrophage surface membrane or cytoskeletal components (Fick et al.,
1984; Loke et al., 1984).
TOXICOLOGY OF WOODSMOKE 273

In humans, health effects seem to be related to host age at the time of
woodsmoke exposure. In adults, effects include prolonged inhalation of
woodsmoke contributed to chronic bronchitis (Rajpandey, 1984), chronic
interstitial pneumonitis and fibrosis (Ramage et al., 1988), cor pulmonale,
interstitial lung disease, pulmonary arterial hypertension (Sandoval et al.,
1993), and altered pulmonary immune defense mechanisms (Demarest et
al., 1979; Ramage et al., 1988).
While adverse effects of prolonged woodsmoke exposures on adults are
notable, children appear to be at greatest risk. Exposure of preschool chil-
dren living in homes heated with woodburning stoves or in houses with
open fireplaces yielded these effects: decreased pulmonary lung function in
young asthmatics (Koenig et al., 1993); increased incidence of acute bron-
chitis and severity/frequency of wheezing and coughing (Butterfield et al.,
1989); and increased incidence, duration, and possibly severity of acute
respiratory infections (Honicky et al., 1983, 1985; Rajpandey, 1984; Morris
et al., 1990; Collings et al., 1990; Honicky & Osborne, 1991; Kammen et
al., 1998). Even in those few epidemiological studies that failed to correlate
woodsmoke exposure with respiratory disease/symptoms (Anderson, 1978;
Tuthill, 1985; Browning et al., 1990), the authors concluded that wood-
smoke pollution may have aggravated symptoms of respiratory disease and
should not be disregarded as a possible contributing factor to increased res-
piratory infections in young children.
THE IMMUNE SYSTEM AS A TARGET OF WOODSMOKE TOXICITY
In addition to the aforementioned health effects associated with inhaled
woodsmoke and/or its components, many of the constituents have also been
shown to alter pulmonary immune defense mechanisms in a persistent and
often progressive manner (Jakab, 1977, 1992, 1993; Speizer et al., 1980;
Hatch et al., 1981; Aranyi et al., 1983; Samet et al., 1987; Pierson et al.,
1989; Burrell et al., 1992; Jakab & Hemenway, 1993; Zelikoff et al., 1999;
Thomas & Zelikoff, 1999; Zelikoff, 2000). For example, studies have shown
that in the absence of an inflammatory response, inhalation exposure of
mice for 4 d to 15 ppm formaldehyde following bacterial challenge im-
paired intrapulmonary killing of
Staphylococcus aureus
24 h after expo-
sure; the same effect on lung antibacterial defenses was produced by
formaldehyde at 1 ppm when exposure preceded, and was then continued
after, bacterial challenge (Jakab, 1992). In the same study, F
cg
receptor-
mediated phagocytosis by alveolar macrophages recovered from mice
exposed to 10 mg/m
3
carbon black and 5 ppm formaldehyde (4 h/d, 4 d)
was progressively suppressed up to 25 d following exposure. In a later
study by the same investigator (Jakab, 1993), coexposure of mice to carbon
black (10 mg/m
3
, 4 h/d, 4 d) and acrolein (2.5 ppm) suppressed intrapul-
monary killing of
S. aureus,
impaired elimination of
Listeria monocytogenes
and influenza A virus, and enhanced intrapulmonary killing of
Proteus mira-
274 J. T. ZELIKOFF ET AL.

bilis;
it was suggested that the observed biologic effect was due to carbon
particles acting as vehicles to carry acrolein into the deep lung. In addition,
the same coexposure regime persistently suppressed alveolar macrophage-
mediated tumor necrosis factor-
a
(TNF
a
) production and phagocytosis;
phagocytic activity was significantly reduced at 1 through 11 d following
exposure, while TNF
a
production was depressed after 4 d and reached
control levels by d 20. Studies by this laboratory investigating the immuno-
toxicity of inhaled ambient PM (which could include particles generated
from woodburning) demonstrated the ability of particulates <2.5 µm con-
centrated from New York City air to exacerbate an ongoing
Streptococcus
pneumoniae
infection in PM-exposed rats (Zelikoff et al., 1999, in press).
Thus, many respirable pollutants found in woodsmoke can offset the bal-
ance necessary for immunoregulation of the lung. This disruption in home-
ostasis may produce a cascade of detrimental secondary events, including
pathogenesis and compromised host resistance which may lead to increased
respiratory infections.
While only a limited number of studies have investigated the effects of
whole woodsmoke emissions on pulmonary immunity, it appears that host
defense and/or immune cell function is depressed in a manner similar to that
produced by many of the individual woodsmoke constituents (Demarest et
al., 1979; Fick et al., 1984; Loke et al., 1984; Zelikoff et al., 1995a, 1995b).
For example, a single inhalation exposure of rabbits to smoke from the py-
rolysis of Douglas fir wood produced an increase in the total number of
recovered pulmonary macrophages and a transitory decrease in macrophage
adherence to glass (Fick et al., 1984). Moreover, this same exposure regime
decreased macrophage uptake of the gram-negative bacterial pathogen
Pseudomonas aeruginosa
in the absence of an inflammatory response or
changes in macrophage viability. In another study, a single inhalation expo-
sure of Douglas fir-generated woodsmoke altered macrophage morphology
and membrane ultrastructure (Loke et al., 1984). Inhaled woodsmoke has
also been reported to alter the chemotactic migration of bronchopulmonary
lavaged human macrophages (Demarest et al., 1979).
The aforementioned studies have provided some evidence that inhala-
tion of woodsmoke effluents can alter pulmonary immune defense mecha-
nisms, and that the macrophage, a primary defense of the deep lung that
provides a link between the nonspecific and specific defense systems of the
respiratory tract, is the likely target for woodsmoke-induced immunotoxicity.
However, some of the most compelling evidence demonstrating the ability
of woodsmoke to modulate pulmonary immunocompetence comes from
animal toxicology studies performed in this laboratory (Zelikoff et al.,
1995a, 1995b). For these laboratory studies, 3-mo-old Sprague-Dawley rats
were exposed repeatedly (1 h/d, 4 d) to a single concentration of wood-
smoke (i.e., 750 µg PM
2.5
/m
3
) generated from red oak burned in a combus-
tion furnace, originally developed for generating coal fly ash (Chen et al.,
1990) and later adapted for woodburning (Figure 1).
TOXICOLOGY OF WOODSMOKE 275

Narrowly size-classified wood dusts (i.e., 53–63 µm) produced through
mechanical grinding, were used for all experiments. The effluent concentra-
tions of CO, PAH (measured as benzo
[
a
]
pyrene), PM
2.5
, and NO
X
used in
these studies were within the range of those measured indoors during non-
airtight/airtight stove operation (Traynor et al., 1987). Mass median diame-
ter of the emitted particles was 0.16 µm (
s
g
= 2.23), which is within the
same particle size range shown to be released during the burning of oak
wood in a residential fireplace (Hildemann et al., 1991).
At 3, 24, 72, and 120 h following the final woodsmoke exposure, rats
were intratracheally instilled with the pneumonia-producing bacteria
Staphy-
276 J. T. ZELIKOFF ET AL.
FIGURE 1. Combustion furnace for generating woodsmoke. The generation system consists of a feeder,
laboratory-scale laminar-flow drop-tube furnace, and a collection probe. Wood dust is carried in a
nitrogen gas stream and injected axially downward into the furnace, where the particles are ignited and
burned in a narrow zone along the furnace axis. The temperature of combustion, as well as the bulk gas
temperature, is controlled by the partial pressure of oxygen in the O
2
/N
2
bulk gas mixture. At the exit of
the collection probe, a three-stage virtual impactor was used to remove particles larger than 10 µm and
the remaining particles and gas mixture then entered the exposure chamber.

lococcus aureus
to assess effects upon pulmonary clearance, or were sacri-
ficed and their lungs either lavaged for recovery of pulmonary macrophages
or fixed for histopathological examination (Zelikoff et al., 1995a, 1995b).
Inhalation of woodsmoke emissions for 4 d (1 h/d) progressively reduced
(compared to control) the in vivo clearance/killing of
S. aureus.
Effects of
inhaled woodsmoke on intrapulmonary clearance appeared as early as 3 h
following the final woodsmoke exposure and persisted for up to 5 d; killing/
clearance was reduced to 60% of control values after 3 h and then progres-
sively declined to 2% after 5 d. While the mechanisms by which wood-
smoke may have acted to persistently suppress bacterial clearance are not
yet clear, results from this part of the study demonstrated that short-term
repeated inhalation of woodsmoke generated from the burning of a com-
mon hardwood used for home heating compromised pulmonary host resis-
tance against an infectious, pneumonia-producing lung pathogen well after
exposures ceased.
In this same study, both phagocytic activity and superoxide production
by macrophages recovered from smoke-exposed animals were decreased
(compared to control values) in a time-dependent manner. The persistent
effects of short-term exposure to woodsmoke on F
c
-dependent opsonized
particle uptake were similar to previous studies that demonstrated a pro-
gressive decrease in F
c
-receptor-mediated phagocytosis that began after 4 d
and was persistent for up to 25 d following repeated coexposure to carbon
black and the woodsmoke constituent formaldehyde (Jakab, 1992). It was
concluded from this latter study that the observed onset delay and persis-
tence of effects were due to formaldehyde desorption from the particle over
an extended period of time, resulting in a slow accumulation of an internal
dose, which, in turn, produced a continuous progressive effect. Given that
woodsmoke is a mixture of gases and respirable particulates, a similar ex-
planation could apply to the study with red oak effluents. Effects upon
macrophage function along with those observed on bacterial clearance
may help explain the increased incidence of respiratory infections observed
in woodsmoke-exposed children, particularly those under 5 yr of age living
in developing nations.
Even though information concerning the immunomodulating potential
of inhaled woodsmoke is rather sparse (Demarest et al., 1979; Loke et al.,
1984; Fick et al., 1984; Zelikoff et al., 1995a, 1995b), it appears that only a
brief exposure to woodsmoke can alter intrapulmonary bacterial clearance
and macrophage-mediated immunity. However, whether similar effects
occur following long-term exposure, a scenario more reflective of the
human situation, remains to be seen.
SUMMARY
This mini-review has provided an overview of the health effects associ-
ated with exposure to woodsmoke and its individual constituents. In gen-
TOXICOLOGY OF WOODSMOKE 277

eral, combustion effluents from woodburning devices are increasing world-
wide, and this has resulted in greater public exposure and increased con-
cern by exposed individuals. While more studies are needed to determine
the effects of long-term exposure, and the particular woodsmoke con-
stituent(s) that may be responsible for the observed toxicities, it appears
clear that inhalation of combustion products from wood can have a signifi-
cant impact upon pulmonary homeostasis and/or exacerbation of ongoing
disease processes, especially for those members of the population deemed
most susceptible (i.e., young children, asthmatics, elderly, and individuals
with ongoing cardiopulmonary disease).
Because of public outcry, a number of health-related agencies have
offered some recommendations to individuals using woodburning devices,
including consideration for your neighbors—that is, the smoke you gener-
ate also affects your neighbors “lungs”; burn cleanly and use only dry
wood; avoid burning wood during hazy windless days and nights when
temperature inversions might trap woodsmoke and other pollutants close to
the ground; if possible, convert your woodburning fireplace to use natural
gas or propane; and if your woodstove was manufactured before July 1988,
replace it with one that is certified by the U.S. Environmental Protection
Agency (British Columbia Ministry of the Environment, 1995; American
Lung Association of Washington State, 1998; American Lung Association,
2000). Regarding the use of U.S. EPA-certified stoves, while it is true that
these stoves generate only about half as much PM as uncertified ones (i.e.,
4.0 vs. 10 µg PM/h, respectively), they still create as much particulate pol-
lution as 12,000 houses heating with propane or natural gas.
Overall, more resources need to be devoted to woodsmoke research,
particularly in the areas of air pollution measurements and adverse health
effects, so as to better understand this continuing dilemma (American Lung
Association, 2000).
REFERENCES
Alfheim, I., and Ramdahl, R. 1984. Contribution of wood combustion to indoor air pollution as measured
by mutagenicity in Salmonella and polycyclic aromatic hydrocarbon concentration. Environ.
Mutagen. 6:121–130.
American Lung Association. 2000. Residential wood combustion. Washington, DC: Committee: National
Air Conservation Commission/Scientific Assembly on Environmental and Occupational Health.
American Lung Association of Washington State. 1998. Document on woodsmoke pollution, http://www.
ALA.gov
Anderson, E. W., Andelman, R. J., and Strauch, J. M. 1973. Effect of low-level carbon monoxide expo-
sure on onset and duration of angina pectoris—A study of ten patients with ischemic heart disease.
Ann. Intern. Med. 79:46–50.
Anderson, H. R. 1978. Respiratory abnormalities in Papua New Guinea children: The effects of locality
and domestic woodsmoke pollution. Int. J. Epidemiol. 7:63–72.
Aranyi, C., Graf, J. L., O’Shea, W. J., Graham, J. A., and Miller, F. F. 1983. The effects of intratra-
cheally administered coarse mode articles on respiratory tract infection in mice. Toxicol. Lett. 19:
63–72.
British Columbia Ministry of Environment. 1995. Health effects of inhalable particles: Implications for
278 J. T. ZELIKOFF ET AL.

British Columbia—Overview and conclusions. British Columbia, Canada: Department of Medicine,
University of British Columbia, Vancouver Hospital and Health Sciences Centre for BC Environ-
ment.
Brizio-Molteni, L., Piano, G., Rice, P. L., Warpeha, R., Fresco, R., Solliday, N., and Molteni, A. 1984.
Effect of wood combustion smoke inhalation on angiotensin-1 converting enzyme in the dog. Ann.
Clin. Lab. Sci. 14:381–389.
Browning, K. G., Koenig, J. Q., Checkoway, H., Larson, T. V., and Pierson, W. E. 1990. A questionnaire
study of respiratory health in areas of high and low ambient woodsmoke pollution. Pediatr.
Asthma Allergy Immunol. 4:183–191.
Burrell, R., Flaherty, D. K., and Sauers, L. J., eds. 1992. In Toxicology of the immune system: A human
approach. New York: Van Nostrand Reinhold.
Butcher, S. S., and Sorenson, E. M. 1979. A study of woodstove particulate emissions. Air Pollut.
Control Assoc. 29:724–728.
Butterfield, P., Edmundson, E., LaCava, G., and Penner, J. 1989. Woodstoves and indoor air. J. Environ.
Health 59:172–173.
Chapin, F. S. 1974. Human activity patterns in the city. New York: Wiley-Interscience.
Chen, L. C., Lam, H. F., Kim, E. J., Guty, J., and Amdur, M. O. 1990. Pulmonary effects of ultrafine coal
fly ash inhaled by guinea pigs. J. Toxicol. Environ. Health 29:169–184.
Collings, D. A., Martin, K. S., and Sithole, S. D. 1990. Indoor woodsmoke pollution causing lower res-
piratory disease in children. Trop. Doctor 20:151–155.
Cooper J. A. 1980. Environmental impact of residential wood combustion emissions and its implica-
tions. Air Pollut. Control Assoc. 30:855–861.
Dasch, J. M. 1982. Particulate and gaseous emissions from woodburning fireplaces. Environ. Sci.
Technol. 16:639–645.
Demarest, G. M., Hudson, L. D., and Altman, L. C. 1979. Impaired alveolar macrophage chemotaxis in
patients with acute smoke inhalation. Am. Rev. Respir. Dis. 119:279–286.
Fick, R. B., Jr., Paul, E. S. Merrill, W. W. Reynolds, H. Y., and Lake, J. S. 1984. Alterations in the
antibacterial properties of rabbit pulmonary macrophage exposed to woodsmoke. Am. Rev. Respir.
Dis. 129:76–81.
Franco, E. 1998. Wood stoves linked to mouth cancer. Int. J. Epidemiol. 27:936–940.
Gupta, B. N., Mathur, N., Mahendra, P. N., and Srivastava, A. K. 1997. A study of the household envi-
ronmental risk factors pertaining to respiratory diseases. Energy Environ. Rev. 13:61–67.
Hatch, G., Slade, R., Boykin, E., Hu, P. C., Miller, F. J., and Gardner, D. E. 1981. Correlation of effects
of inhaled versus intratracheally injected metals on susceptibility to respiratory infection in mice.
Am. Rev. Respir. Dis. 124:167–173.
Hildemann, L. M., Markowski, G. R. Jones, M. C., and Cass, G. R. 1991. Submicrometer aerosol mass
distributions of emissions from boilers, fireplaces, automobiles, diesel trucks and meat cooking
operations. Aerosol Sci. Technol. 14:138–152.
Honicky, R. E., and Osborne, J. S. 1991. Respiratory effects of wood heat: Clinical observations and epi-
demiologic assessment. Environ. Health Perspect. 95:105–109.
Honicky, R. E., Akpom, C. A., and Osborne, J. S. 1983. Infant respiratory illness and indoor air pollution
from a woodburning stove. Pediatrics 71:126–128.
Honicky, R. E., Osborne, J. S., and Akpom, C. A. 1985. Symptoms of respiratory illness in young chil-
dren and the use of woodburning stoves for indoor heating. Pediatrics 75:587–593.
Hytönen, S., Alfheim, I., and Sorsa, M. 1983. Effect of emissions from residential woodstoves on SCE
induction in CHO cells. Mutat. Res. 118:69–75.
International Institute for Population Sciences. 1995. National family health survey (MCH and Family
planning): India 1992–93. Bombay: International Institute for Population Sciences.
Jakab, G. J. 1977. Adverse effect of a cigarette smoke component, acrolein, on pulmonary antibacterial
defenses and on viral-bacterial interactions in the lung. Am. Rev. Respir. Dis. 115:33–40.
Jakab, G. J. 1992. Relationship between carbon black particulate-bound formaldehyde, pulmonary
antibacterial defenses, and alveolar macrophage phagocytosis. Inhal. Toxicol. 4:325–342.
Jakab, G. J. 1993. The toxicologic interactions resulting from inhalation of carbon black and acrolein on
pulmonary antibacterial and antiviral defenses. Toxicol. Appl. Pharmacol. 121:167–175.
TOXICOLOGY OF WOODSMOKE 279

Jakab, G. J., and Hemenway, D. R. 1993. Inhalation co-exposure to carbon black and acrolein sup-
presses alveolar macrophage phagocytosis and TNF-
a
release and modulates peritoneal macro-
phage phagocytosis. Inhal. Toxicol. 5:265–279.
Kammen, D. M., Wahhaj, G., and Yiadom, M. Y. 1998. Acute respiratory infections (ARI) and indoor air
pollution (with emphasis on children under five in developing countries). EHP Activity No. 263-
CC, U.S. EPA.
Kerns, W. D., Parkov, K. L., Donofrio, D. J., Gralla, E. J., and Swenberg, J. A. 1983. Carcinogenicity
of formaldehyde in rats and mice after long-term inhalation exposure. Cancer Res. 43:4382–
4392.
Koenig, J. Q., and Pierson, W. E. 1991. Air pollutants and the respiratory system: Toxicity and pharma-
cologic interventions. Clin. Toxicol. 29:401–411.
Koenig, J. Q., Covert, D. S., Larson, T. V., Maykuut, N., Jenkins, P., and Pierson, W. E. 1988.
Woodsmoke: Health effects and legislation. Northwest Environ. J. 4:41–54.
Koenig, J. Q., Larson, T. V., Hanley, Q. S., Rebolledo, V., Dumler, K., Checkoway, H., Wang, S. Z.,
Lin, D., and Pierson, W. E. 1993. Pulmonary function changes in children associated with fine
particulate matter. Environ. Res. 63:26–38.
Lachocki, T. M., Church, D. F., and Pryor, W. A. 1989. Persistent free radicals in woodsmoke: An ESR
spin trapping study. Free Radical Biol. Med. 7:17–21.
Lao, Y. J. 1983. Particulate emissions from woodstoves in a residential area. J. Toxicol. Environ. Health
46:115–117.
Larson, T. V., and Koenig, J. Q. 1994. Wood smoke: Emissions and noncancer respiratory effects. Annu.
Rev. Public Health 15:133–156.
Larson, T. V., Yuen, P., and Maykut, N. 1992. Weekly composite sampling of PM
2.5
for total mass and
trace elements analysis. In Transactions of the Air and Waste Management Association Specialty
Conference on PM
10
Standards and Non-traditional Particulate Source Controls, ed. J. Chow, pp.
112–130 ISBN 0-92-32-04-09. Pittsburgh, PA.
Liang, C. K., Quan, N. Y., Cao, S. R., He, X. Z., and Ma, F. 1988. Natural inhalation exposure to coal
smoke and woodsmoke induces lung cancer in mice and rats. Biomed. Environ. Sci. 1:42–50.
Lipari, F., Dasch, J. M., and Scruggs, W. F. 1984. Aldehyde emissions from woodburning fireplaces.
Environ. Sci. Technol. 18:326–330.
Lipfert, F. W., and Dungan, J. L. 1983. Residential firewood use in the United States. Science 219:
1425–1427.
Loke, J. E., Virgulto, J. A., and Smith, W. 1984. Rabbit lung after smoke inhalation. Arch. Surg. 119:
956–959.
Malik, S. K. 1985. Exposure to domestic cooking fuels and chronic bronchitis. Indian J. Chest Dis. Allied
Sci. 27:171–174.
Maschandreas, D. J., and Zabransky, J. 1980. Comparison of indoor-outdoor concentrations of atmos-
pheric pollutants. Final Report for Electric Power Research Institute, GEOMET Technologies, Inc.,
contract EP1301-1, Palto Alto, CA.
Mishra, V., and Retherferd, R. D. 1997. Cooking smoke increases the risk of acute respiratory infection
in children. Natl. Family Health Surv. Bull. 8:1–4.
Morris, K., Morganlander, M., Coulehan, J. L., Gahagen, S., and Arena, V. C. 1990. Wood-burning stoves
and lower respiratory tract infection in American Indian children. Am. J. Dis. Child. 144:105–108.
National Research Council. 1981. Indoor pollutants. Committee on Indoor Pollutants. Washington, DC:
National Academy Press.
Nieman, G. F., Clark, W. R., Goyette, D., Hart, K. E., and Bredenberg, C. E. 1988. Woodsmoke inhala-
tion increases pulmonary microvascular permeability. Surgery 105:481–487.
Nolte, C. G., Schauer, J. J., Cass, G. R., and Simoneit, B. R. T. 2001. Highly polar organic compounds
present in wood smoke in the ambient environment. Environ. Sci. Technol. 35:1912–1919.
Pandey, M. R. 1984. Domestic smoke pollution and chronic bronchitis in a rural community of the hill
region of Nepal. Thorax 39:337–339.
Pandey, M. R., Boleji, J., Smith, K. R., and Wafula, E. 1989. Indoor air pollution in developing countries
and acute respiratory infection in children. Lancet 25:427–429.
280 J. T. ZELIKOFF ET AL.

Perez-Padilla, R., Regaldo, J., and Vedal, S. 1996. Exposure to biomass smoke and chronic airway dis-
ease in Mexican women: A case-control study. Am. J. Respir. Crit. Care Med. 154:701–706.
Pierson, W. E., Koenig, J. Q., and Bardana, E. J. 1989. Potential adverse health effects of woodsmoke.
West. J. Med. 151:339–342.
Pope, C. A. 1991. Respiratory hospital admissions associated with PM
10
pollution in Utah, Salt Lake,
and Cache Valleys. Arch. Environ. Health 46:90–97.
Rajpandey, M. 1984. Domestic smoke pollution and chronic bronchitis in a rural community of the Hill
Region of Nepal. Thorax 39:337–339.
Ramage, J. E., Roggli, V. L., Bell, D. Y., and Piantadosi, C. A. 1988. Interstitial lung disease and domes-
tic woodburning. Am. Rev. Respir. Dis. 137:1229–1232.
Samet, J. M., Marbury, M. C., and Spengler, J. D. 1987. Health effects and sources of indoor air pollu-
tion. Part I. Am. Rev. Respir. Dis. 136:1486–1508.
Samet, J. M., Marbury, M. C., and Spengler, J. D. 1988. Health effects and sources of indoor air pollu-
tion. Part II. Am. Rev. Respir. Dis. 137:221–242.
Sandoval, J., Salas, J., Martinez-Guerra, M. L., Gomez, A., Martinez, C., Portales, A., Palomar, A.,
Villegas, M., and Barrios, R. 1993. Pulmonary arterial hypertension and cor pulmonale associated
with chronic domestic woodsmoke inhalation. Chest 103:12–20.
Schwartz, J. 1991. Particulate air pollution and daily mortality: A synthesis. Public Health Rev. 92:39–
60.
Schwartz, J. 1993. Particulate air pollution and chronic respiratory disease. Environ. Res. 62:7–13.
Sexton, K., Liu, K. S., Treitman, R. D., Spengler, J. D., and Turner, W. A. 1986. Characterization of
indoor air quality in woodburning residencies. Environ. Int. 12:265–278.
Smith, K. R., ed. 1987. Air pollution and health: A global review. New York: Plenum Press.
Smith, K. R. 1993. Fuel combustion, air pollution exposure, and health: The situation in developing
countries. Annu. Rev. Energy Environ. 18:529–566.
Smith, K. R. 2000. National burden of disease in India from indoor air pollution. Proc. Natl. Acad. Sci.
USA 97:13286–13293.
Smith, K. R., and Liu, Y. 1994. Indoor air pollution in developing countries. Epidemiol. Lung Cancer
74:151–184.
Sobue, T. 1990. Association of indoor air pollution and lifestyle with lung cancer in Osaka, Japan. Int. J.
Epidemiol. 19(suppl. 1):s62–s66.
Speizer, F. E., Ferris, B., Bishop, Y. M., and Spengler, J. 1980. Respiratory disease rates and pulmonary
function in children associated with NO
2
exposure. Am. Rev. Respir. Dis. 121:3–10.
Szalar, A. 1972. The use of time: Daily activities of urban and suburban populations in twelve countries.
The Hague: Mouton.
Thomas, P. T., and Zelikoff, J. T. 1999. Air pollutants: Modulators of pulmonary host resistance against
infection. In Air pollutants and effects on health, eds. S. L. Hogate, H. S. Koren, J. M. Samet, and
R. L. Maynard, pp. 420–450. London: Academic Press.
Thorning, D. R., Marianne, L. H., Hudson, L. D., and Schumacher, R. L. 1982. Pulmonary responses to
smoke inhalation: Morphologic changes in rabbits exposed to pine woodsmoke. Hum. Pathol. 13:
355–364.
Traynor, G. W., Apte, M. G., Carruthers, A. R., Dillworth, J. F., Grimsrud, D. T., and Gundel, L. A.
1987. Indoor air pollution due to emissions from wood-burning stoves. Environ. Sci. Technol. 21:
691–697.
Tuthill, R. W. 1984. Woodstoves, formaldehyde, and respiratory disease. Am. J. Epidemiol. 120:952–
955.
U.S. Environmental Protection Agency. 1993. A summary of the emissions characterization and non-
cancer respiratory effects of wood smoke. EPA-453/R-93-036. Washington, DC: U.S. EPA.
U.S. Environmental Protection Agency. 1994. Integrated air cancer project. Research to improve risk
assessment of area sources: Woodstoves and mobile sources: Boise, Idaho. Part 1. Air and Energy
Engineering Research Laboratory, Atmospheric Research and Exposure Assessment Laboratory,
Health Effects Research Laboratory. Research Triangle Park, NC: Office of Research and Develop-
ment, U.S. Environmental Protection Agency.
TOXICOLOGY OF WOODSMOKE 281

U.S. Environmental Protection Agency. 2001. Air quality criteria for particulate matter, Vols. 1 and 2.
Office of Research and Development. EPA 600/P-99/002bB. Washington, DC: U.S. EPA.
White, K. L., Kawabata, T. T., and Ladics, G. S. 1994. Mechanisms of polycyclic aromatic hydrocarbon
immunotoxicity. In Immunotoxicology and immunopharmacology, eds. J. H. Dean, M. I. Luster,
A. E. Munson, and I. Kimber, Jr., pp. 123–146. New York: Raven Press.
Wong, K. L., Stock, M. F., Malek, D. E., and Alarie, Y. 1984. Evaluation of the pulmonary effects of
woodsmoke in guinea pigs by repeated CO
2
challenges. Toxicol. Appl. Pharmacol. 75:69–80.
World Health Organization. 1997. Health and environment for sustainable development. Geneva:
World Health Organization.
Zelikoff, J. T. 2000. Woodsmoke, kerosene emissions, and diesel exhaust emissions. In Pulmonary
immunotoxicology, eds. M. D. Cohen, J. T. Zelikoff, and R. B. Schlesinger, pp. 369–387. Boston:
Kluwer.
Zelikoff, J. T., Baker, K., Cohen, M. D., and Chen, L. C. 1995a. Woodsmoke emissions: Effects on pul-
monary immune defense. Toxicologist 256:15.
Zelikoff, J. T., Baker, K., Cohen, M. D., and Chen, L. C. 1995b. Inhalation of woodsmoke compromises
pulmonary host resistance against bacterial infections. Am. Rev. Respir. Dis. 150:89.
Zelikoff, J. T., Nadziejko, C., Fang, K., Gordon, T., Premdass, C., and Cohen, M. D. 1999. Short-term,
low-dose inhalation of ambient particulate matter exacerbates ongoing pneumococcal infections
in Streptococcus pneumoniae-infected rats. Proc. Third Colloq. Particulate Air Pollution and
Human Health 8-94-8-104.
Zelikoff, J. T., Schermerhorn, K. R., Fang, K., Cohen, M. D., and Schlesinger, R. B. 2002. A role for asso-
ciated transition metals in the immunotoxicity of inhaled ambient particulate matter (pm). Environ.
Health Perspect., in press.
282 J. T. ZELIKOFF ET AL.