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Proceedings of the Summer Crash Course Programme 2018 103
EXTENDED ABSTRACT
Traffic Related Air Pollution and Its Impact on Respiratory
Health among Children
Nur Hazirah Hisamuddin, Juliana Jalaludin
Department of Environmental and Occupational Health, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia,
43400 UPM, Serdang, Selangor, Malaysia.
SUMMARY
Exposure to traffic related air pollution (TRAP) is a public health concern particularly in children, who are one of the
most susceptible groups of the population. Children are more vulnerable to such exposure by virtue of their increased
susceptibility and the higher doses received. The materials for this review was obtained from several online databas-
es; PubMed, Proquest, Scopus, Springerlink and Science Direct (year 1990 to 2018). In this review, we emphasized
several relevant studies on respiratory health effects among children living in the proximity to heavy traffic area and
focus on the factors, which contributed to the severity of the health outcomes. Short term TRAP exposure reduces
lung function, increases respiratory symptoms and incidence of asthma and allergic diseases especially for those who
living within 75 m from the heavy traffic area. Preventive measures must be taken in order to protect children from
exposure to traffic air pollutants.
Keywords: PM2.5, Traffic-related air pollution, Respiratory Health, Children
Corresponding Author:
Juliana Jalaludin, PhD
Email: juliana@upm.edu.my
Tel: +60389472397
INTRODUCTION
Traffic related air pollution (TRAP) is the main contributor
to global air pollution. The increasing number of
vehicles remains the most significant source of air
pollution in many urban areas. Traffic is an increasingly
important source of particulate matter (PM), especially
fine PM with an aerodynamic diameter less than 2.5µm
(PM2.5). PM2.5 can penetrate easily into respiratory
tract and reach circulatory system and be more toxic
than coarse particles. There are several epidemiological
studies found that the exposure to TRAP plays important
role in aetiology and prognosis of a large scale of
illnesses, including asthma, impaired lung function,
allergy, adverse birth outcomes, cardiovascular disease
and cancer (1, 2). Exposure to TRAP is a public health
concern particularly in children, who are one of the most
susceptible groups of the population. In this review,
we emphasize a summary of epidemiological studies
conducted on various respiratory health outcomes
among children who lived or attend school near heavy
traffic area.
MATERIALS AND METHODS
This review has been conducted by using the online
databases from scientific journal search engines, which
were Science direct, Springerlink, Pubmed, and Google
Scholar. The year of reviewed publication is within
2000 to 2018 and written in English Language. The
articles used in this study were full-published papers,
including original scientific papers, reviews and letters,
which emphasized on TRAP and respiratory health
outcomes among children only. The identified articles
were chosen by keywords “Heavy Traffic and Children”,
“Traffic Related Air Pollution and Children’s Respiratory
Health”, “Heavy Traffic and Acute Health Effect”.
Occupational exposure was excluded from the search
criteria. The article that is fulfilled the criteria were
reviewed in full.
RESULTS
Based on literature surveys, we found 8 relevant studies
on the association between TRAP exposure and acute
respiratory health effects among children.
Respiratory Symptoms
Questionnaire filled by parent or legal guardians are
commonly used to ascertain respiratory symptoms
among children. A cohort study was conducted to assess
the effect of exposure to TRAP on respiratory health
of 147 asthmatic and 50 healthy children, residing in
Mexico City (3). The subjects were followed up for an
average of 22 weeks to assess the incidence density of
coughing, wheezing and breathing difficulty by referring
to daily records of symptoms and child’s medication.
Malaysian Journal of Medicine and Health Sciences Vol.15 Supp 3, Aug 2019 (eISSN 2636-9346)
104 Proceedings of the Summer Crash Course Programme 2018
The exposure to PM2.5, NO2 and O3 were estimated from
four fixed-sites for central monitoring at locations within
the study area and air monitoring at each school were
conducted to validate the data obtained from the fixed-
site monitoring stations. Statistical analysis showed
that wheezing was related significantly to PM2.5 (95%
CI: 2.4% to 15.5%); NO2 (95% CI: 2.3% to16.4%) and
O3 levels (95% CI: 3.2% to 17.3%). The traffic density
was found significantly related to respiratory symptoms
(coughing and/or wheezing) in asthmatic children. When
accounting for the distance from the child’s residence
to the main avenue, the risk of wheezing decreased
significantly with greater distance (IRR = 0.69; 95% CI:
0.49 to 0.98) with an increase in distance of 212 m.
Venn et al. (4) had conducted study on the effect of living
close to a traffic bearing road on the risk of wheezing in
Jimma, Ethiopia. They have used data from a previous
study conducted by Yemeneberhan et al. (5) on survey of
respiratory symptoms, allergic disease, and demographic
and lifestyle factors among 9844 children and adults
living in 21 administrative districts in Jimma, Ethiopia.
In 2003, the homes of these people were retraced.
The shortest distance to the nearest surfaced road and
traffic flows on these roads were measured. The result
of the study showed that among 3,592 individuals living
within 150 m of a road, the risk of wheeze increased
significantly in linear relation to proximity to the road
(adjusted OR = 1.17 per 30 m proximity; 95% CI,
1.01–1.36). These findings indicate that living in close
proximity to road vehicle traffic is associated with an
increased risk of wheeze, but that other environmental
factors are also likely to be important.
Allergic Disease
Jung et al. (6) had conducted a cross sectional study to
assess the relationship of living near to main roads to
allergic diseases among 5,443 Korean children aged
6-14 years. The diagnosis of allergic disease was made
on the basis of the questionnaire survey completed by
parents and the measurement of allergic sensitization
was made using skin prick test. The TRAP exposure
including the distance to busy roads, the length of main
roads and main road density in the home area were
assessed using geographical information system (GIS).
Based on the data, children living less than 75 m from
the main road were significantly associated with lifetime
allergic rhinitis (AR), past-year AR symptoms, diagnosed
AR and treated AR. Moreover, there was a positive
association between living alongside busy roads and
allergic sensitization.
In another cohort study by Morgenstern et al. (7), they
investigated atopic diseases and allergic sensitization
among 2,860 children at the age of 4 years and 3,061
at the age of 6 years. Based on the study, a strong
positive association were found between the distance
to the nearest main road and hay fever, eczema, and
sensitization. A distance-dependent relationship could
be identified, with the highest odds ratios (ORs) for
children living less than 50 m from busy streets. For
PM2.5 absorbance, statistically significant effects were
found for hay fever (OR, 1.59; 95% CI, 1.11–2.27) and
allergic sensitization to pollen (OR, 1.40; 95% CI, 1.20–
1.64). Moreover, NO2 exposure was associated with
eczema, whereas no association was found for allergic
sensitization.
Asthma
In a study of McConnell et al. (8) on traffic and childhood
asthma, they found that residence within 75 m of a major
road was associated with an increased risk of lifetime
asthma , prevalent asthma and wheeze with odds ratio
1.29 (95% CI: 1.01–1.86), 1.50 (95% CI, 1.16–1.95),
and 1.40 (95% CI, 1.09–1.78) respectively. Interestingly,
the findings revealed that long-term residents with no
parental history of asthma have increased susceptibility
for lifetime asthma, prevalent asthma and recent wheeze
with odds ratio 1.85 (95% CI: 1.11–3.09), 2.46 (95%
CI: 0.48–4.09), and 2.74 (95% CI: 1.71–4.39). They
concluded that residence near a major road is associated
with asthma and the reason for larger effects in those
with no parental history of asthma needs further study.
Another study in New York City was conducted to assess
the association of personal exposure to TRAP and acute
respiratory health among schoolchildren with asthma
(9). Based on statistical analysis, they found relative risks
of wheeze [1.45; 95% confidence interval (CI), 1.03–
2.04)], shortness of breath (1.41; 95% CI, 1.01–1.99),
and total symptoms (1.30; 95% CI, 1.04–1.62) with
an increase in personal elemental carbon. The study
indicated that adverse health associations were strongest
with personal measures of elemental carbon exposure,
suggesting that the diesel soot fraction of PM2.5 is most
responsible for pollution-related asthma exacerbations
among children living near roadways.
Lung Function
Lung function test is a common test used to assess
how well the lungs work, through deep inhalation
and expiration process by using a spirometer. The
measurement reflects that children with the highest
lung function possess the highest lung growth. In this
review, several scientific studies have been identified
demonstrating lung health condition among children
living near the heavy traffic area. Anis and Juliana (1)
had found that there was a significant difference of
indoor PM2.5, lung function abnormality and respiratory
symptoms between exposed and comparative group
with the value of (t=-2.496, p=0.014); (χ2 =17.926,
p=0.000) and (χ22 =7.259, p=0.007) for predicted FEV%
and FVC%; and (p=0.000) respectively. However, it was
reported in the study that overall lung function status
was weakly associated with indoor PM2.5.
Another cohort study by Rice et al. (10) found that
estimation of long-term exposure to ambient pollution,
including proximity to major roadway, PM2.5 and black
Malaysian Journal of Medicine and Health Sciences Vol.15 Supp 3, Aug 2019 (eISSN 2636-9346)
Proceedings of the Summer Crash Course Programme 2018 105
carbon were associated with lower lung function
in Boston children. Statistical analysis showed that
distances greater than or equal to 400 m, living less than
100 m from a major roadway was associated with lower
FVC (−98.6 ml; −176.3 to −21.0). The study indicated
that residential proximity to roadway and prior-year
and lifetime PM2.5 and black carbon exposure were all
associated with lower FVC.
DISCUSSION AND CONCLUSION
Various study designs are used in air quality studies
including cross sectional study and cohort study. Based
on TRAP related literatures, 2 studies used cross sectional
study (1,6) and 6 studies used cohort study design (3,4,7-
10). In cross-sectional survey, the limitation is causal
inference cannot be made whereby the explanation of
causal relationship is limited between traffic exposure
and diseases. As compared to cohort study, the
investigation on health effects in cross sectional study
is conducted at a single point in time and therefore may
create bias in reflecting real exposure. For instance,
in a cross sectional study (6), they had identified the
symptoms of allergic diseases based on parent-reported
questionnaires. Responses could have been dependent
on parents’ awareness on allergic symptoms which may
result in recall bias and probability of misclassification
of disease. Meanwhile in cohort study, the use of rich
information on the confounders could confirm the
association between TRAP and the diseases. Besides,
the prospective nature of cohort study also allow the
evaluation of association between daily changes in air
pollutants level and symptoms which can represent
specific differences in children’s health symptoms over
time (3).
Several exposure metrics are used in TRAP studies
investigating health effects, mainly on central-site
monitoring data (3, 8), modeled exposure variables (7), or
employed proximity to roadway (4, 6, 10). As compared
to study that uses personal measurement, the study has
the ability to obtain daily measures of personal exposure
rather than distance from roadway indices or central site
data. For example, a study (9) found associations using
school-site monitoring for elemental carbon, suggesting
that school-site stationary measurements of elemental
carbon may be representative of average daily personal
exposures across the study participants in urban setting.
However, they found the strongest and most consistent
health–elemental carbon associations with more
accurate personal measure. Therefore, exposure–health
effects studies that rely on exposure measurement from
central-site monitors may be underestimating health
relationships with pollutant. The use of estimated
measures based of near roadway exposure based on
model may not reflect actual personal exposure and
thus lead to some exposure misclassification.
Many studies found that a shorter distance from the
residence to the nearest main road, especially within a
75-m home area, was significantly related to an increased
prevalence of respiratory health symptoms. In German
cohorts, children aged 4 and 6 years living closer than
50m to a busy street had the highest probability of getting
allergic symptoms compared with children living further
away than 50m, 250m and 1000m (7). A significant
association was also found between the prevalence
of asthma and living within 75 m of a major road in
the Southern California Children’s Health Study (8). In
contrast, a study (4) found the prevalence of wheeze in
those living away from roads (>150m) was greater than
those living within 150m of a surface road suggesting
that some other environmental factors may play an
important role in asthma aetiology in this population.
To evaluate the effects of air pollution on health, the
potential involvement of indoor air pollution should be
measured as it could also be responsible for asthma and
allergic disease. Exposure to TRAP also is influenced by
the type of building, the type of traffic on the road, the
presence of physical obstructions between the road and
the home, the amount of time spent at home and exposure
elsewhere (6). Besides, assessment on genetic influences
should be considered as genetic characteristics may also
increase susceptibility to air pollutants (3).
In conclusion, most of the epidemiological studies
demonstrated that children living nearby heavy traffic
area have a greater risk of respiratory health impairment.
Thus, preventive measures must be taken in order
to protect children from exposure to environmental
pollutants.
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