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Received: 19 October 2016 Accepted: 28 January 2017 DOI: 10.1111/ina.12370
ORIGINAL ARTICLE
Airborne endotoxin concentrations in indoor and outdoor particulate matter and their predictors in an urban city Y. Yoda1 | K. Tamura2 | M. Shima1,3 1
Department of Public Health, Hyogo College of Medicine, Nishinomiya, Japan
Abstract
2
Endotoxins are an important biological component of particulate matter and have been
Center for Health and Environmental Risk Research, National Institute for Environmental Studies, Tsukuba, Japan 3
Hyogo Regional Center of Japan Environment and Children’s Study, Hyogo College of Medicine, Nishinomiya, Japan Correspondence Masayuki Shima, Department of Public Health, Hyogo College of Medicine, Nishinomiya, Hyogo, Japan. Email:
[email protected] Funding information Grants-in-Aid for Scientific Research, Grant/ Award Number: 23249034, 25670327, and 15H04790; Japan Society for the Promotion of Science (JSPS)
associated with adverse effects on human health. There have been some recent studies on airborne endotoxin concentrations. We collected fine (PM2.5) and coarse (PM10-2.5) particulate matter twice on weekdays and weekends each for 48 hour, inside and outside 55 homes in an urban city in Japan. Endotoxin concentrations in both fractions were measured using the kinetic Limulus Amebocyte Lysate assay. The relationships between endotoxin concentrations and household characteristics were evaluated for each fraction. Both indoor and outdoor endotoxin concentrations were higher in PM2.5 than in PM10-2.5. In both PM2.5 and PM10-2.5, indoor endotoxin concentrations were higher than outdoor concentrations, and the indoor endotoxin concentrations significantly correlated with outdoor concentrations in each fraction (R2=0.458 and 0.198, respectively). Indoor endotoxin concentrations in PM2.5 were significantly higher in homes with tatami or carpet flooring and in homes with pets, and lower in homes that used air purifiers. Indoor endotoxin concentrations in PM10-2.5 were significantly higher in homes with two or more children and homes with tatami or carpet flooring. These results showed that the indoor endotoxin concentrations were associated with the household characteristics in addition to outdoor endotoxin concentrations. KEYWORDS
coarse particulate matter, endotoxin, fine particulate matter, household characteristics, indoor environment, outdoor air quality
1 | INTRODUCTION
with wheezing at age 3 years.6 On the other hand, some studies have
Endotoxins, important biological components of airborne particu-
tective against onset of asthma in childhood.2,7
shown that high exposure to endotoxins during early infancy was prolate matter (PM), are active lipopolysaccharides, which are cell wall
Many previous studies have evaluated the effects of endotoxins
components of the outer membrane of gram-negative bacteria.1
on human health using the concentrations in house dust collected
Exposure to endotoxins is known to induce pulmonary inflammation
from flooring or bedding in the homes by vacuuming, as a surrogate
with a recruitment of macrophages and neutrophils.2,3 Previous stud-
for exposure to airborne endotoxins.5,6,8-10 However, the concentra-
ies have shown that exposure to endotoxins in settled house dust is
tions of indoor airborne endotoxins may also be affected by factors
associated with exacerbation of respiratory allergic diseases including
within living environments other than house dust and endotoxins that
asthma, and with increased asthma prevalence.4,5 A birth cohort study
have infiltrated from outdoor air.11 In a longitudinal study, endotoxin
reported that exposure to endotoxins during infancy was associated
levels in house dust were found to not be significantly associated with
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. © 2017 The Authors. Indoor Air Published by John Wiley & Sons Ltd. Indoor Air. 2017;27:955–964.
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the levels of airborne endotoxins.12 Therefore, direct measurements of airborne endotoxins are needed to evaluate the effects of exposure to endotoxins on human health accurately.4 PM with a wide range of sizes is suspended in outdoor air. Exposure
Practical implications • Exposure to endotoxins, important biological components of airborne particulate matter (PM), is reported to
to fine PM less than 2.5 μm in diameter (PM2.5) and coarse PM with
have adverse effects on human health. This study showed
a diameter between 2.5 and 10 μm (PM10-2.5) has adverse effects on
the endotoxin concentrations in fine (PM2.5) and coarse
human health.13-15 PM2.5 and PM10-2.5 are present in indoor as well
(PM10-2.5) particulate matter collected inside and outside
as outdoor air, and are reported to have adverse effects on respira-
homes in an urban city. For both PM2.5 and PM10-2.5, in-
tory morbidity in asthmatic patients.16 Recently, some studies have
door endotoxins may arise from indoor sources in addi-
analyzed the endotoxin concentrations in airborne particles,17-19 and
tion to the infiltration from outdoor air. The household
the endotoxin concentrations in each fraction after sampling airborne
factors associated with indoor endotoxin concentrations
PM2.5 and PM10-2.5 separately according to aerodynamic diameters
are considered to be different depending on the particle
have been reported.20-23 The adverse effects of exposure to endotox-
size fractions. Further studies with larger samples and
ins in PM2.5 and PM10 on lung function and symptoms were reported
longer sampling periods are necessary for the more de-
lyzing airborne endotoxins have not been standardized.25
concentrations.
in asthmatic children.24 However, the methods for sampling and ana-
tailed evaluation of the predictors of indoor endotoxin
In the present study, we collected PM2.5 and PM10-2.5 inside and outside homes of pregnant women who participated in a birth cohort study in Japan. The endotoxin concentrations in PM2.5 and PM10-2.5 were analyzed, and the indoor and outdoor concentrations were compared for each fraction. We then evaluated the relationships of the indoor endotoxin concentrations with various household characteristics.
hour using a timer. The sampling was conducted in five homes per week. We collected PM2.5 and PM10-2.5 using portable air samplers (MP- Σ300N; Sibata Scientific Technology Inc., Tokyo, Japan) equipped with cascade impactors (ATPS-20H; Sibata Scientific Technology Inc.) with
2 | METHODS 2.1 | Study design
a flow rate of 1.5 L/min. For collection of a parallel sample, two air samplers were placed on furniture or a stand at a height of 1.0-1.5 m in the living room or family room where the subjects spent the majority of their time when awake, and the other two samplers were also
This study was conducted as an adjunct study outlined in the Japan
placed at 1.0-1.5 m above floor level in areas outside the house, such
Environment and Children’s Study (JECS) protocol paper.26 The JECS
as the veranda, porch, or under the eaves. PM samples were collected
is an ongoing birth cohort study that began in 2011 to evaluate the
on Teflon-coated glass fiber filters (Pallflex TX40H120, Ann Arbor, MI)
effects of various environmental factors on children’s health and de-
and quartz filters (Whatman Inc., Florham Park, NJ) for the measure-
velopment, and is being conducted in 15 regions across Japan. The
ment of mass concentrations and endotoxins of PM, respectively.
study protocol was approved by the Ministry of the Environment of
The mass concentrations of PM2.5 and PM10-2.5 were measured
Japan. The purpose of this study was to examine the role of endotoxin
by weighing the glass fiber filters before and after sampling using an
exposure during pregnancy in Amagasaki, Japan, one of the study re-
ultra-microbalance with a sensitivity of 0.1 μg (UMX-2, Mettler-Toledo
gions of the JECS. Amagasaki is an industrial city located in Hyōgo
Inc., Columbus, OH), after storage for more than 24 hour at a constant
Prefecture in western Japan. The population of Amagasaki is approxi-
temperature (23±0.2°C) and relative humidity (50±1%). Quartz fiber
mately 466 000 (March 2014), and its area is approximately 49.8 km2.
filters for the endotoxin assay were sterilized by dry heat at 250°C for
The subjects of this study were pregnant women selected from the
2 hour before use. After air sampling, the quartz filters were stored at
JECS participants in Amagasaki. The study protocol was approved by
−30°C until the analyses.
the Ethics Committee of Hyogo College of Medicine, and written informed consent was obtained from all participants.
Household characteristics were evaluated using a questionnaire (Appendix in Supporting Information). We obtained meteorological data such as ambient temperature and relative humidity at the nearest
2.2 | Home visits and sample collection We visited the homes of 55 pregnant women who participated in the JECS study between February 1, 2014, and July 31, 2014. All of
monitoring station from the Japan Meteorological Agency.27
2.3 | Endotoxin assay
them were non-smokers, and it was confirmed that none of the other
Endotoxins were analyzed using the kinetic Limulus Amebocyte Lysate
household members smoked in the home. Air samples were collected
assay (Pyrostar ES-F test, Wako Pure Chemical Industries, Ltd., Osaka,
inside and outside the house, twice in each home, once during week-
Japan). For the extraction of endotoxins, the quartz fiber filter was
days (from 0:00 on Thursday to 24:00 on Friday) and once on the
transferred into an endotoxin-free test tube with 1.9 mL endotoxin-
weekends (from 0:00 on Saturday to 24:00 on Sunday) each for 48
free water and 0.1 mL endotoxin extracting solution. After stirring for
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YODA et al.
T A B L E 1 Descriptive statistics of endotoxin and mass concentrations of particulate matter Weekdays n
GM
Weekends (95% CI)
Median
(Range)
n
GM
(95% CI)
Median
(Range)
P value*
3
Endotoxin (EU/m ) Indoor PM2.5
55
0.13
(0.10, 0.16)
0.15
(0.01, 0.57)
55
0.16
(0.13, 0.20)
0.16
(0.03, 1.09)
.112
Outdoor PM2.5
55
0.09
(0.08, 0.11)
0.10
(0.02, 0.41)
55
0.12
(0.10, 0.15)
0.11
(0.01, 0.72)
.052
Indoor PM10-2.5
55
0.09
(0.07, 0.11)
0.07
(0.01, 0.36)
54
0.13
(0.10, 0.16)
0.13
(0.02, 0.80)
.022
Outdoor PM10-2.5
55
0.07
(0.06, 0.09)
0.10
(0.03, 0.27)
55
0.10
(0.08, 0.11)
0.08
(0.04, 0.36)
.014
Mass concentration (μg/m3) Indoor PM2.5
55
11.3
(9.4, 13.4)
12.2
(3.1, 32.5)
55
11.9
(10.3, 13.8)
10.6
(4.6, 45.8)
.625
Outdoor PM2.5
55
13.2
(11.2, 15.6)
13.0
(4.7, 40.0)
55
12.8
(10.7, 15.4)
12.0
(1.2, 46.7)
.816
Indoor PM10-2.5
55
4.9
(4.0, 6.1)
4.9
(1.1, 33.3)
55
5.4
(4.4, 6.7)
5.1
(1.0, 33.3)
.529
Outdoor PM10-2.5
55
6.1
(5.0, 7.5)
5.0
(2.4, 47.1)
55
6.5
(5.3, 8.1)
5.8
(2.0, 50.3)
.658
GM, geometric mean; CI, confidence interval; EU, endotoxin units; PM2.5, particulate matter less than 2.5 μm in aerodynamic diameter; PM10-2.5, particulate matter ranging from 2.5 to 10 μm in aerodynamic diameter. *Comparison between weekdays and weekends.
10 seconds, the tube was sonicated in a water bath for 20 minute
and random effects and is suitable for a study in which multiple mea-
and allowed to stand at room temperature for 40 minute. The tube
surements are conducted for each subject. We fit a block-diagonal
was then centrifuged at 1000 g for 5 minute at 4°C for clearing of
covariance structure in the models to account for the repeated mea-
the aqueous extracts of quartz fibers and particles. The supernatant
surements at the same home. The following variables were included in
was used for the endotoxin assay conducted using a Toxinometer (ET-
the models: the number of children, presence of a pet in the home, use
6000, Wako Pure Chemical Industries, Ltd., Osaka, Japan). Negative
of air purifier, type of flooring, structure of house, floor level, windows
control quartz filters were extracted and analyzed as field blanks with
open time, temperature, relative humidity, and outdoor endotoxin
an air sample. All glassware and devices were sterilized by dry heat at
concentrations. The results were shown as percent changes and 95%
250°C for 2 hour before use. All measurements were performed in
CIs in indoor endotoxin concentrations. A P-value of
