Total and lobar depositions of fungal particles in the human lung were calculated for the workers in a cotton spin factory using an updated version of the Monte Carlo transport and deposition code IDEAL. The study is based on nasal breathing under light exercises activity with a standard functional residual capacity (FRC) of 3300 ml, tidal volume (VT) of 1250 ml and breathing frequency (f) of 20 min1 . The present calculation is based on our previous measurements of the size distribution of fungal particles in the cotton spin factory using six-stage Andersen impactor as a viable sampler. The measurements were carried out in the two main working departments: carding department (Dept1) as a model for high dust concentration area and spinning department (Dept2) as a model for low dust concentration area. It was found that the total deposition of fungal particles is higher in the carding and blowing department (Dept1) than that in the spinning department (Dept2). For lobar deposition, it was found that the deposition of Aspergillus niger and Penicillium has the highest deposition in the RL and LL lobes. These predictions show two distinct deposition maxima at the bronchial and the acinar regions with the highest deposition being in the acinar region. In all cases, the deposition reaches its maximum at generation 12 in the bronchial region and at generation 22 in the acinar region. The results reveal a positive relationship between the deposition of biological particles and some respiratory diseases.
Trang 1ORIGINAL ARTICLE
Theoretical deposition of fungal aerosol particles
in the human respiratory tract
Physics Department, Faculty of Science, Minia University, Minia, Egypt
Received 10 March 2011; revised 13 June 2011; accepted 21 June 2011
Available online 23 July 2011
KEYWORDS
Biological particles;
Stochastic lung model;
Cotton dust;
Deposition
Abstract Total and lobar depositions of fungal particles in the human lung were calculated for the workers in a cotton spin factory using an updated version of the Monte Carlo transport and depo-sition code IDEAL The study is based on nasal breathing under light exercises activity with a stan-dard functional residual capacity (FRC) of 3300 ml, tidal volume (VT) of 1250 ml and breathing frequency (f) of 20 min1 The present calculation is based on our previous measurements of the size distribution of fungal particles in the cotton spin factory using six-stage Andersen impactor
as a viable sampler The measurements were carried out in the two main working departments: carding department (Dept1) as a model for high dust concentration area and spinning department (Dept2) as a model for low dust concentration area It was found that the total deposition of fungal particles is higher in the carding and blowing department (Dept1) than that in the spinning depart-ment (Dept2) For lobar deposition, it was found that the deposition of Aspergillus niger and Pen-icilliumhas the highest deposition in the RL and LL lobes These predictions show two distinct deposition maxima at the bronchial and the acinar regions with the highest deposition being in the acinar region In all cases, the deposition reaches its maximum at generation 12 in the bronchial region and at generation 22 in the acinar region The results reveal a positive relationship between the deposition of biological particles and some respiratory diseases
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Introduction
Biological aerosol particles, such as bacteria, fungal cells, viruses, are airborne particles that are living, contain living organisms, or are released from living organisms Although many of them are nonpathogenic, there is increasing evidence that exposure to such bioaerosols is associated with a wide range of health effects including infectious diseases, acute toxic effects, allergies, and cancer[1] Cotton dust represents the ma-jor contributor to such respiratory problems and its effect on pulmonary function among workers employed in cotton-spin-ning mills is well known[2]
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2090-1232 ª 2011 Cairo University Production and hosting by
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doi: 10.1016/j.jare.2011.06.002
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Cairo University Journal of Advanced Research
Trang 2Diseases caused by inhalation of different biological
parti-cles depend not only on the biological properties and chemical
composition of these biological particles but also on the
num-ber of particles inhaled and the site of their deposition in the
respiratory system The deposition site is directly related to
the aerodynamic diameter of the particles Particles larger than
10 lm have a low probability of entering and traveling the
nasopharyngeal region of the respiratory tract, while particles
of 5–10 lm diameter are mainly deposited in the upper
respira-tory tract Moreover, particles smaller than 5 lm, called
respi-rable fraction, are able to penetrate into lung alveoli causing
allergic alveolitis and other serious illnesses[3–5] Upon
inha-lation of ambient aerosols, the initial deposition of inhaled
particles in the human respiratory tract may have a significant
role in the development of lung diseases if the particles are not
sufficiently removed from the lung Therefore, the main
objec-tive of the study was to determine the deposition of bioaerosol
particles in the human respiratory tract applying the stochastic
lung model and the standard nasal breathing parameters, for
light exercise activity, ICRP[6] In order to find out the air
quality at different departments of the mill, the experimental
size distribution parameters of bioaerosols from our previous
study in the cotton spin factory of Minia city/Egypt[7]were
used in this study The present investigation should help to
characterize the final fate of the inhalable particles inside the
respiratory tract and to introduce some solutions to minimize
the risk of working in such occupational environments
Methodology
Deposition of inhaled particles was calculated using an
up-dated version of the Monte Carlo transport and deposition
code IDEAL[8,9], which is based on a stochastic
morphomet-ric model of the human lung[10]
In the Monte Carlo transport and deposition model, the
random walk of inspired particles through a stochastically
gen-erated airway branching system is simulated by randomly
selecting a sequence of airways for each individual particle
To further improve the performance of the Monte Carlo
meth-od, the statistical weight technique was applied For a detailed
description of this method the reader is kindly referred to the
work of Koblinger and Hofmann[8]
Particle deposition in individual airways due to various
physical deposition mechanisms, diffusion, inertial impaction
and gravitational settling was computed by the commonly
used analytical deposition equations for straight and bent
tubes, i.e., deposition of an individual particle is based on
the average deposition behavior of many particles Deposition
by Brownian motion in upper bronchial airways was
deter-mined by the empirical equation proposed by Cohen and
Asgharian[11]where the deposition by diffusion gDis given
by:
gD¼ a0Da 1; 109<D < 104
gD¼ a2Da3; 109<D < 104
The numerical values of the coefficients are:
a0¼ 7:389; a1¼ 0:674; a2¼ 2:965; a3¼ 0:568
and D¼pLD
4Q
where D is the diffusion coefficient, L the airway length, Q is the flow rate through the airway and D = kTB; where k is the Boltzmann constant, T the absolute temperature and Q
is the particle mobility
The magnitude of deposition by inertial impaction in upper bronchial airways was calculated according to Yeh and Schum
[12]where the impaction deposition probability PIis given by:
PI¼ 1 2
pcos
1ðh stÞ þ1
psin½2 cos1ðh stÞ for h st < 1
PI¼ 1 for h st P 1 where h is the bend angle or branching angle (in radians), st is the Stokes’ number =Cqp r 2
9lR ; where C is the Cunningham slip correction factor, qpthe density of the particle, rpthe radius
of the particle, m the mean flow velocity, l the viscosity of the fluid and R is the radius of the tube or airway
The deposition by gravitational settling was calculated according to Yeh and Schum [12] where the sedimentation deposition probability Psis given by:
Ps¼ 1 exp 4gCqpr
2Lcos / 9plRt
where qpis the density of the particle, / is the inclination angle relative to gravity
The study is based on nasal breathing under light exercises activity with a standard functional residual capacity (FRC) of
3300 ml, tidal volume (VT) of 1250 ml and breathing frequency (f) of 20 min1[6] The present calculation based on our previ-ous measurements of the size distribution of fungal particles in the cotton spin factory in Minia city (Egypt) The measure-ments were carried out in the two main working departmeasure-ments: carding department (Dept1) as a model for high dust concen-tration area and spinning department (Dept2) as a model for low dust concentration area Six-stage Andersen impactor was used as a viable particle sampler for collection and mea-surement of concentration and size distribution of bioaerosols Detailed description of this experimental study is given in Ab-del Hamid et al.[7]
Results and discussion The most dominant fungal genus found in the spin factory dur-ing our previous experimental results were Aspergillus and Penicilliumspecies with a size lying in the respirable particles range (<5 lm) The mean concentration of the total fungi was 1215 cfu/m3 and 396 cfu/m3with aerodynamic diameter (dae) of 2.6 lm and 2.3 lm at Dept1 and Dept2, respectively The concentration of Aspergillus niger was 996 cfu/m3 at Dept1 (dae= 2.8 lm) and 243 cfu/m3at Dept2 (dae= 2.2 lm)
On the other hand the mean concentration of the Penicillium was 88 cfu/m3at Dept1 (dae= 1.5 lm) and 25 cfu/m3at Dept2 (dae= 1.3 lm) The total and lobar depositions are calculated for these species by applying the stochastic lung model and using the experimental parameters of these size distributions
Fig 1illustrates the deposition dose of A niger, Penicillium and total fungal particles at carding and blowing (Dept1) and spinning (Dept2) departments The figure shows that the depo-sition of both species as well as the total fungi is higher at Dept1 than that at Dept2 where the concentration of A niger
Trang 3and Penicillium is higher at Dept1 Early processes in textile
mill (such as carding and blowing processes) are very dusty
job and accompanied by more respiratory problems than
spin-ning and twisting processes[13] Our previous study[7]reveals
that the respiratory symptoms (cough, expectoration, dyspnea,
chest wheeze) and abnormal X-ray findings mainly the increase
in bronchovascular marking and hyperinflation patterns were
obviously more observed among the workers within the
card-ing and blowcard-ing than the spinncard-ing and twistcard-ing departments of
the cotton mill The experimental study on an animal model
[14] demonstrated that cotton dust that includes respirable
particles is associated with the pathogenesis of emphysema
Our previous study[7]and other several studies[15–18]have
shown a progressive decline in ventilatory pulmonary function
in exposed workers This could show the positive relationship
between the deposition of these particles and the respiratory
problems
Inhalation of cotton dust has been shown to lead to a
neu-trophilic response in airway probably due to fungal active
par-ticles In our experimental study [7], the majority of positive
sputum cultures showed fungal growth which is more
preva-lent among exposed workers The study revealed also that
cot-ton dust, which often acts as a carrier for biological particles, is
more strongly associated with chronic airflow limitation as
shown by the increased of respiratory symptoms including
chronic cough, chronic sputum, progressive dyspnea and chest
wheeze among exposed workers which came in agreement with
results reported by Fishwick et al.[15]and Noweri et al[19]
Moreover, the incidence of symptoms among carding workers
who were more exposed to high concentration of cotton dust
was higher where the total deposition of fungal particles in
the lung is higher in the carding department than that in the
spinning department (seeFig 1) These are parallel with the
finding of Altin et al [16], Fishwick et al [20], Seboxa and
Abebe[21]
The computed deposition patterns for A niger and
Penicil-liumunder light exercise breathing conditions[6]at Dept1 and
Dept2 are shown inFig 2 The deposition fraction of A niger
is slightly higher than that of Penicillium in the bronchial
re-gion and reaches its maximum at generation 12 while at the
acinar region the deposition fraction of Penicillium becomes
higher reaching its maximum at generation 22 at Dept1
(Fig 2a) and shifts to generation 21 for A niger at Dept2 (Fig 2b) This could be attributed to the aerodynamic diame-ter of these particles where the Penicillium particles have the ability to penetrate deeper into the airways The same tenden-cies of the deposition fraction as a function of the generation number were observed by Yeh and Schum[12]
There are some phenomena impacts on the primary deposi-tion patterns Airway clearance may have one of the most important effects on the primary deposition patterns, influenc-ing the health effects of the inhaled particles Several different clearance mechanisms are at play in the airways, like particle trapping and clearance by secreted mucus, uptake by airway macrophages, or uptake by airway epithelium In the tracheo-bronchial region, mucociliary transport, coughing, and pene-tration into epithelium are the most important ones Another phenomenon that affects the deposition patterns is the aspira-tion Aspiration is the inhalation of the oropharyngeal parti-cles into the lower airway causing lung diseases [22,23] Sturm and Hofmann[24]assumed different clearance scenar-ios for the alveolar, bronchiolar, and bronchial lung region and evacuation of particles commonly takes place via the
0
20
40
60
80
100
Fungal particles
Carding and blowing department Spinning department
Fig 1 Deposition dose of fungal particles in the lung of the
workers at carding and spinning departments
0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.018
Generation number
A niger
Fig 2a Deposition fraction of A niger and Penicillium in the lung of workers at carding and blowing departments
0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.018 0.020
Generation number
A niger
Fig 2b Deposition fraction of A niger and Penicillium in the lung of workers at the twisting and spinning departments
Trang 4Table 1 Lobar deposition of fungal particles at Dept1 and Dept2.
fraction
Dept1:
Dept2:
RU: right upper lobe; RM: right middle lobe; RL: right lower lobe; LU: left lower lobe; LL: left lower lobe.
0.000
0.001
0.002
0.003
0.004
0.005
0.006
Generation number
RU RM RL LU LL
Total fungi at Dept1
Fig 3a Lobar deposition of total fungal particles in the lung of
workers at carding and blowing departments RU: right upper
lobe; RM: right middle lobe; RL: right lower lobe; LU: left lower
lobe; LL: left lower lobe
0.000 0.001 0.002 0.003 0.004 0.005 0.006
Generation number
RU RM RL LU LL
A niger at Dept1
Fig 4a Lobar deposition of A niger in the lung of workers at carding and blowing departments
0.000 0.001 0.002 0.003 0.004 0.005 0.006
Generation number
RU RM RL LU LL
A niger at Dept2
Fig 4b Lobar deposition of A niger in the lung of workers at twisting and spinning departments
0.000
0.001
0.002
0.003
0.004
0.005
0.006
Generation number
RU RM RL LU LL
Total fungi at Dept2
Fig 3b Lobar deposition of total fungal particles in the lung of
workers at twisting and spinning departments RU: right upper
lobe; RM: right middle lobe; RL: right lower lobe; LU: left lower
lobe; LL: left lower lobe
Trang 5airway and extrathoracic path to the gastrointestinal tract or
via the transepithelial path to the lymph nodes and blood
vessels
The deposition fractions are computed for each individual
generation number in each of the five lobes of the human lung
The relative lobar distribution is presented inTable 1for A
ni-gerand Penicillium at both departments The deposition
frac-tions are the highest in the right lower (RL) and left lower (LL)
lobes while the lowest deposition fraction is found in the right
middle (RM) lobe This could be attributed to the dependence
of the distribution flow on the lobar volumes[12]as shown in
Table 1
More detailed localization of the deposition sites can be
ob-tained by plotting lobar deposition fractions as a function of
generation number Deposition patterns for the total fungal
particles, A niger and Penicillium are demonstrated inFigs 3–
5at both departments In general, deposition fractions are the
highest in the right lower (RL) and left lower (LL) lobes while
the lowest deposition is found in the right middle (RM) lobe
The figures show also two distinct deposition maxima at the
bronchial and acinar regions with the highest deposition being
in the acinar region
For the fungal particles in Dept1 shown inFig 3athe max-imum deposition of total fungi in the bronchial region is achieved at generation 12 and 13 for RL lobe and at genera-tion 12 for LL lobe In the alveolar region the highest deposi-tion is achieved at generadeposi-tion 22 for RL and LL lobes The same tendency is observed for the particles in Dept2 (Fig 3b) with a shift to generation 13 for the RL lobe The deposition fraction in Dept2 is higher than that in Dept1 for all lobes
Lobar deposition of A niger particles is illustrated inFig 4
at Dept1 and Dept2 The deposition reaches its maximum va-lue at generation 12 in the bronchial region and generation 22
in the acinar region (Fig 4a) with a shift to generation 23 for the RL lobe with a higher deposition in Dept2 (Fig 4b) The distribution of Penicillium particles in Dept1 shown in
Fig 5aproduces 0.67% deposition fraction at generation 22 This percentage increased to 0.74% at the same generation
in Dept2 (Fig 5b)
Bronchial reactivity is increased in most workers with bys-sinosis and fall in indices of small airways diseases has been ta-ken to suggest that physiological response may begin in the peripheral airways [25] These findings reflect the practical importance of the present results where the deposition fraction
of the fungal particles is the highest in the right left lower lobes (Figs 3–5) as well as the highest deposition is found in the aci-nar region From this we come to important evidence that there is a positive relationship between the deposition of bio-logical particles and some respiratory diseases
Conclusion Total and lobar depositions of fungal particles in the human lung were calculated for the workers in a cotton spin factory
on the basis of stochastic lung model and the standard nasal breathing parameters for light exercise activity The deposition dose of fungal particles is higher in the carding department (Dept1) as a model for high dust concentration area than that
in the spinning department (Dept2) as a model for low dust concentration area The lobar deposition of A niger and Pen-icillium has the highest deposition in the RL and LL lobes while the lowest deposition is found in the right middle (RM) lobe These predictions show two distinct deposition maxima at the bronchial and the acinar regions with the high-est deposition being in the acinar region In all cases, the depo-sition reaches its maximum at generation 12 in the bronchial region and at generation 22 in the acinar region
Our results come to important evidence that there is a po-sitive relationship between the deposition of biological parti-cles in the airways and some respiratory diseases With the end of this study some recommendations have been introduced that could help in minimizing the risk of working in such occu-pational environments: (1) keep a good ventilation to prevent the growth of microorganisms where high relative humidity and poor ventilation represent a good media for the growth
of bioaerosols, (2) regular medical check up for the workers, which always does not take issue with developing countries,
to investigate any early diseases where there is a long time elapse between the start of working in the mill and the diagno-sis of certain cancers that could reaches to 10 years for
0.000
0.001
0.002
0.003
0.004
0.005
0.006
0.007
Generation number
RU RM RL LU LL
Penicillium at Dept1
Fig 5a Lobar deposition of Penicillium particles in the lung of
workers at carding and blowing departments
0.000
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0.008
Generation number
R U
R M
R L
LU
LL
Penicillium at Dept2
Fig 5b Lobar deposition of Penicillium in the lung of workers at
twisting and spinning departments
Trang 6chial carcinoma and more than 10 years for mesotheliomas, (3)
exchange of workers between different departments of the mill
could reduce the exposure time in the dirty job departments,
(4) Use of a good quality masks during the exposure time helps
in reducing the uptake of particles via the respiratory system
Acknowledgments
I would like to introduce my deep thanks to Prof Werner
Hofmann, Division of Physics and Biophysics, Department
of Materials Engineering and Physics, University of Salzburg,
Salzburg, Austria, for his help throughout this research
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