Occupational Diseases and Environmental Medicine, 2016, 4, 1-7
Published Online February 2016 in SciRes. http://www.scirp.org/journal/odem
How to cite this paper: Neghab, M., Toosi, S.M. and Azad, P. (2016) Respiratory Morbidity Associated with Long-Term Oc-
cupational Inhalation Exposure to High Concentrations of Hydrated Calcium Sulfate Dust. Occupational Diseases and Envi-
ronmental Medicine, 4, 1-7. http://dx.doi.org/10.4236/ode m. 2016.41001
Respiratory Morbidity Associated with
Long-Term Occupational Inhalation
Exposure to High Concentrations of
Hydrated Calcium Sulfate Dust
Masoud Neghab1, Samira Mirzaei Toosi2*, Parisa Azad2
1Research Center for Health Sciences, Shiraz University of Medical Sciences, Shiraz, Iran
2Student’s Research Committee, Shiraz University of Medical Sciences, Shiraz, Iran
Received 15 October 2015; accepted 24 November 2015; published 27 November 2015
Copyright © 2016 by authors and Scientific Research Publishing Inc.
This work is licensed under the Creative Commons Attribution-NonCommercial International License (CC
http://creativecommo ns.org/licenses/ by-nc/4.0/
Despite wide application of hydrated calcium sulfate, possible respiratory effects of long-term
occupational exposure to high concentrations of this chemical have only been investigated in a
limited number of epidemiological studies. This study is undertaken to examine this issue, more
thoroughly. This cross-sectional study is carried out at a local gypsum plant in Shiraz, capital of
Fars province situated in south western Iran. All exposed subjects (20 male workers) and 20
healthy non-exposed male individuals as the referent group are investigated. Prevalence of res-
piratory symptoms among the studied subjects is evaluated and they undergo spirometry test
(twice for the exposed group and once for the unexposed employees). Moreover, to assess the
extent to which workers are exposed to gypsum dust and using standard methods, inhalable and
respirable fractions of this compound are measured in different dusty worksites. Average air-
borne concentration of inhalable dust fraction is estimated to be 24 ± 14.76 mg/m 3 which is
higher than the recommended threshold limit value (TLV) for this chemical. Respiratory symp-
toms such as phlegm, wheezing and dyspnea are significantly more prevalent in exposed sub-
jects than in non-exposed employees (p < 0.05). The results of ventilatory function tests (pre-
shift) don’t show any significant differences between both groups. However, some post-shift pa-
rameters of ventilatory function such as FVC, FEV1 and FEV1/FVC ratio are significantly lower
than those of preshift and referent group. Exposure to high atmospheric concentrations of gyp-
sum dust is associated with a significant increase in the prevalence of respiratory symptoms along
with acute reversible significant decreases in some parameters of ventilatory function.
*Corresponding a uthor.
M. Neghab et al.
Gypsum Dust, Occupational Exposure, Respiratory Symptoms, Ventilatory Function Tests
1. Introduction
Gypsum, calcium sulfate dihydrate (CaSO4. 2H2O), is a naturally occurring mineral consisting of 79% calcium
sulfate and 21% water [1]. Gypsum is obtained from heating process of gypsum rock [2]. Calcium sulfate dihy-
drate is a colorless, solid inorganic substance with hygroscopic properties [3]. The production sources of this
substance vary and it may be contaminated with quartz [4]. Workers employed in the processing of gypsum rock
may be exposed to high atmospheric concentrations of gypsum dust via inhalation, ingestion, skin and/or eye
contact [5]. It is classified as a nuisance dust [4]. Limited information exists as to the respir atory effects of gyp-
sum dust. This, presumably, is due to the general belief that the substance is harmless due to its short half-life (in
the order of a few wee k s or, a t m ost , months) [4] [6] [7].
Tracheobronchial mucus membrane and upper respiratory tract irritation, laryngitis and sor e throat as well as
symptoms such as cough and wheezing have been reported as a result of inhalation exposure to this substance [5]
[8]-[10]. Reduced lung functional capacities have also been reported as a result of exposure to this substance
[11]. Some studies have indicated that gypsum dust after years of extreme exposure is able to produce micro-
nodular opacities in the lungs [12] [13].
In contrast, some epidemiological studies of workers exposed to pure gypsum have not found evidence of any
pulmonary illnesses or prevalence of lung fibrosis or pneumoconiosis and, even some authors have introduced
calcium sulfate as a protective dust to pr event silicosis [14] [15]. In a study of 241 employees in gypsum mines,
results of chest X-rays suggest that observed lung shadows are more prevalent in workers employed in mines
with higher quartz concentration than others [16].
It is estimated that more than 13 million tons of gypsum is annually produced in Iran and a large number of
workers are occupationally exposed to this substance in mines, furnaces, construction, etc. [17]. Although , gyp-
sum dust is classified as a nuisance dust and apparently, causes a benign pneumoconiosis [18]. Limited informa-
tion exists as to the respiratory health of workers following long term heavy inhalation exposure to this sub-
stance and no conclusive solid evidence is accessible in this regard.
This study is, therefore, carried out with the following objectives:
1) To asses s t he degree to which work e rs of a gypsum production plant are exposed to gypsum dust;
2) To determine the prevalence of respiratory symptoms, if any, among workers who are exposed to gypsum
dust as compared with a non-e xp osed refere nt population;
3) To ascertain if gypsum dust induces any significant changes in the parameters of ventilatory function.
2. Materials and Methods
2.1. Subjects and Study Design
This cross-sectional study was carried out at a local gypsum producing plant in Shiraz, capital of Fars province
in Iran. All subjects (20 males) with a history of past and present exposure to gypsum dust were investigated.
Simultaneously, 20 healthy non-exposed males, with similar demographic characteristics, were chosen from
clerical stuff of an educational center by simple random sampling technique and served as the referent group.
All subjects voluntarily participated in the study. The study was performed in accordance with the Helsinki
Declaration of 1964 as revised in 2007 [19].
2.2. Measurements of Investigated Variables
2.2.1. Respiratory Illness
Subjects were interviewed and respiratory symptom questionnaire, as suggested by the American Thoracic So-
ciety [20], were filled out for them. The questionnaire contained questions concerning respiratory symptoms
such as cough, wheezing and dyspnea, smoking habits, occupational history, preexisting medical conditions and
family history of each employee.
M. Neghab et al.
Prevalence of symptoms of respiratory diseases was then calculated from the data extracted from the com-
pleted questionna ires.
2.2.2. Ventilatory Function Tests
Ventilatory function tests were performed on site, using a portable calibrated ST-150 spirometer analyzer (Fu-
kuda Sangyo Inc. Japan) according to the guidelines of the American Thoracic Society [21]. For evaluation of
cross shift changes, ventilatory function tests were measured twice for the exposed workers (after a 48 hour ex-
posure free period (before shift) and at the end of the work shift (post-shift)) and once for the unexposed em-
ployees. Ventilatory parameters included mean percentage predicted Vital Capacity (VC), Forced V ital Cap acity
(FVC), Forced Expiratory Volume in the 1st second (FEV1) and Peak Expiratory Flow (PEF). Spirometer was
calibrated, at least twice a day, with a 3-liter syringe in accordance with the spirometer manufacturer’s standard
protocol. Detailed information regarding ventilatory function tests is to be found in other publications of the au-
thors [22].
2.2.3. Measurement of Atmospheric Concentrations of Gypsum Dust
To assess the extent to which workers were exposed to gypsum dust, using NIOSH method [23], its atmospheric
concentrations (respirable and inhalable dust fractions) were determined in three work areas, and the mean air-
borne concentration was expressed in mg/m3. Air samples were collected using personal dust samplers (Casella,
London, UK) equipped with cyclone and a Millipore PVC membrane filters (5 μm pores) in order to separate
respirable and inhalable fractions. Pretest experiments showed that the appropriate sampling time was about 120
2.3. Data Analysis and Statistical Procedures
Student’s t-test, chi-squared, Fisher’s exact test, logistic and multiple linear regression analyses were used to
analyze the data. In all the statistical comparisons, a p-value of less than 0.05 was considered signif icant. Statis-
tical tests were conducted using SPSS V19.0 on a personal computer.
3. Results
The average (mean ± SD) age (yr), BMI (kg/m2), duration of exposure (length of employment for referent sub-
jects), (yr) and number of cigarettes smoked and airborne concentrations of gypsum dust (mg/m3) are presented
in Table 1. As shown, no significant differences were noted between exposed and non-exposed subjects as far as
confounding variables were concerned. Additionally, the mean atmospheric concentration of gypsum dust was
higher than the current TLV value of 10 mg/m3 [24].
Prevalence rates of respiratory symptoms are shown in Table 2. As shown, symptoms such as phlegm,
wheezing and dyspnea were significantly more common among exposed individuals. The parameters of ventila-
tory function were also measured for both groups. Table 3 presents predicted percentages of VC, FVC, FEV1,
FEV1/FVC ratio and PEF. The results showed that exposure to gypsum dust was associated with significant
Table 1. Comparison of demographic variables, smoking habits and level of exposure to gypsum dust.
Variable Exposed (n = 20) Non-Exposed (n = 20) P-Value
Age (mean ± SD, yr) 37.70 ± 9.69 42.15 ± 11.25 0.188
BMI (mean ± SD, kg/m2) 25.12 ± 4.24 25.33 ± 3.57 0.968
Length of exposure/employment (mean ± SD, yr) 12.25 ± 7.08 10.30 ± 9.41 0.46
No. (%) smokers 3 (10%) 4 (20%) 0.33††
Number of cigarettes smoked per day (mean ± SD) 12.50 ± 3.53 11.50 ± 9.25 0.89
Length of smoking (mean ± SD, yr) 14 ± 11 22 ± 9.32 0.36
Respirable concentration of gypsum dust (mg/m3) (mean ± SD) 15.80 ± 11.83 N/A N/A
Inhalable concentration of gypsum dust (mg/m3) (mean ± SD) 24 ± 14.76 N/A N/A
Notes: BMI = body mass index (kilograms per square meters); = independent sample t test, ††= χ2 or Fisher’s exact test. Number of air samples = 9.
M. Neghab et al.
cross shift decrements in FEV1, FVC and FEV1/FVC ratio. Addition ally, some post shift parameters of ventila-
tory function were significantly lo wer than those of non-exposed subjects (p < 0.05). Conversely, no significant
differences were noted between the pre-shift ventilatory function tests values of exposed subjects as compared to
referent individuals.
The association between exposure to gypsum dust and the prevalence of respiratory symptoms is displayed in
Table 4. Logistic linear regression analysis showed that after adjusting for important confounders (i.e. age, BMI
and smoking habits) there was statistically significant association between exposure to gypsum dust with the
prevalence of phlegm, wheezing, and dyspnea (p < 0. 05).
Similarly, association between exposure to gypsum dust and changes in the parameters of ventilatory function
is displayed in Table 5 . The resu lts of statistical an alysis reve aled that after adjusting for age, BMI and smoking
habits, there were significant associations between exposure to gypsum dust with FVC and FEV1, in that expo-
sure to gypsum dust resulted in an average of ~7 units of decrement in these parameters.
Table 2. Frequency of respiratory symptoms among exposed and non-exposed subjects (%).
Symptoms Exposed (n = 20) No (%) Non-Exposed (n = 20) No (%) P-Value
Cough 7 (35 %) 2 (10%) 0.064
Phlegm 10 (50%) 3 (15%) 0.02*
Productive cough 3 (15%) 1 (5%) 0.3
Wheezing 8 (40%) 1 ( 5% ) 0.01*
Dyspnea 13 (65%) 6 (30%) 0.028*
Chi-squared or Fisher’s exact test, *Significant l y different from its corresponding value f or the non-e xposed group.
Table 3. Percentage predicted lung function among exposed and non-exposed subjects.
Parameters Exposed (n = 20) Non-Exposed
(n = 20)
Pre-Shift vs.
Pre-Shift vs.
Post-Shift vs.
Pre-Shift Post-Shift
VC 91.4 ± 11.16 91.5 ± 12.12 94.7 ± 15.17 0.88 0.18 0.18
FVC 95.75 ± 12.6 85.15 ± 11.88 96 ± 14.74 0.009 0.39 0.015*
FEV1 92.65 ± 11.59 89.1 ± 11.76 96.8 ± 11.18 0.023 0.12 0.013*
FEV1/VC 101.7 ± 9 98.68 ± 12.6 103.36 ± 10.17 0.28 0.33 0.07
FEV1/FVC 97.26 ± 9.24 101.41 ± 8.08 101.63 ± 7.4 0.032 0.09 0.45
PEF 93.25 ± 21.28 89 .9 ± 23.49 87.6 ± 21.73 0.41 0.24 0.46
Paired t-test, ††Significantly different from non-exposed values (independent t-test), *Significantly different from its corresponding value for the
non-expose d gro up.
Table 4. Association between exposure to gypsum dust and prevalence of respiratory symptoms.
Outcome β Odds Ratio P-Value
Cough 1.29 5.4 0.07
Phlegm 1.73 5.6 0.024
Productive cough 0.78 2.19 0.53
Wheezing 2.53 12.66 0.024
Dyspnea 1.94 6.96 0.013
††Binary logistic regression.
M. Neghab et al.
Table 5. Association between exposure to gypsum dust and changes in the parameters of ventilatory function.
Parameters B SE P-Value
VC 2.85 3.95 0.47
FVC 7.51 3.8 0.05
FEV1 7.4 3.22 0.028
FEV1/VC 0.32 2.59 0.9
FEV1/FVC 5.69 3.62 0.1
PEF 0.38 7.64 0.9
Multiple l inear r egres sion model, B: Average units of decrement in each parameter of ventilatory function of exposed subjects compared to their un-
exposed count erpart s , SE: Standard error.
4. Discussion
This study was undertaken to investigate the res piratory effects of long-term occupational inhalation exposure to
high concentrations of calcium sulfate dust.
Subjects were exposed to gypsum dust at a concentration that exceeded its current threshold limit value (TLV)
of 10 mg/m3.
Given the data provided, both groups were similar as far as demographic variables were concerned (Table 1).
None of the subjects had past medical or family history of respiratory illnesses or any other chest operations or
injuries. Given the above, and the fact that all important confounders were controlled and accounted for in this
study, an increased prevalence of respiratory symptoms (phlegm, wheezing and dyspnea) along with signifi-
cantly reduced lung functional capacities (FVC and FEV1) may well be explained by exposure to gypsum dust.
When smokers of both groups were separated and the data of non-smokers were reanalyzed, similar results were
obtained, indicating that the findings of the study are independent from the role of smoking as a confounder. The
results of linear and logistic regression analyses provided further support for this proposition.
Prevalence of respiratory symptoms was significantly higher in exposed group (Table 2) which is consistent
with the results of other studies in which phlegm and dyspnea [25], irritation of mucous membranes and upper
respiratory tract [8] [10] cough, sneeze and runny nose [5] have been reported as a result of y exposure to gyp-
sum dust.
Similarly, acute exposure to dust concentrations in excess of the PEL/TLV has been shown to result in
coughing, dyspnea, wheezing, general irritation of the nose, throat, and upper respiratory tract, and impaired
ventilatory function [26].
To the best of authors’ knowledge, the distinction between possible short (acute) and long (chronic) respira-
tory effects of exposure to gypsum dust in comparison with an appropriate referent group has not been investi-
gated earlier. In the present study, in order to differentiate between these effects, spirometery was conducted
prior to and after exposure to gypsum dust.
As shown in Table 3 , significant decrements were noted in most parameters of ventilatory function after ex-
posure. These results are thought to support the hypothesis that exposure to gypsum dust induces acute adverse
effects over the course of a work shift. Similarly, most post-shift parameters of ventilatory function of exposed
subjects were lower than those of referent individuals and the differences were significant for FVC and FEV1.
In contrast, preshift values were not significantly different from those of referent subjects.
These findings provide additional evidence to support the contention that exposure to gypsum dust is asso-
ciated with acute reversible ventilatory disorders. These conclusions are also further supported by the results of
Table 5, which showed that after adjusting for important confounders, significant associations were present be-
tween decrements in some parameters of ventilatory function and exposure to gypsum dust.
Interestingly, no significant differences were noted between preshift parameters of ventilatory function with
those of the referent group. This observation provides circumstantial evidence to support the notion that under
the exposure scenario of this study in terms of severity and length of exposure, gypsum dust does not induce
chronic irreversible effects on lungs’ functional capacities.
These findings are in line with the results of some other previous studies. For instance, Burilkov did not find
M. Neghab et al.
any lung diseases from exposure to natural gypsum dust unless in the presence of silica [27]. Similar findings
have been reported by others [14] [15].
Absence of any chronic respiratory disorders as a result of exposure to gypsum dust may be explained, at least
in part, by the fact that gypsum dust due to its high solubility and thus very short half-life [27] [28] is rapidly
cleared from the lungs via dissolution and mechanisms of particle clearance [29]. It has also been emphasized
that reported chronic lu ng diseases attributed to gypsum dust may have been related to its silica impurities [13 ]
[15] [16] [27] [30].
A cause and effect relationship cannot be established from cross-sectional studies, such as the present study.
Therefore, due to this inherent limitation, our findings might b e viewed with certain degree of skepticism and
interpreted tentatively. While the authors agree with this view, the y reiterate that the following few lines of cir-
cumstantial eviden c e indicate that th eir findings are very likely to be the results of exposure to gypsum dust:
First, the exposed subjects, when employed, were free from any preexisting medical conditions, particularly
those involving re s piratory sympt oms.
Second, apart from gypsum dust, the exposed individuals had no history of exposure to other chemicals
known to cause respiratory disorders prior to their employment in the plant or during the course of their em-
ployment, thereafter.
Third, changes occurred during a work shift following exposure to gypsum dust, and were reversible, once
exposure ceased.
Fourth, after adjusting for important confounders, significant associations observed between exposure to
gypsum dust and the prevalence of respiratory symptoms and reduced ventilatory capacities.
Fifth, similar findings were found when the data of non-smokers were analyzed.
5. Conclusions
Our findings showed that occupational exposure to high concentrations of gypsum dust was associated with a
significant increase in the prevalence of respiratory symptoms and significant acute reversible decrements in
some parameters of ventila t ory functi on.
To reduce workers’ exposure to gypsum dust, engineering controls such as local exhaust ventilation systems,
administrative measures and/or the use of personal protective equipment are recommended.
Additional follow up epidemiological studies with larger sample sizes and sufficiently long follow ups are
thought to be absolutely necessary and sensible to further confirm these initial observations and to assess possi-
ble ramifications of lo ng -term exposure to high concentrations of gypsum dust.
Funding through Shiraz University of Medical Sciences, Vice Chancellor for Research Affairs, grant No. 9334
partially supported these investigations. The authors also wish to sincerely thank Dr. Hassanzadeh, profes sor of
clinical epidemiology, for his assistance in logistic and linear regress ion analyses of the data.
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