Journal of Environmental Protection, 2013, 4, 65-73
http://dx.doi.org/10.4236/jep.2013.48A1009 Published Online August 2013 (http://www.scirp.org/journal/jep)
65
Effects of Gasoline Inhalation on Menstrual
Characteristics and the Hormonal Profile of Female
Petrol Pump Workers
Christopher E. Ekpenyong, Koofreh Davies, Nyebuk Daniel
Department of Physiology, Faculty of Basic Medical Sciences, University of Uyo, Uyo, Nigeria.
Received May 15th, 2013; revised June 28th, 2013; accepted July 30th, 2013
Copyright © 2013 Christopher E. Ekpenyong et al. This is an open access article distributed under the Creative Commons Attribu-
tion License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
cited.
ABSTRACT
Increasing numbers of young women are employed as gasoline station attendants in most developing countries despite
the lack of empirical data on the adverse reproductive health effect of this solvent. This study therefore sought to assess
the effects of gasoline inhalation on the serum sex hormone profile and menstrual characteristics of female gasoline
station attendants in Nigeria, given the global increase in the rate of infertility and the existing evidence on the repro-
ductive toxicity of gasoline constituents. A site-by-site cross-sectional study of 117 female gasoline pump attendants
and 118 age-matched controls was carried out between September 2011 and November 2012. The following 3 instru-
ments were used for data collection: a semi-structured questionnaire, a female sex hormone profile assay and exposure
status measures. The prevalence of menstrual disorders among the exposed and unexposed women was 37.2% and
28.5% respectively. Exposure to gasoline was significantly associated with disorders in both menstrual cycle length and
quantity of flow. Specifically, exposed women had a greater than threefold increased risk of a menstrual disorder, with
an odds ratio (OR) of 3.25 for abnormal cycle length and OR of 4.16 for abnormal quantity of flow. In addition, longer
duration of exposure (>1 year) was significantly associated with higher likelihood of menstrual disorders. There were
also persistent low serum levels of estradiol, and fluctuating levels of other reproductive hormones. Gasoline inhalation
may interfere with ovarian functions leading to disordered menstrual characteristics and female sex hormone profiles, as
well as future reproductive impairment.
Keywords: Adverse Reproductive Outcome; Female Worker; Gasoline Inhalation
1. Introduction
In recent years, there has been a significant influx of fe-
male workers in petrochemical firms, and a considerable
proportion of these workers are of reproductive age [1].
This scenario carries significant public health concern
and has been an important issue in occupational medicine
[2] due to the potential adverse effects of occupational
exposure to toxic gasoline constituents on female repro-
ductive endpoints, especially given the increased rate of
infertility in both developed [3] and developing coun-
tries.
Among the numerous constituents of petroleum prod-
ucts, gasoline constituents (benzene, toluene, ethyl ben-
zene and xylene (BTEX)) are designated as the most
toxic compounds to humans [4]. These compounds are
volatile and lipophilic in nature, and workers may be
exposed through inhalation, ingestion or dermal routes
[5]. These exposures can be accidental or intentional and
are insidious in nature [6,7]. It is generally considered
that dermal absorption of gasoline does not contribute
significantly to systemic toxicity [8].
Evidence, however, favours the view that BTEX in
gasoline may be important human reproductive toxins. In
addition, the relationship between exposure to these or-
ganic solvents and adverse reproductive outcomes, such
as congenital malformation, chromosomal abnormalities
and altered fertility, has been repeatedly tested and
documented in experimental animals [9].
However, the epidemiologic data associating gasoline
with human reproductive health, with particular reference
to its effect on female sex hormones and menstrual char-

Effects of Gasoline Inhalation on Menstrual Characteristics and the
Hormonal Profile of Female Petrol Pump Workers
66
acteristics, are limited. Gasoline constituents (BTEX) are
regarded as reproductive toxicants [10], and as such, they
can act as environmental endocrine disruptors [11],
which are defined as exogenous agents that can modulate
or interfere with the production, release, transport, me-
tabolism, binding, actions and elimination of the natural
hormones in the body [12,13]. The ovaries are the target
organs for injury caused by these reproductive and endo-
crine toxicants [14], although their effects on other endo-
crine organs such as the hypothalamus, pituitary, adre-
nals, thyroid, parathyroid and pancreas are also well
documented [15]. For instance, evidence has accumu-
lated that benzene and its analogues affect the luteal
functions of female workers in petrochemical industries
[16]. In addition, benzene fume inhalation has been
shown to affect the hypophysis and the extension of
ovarian functional status in rats [17]. Moreover, the
documented adverse health effects of gasoline include
female infertility, spontaneous abortion, birth defects,
and intrauterine growth retardation.
These adverse reproductive health effects may initially
be signalled by the presence of altered menstrual charac-
teristics, and the study by Rowland et al. [18] identified
long and/or irregular cycles as being associated with in-
fertility and foetal loss during the most recent pregnancy
[18]. Menstrual disorders have also been reported among
women in occupations such as farmers, health workers,
dancers, athletes, semiconductor manufacturers and liq-
uid crystal display workers [19,20], although scant data
exist concerning the menstrual characteristics of women
working as petrol pump attendants in gasoline stations,
despite the influx of a large number of women (at the
peak of reproductive age) into this occupation in Nigeria.
Menstrual outcomes are important potential indicators
or markers of other health outcomes, such as infertility,
osteoporosis, breast and lung cancer, anaemia, pancyto-
paenia, increased rate of leukaemia, neurological distur-
bances, and breathlessness, which are also known to be
associated with exposure to BTEX compounds [20-22].
Also, in most cases, individuals are unaware of reproduc-
tive hazards resulting from these occupational exposures
until they are interested in child birth [1]. It was therefore
felt that a study to investigate the effect of gasoline inha-
lation on the menstrual characteristics and hormonal pro-
files of female petrol pump workers, who receive con-
tinuous occupational exposure and whose future repro-
ductive performance depends on the integrity of their
reproductive organs, would be valuable.
2. Material/Methods
2.1. Subject and Methods
This study took place in the Uyo metropolis of South-
South Nigeria between September 2011 and November
2012. Several commercial petrol stations were selected
as study sites based on their geographical location to
represent the entire study area. Two hundred and thirty-
five female respondents (117 petrol pump workers and
118 age-matched control subjects) participated in this
survey.
The inclusion criteria were as follows: age between 18
and 40 years, not pregnant or breast feeding, no use of
oral contraceptives during the previous year, no history
of menstrual disorder/irregularity prior to employment as
a gasoline pump worker, no history of treatment for
menstrual disorders prior to employment, no sexually
transmitted infections or pelvic inflammatory disease,
fertility, no history of any abdominal surgery, good die-
tary intake and moderate physical activity status for the
previous year, normal body mass index and the absence
undue perceived stress.
2.2. Survey Methods
Three survey instruments were used in this study: a semi-
structured questionnaire adapted from previous studies
on menstrual cycle characteristics [23,24]; assays to
measure plasma female sex and other related hormones;
and an exposure assessment tool. The questionnaire con-
sisted of two sections and contained open-ended ques-
tions and probes aimed at exploring the socio-demo-
graphic profile and menstrual characteristics of the re-
spondents.
Section one contained seven open-ended questions
structured to obtain information regarding the partici-
pants’ age (years), educational status, marital status, du-
ration on the job, physical activity status, nutritional
habit and presence or absence of perceived stress. The
age of the respondents was stratified into 3 groups: 18 -
25, 26 - 35 and 36 - 40 years. Educational status was
divided into 3 groups according to the level of education
attained, i.e., primary, secondary or tertiary education.
Marital status was classified as single, married or di-
vorced. Body mass index was calculated as weight/height
(kh/m2), and subjects were defined as normal (<25),
overweight (25.0 - 29.9) or obese (≥30) according to the
WHO classification [25]. Perceived stress was assessed
using the perceived stress scale; the values were scored
on a 4-point Likert scale and interpreted as no stress (0 -
1), low stress (2 - 3) or high stress (≥4).
The duration on the job was stratified into two groups:
those who had worked for less than one year and those
who had worked for more than one year.
Part two of the questionnaire consisted of ten ques-
tions aimed at obtaining information on the respondents’
past and present obstetric and gynecologic history, with

Effects of Gasoline Inhalation on Menstrual Characteristics and the
Hormonal Profile of Female Petrol Pump Workers
67
special emphasis placed on the age at menarche, contra-
ceptive history and menstrual cycle characteristics
(length/duration and quantity of flow) for the previous
year. To categorise the respondents’ menstrual cycle
length, they were asked “how many days are there from
the first day of one menstrual period to the first day of
the next period?” The answer categories included 24
days or less, 25 - 30 days, 31 - 35 days and greater than
35 days. Based on the answers given, the participants
were divided into three groups, including those with a
short cycle length (defined as a cycle that last for less
than 24 days), those with a long cycle (>35 days) and
those with a normal cycle length (24 - 35 days). The
choice of these cut-off points was based on previous re-
search into menstrual cycles [23,24].
To estimate the quantity of the menstrual flow, the
participants were asked how many menstrual hygiene
pads they typically needed to change per day and
whether there had been an increase or decrease within the
past three months or more.
Those with a noticeable decrease in the number of
pads required due to a reduced quantity of flow were
grouped as having a scant/light flow, whereas those with
a noticeable increase in the number of pads required due
to an increase in quantity of flow were grouped as having
a heavy menstrual flow. Participants with a normal flow
were those with no indication to increase or decrease the
number of sanitary pad required during menstruation.
For the female sex hormone profile assay, participant
blood samples were obtained from the cubital vein on the
arm in the Department of Chemical Pathology of the
University of Uyo Teaching Hospital, Uyo, Nigeria. The
menstrual cycle phase of the participants when the blood
was taken was noted, as the normal levels of these hor-
mones vary according to the cycle phase. Based on the
serum levels of the hormones and in comparison to the
normal range, according to the cycle phase, the partici-
pants were classified as having normal, high or low lev-
els of sex hormones.
The concentration of the BTEX compounds at each of
the gasoline stations was assessed and used to monitor
the attendants’ exposure. Personal samples were col-
lected in sorbent tubes containing activated charcoal (80
- 100 mesh), which were mounted in the breathing zone
of the gasoline pump attendants. The air around the
breathing zone was drawn through the activated charcoal;
it was then absorbed by the carbon disulphide and ana-
lysed using gas chromatography (Perkin Elmer Auto
System XL GL) with a flame ionisation detector. The
instrument was positioned to established contact with the
air inhaled by the exposed participants. Similar assess-
ments were repeated few kilometres away from gasoline
stations.
2.3. Statistical Analysis
Frequencies and percentages were computed for the
demographic characteristics of the subjects. The Chi-
squared test was employed to test the association be-
tween menstrual characteristics and exposure to petro-
leum products.
Furthermore, a logistic regression model was also used
to examine the association between exposure to petro-
leum products and menstrual disorders without and with
adjustment for other possible confounders. This analysis
was also performed to investigate the effect of exposure
duration on menstrual disorders among exposed indi-
viduals. Hence, crude and adjusted odd ratios and 95%
confidence intervals were estimated. All of the statistical
computations were enhanced using the statistical package
for social sciences (SPSS 20.0). P values < 0.05 were
considered to be statistically significant.
3. Results
The socio-demographic variables of the 235 women who
participated in this study revealed that 117 (49.8%) were
exposed and 118 (50.2%) were unexposed. In addition,
37.9% were between the ages of 18 and 25 years, 54.5%
were between 26 to 35 years, and 7.7% were between 36
and 40 years.
Of the total participants, 10.6% had a primary level of
education, 85.1% had a secondary level of education, and
4.3% had a tertiary level of education. In addition, 71.1%
were single, 27.7% were married, and 1.3% was divorced.
Those with a perceived high level of stress constituted
51.5% of the women, whereas 48.5% demonstrated a low
perceived level of stress. In addition, 73.2% had a normal
BMI, 20.0% were overweight, and 6.8% were obese (Ta-
ble 1).
The overall prevalence of menstrual disorders among
the exposed and unexposed women was 37.2% and
28.5%, respectively. The results of the univariate analy-
sis showed that exposure to gasoline inhalation was sig-
nificantly associated with disorders in both menstrual
cycle length (P = 0.009) and quantity of flow (P = 0.002).
The prevalence of abnormal cycle length and quantity of
flow among the exposed and unexposed women was
27.3% and 36.8% for exposed women and 11.9% and
20.3% for unexposed women, respectively (Table 2).
The results of the reproductive hormone profile assay
showed that the serum levels of estradiol were consis-
tently low in most respondents with menstrual irregulari-
ties regardless of the duration of exposure, whereas the
levels of other reproductive hormones (FSH, LH, pro-
gesterone and prolactin) fluctuated (Table 3).
The multiple logistic regression analysis showed sig-
nificant associations between exposure to gasoline and

Effects of Gasoline Inhalation on Menstrual Characteristics and the
Hormonal Profile of Female Petrol Pump Workers
68
Table 1. Frequency distributions of demogr aphic characteristics of respondents according to exposure to gasoline.
Demographic Factors Total (N = 235) Exposed (N = 117) Unexposed (N = 118) X2 P value
Age (years)
18 - 25 89 (37.9) 42 (35.9) 47 (35.9)
26 - 35 128 (54.5) 67 (57.3) 61 (51.7)
36 - 40 18 (7.7) 8 (6.8) 10 (8.5)
0.78 0.677
Education Level
Primary 25 (10.6) 14 (12.0) 11 (9.3)
Secondary 200 (85.1) 99 (84.6) 101 (84.6)
Tertiary 10 (4.3) 4 (3.4) 6 (5.1)
0.78 0.678
Marital Status
Single 167 (71.0) 88 (75.2) 79 (67.0)
Married 65 (27.7) 27 (23.1) 38 (32.2)
Divorced 3 (1.3) 2 (1.7) 1 (0.8)
2.68 0.262
Perceived Stress
High 121 (51.5) 63 (53.8) 58 (49.2)
Low 114 (48.5) 54 (46.2) 60 (50.8)
0.35 0.556
BMI
Normal 172 (73.2) 85 (72.6) 87 (73.7)
Overweight 47 (20.0) 25 (21.4) 22 (18.6)
Obese 16 (6.8) 7 (6.0) 9 (7.6)
0.460 0.794
Values in parenthesis are percentages.
Table 2. Frequency distributions of menstr ual characteristics of respondents according to exposure.
Outcome Total (n = 235) Exposed (n = 117) Unexposed (n = 118) X2 P
Cycle length (days)
Short 36 (15.3) 24 (20.5) 12 (10.2)
Long 10 (4.3) 8 (6.8) 2 (1.7)
Normal 189 (80.4) 85 (72.6) 104 (88.1)
9.51 0.009**
Quantity of flow
Light 38 (16.2) 29 (24.8) 9 (7.6)
Heavy 29 (12.3) 14 (12.0) 15 (12.7)
Normal 168 (71.5) 74 (63.2) 94 (79.7)
12.94 0.002**
**P < 0.01, significant at 1%. Values in parenthesis are percentages.

Effects of Gasoline Inhalation on Menstrual Characteristics and the
Hormonal Profile of Female Petrol Pump Workers
69
Table 3. Frequency distributions of the menstrual characteristics and hormonal profiles of respondents accor ding to the du-
ration of exposure.
<1 year (n = 47) >1 year (n = 70)
Outcome
E2 P3 LH FSH ProlactinE2 P3 LH FSH Prolactin
Normal 3 (37.5) 5 (62.5) 5 (62.5)6 (75.0)5 (62.5)8 (50) 7 (43.8)8 (50) 6 (37.5)8 (50)
High 1 (12.5) 2 (25) 2 (25.0)1 (12.5)2 (25) 2 (12.5)4 (25) 5 (31.2) 4 (25) 5 (31.2)
Cycle length
Short (n = 24)
Low 4 (50) 1 (12.5) 1 (12.5)1 (12.5)1 (12.5)6 (37.5)5 (31.2)3 (18.8) 6 (37.5)3 (18.8)
Normal 2 (50.0) 2 (50.0) 3 (75.0)1 (25) 3 (75) 1 (25) 3 (75) 3 (75) 2 (50) 2 (50)
High 0 (0) 1 (25.0) 0 (0) 2 (50) 1 (25) 1 (25) 1 (25) 1 (25) 1 (25) 1 (25)
Long (n = 8)
Low 2 (50.0) 1 (25.0) 1 (25.0)1 (25) 0 (0) 2 (50) 0 (0) 0 (0) 1 (25) 1 (25)
Normal 25 (71.4) 23 (65.7) 26 (74.3)30 (85.7)27 (77.1)40 (80)42 (84)45 (90) 37 (74) 43 (86)
High 7 (20.0) 8 (22.9) 5 (14.3)3 (8.6) 5 (14.3)6 (12) 5 (10) 3 (6) 7 (14) 5 (10) Normal (n = 85)
Low 3 (8.6) 4 (11.4) 4 (11.4)2 (5.7) 3 (8.6) 4 (8) 3 (6) 2 (4) 6 (12) 2 (4)
Normal 3 (60) 4 (80) 3 (60) 3 (60) 3 (60) 5 (55.6)6 (66.7)6 (66.7) 6 (66.7)5 (55.6)
High 1 (20) 1 (20) 2 (40) 0 (0) 2 (40) 2 (22.2)1 (11.1)2 (22.2) 1 (11.1)3 (33.3)
Quantity of flow
Heavy (n = 14)
Low 1 (20) 0 (0) 0 (0) 2 (40) 0 (0) 2 (22.2)2 (22.2)1 (11.1) 2 (22.2)1 (11.1)
Normal 8 (57.1) 9 (64.3) 7 (50) 7 (50) 7 (50) 7 (46.7)7 (46.7)8 (53.3) 8 (53.3)7 (46.7)
High 2 (14.3) 2 (14.3) 3 (21.4)5 (35.7)4 (28.6)3 (20) 4 (26.6)4 (26.6) 4 (26.6)3 (20) Light (n = 29)
Low 4 (28.6) 3 (21.4) 4 (28.6)2 (14.3)3 (21.4)5 (33.3)4 (26.6)3 (20) 3 (20) 5 (33.3)
Normal 20 (71.4) 22 (78.6) 23 (82.1)23 (82.1)24 (85.7)34 (73.9)35 (76.1)37 (80.4) 39 (84.8)36 (78.3)
High 4 (14.3) 2 (7.1) 3 (10.7)1 (3.6) 2 (7.1) 5 (10.9)6 (13.0)4 (8.7) 4 (8.7) 6 (13.0)
Normal (n = 74)
Low 4 (14.3) 4 (14.3) 2 (7.1) 4 (14.3)2 (7.1) 7 (15.2)5 (10.9)5 (10.9) 3 (6.5) 4 (8.7)
Normal Rang (NR) for Estradiol (E2) 60 - 150 pg/ml; Progesterone (P3) 0.5 - 2.3 ng/ml (Follicular phase) or 2 - 25 ng/ml (Luteal phase); Prolactin 1.8 - 19
ng/ml; FSH < 10 miu/ml (Follicular phase), 5 - 16 miu/ml (Midcycle), or < 10 miulml (Luteal phase); LH < 27 miu/ml (Follicular phase), 34 - 90 miu/ml (Mid-
cycle), or < 15 miu/ml (Luteal phase).
menstrual cycle length (P = 0.016) and quantity of flow
(P = 0.0012), after adjustments were made for potential
confounders, such as age, marital status, educational
level, perceived stress and body mass index. Specifically,
exposed women had a greater than three-fold increased
risk of a menstrual disorder (odds ratio (OR)adjusted: 3.25,
confidence interval (C.I): 1.347 - 5.781), with an OR of
3.25 for abnormal cycle length and an OR of 4.16 for
abnormal quantity of flow. In addition, longer duration of
exposure (>1 year) was significantly associated with a
higher likelihood (OR: 4.15, C.I: 2.224 - 14.004) of men-
strual disorders (Table 4).
Table 5 shows that a higher rate of exposure to in-
haled gasoline compounds by petrol pump attendants was
detected, as evidence by a higher concentration of these
compounds (BTEX) at the location of the meter and in
the immediate vicinity of the gasoline stations; in con-
trast, decreased concentrations were detected as the dis-
tance increased, and these compounds were almost un-
detectable few kilometres away from the gasoline sta-
tions.
4. Discussion
The present study observed a higher rate of exposure to
gasoline inhalation by gasoline station attendants com-
pared to control individuals. This finding was evidenced
by the higher concentration of gasoline constituents (spe-
cifically BTEX compounds) at the location of the meter
point and within the immediate vicinity of the gasoline
stations in comparison to few kilometres away from the
gasoline stations.
Findings also indicated that exposed participants had a
significantly higher prevalence of menstrual disorders in

Effects of Gasoline Inhalation on Menstrual Characteristics and the
Hormonal Profile of Female Petrol Pump Workers
70
Table 4. Logistic regression showing associations between exposure status and duration of exposure to gasoline inhalation
and menstrual disorders of the participants (OR and 95% C.I).
Variables Crude OR (95% C.I) P Adjusted OR (952% C.I) P
Exposure status
Unexposed 1.00 (references) 1.00 (reference)
Exposed 5.40 (2.439 - 11.957)
<0.001
3.04 (2.199 - 8.607)
<0.001***
Exposure duration
<1 year 1.00 (reference) 1.00 (reference)
>1 year 3.41 (2.617 - 15.679)
<0.001
4.15 (2.224 - 14.004)
<0.001***
Cycle length
Unexposed 1.00 (reference) 1.00 (reference)
Exposed 3.04 (2.025 - 5.417)
0.025
3.25 (1.347 - 5.781)
0.016*
Quantity of flow
Unexposed 1.00 (reference) 1.00 (reference)
Exposed 4.02 (1.073 - 9.467)
0.006
4.16 (1.632 - 10.752)
0.0012***
*P < 0.05, significant at 5%; ***P < 0.001, significant at 0.1%. Adjusted for age, marital status, psychosocial stress and educational level.
Table 5. Concentrations of BTEX compounds at gasoline stations and outside of gasoline stations (Me an ± SD).
BTEX compound (PPM) Gasoline station Outside gasoline station
(few Km away) Threshold limit values TLV (PPM)
Benzene 0.67 ± 0.003 0.02 ± 0.001 0.5
Toluene 15.02 ± 0.001 2.12 ± 0.003 20
Ethylbenzene 78.20 ± 0.0014 <DL 100
Xylene 56.05 ± 0.006 5.53 ± 0.007 100
DL: Detection Limit. The detection limits for the BTEX compounds listed above were 0.07, 0.06, 0.05 and 0.05 PPM, respectively [4].
comparison to unexposed women. The menstrual disor-
ders observed among the exposed were more prevalent
among those who had been exposed for more than 1 year.
Associated with these menstrual disorders were persis-
tently low serum estradiol (E2), and fluctuating levels of
other reproductive hormones (LH, FSH, prolactin and
progesterone). These hormonal patterns modelled the
previous pattern identified in women with accelerated
follicular depletion with intact hypothalamic pituitary
action [26]. We therefore hypothesised that inhaled gaso-
line compounds (specifically BTEX compounds) may
affect ovarian function. BTEX compounds have been
designated the most toxic constituents of gasoline for
humans [4], particularly in regards to their effect on the
reproductive system, as the ovaries are the main target
organ for injury resulting from these reproductive and
endocrine toxicants [14]. This assertion is in line with
existing evidence demonstrating a direct action of BTEX
on ovarian structures and functions, thereby interfering
with the release of ovarian hormones (E2 and P3) and the
ovarian response to physiological hypothalamic-pituitary
action [27]. Existing research [16,28] further indicates an
association between benzene and ovarian hypo- and hy-
perplasia, as well as reductions in the duration of the
luteal phase of the menstrual cycle. Benzene is also
known to reduce the release of estradiol prior to ovula-
tion, as well as the release of FSH at the early follicular
phase and the release of progesterone at the early luteal
phase [16].
Toluene inhalation has been shown to increase the in-
cidence of maternal and foetal morbidity and embryonic
malformation [29], and this compound also reduces the
hypothalamic level of gonadotropin releasing hormone
(GnGH) and the plasma level of gonadotropins [27]. In

Effects of Gasoline Inhalation on Menstrual Characteristics and the
Hormonal Profile of Female Petrol Pump Workers
71
addition, xylene was shown to decrease plasma levels of
progesterone and estradiol. Although these adverse re-
productive health effects are known and well docu-
mented, it is noteworthy that they are not always present
in all exposed individuals. For example, and similar to
previous studies, we found that not all exposed gasoline
workers developed abnormal menstrual characteristics or
deranged reproductive hormone profiles. There are mul-
tiple interpretations for this finding, including inter-indi-
vidual differences due to variations in the pulmonary
absorption, distribution, action, metabolism and excre-
tion of inhaled gasoline compounds, which further de-
pend on blood gas values and the fat-blood partition co-
efficient [30].
Nonetheless, it is recognised that such differences
could be due to the effects of other un-modifiable con-
founders, including the age of the participants. In the
present study, 36%, 6.8% and 57.3% of the exposed par-
ticipants were within the perimenarchial, premenopausal
and peak reproductive ages, respectively.
Several lines of evidence have shown that changes in
hormonal patterns, and hence menstrual irregularities
with age, may be a consequence of the age-related de-
cline in ovarian follicle reserve, leading to a decrease in
ovarian factors (e.g., inhibin B) important for the regula-
tion of ovarian pituitary feedback and a secondary de-
cline in luteal function [31]. Such changes are common
among women near the perimenarchial and premeno-
pausal ages. The effects of inhaled solvents may also
have been exacerbated in subjects within these age limits,
with less of an effect for those within peak reproductive
age.
In a similar manner, earlier studies [27,32,33] showed
that the deleterious effects of a potentially toxic solvent
on the endocrine system generally require longer dura-
tions of exposure and repeated absorption [15]. This may
provide an explanation for the positive correlation be-
tween the duration of exposure and the severity of the
reproductive dysfunction present in a subset of the fe-
male workers in the present study. Moreover, as in pre-
vious studies that compared other constituents of gaso-
line, benzene was found to be present in concentrations
high enough to cause adverse reproductive health out-
comes, and the plausibility of these findings is supported
by the study of Sexton et al. [34].
According to that study, exposure to benzene above
the threshold limit value was associated with higher ad-
verse reproductive effects [34]. This assertion was later
supported by the study of Mehrjerdi et al. [35], which
was conducted at gas stations in the Yaza province.
These authors found that, compared to other constituents
of BTEX compounds, benzene was present in concentra-
tions above the threshold limit value (0.5 PPM). In con-
trast, toluene, ethylbenzene and xylene demonstrated
mean concentrations below the threshold limit [4], as
observed in the present study.
Previous studies have proposed several conflicting
opinions regarding the putative mechanisms of action of
endocrine disrupters such as BTEX compounds that lead
to adverse reproductive outcomes. While some of these
authors have speculated on the direct effect of endocrine
disrupters on steroidogenesis [2], by directly interfering
with steroidogenic enzymes and acting as potent enzyme
inhibitors to produce a low concentration of female sex
hormones, others found less consistent or no effect on
steroidogenic enzymes and hence hormone synthesis
[13].
These apparently conflicting observations can be re-
solved when certain facts are considered, including dif-
ferences in chemical properties and the molecular prop-
erties and pharmacodynamics of different endocrine dis-
rupters. Other possible mechanisms include solvent in-
terference with the hepatic microsomal enzyme system
responsible for endogenous hormone metabolism [15]. In
addition, Guisti et al. [35] proposed the alteration of
uterine structure as a potential mechanism, and according
to Kim et al. [2], BTEX compounds may exert their ac-
tions at the level of the hypothalamic-pituitary axis to
interfere with trophic hormones secretion and lead to
down-regulation of gonadotropin releasing hormone
(GnRH), GnRH receptors and pituitary-1 receptor
mRNA levels. In particular, these authors [2] demon-
strated that injection of toluene and xylene led to a sig-
nificant reduction in the serum concentrations of GnRH,
GnRH receptor and pituitary-1 mRNA in experimental
animals [2]. Furthermore, knowledge of the different
levels of action of endocrine disrupters may help differ-
entiate hypothalamic-pituitary dysfunction from direct
germ cell injury [19]; in hypothalamic-pituitary dysfunc-
tion, the serum levels of gonadotropin hormones (FSH
and LH) are low, whereas in germ cell affectation, high
FSH levels with associated low E2 serum concentrations
are typical.
In support of the persistently low levels of E2 but fluc-
tuating levels of FSH and LH observed in most exposed
participants with menstrual disorders in the present study,
it may be accurate to conclude, in agreement with previ-
ous studies [27], that BTEX compounds interfere with
the ovarian cycle (particularly during the follicular phase)
in individuals exposed to gasoline fumes. The differences
in the serum levels of FSH and LH observed among ex-
posed participants may be ascribed to differences in the
regulation of FSH and LH secretion and diminished E2
concentrations at the hypothalamic or pituitary levels or
differential sensitivity to gonadotropin releasing hor-
mones [36].

Effects of Gasoline Inhalation on Menstrual Characteristics and the
Hormonal Profile of Female Petrol Pump Workers
72
5. Conclusion
The present study provides additional evidence to sup-
port the positive association between exposure to gaso-
line inhalation and the development of adverse reproduc-
tive endpoints, including menstrual and reproductive
hormone profile abnormalities suggestive of ovarian
functional affectations, specifically during the follicular
phase. However, this association is likely influenced by
several modifiable and un-modifiable confounders.
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