Health risk assessment of benzene exposure among workers in gasoline stations in Northeastern Thailand
Article information
Abstract
Benzene exposure affects gasoline station personnel, and prior studies have shown that working at gasoline stations has a greater effect on neurological symptoms. This study aims to examine the risk of benzene exposure and evaluate workers’ knowledge and preventive practices regarding benzene at gasoline stations in Northeastern Thailand. A questionnaire was utilized to collect data on general knowledge and preventive practices from 82 employees across 57 gasoline stations. Twelve specific benzene samples were collected, with two samples obtained from each of six gasoline stations: one from the gasoline refueling zone and one from the office area. Sampling adhered to the NIOSH-1501 standard using personal pumps. A gas chromatograph (GC) equipped with a flame ionization detector (FID) was employed to detect benzene. Descriptive statistical analysis was conducted to determine frequency, percentage, mean, maximum, and minimum values. Our findings revealed that benzene concentrations in all samples were below the detection threshold (0.001 mg/kg) during the 8-hour work shift. Strikingly, despite this low measured exposure and acceptable non-cancer risk levels, every work group was still classified as having a significant cancer risk according to the risk assessment models. The study also indicated that 50.0% of workers had a moderate understanding of benzene, whereas 45.1% had a low level of knowledge. Moreover, self-protective measures were inadequate, with workers neglecting to wear protective gloves while handling benzene, delaying gasoline removal until task completion, and consuming food and beverages in the workplace. Our findings provide more evidence about the health risk associated with benzene exposure among gasoline station workers. Therefore, organizations and relevant agencies must prioritize improving workers’ understanding of safe chemical management to ensure proper handling and minimize exposure to carcinogenic substances that may increase cancer risk.
Introduction
Benzene, a volatile organic chemical (VOC) among the BTEX group (benzene, toluene, ethylbenzene, and xylene), is acknowledged as a significant environmental and occupational health risk. Benzene is a prevalent air contaminant in urban and industrial environments due to its extensive application in industrial processes, petroleum refining, and as a component of gasoline. The International Agency for Research on Cancer (IARC) categorizes benzene as a Group 1 human carcinogen, signifying substantial evidence of its carcinogenicity in humans, including its associations with leukemia and other hematological malignancies. The U.S. Environmental Protection Agency (U.S. EPA) classifies benzene as a Class A human carcinogen, indicating its confirmed ability to induce cancer in humans [1,2]. Prolonged exposure to benzene, even at minimal concentrations, has been associated with bone marrow suppression, aplastic anemia, and immune system dysfunction [3-5]. Previous research indicates that the health of gas station workers is compromised by exposure to benzene from gasoline vapor emissions [6-8].
In Thailand, previous research has revealed that benzene exposure had an impact on gas station employees [9,10]. Higher exposure risks were found in urban areas than in the suburbs, with benzene being the most important factor in causing non-cancer risk in high-traffic urban areas [11]. The research conducted by Allahabady et al. (2022) revealed that the mean benzene concentration in the atmosphere at petrol stations was approximately 5.5 times the permissible limit [12]. In addition, previous studies have confirmed that working at gas stations in Thailand has a greater impact on neurological symptoms [10,13]. Warinchamrap District, Ubon Ratchathani Province, Thailand, had 57 gasoline stations located along primary roadways, consistently frequented by numerous people. There were two main types of staff at these stations: operators and back-office staff, who frequently come into contact with benzene. No previous research has assessed the risk of benzene exposure among workers at gasoline stations in Warinchamrap District. Therefore, the researcher aimed to investigate the risk of benzene exposure and assess the knowledge and prevention practices regarding benzene among workers at these gasoline stations in order to provide important information to relevant agencies for addressing health issues among station personnel.
Materials and Methods
This research is a cross-sectional descriptive study employing U.S. EPA quantitative methods to assess the risk of benzene exposure among operational and back-office workers at gasoline stations, considering both carcinogenic and non-carcinogenic risks. The study also aims to evaluate workers' knowledge and preventive practices regarding benzene exposure. The study period spans from June 2024 to December 2024.
Population and sample
Population: The study targets individuals aged 18 and older employed at gasoline stations. In Warinchamrap District, there are a total of 57 stations and 150 employees.
The sample group was selected using the population proportion estimation formula.
Where;
n = sample size
N = population size (150 workers)
Zα/2 = coefficient under the standard normal curve at 95% confidence level, Z (0.025) = 1.96
p = proportion of abnormal symptoms due to benzene exposure among fuel service workers according to literature review, p = 0.684 [14]
e = precision of the estimate, e = 0.068
n=
n=81.99≈82
The researchers utilized accidental sampling to collect data from 82 workers at gasoline stations in Warinchamrap District, Ubon Ratchathani Province. The researchers administered interviews to the participants to collect questionnaires. The sample group was divided into two similar exposure groups: one group engaged in refueling activities and one group operating in the office.
Benzene sampling: Benzene samples were collected from six stations by purposive sampling. Two samples were obtained from each station: one from the gasoline refueling area and one from the office area, resulting in a total of twelve samples.
Research tools
1. The questionnaire consists of three sections: general information, knowledge of benzene, and self-protection practices during work. The details include:
1) General information includes gender, age, weight, education level, employment status, daily work duration, years of work experience, weekly workdays, annual workdays, smoking history, congenital diseases, knowledge of benzene safety, sources of benzene exposure from other activities, and abnormal symptoms experienced during work.
2) Knowledge of benzene consists of 10 questions, each with a binary choice: true or false. The knowledge levels are categorized into three levels: high, moderate, and low.
3) Preventive practices against benzene exposure in the workplace consist of 10 multiple-choice questions, each with three options: regularly practiced, sometimes practiced, and never practiced. The practice levels are categorized into three levels: high, moderate, and in need of improvement.
2. Instruments and tools for atmospheric benzene sampling, accompanied by a sample collection record, include a dry calibrator, calibration jar, personal air sampling pump, activated charcoal tube, and tube holder.
Research tool quality assessment
1. Content validity was examined by three experts, and the Item Objective Congruence (IOC) Index ranged from 0.67 to 1.00.
2. The reliability of the questionnaire was tested through a trial with 30 workers at gasoline service establishments in Ubon Ratchathani Municipality, Ubon Ratchathani Province. The reliability test include:
Section 1: Knowledge of benzene – assessed using Kuder-Richardson statistics. The KR-20 computation yielded a confidence rating of 0.7, which is considered satisfactory [15].
Section 2: Preventive practices from benzene exposure at work – evaluated using Cronbach's Alpha Coefficient, which gave a confidence value of 0.7, deemed acceptable [16].
Data collection and analysis
1. Interviews were conducted with 82 workers employed at 57 gasoline stations in Warinchamrap District, Ubon Ratchathani Province.
2. Atmospheric benzene sampling at gasoline stations was performed in accordance with the NIOSH method 1501 standard, using the following specifications:
1) Calibrate the air pump using a GilAir Plus calibrator, adjusting the flow to ≤20 L/min three times to ensure a constant, accurate rate.
2) Collect benzene samples in the workplace atmosphere following NIOSH Method 1501 by sampling at fuel refilling and office areas. A personal pump (GilAir Plus Digital Air Sampling Pump) with an adjustable flow rate below 200 mL/min was used for sampling. The air at the sampling site was drawn through activated carbon adsorbent tubes to capture the desired compounds. Use an activated charcoal tube containing 100/50mg of activated charcoal powder. To perform the sampling, each sampling pump is initially calibrated using primary calibration by placing the flowmeter and pair. The pump flow rate was set at 0.2 L/min during the sampling phase, with each sample collected over a duration of approximately 8 hours. All sorbent tubes were positioned around 1.5 meters (breathing zone) above ground level. During each sampling, both ends of the absorber tube were broken, and the tube was affixed to the pump inlet, following the directional arrow indicating airflow. For every 10 adsorbents, two were designated as control samples. After completing sample collection, remove the sampling tube from the pump. Seal both ends of the sampling tube with parafilm and attach a label indicating the sample number. Place the sample-collecting tube into a ziplock bag, ensuring each sample collection tube and blank are enclosed in separate bags. After sampling, transport the tubes to an accredited private laboratory at a temperature of 4°C.
3) Extract benzene adsorbed in the charcoal tube utilizing carbon dioxide (CO₂) as a solvent to facilitate the removal of benzene from the tube, thereby preparing the sample for subsequent analysis. The extraction pipe is connected to the sample pump system, which is activated to suck carbon dioxide into the extraction pipe, facilitating the evaporation of benzene for subsequent analysis in the gas chromatography machine. Dilution is achieved by regulating the flow rate of nitrogen gas (N₂) as a carrier, enabling the optimal dilution of high benzene concentrations. A gas chromatograph (GC) will be employed to isolate benzene from other constituents present in the sample. An injector will introduce the prepared sample into the machine at a temperature range of 180-250°C, which is optimal for vaporizing benzene from the sample, allowing it to travel into the column. The column will be covered with silica, serving as a stationary phase to facilitate the separation of benzene from other compounds according to their mobility across the column. The initial column temperature will be set at 40-60°C to commence the separation gradually. The temperature will then be incrementally raised over a period of 10-20 minutes, in accordance with the established temperature protocol, to ensure the successful separation of compounds, reaching a maximum temperature of 250°C to fully separate benzene. After benzene is separated from other components, it will be directed to the flame ionization detector (FID), an instrument utilized to detect benzene. Upon the combustion of benzene, the carbonaceous materials are ionized, generating an electric current that can be quantified in correlation with the amount of benzene present in the investigated sample.
4) Assess the health risk of benzene exposure among workers in gasoline stations. Determine the daily exposure utilizing the following formula:
Where;
Intake = chronic daily intake of benzene via inhalation (mg/kg-day)
CA = contaminant benzene concentration in air (mg/m3)
IR = inhalation rate = 1.3 m3/hour [17]
ET = exposure time (hours/day)
EF = exposure frequency (days/year)
ED = exposure duration (years)
BW = body weight (kg)
AT = number of days a person lives (days)
The characterization of cancer risk was assessed as follows:
Where:
CSF = cancer potential (slope) factor (mg/kg-day) = 0.0273 [18]
CDI = exposure of benzene concentration in air (mg/kg-day)
If Risk > 1 x 10-6 , it indicates carcinogenic effects on workers; if Risk ≤1 x 10-6 , it is considered an acceptable level.
The assessment of non-cancer risk involves calculating the Hazard Quotients (HQ) for long-term exposure to inhaled benzene, adhering to U.S. EPA guidelines.
Where:
Intake = exposure of benzene concentration in air (mg/kg/day)
RfD = reference dose of benzene = 4 x 10-3 mg/kg-day (according to U.S.EPA-IRIS) [19]
If HQ > 1, it indicates adverse non-carcinogenic effects on workers; if HQ ≤1, it is considered an acceptable level.
Data analysis
Quantitative data were analyzed using the mean and standard deviation, whereas qualitative analysis was assessed using descriptive statistics such as frequency and percentage distributions.
The carcinogenic and non-carcinogenic risk assessment data were examined using descriptive statistics, including frequency and percentage, in accordance with the model established by the U.S. Environmental Protection Agency (U.S. EPA)
Ethical aspects
The study was conducted in accordance with the Declaration of Helsinki and approved by the Ethics Committee of Ubon Ratchathani University (code UBU-REC-174/2567, November 12, 2024).
The researcher explained the project to participants and secured their signed consent prior to initiating data collection.
Results
Workers’ Characteristics and symptoms
Of the sample group, 51.2% were male, 70.7% were aged between 18 and 35 years, 61.0% weighed between 51 and 70 kg, 62.2% had a high school education, 61.0% were single, 32.9% were smokers, and 11.0% had a congenital disease. Additionally, 47.6% of the workers demonstrated knowledge of benzene safety, with company-provided training being the primary source of knowledge for 40.2%. All the workers (100.0%) experienced daily benzene exposure, with the highest exposure occurring during gasoline-filling operations at 98.8% (Table 1).
Characteristics of gasoline station workers (n=82).
The chart shows the percentage of workers (n=82) reporting specific symptoms associated with benzene exposure. Headache (32.9%), dizziness (25.6%), and eye irritation (24.4%) are the most common symptoms, indicating notable impacts on the nervous and visual systems (Figure 1).
Workers’ symptoms associated with benzene exposure.
Workers' knowledge of benzene
The survey on workers' knowledge regarding benzene revealed that 50.0% possessed a moderate level of knowledge, 45.1% had a low level, and 4.9% showed a good level (Table 2).
Workers' knowledge level regarding benzene (n=82).
The sample group misunderstood that wearing protective equipment, such as a cotton face mask, can prevent benzene fumes from entering the body (7.3%), that benzene is exclusively contained in gasoline (23.2%), and that washing hands with only clean water after completing their daily tasks is sufficient (28.0%) (Table 3).
Workers' knowledge regarding benzene (n=82).
Workers' self-protection practices against benzene exposure
The findings regarding the levels of preventive practices among workers indicated that the sample group's behaviors were categorized as good, moderate, and in need of improvement at rates of 51.2%, 47.6%, and 1.2%, respectively (Table 4). Nevertheless, it was observed that the sample group failed to protect themselves from hazardous work conditions. For example, the workers neglected to use protective gloves while handling benzene, postponed the removal of gasoline until after completing their tasks, and consumed food and beverages in the work environment. The respective practice percentages for these behaviors were 39.0%, 30.5%, and 20.7%. (Table 5).
Levels of workers' self-protection practices against benzene exposure (n=82).
Workers' self-protection practices against benzene exposure (n = 82).
Benzene contamination in working areas
By measuring the amount of benzene in the workplace, it was found that all samples had benzene concentrations below the detection limit, at 0.001 ppm, which is lower than ACGIH benzene standard (TLV-TWA) of 0.02 ppm [20] (Table 6).
Benzene concentration in the workplace over 8 hours.
Health risk assessment of benzene exposure among workers
According to the health risk assessment of benzene exposure among workers, the variables used to assess health risk are presented in Table 7.
Variables used to evaluate health risk.
The chronic daily intake of benzene via inhalation was estimated, revealing that operational workers had an intake range of 2.45 × 10-4 to 8.72 × 10-4 mg/kg-day, whereas office workers had an intake range of 2.05 × 10-4 to 5.57 × 10-4 mg/kg-day (Table 8). Operational workers were found to have a cancer risk of benzene via inhalation, with a range of 6.70 × 10⁻⁶ to 2.38 × 10⁻⁵, whereas office workers had a range 5.60 × 10-6 to 1.52 × 10-5. When interpreting the carcinogenic risk, it was determined that all operational and office workers (100%) exhibited an unacceptable risk value (Table 9). The non-cancer risk assessment revealed that operational workers exhibited a hazard quotient ranging from 0.0613 to 0.218, while office workers had a range of 0.0512 to 0.139. In evaluating non-carcinogenic risk, it was found that all operational and office workers (100%) exhibited an acceptable value (Table 10).
Chronic daily intake of benzene via inhalation.
Cancer risk of benzene via inhalation.
Non-cancer risk of benzene via inhalation.
Discussion
Workers' knowledge of benzene were found to be at a moderate to low level, indicating that many workers still misunderstood several concerns. These include the belief that wearing a cotton face mask can prevent benzene fumes from entering the body, that benzene is exclusively contained in gasoline, and that after completing their daily tasks, washing hands with only clean water is sufficient. Employees possess limited knowledge that may lead to inappropriate behaviors and benzene exposure while working. According to this study, workers exhibited atypical symptoms from benzene exposure at work, including headache (32.9%), dizziness (25.6%), eye irritation (24.4%), and stinging nose (23.2%). Prolonged occupational exposure to volatile organic compounds (VOCs) from fuel, especially gasoline, was linked to systemic health problems in workers. Documented consequences encompassed hematological diseases and central nervous system (CNS) effects, including neurotoxicity and potential neuroinflammation[21-22]. This is consistent with Tongsantia et al. (2021), who found that the five most prevalent adverse symptoms—fatigue, headache, dizziness, nasal congestion, and rhinorrhea—were recorded among workers exposed to benzene [23].
The preventive practices of workers handling benzene revealed that the sample group's behaviors were classified as good and moderate at 51.2% and 47.6%, respectively. However, it was noted that the sample group inadequately protected themselves against hazardous working conditions, including the failure to wear protective gloves while handling benzene, delaying the removal of gasoline until task completion, and consuming food and beverages in the workplace. It is possible that workers may operate under corporate policies that stipulate explicit safety criteria, including defined penalty elements. In Thailand, regulations governing establishments are issued by the Ministry of Labor, which enforces occupational health and safety operations; the Occupational Health and Safety Act 2011 applies to establishments and employees. Consequently, workers are adhering to workplace safety laws and regulations to the greatest possible level. Nevertheless, the implementation of benzene prevention measures in the workplace still results in nearly half of the employees exhibiting moderate practice levels. The organization must enhance its discipline in monitoring and guidance, including providing information regarding benzene, its heightened risks and preventive measures. It is evident that 52.4% of employees have never received education on benzene exposure. The lack of benzene exposure training of workers represents a significant occupational health hazard. Training is a crucial component of occupational health and safety initiatives, especially for those regularly exposed to Group 1 carcinogens like benzene. Adequate training may improve preventive strategies and reduce the risk of harmful exposures to benzene or other toxic substances [24].
According to the results of this risk assessment, the non-cancer risk assessment indicated that all operational and office workers show an acceptable level of risk. However, the cancer risk associated with benzene inhalation revealed that both groups (100%) exhibited an unacceptable level of risk. The chronic daily inhalation of benzene, included in the model for assessing cancer risk in gasoline station workers, is affected by various characteristics, such as exposure duration, frequency, weight, and lifespan. Interestingly, office workers frequently possess longer-term job experience at gasoline stations than operational workers, probably because of the elevated turnover rate among operational personnel. Consequently, when assessing cancer risk, office workers have a risk level similar to that of operational workers. This study, aligning with Muda et al. (2023), confirmed elevated carcinogenic risks for gas station workers in locations such as Bangkok, Shiraz, Brazil, Ardabil, and Johannesburg [8]. Additionally, the study by Hoseini et al., indicated that the highest cancer risk levels of benzene were recorded [25].
Conclusions
Our findings indicated that, at low benzene exposure levels with environmental aerosol concentrations of 0.001 ppm during an 8-hour work shift, both operational and office workers exhibited an unacceptable cancer risk associated with benzene inhalation. Fifty percent of workers possessed a moderate understanding of benzene, whereas 45.1% demonstrated a low level of expertise. Moreover, the preventive measures among workers indicated insufficient protection from hazardous conditions, such as neglecting to wear protective gloves while handling benzene, postponing gasoline removal until tasks were completed, and consuming food and beverages in the workplace. Implementing regular training, adjusting work schedules, and ensuring the proper use of PPE—including protective gloves, half-mask air-purifying respirators with organic solvent cartridges, or polyurethane foam masks—are essential to reducing health risks [26]. Therefore, organizations and relevant agencies must prioritize enhancing employees’ knowledge of chemical safety, chemical management, appropriate personal protective equipment, and first-aid procedures to ensure safer handling practices and minimize exposure to carcinogenic substances that may elevate cancer risk. This study utilized a sample of only 12 benzene samples from six stations, while the study population included 57 stations, due to budgetary constraints in the research. The researchers initially selected stations with substantial staffing and a high volume of oil and vehicles requiring service to represent the worst-case scenario of the study group. The collection of merely 12 samples from 6 stations may not accurately represent the total population. Further studies should evaluate suitable sampling procedures. This cross-sectional study gathers data at a single point in time, indicating associations without proving causality, whereas self-reported data may suffer from recollection biases and contextual limitations, thereby reducing the accuracy and validity of the results.
Notes
Acknowledgement
This research was a collaboration between Ubon Ratchathani University and gasoline stations in Warinchamrap District, Ubon Ratchathani Province. The authors would like to express their gratitude to all workers working at the gasoline stations.
Conflict of interest
The authors declare no conflicts of interest.
CRediT author statement
LB: Conceptualization, Methodology, Data curation, Software, Writing- Original draft preparation, Visualization, Writing- Reviewing and Editing; NK: Conceptualization, Methodology, Data curation, Visualization, Writing- Reviewing and Editing; PK: Conceptualization, Methodology, Data curation, Visualization, Writing- Reviewing and Editing; WP: Conceptualization, Methodology, Data curation, Visualization, Investigation, Writing- Reviewing and Editing; PR: Software, Writing- Original draft preparation, Visualization, Investigation, Supervision, Writing- Reviewing and Editing, Writing- Reviewing and Editing; ST: Methodology, Software, Visualization, Investigation, Writing- Reviewing and Editing.