Abstract Volatile organic compounds (VOCs) in ambient air remain a public health concern due to their potential short and long-term health effects. This study aimed to measure VOC concentrations and assess related health risks in the industrial estate of Rayong city, Thailand. Daily VOC levels were continuously monitored at three Air Quality Monitoring stations in Maptaphut City Municipality from January to December 2024. Mean concentrations of vinyl chloride, benzene, and ethylbenzene varied significantly across the monitoring sites (P < 0.05), while total VOC levels did not differ between the dry and wet seasons (P > 0.05). Meteorological factors, particularly air temperature and relative humidity, appeared to influence VOC levels. Notably, ambient concentrations of 1,3-butadiene (1.13 ± 1.06 to 1.49 ± 1.91 µg/m³) exceeded the annual standard of 0.33 µg/m³ set by the Pollution Control Department. Principal component analysis (PCA) identified several emission sources, including synthetic rubber and thermoplastic resin production, wastewater treatment, vehicle exhaust, industrial solvent use, and emissions from PVC-related processes. Carcinogenic equivalency (CEQ) values were highest near petrochemical facilities producing plastic resins or polymers and areas linked to wastewater treatment, reflecting the presence of carcinogenic VOCs. Despite elevated levels of 1,3-butadiene, both carcinogenic and non-carcinogenic risk assessments suggested no immediate adverse health effects for the surrounding population. However, the findings highlight the need for continued monitoring, particularly due to the long-term cancer risk associated with 1,3-butadiene.

Keywords: Volatile organic compounds (VOCs), Health risk assessment, Industrial area, Principal component analysis (PCA), Carcinogenic equivalency (CEQ)

Funding: The authors are grateful for the research funding provided by King Mongkut’s University of Technology North Bangkok, contract no. KMUTNB-68-BASIC-48.

Citation:  Bootdee, S. and Phantu, S. 2026. Investigation and health risk assessment of volatile organic compounds (VOCs) emitted from industrial estate, Rayong city, Thailand in 2024. Natural and Life Sciences Communications. 25(2): e2026032.

Graphical Abstract:

INTRODUCTION

Volatile organic compounds (VOCs) are emitted as gases from certain solids or liquids. VOCs form a large, diverse group of organic chemicals that are gaseous at room temperature. The VOCs are a group of organic compounds occurring in the air. Both NOx and VOCs are significant precursors in photochemical reactions and the generation of secondary air pollutants, which are associated with ozone (O₃) levels in ambient air (Berenjian et al., 2012; Zheng et al., 2023). VOCs are released from various sources, including both those generated by humans and those of natural origin. VOCs generally originate from anthropogenic sources, including automobile exhaust emissions resulting from both complete and incomplete burning of gasoline, gasoline evaporation from engines and tanks, and solvents utilized in industrial and indoor commercial and home applications (Saleem et al., 2022; Wang et al., 2023; Zheng et al., 2023; Lv et al., 2024). VOCs are usually emitted from natural sources such as livestock farms, vegetation, and wildfires (Sharma et al., 2016; Kim et al., 2024). Suwattiga and Limpaseni (2005) reported the source of VOC emissions, including 36% of VOCs from gasoline vehicles, 6% from diesel vehicles, 12% from fuel oil boilers, 12% from gasoline vapor, 5% from paint and thinner vapor, 10% from burning biomass, 3% from cooking food, 8% from municipal waste, and 8% from sources that weren't explained. Therefore, VOCs contaminated in ambient air are emitted from various sources such as vehicles (Suwattiga and Limpaseni, 2005), gas stations (Allahabady et al., 2022), agricultural wastes (Odekanle et al., 2022), industrial estates (Chen et al., 2024), and liquefied petroleum gas (Mihajlović et al., 2021).

VOCs are important atmospheric species that contribute to alterations in atmospheric chemistry. The emissions of VOCs from biomass burning and the VOC chemistry in fire plumes are relatively uncertain (Uttamang et al., 2023). Saeaw and Thepanondh (2015) reported that concentrations of total VOC emissions from the Maptaphut estate in Rayong Province were 24.4-70.9 µg/m³, while the source apportionment of total VOC emissions from the industrial area of Rayong Province in Thailand indicated that 42 to 57% originated from mobile sources, 15 to 45% from industrial processes, and 3 to 10% from household chemical usage. Additionally, the source of VOCs in the community area in a petrochemical industrial area of Maptaphut estate in Rayong province was benzene, total xylene, and ethylbenzene emitted from gasoline combustion, identified as vehicle emissions. Vinyl chloride and 1,2-dichloroethane are emitted from the polyvinyl chloride (PVC) industry's raw materials, while toluene, styrene, and 1,3-butadiene are released from industrial origins (Pinthong et al., 2022). Zhang et al. (2017) revealed that the total ambient VOC emissions from the Jinan petroleum refinery in China amounted to 50.7 µg/m³. The significant VOCs identified include ethane (24.58 µg/m³), ethene (3.94 µg/m³), ethylbenzene (0.82 µg/m³), 1,3-butadiene (0.82 µg/m³), benzene (0.24 µg/m³), and toluene (0.08 µg/m³), among others. Kim et al. (2024) showed that the VOCs emitted from the multi-industrial city of Ulsan, South Korea, included 18.3% toluene (6.37 µg/m³), 13.4% m, p-xylene (4.69 µg/m³), 7.7% ethylbenzene (2.70 µg/m³), and 4.8% benzene (1.69 µg/m³), indicating significant effects of industrial emissions. Moreover, the concentrations of 1,2-dichloroethane, benzene, and 1,3-butadiene emissions from the industrial estate of Rayong city were 4.38 ± 1.99 µg/m³, 1.99 µg/m³, and 2.48 ± 0.61 µg/m³, respectively. Then, the levels of 1,2-dichloroethane, benzene, and 1,3-butadiene exceeded the annual VOC standards by 2.71, 2.58, and 38.00 times (Nakyai et al., 2025).

VOCs include a variety of chemicals, some of which may have short- and long-term adverse health effects. Concentrations of many VOCs are consistently higher indoors (up to ten times higher) than outdoors. VOCs such as benzene, vinyl chloride, 1,2-dichloroethane, trichloroethylene, dichloromethane, 1,2-dichloropropane, tetrachloroethylene, chloroform, and 1,3-butadiene are listed by the Pollution Control Department (PCD) of Thailand as hazardous pollutants that require monitoring (PCD, 2025). Exposure to VOCs can lead to both acute and chronic toxicity in humans. Short-term effects of VOC exposure commonly include irritation of the eyes, nose, throat, and skin, along with symptoms such as headaches, nausea, dizziness, fatigue, and shortness of breath (US-EPA, 2007). Increased concentrations of VOCs can adversely affect health. Long-term exposure to low levels at or exceeding legal limits may be linked to respiratory system problems, including lung tissue damage, respiratory tract irritation, and the exacerbation of pulmonary conditions such as asthma, as well as DNA strand breaks, chromosomal aberrations, mutations, and disruptions in blood cell and vessel function, leading to hematological disorders and injuries (Zhou et al., 2020; Saeedi et al., 2024).

Based on the information submitted, the researcher chose to measure VOC concentrations in ambient air and conduct a health risk assessment within the industrial estate during the rainy, cold, and hot seasons.

MATERIALS AND METHODS

Sampling sites and VOC concentrations

Researchers studied and selected sampling sites in an industrial estate in Rayong province, Thailand. Rayong province's industrial estate lies on the eastern coast of the Gulf of Thailand. The city plays a crucial role in Thailand's industry. The Maptaphut industrial estate covers 8,012.39 acres in Rayong province and is the main industrial estate. Petrochemical and chemical manufacturing facilities, steel and metal industries, machinery and equipment production, coal-powered electricity plants, petroleum refineries, residential districts, and transportation infrastructure dominate the region.

The VOC concentrations provided secondary data for this investigation from the Air Quality Monitoring Station (AQM) of Maptaphut City Municipality. Three AQMs in Maptaphut City Municipality in Rayong city continuously recorded VOC concentrations with the represented IA 1-3 symbol. The IA1 is located in the community area (12º 43' 50.2674"N and 101º 9' 20.2314"E), approximately 2.53 km from the petrochemical industry, which mostly produces plastic resins or polymers molded into products used for food packaging, automotive components, medical devices, electrical appliances, and infrastructure, including pressure-resistant pipes and telecommunication cables, among others. And then, the IA2 is in the public health center and the nearby government office (12º 42' 31.2114" N and 101º9'57.168" E). It is close to the roadside. Furthermore, this sampling site took place 1.38 km away from the oil refineries. The IA3 has been included in the school and community (12º 41' 8.3688" N and 101º 7' 1.218" E). The site is situated approximately 600 m from the liquefied natural gas (LNG) industry and near a high-traffic crossroads during peak times.

VOC concentrations were continuously monitored and recorded at three AQM stations located within Maptaphut City Municipality. The continuous sampling utilized networked online gas analyzers, specifically equipped with Gas Chromatography-Flame Ionization Detectors (GC-FIDs, Baseline 9100, Ametek, USA). The daily real-time measurement focused on the continuous collection of data for vinyl chloride, benzene, toluene, ethylbenzene, p-xylene, and 1,3-butadiene, spanning an entire year from January to December in 2024. The daily meteorological parameters, including wind speed (WS), relative humidity (RH), total precipitation (Rain), air temperature (Temp), and air pressure (PS), were obtained from AQM of Maptaphut City Municipality. The industrial estate remained from January to December 2024, covering both the dry season (January to April and November to December) and the wet season (May to October). The daily sample data started at 00:00 and ended at 23:00 the following day (24 hours). In that time, about 910 data points were recorded from three AMQ stations. Figure 1 depicts the sampling sites.

Figure 1. Sampling sites of Air Quality Monitoring Station (AQM) in Map Ta Phut Town Municipality.

Inhalation of health risk assessment

Non-carcinogenic risk assessment

The hazard quotient (HQ) is a guideline used to evaluate the non-carcinogenic risk associated with human exposure to air contaminants. It was estimated that both children and adults could inhale VOCs through the inhalation exposure pathway (Abd Hamid et al., 2019; Kawichai et al., 2022). Equation (1) calculates the HQ as the ratio of toxicological effects based on the exposure concentration via inhalation (EC_Inh) and the reference concentration (RfC) for each VOC, as shown in Table 1.

When the HQ >1.0 signifies an opportunity of non-carcinogenic effects on health, whereas HQ<1.0 means no significant risk or negligible hazards. The EC_Inh for each VOC exposure was determined utilizing Equation (2).

Where EC is the EC of pollutants (µg/m³), C is individual VOC concentrations (µg/m³), ED is the exposure duration (days), EF is the exposure frequency (days/year), ET is the exposure time (hours/day), and AT is the average time (hours). The values of these parameters were shown in Table 2, which is referred to by Morakinyo et al. (2017) and Prasertsin and Nathapindhu (2020).

Table 1. The reference concentration (RfC), inhalation unit risk (IUR), and cancer slope factors (SF) for health risk assessment from the inhalation route for VOCs.

Carcinogenic risk assessment

The cancer risk (CR_Inh) associated with each carcinogenic VOC was determined by assessing the long-term risk of cancer development due to ongoing exposure to these substances, applying an exact method (Abd Hamid et al., 2019; Kawichai et al., 2022). To determine the cancer risk, we investigated the risks linked to each carcinogenic VOC, including vinyl chloride, benzene, ethylbenzene, and 1,3-butadiene, as illustrated by Equation (3).

Table 2. Parameters for health risk assessment for the inhalation route for VOCs.

Carcinogenic equivalency (CEQ) is a risk assessment method applied to determine the potential carcinogenicity of volatile organic compounds (VOCs) in relation to reference material. This parameter defines the combined carcinogenic potential of a mixture compared to a particular amount of reference VOC carcinogen, generally benzene (Chen et al., 2024). The CEQ for a VOC has been calculated by multiplying the VOC concentration by the ratio of the cancer slope factors (SF) of the individual VOC to that of benzene, as illustrated in Equation (4).

Data analysis

The VOC concentrations and meteorological parameters were statistically analyzed using SPSS Statistics (Version 28). The VOC concentrations at three sampling sites within the industrial estate in Rayong City were tested for normality using the Kolmogorov–Smirnov test (P < 0.05), which indicated a non-normal distribution. The Mann-Whitney U and Kruskal-Wallis tests were utilized to statistically assess individual VOC concentrations across three sampling sites and seasons at the industrial estate in Rayong City. Moreover, the association between meteorological parameters and VOC concentrations was assessed using Pearson's correlation analysis.

Finally, we statistically analyzed the source identification of VOC concentrations in ambient air at the industrial estate in Rayong City using principal component analysis (PCA), which widely tests the sources of air pollution, agriculture, and the environment (Kawichai et al., 2020; Teravecharoenchai et al., 2021; Chen et al., 2024). In the PCA for source identification, daily VOC concentrations were standardized to achieve simulations of results from data sets of only the concentrations of detection data that were evaluated. The PCA is performed by decomposing the variance matrix of the dataset into a collection of eigenvalues and eigenvectors. The eigenvalues indicate the amount of variance along each principal component (PC), whereas the eigenvectors indicate the positions of the PCs. The varimax method is the most effective and commonly employed orthogonal rotation method for conducting rotation. Components possessing eigenvalues over 1 were preserved. Furthermore, loadings above 0.5 are considered significant for source attribution (Maskey et al., 2018; Mabel and Olayemi, 2020).

RESULTS

VOCs concentrations

Table 3 displays the concentration of volatile organic compounds (VOCs) released from the industrial estate in Rayong city, Thailand. The average concentrations of VOCs for all sampling sites in descending order were ethylbenzene (2.17 ± 4.48 to 11.0 ± 11.7 µg/m³), toluene (1.78 ± 1.66 to 4.06 ± 4.42 µg/m³), 1,3-butadiene (1.13 ± 1.06 to 1.49 ± 1.91 µg/m³), p-xylene (0.85 ± 0.36 to 1.33 ± 1.38 µg/m³), benzene (0.60 ± 0.63 to 1.24 ± 0.43 µg/m³), and vinyl chloride (0.03 ± 0.03 to 0.87 ± 1.64 µg/m³). The highest values of benzene (1.24 ± 0.43 µg/m³) and toluene (4.06 ± 4.42 µg/m³) were found at the IA1 site, while the highest mean annual values of ethylbenzene (11.0 ± 11.7 µg/m³) and p-xylene (1.33 ± 1.38 µg/m³) were emitted from the IA2 site. IA1 is located within a community area and close to a petrochemical facility that produces plastic resins and polymers. The ambient VOCs at this site are likely influenced by both traffic emissions and nearby industrial activity. IA2 is situated near several oil refineries, and this monitoring station is also positioned close to a roadside, which may contribute additional traffic-related VOCs. The IA3 site reported that the vinyl chloride (0.87 ± 1.64 µg/m³) and 1,3-butadiene (1.49 ± 1.91 µg/m³) concentrations were the highest values. The IA3 is situated in the school and community area near a high-traffic crossroads during peak times and is close to the liquefied natural gas (LNG) industry. Previous study of ambient VOC concentration at the Map Ta Phut industrial estate in Rayong province. They found that the major VOCs in the community area were benzene, total xylene, and ethylbenzene. In contrast, samples from the industrial estates showed higher levels of vinyl chloride and 1,2-dichloroethane, which are raw materials used in the PVC industry, as well as toluene, styrene, and 1,3-butadiene released from industrial processes (Pinthong et al., 2022). Furthermore, the total volatile organic compounds (VOCs) during the dry seasons at the IA1, IA2, and IA3 sites were 8.88, 22.33, and 12.05 µg/m³, whereas they were 11.45, 9.20, and 8.45 µg/m³ during the wet season, respectively (Figure 2).

The VOC concentrations at three sampling sites within the industrial estate in Rayong City displayed a non-normal distribution. The Mann-Whitney U and Kruskal-Wallis tests were applied to statistically evaluate individual VOC concentrations across three sampling sites within the industrial estate in Rayong City (Table 3). The results indicated that the mean concentrations of vinyl chloride, benzene, and ethylbenzene differed significantly among the sampling sites (P < 0.05). The vinyl chloride values emitted from the IA1, IA2, and IA3 sites were significantly different (P < 0.05), while the concentrations of benzene and ethylbenzene in the IA2 and IA3 sites were not significantly different (P > 0.05). Moreover, 1,3-butadiene, toluene, and p-xylene levels were not significantly different among sampling sites (P > 0.05). However, the total VOC concentrations during the dry season were not significantly different from the wet season in all sites (P > 0.05).

Table 3. The VOC concentrations emitted from an industrial estate in Rayong city in 2024.

Note:  ND: no data. Mann-Whitney U test for individual VOCs in the industrial estate. a, b, c is a significant difference in each site at the industrial estate in Rayong City for using the Kruskal-Wallis test (P-value > 0.05).

Figure 2. Total VOC concentrations during wet and dry seasons emitted from an industrial estate in Rayong city in 2024.

Table 4 illustrates the correlation between VOC concentrations and meteorological parameters in the Rayong Industrial Estate in 2024. Research results revealed that toluene showed a significant negative correlation with relative humidity (r = -0.166 to -0.266, P < 0.01) and air temperature (r = -0.263 to -0.315, P < 0.01), while benzene and ethylbenzene were positively correlated with air temperature and relative humidity in some sites. Moreover, a moderately significant correlation was seen between toluene and pressure (r = -0.488, P < 0.01) at the IA2 site. The correlation between benzene and atmospheric pressure in the IA2 site was strong and significantly positive (r = 0.713), while benzene and air temperature (r = 0.220) and wind speed (r = 0.253) were positively correlated (P < 0.01). 

Table 4. Pearson’s correlation coefficients (r) between VOC concentrations and meteorological parameters in a Rayong Industrial Estate (2024).

Note: **Correlation is significant at the 0.01 level (2-tailed); * Correlation is significant at the 0.01 level (2-tailed)

Source apportionment of VOCs by principal component analysis (PCA)

The results of the PCA classifying the sources of VOCs at an industrial estate in Rayong city are shown in Table 5. A threshold of 0.50 for factor loadings was determined to assess statistical significance. Principal component analysis (PCA) accounted for 58 to 77% of the cumulative variance, with eigenvalues from the varimax-rotated factor analysis exceeding 1. At the IA1 site, four components were identified and explained, with cumulative variance ranging from 23% to 77% depending on the site and eigenvalues ranging from 1.028 to 1.376. The component includes vinyl chloride and p-xylene for PC1, 1,3-butadiene for PC2, ethylbenzene for PC3, and toluene for PC4. These components were slurry, open equipment, vessel, and raw material in PVC industrial emissions, synthetic rubber and thermoplastic resin production, wastewater treatment, and vehicle exhaust (Chen et al., 2016; Hosaini et al., 2017; Sukiit et al., 2021; Malakan et al., 2022; Pinthong et al., 2022; Kim et al., 2024). At the IA2 site, the cumulative variance ranged from 37% to 71%, and the eigenvalues ranged from 1.027 to 2.217. PC1 was comprised significantly of toluene, ethylbenzene, and p-xylene, which indicates industrial solvent usage. The compounds PC2 and PC3 are vinyl chloride and 1,3-butadiene, which are classified as belonging to the oil refinery, slurry, open equipment, vessel, and raw material in PVC industrial emissions, as well as the synthetic rubber and thermoplastic resins industry and wastewater treatment (Chen et al., 2016; Hosaini et al., 2017; Sukiit et al., 2021; Kim et al., 2024). Moreover, the IA3 site indicated that three factors, including 1,3-butadiene (PC1), benzene (PC2), and vinyl chloride (PC3), for the cumulative variance ranged from 24 to 58%, and the eigenvalues ranged from 1.003 to 1.449. The components were classified as sources from the synthetic rubber and thermoplastic resins industry and wastewater treatment, vehicle exhaust, and slurry, open equipment, vessel, and raw material in PVC industrial emissions, respectively (Chen et al., 2016; Hosaini et al., 2017; Malakan et al., 2022; Pinthong et al., 2022; Kim et al., 2024).

Health risk assessment of VOCs

Non-carcinogenic risk assessment for VOCs

Non-carcinogenic risks are health problems that occur in an organism due to VOC exposure, excluding cancer, which is calculated by the Hazard Quotient (HQ) in the study of inhalation routes to VOCs for children and adult groups, as shown in Table 6. In the Rayong City industrial estate, inhalation exposure to all VOCs posed no significant non-carcinogenic risk, as indicated by HQs that remained below 1.0. The highest of HQ values for 1,3-butadiene for children and adult groups, which showed no effects on non-carcinogenic risk.

Table 5. Rotated principal component loadings of VOC concentrations emitted from an industrial estate in Rayong city in 2024.

Table 6. Hazard quotient (HQ) associated with VOCs exposure affects both children and adults in an industrial estate located in Rayong city.

Carcinogenic risk assessment for VOCs

The cancer risk (CR_Inh) for inhalation exposure routes was estimated to assess the potential for cancer of VOCs on humans, including vinyl chloride, 1,3-butadiene, benzene, and ethylbenzene. Table 7 presents the cancer risk (CR) of VOCs for children and adults exposed within the industrial estate in Rayong city. The results of CR_Inh for inhalation exposure routes for children and adult groups calculated that the risk was below 10⁻⁶, indicating that the no risk from all VOCs related to cancer. The CR_Inh values of 1,3-butadiene for both age groups in the industrial estate of Rayong City were between 10⁻⁶ and 10⁻⁴, indicating that the cancer risk from VOCs was seen as acceptable over a lifetime.

Table 7.  Cancer risk (CR_Inh) associated with VOCs exposure affects both children and adults in an industrial estate located in Rayong city.

The carcinogenic equivalency (CEQ) is a method of risk evaluation applied to evaluate the possible carcinogenicity of volatile organic compounds (VOCs) such as vinyl chloride, 1,3-butadiene, benzene, and ethylbenzene. Figure 2 illustrates that the CEQ values in the industrial estate, Rayong city, were 1.91 ± 1.21 µg/m³, 0.72 ± 0.41 µg/m³, and 1.64 ± 1.38 µg/m³ for IA1, IA2, and IA3, respectively. The highest CEQ value was found at the IA1 site, while the lowest values of CEQ were found in the IA2 site, as shown in Figure 3.

Figure 3. Carcinogenic equivalency (CEQ) of volatile organic compounds (VOCs) in an industrial estate located in Rayong city.

DISCUSSION

We performed an analysis of the average VOC concentrations emitted from Rayong City, Thailand's major petrochemical industrial estate. It was found that the concentrations of VOCs in all sampling sites in descending order were ethylbenzene (2.17 ± 4.48 to 11.0 ± 11.7 µg/m³)> toluene (1.78 ± 1.66 to 4.06 ± 4.42 µg/m³) >1,3-butadiene (1.13 ± 1.06 to 1.49 ± 1.91 µg/m³) > p-xylene (0.85 ± 0.36 to 1.33 ± 1.38 µg/m³) > benzene (0.60 ± 0.63 to 1.24 ± 0.43 µg/m³) > vinyl chloride (0.03 ± 0.03 to 0.87 ± 1.64 µg/m³). Moreover, the results revealed mean levels of vinyl chloride, benzene, and ethylbenzene were significantly different among their mean levels in each sampling site (P < 0.05). The total VOC concentrations during the dry season were not significantly different from the wet season in all sites (P > 0.05). The investigation of VOC emissions from the petrochemical industrial complex in Taiwan found that the amounts released each year were 117.7 tons of benzene, 44.6 tons of vinyl chloride, 42.4 tons of ethylbenzene, and 22.3 tons of 1,3-butadiene (Chen et al., 2016). Moreover, Pinthong et al. (2022) revealed that the VOCs emitted from the Maptaphut industrial area included benzene, total xylene, and ethylbenzene as main indicators of gasoline burning in automobiles, whereas industrial sources emitted toluene, styrene, vinyl chloride, and 1,3-butadiene. Similar to this study, Kim et al. (2024) showed that the volatile organic compounds (VOCs) emitted from the multi-industrial city of Ulsan, South Korea, included 18.3% toluene (6.37 µg/m³), 13.4% m, p-xylene (4.69 µg/m³), 7.7% ethylbenzene (2.70 µg/m³), and 4.8% benzene (1.69 µg/m³), indicating significant effects of industrial emissions. Malakan et al. (2022) reported that VOC emission inventories from industrial sources and mobile sources in the Maptaphut industrial estate included benzene, 1,3-butadiene, and vinyl chloride at 5.11, 3.19, and 37.78 tons/year, respectively, while mobile sources emitted benzene and 1,3-butadiene at 73.89 and 9.96 tons/year, respectively. In 2024, the ambient concentrations of 1,3-butadiene (1.13 ± 1.06 to 1.49 ± 1.91 µg/m³) at three sites in the industrial estate of Rayong city exceeded the annual standard (0.33 µg/m³) set by the Pollution Control Department (PCD). In a similar study by Nakyai et al. (2025), concentrations of 1,3-butadiene emitted from industrial estates in Rayong Province during the rainy and cold seasons exceeded the annual standards of PCD.

Moreover, the result of the association between VOC concentrations and meteorological parameters at the Rayong industrial estate in 2024 was obtained using Pearson’s correlation. Toluene had a substantial negative connection with relative humidity (r = -0.166 to -0.266) and air temperature (r = -0.263 to -0.315) across all sites. Volatile organic compound concentrations decreased with increasing relative humidity and air temperature. The increase in temperature enhances vertical mixing and the overall dispersion of the pollutants. Furthermore, increased relative humidity enhances the wet scavenging or washout effect, facilitating the removal of VOCs from the atmosphere. Moreover, wind speed and total rainfall were increased to reduce VOCs in ambient air (Nakyai et al., 2025).

Benzene and ethylbenzene were positively correlated with air temperature and relative humidity in some sites. The correlation between benzene and atmospheric pressure in the IA2 site was strong and significantly positive (r = 0.713), while benzene and air temperature (r = 0.220) and wind speed (r = 0.253) were positively correlated. The IA2 site is located close to the high traffic density, various government buildings, and the oil refineries. The main results are that BTEX compounds are hydrophobic compounds whose adsorption effects and solubility decrease in water vapor. Consequently, elevated temperature and high relative humidity increased benzene and ethylbenzene levels in the ambient air. Meteorological circumstances influence the various components due to their high Henry's law constant, low water solubility, and low polarity (Xu and Zhang, 2011; Zhou et al., 2017).

The PCA evaluating the sources of VOCs in the industrial estate in Rayong City indicated that the IA1 site comprised vinyl chloride and p-xylene for PC1, signifying the presence of petrochemical companies, including slurry, open equipment, vessels, and raw material in PVC industrial emissions. The IA1 site is located close to the community, approximately 2.53 km from the petrochemical factory, which mainly manufactures plastic resins or polymers that are molded into products used for food packaging, automotive parts, medical instruments, electrical devices, and infrastructure, such as pressure-resistant pipes and telecommunication cables, among others. Moreover, Malakan et al. (2022) revealed that industrial sources of VOC emissions, including stack, wastewater treatment, slurry, open equipment, and vessels, contributed 37.78 tons/year from the Maptaphut petroleum and petrochemical industrial estates. Sass et al. (2005) and Pinthong et al. (2022) confirmed that industrial sources released toluene, styrene, vinyl chloride, and 1,3-butadiene from using raw material in the PVC industry. PC2, PC3, and PC4 indicated 1,3-butadiene, ethylbenzene, and toluene, respectively. The sources were classified as synthetic rubber and thermoplastic resins, and vehicular emissions. Chen et al. (2016) reported that the source of 1,3-butadiene is emissions from plastic and rubber, nitrile rubber, and acrylonitrile copolymer resins. Sukjit et al. (2021) reported that 1,3-butadiene in ambient air at Maptaphut estates emitted from wastewater treatment plants was about 92% from the synthetic rubber industry. Moreover, ethylbenzene and toluene are released from industrial activity, vehicular exhaust, and gasoline evaporation (Hosaini et al., 2017; Kim et al., 2024).

Additionally, PC1 for the IA2 site was predominantly composed of toluene, ethylbenzene, and p-xylene, implying the possibility of mixed vehicle exhaust and industrial solvent usage (Malakan et al., 2022; Pinthong et al., 2022). The IA2 site is located close to the public health center and a nearby government building. It is adjacent to the roadway. Moreover, this sampling site was located 1.38 km from the oil refineries. Malakan et al. (2022) reported that mobile sources, including motorcycles, passenger cars, vans and pickups, trucks, and buses, emitted 73.39 tons/year of benzene and 9.96 tons/year of 1,3-butadiene from the Maptaphut petroleum and petrochemical industrial estates. Similar research from Pinthong et al. (2022) revealed that the high VOC concentrations emitted from Maptaphut petrochemical industrial areas in Thailand were found to be benzene, total xylene, and ethylbenzene emitted from gasoline combustion in mobile motors, while industrial sources released toluene, 1,3-butadiene, styrene, 1,2-dichloroethane, and vinyl chloride. Kim et al. (2024) investigated the source of VOCs released from the multi-industrial city of Ulsan in South Korea using the positive matrix factorization model (PMF). They found that toluene, ethylbenzene, benzene, m, p, o-xylene, ethyl acetate, and vinyl acetate were related to petrochemical and non-ferrous industrial activity and industrial solvent usage. The compounds PC2 and PC3 were vinyl chloride and 1,3-butadiene, which are classified as belonging to the oil refinery and slurry, open equipment, and vessels, as well as the synthetic rubber and thermoplastic resins industry and wastewater treatment (Chen et al., 2016; Sukjit et al., 2021). Moreover, the IA3 site indicated that three factors, including 1,3-butadiene (PC1), benzene (PC2), and vinyl chloride (PC3), were classified as sources from the synthetic rubber and thermoplastic resins industry and wastewater treatment, vehicle exhaust, and the slurry, open equipment, vessels, and raw material in PVC industrial emissions, respectively. The IA3 site is in the school and community area. The location is approximately 600 meters from the liquefied natural gas (LNG) industry and close to a heavily trafficked intersection during peak times. The polymerization of the polyvinyl chloride (PVC) industry is emitted from vinyl chloride (Chen et al., 2016; Pinthong et al., 2022), while 1,3-butadiene is related to plastic and rubber industrial processes (Chen et al., 2016; Sukjit et al., 2021) and oil refineries (Pinthong et al., 2022). Hosaini et al., (2017) reported that principal component analysis (PCA) identified toluene and benzene as the main sources of ambient VOCs in Kuala Lumpur, Malaysia, which were associated with gasoline evaporation and vehicle exhaust emissions.

Non-carcinogenic risk assessments in the study of inhalation routes to VOCs for children and adult groups in the industrial estate of Rayong City are calculated by the Hazard Quotient (HQ). It was found that the inhalation exposure to all VOCs posed no significant non-carcinogenic risk, as indicated by HQs that remained below 1.0, which were no effects of non-carcinogenic risk. Moreover, the cancer risk (CR_Inh) of VOCs attached to children and adults exposed to the industrial estate, Rayong City. The results of CR_Inh for inhalation exposure routes for children and adult groups calculated that the risk was below 10⁻⁶, indicating that there is no risk from all VOCs related to cancer. However, the CEQ values in the industrial estate, Rayong city, were 1.91 ± 1.21 µg/m³, 0.72 ± 0.41 µg/m³, and 1.64 ± 1.38 µg/m³ for IA1, IA2, and IA3, respectively. The highest CEQ value was obtained at the IA1 site, which contained high levels of carcinogenic VOCs, including vinyl chloride, 1,3-butadiene, and benzene, associated with the petrochemical industries primarily producing plastic resins or polymers. Although both non-carcinogenic and carcinogenic risks associated with VOCs have shown no adverse impact on human health, previous studies found that exposure to benzene and 1,3-butadiene significantly decreases DNA repair capacity in children, with both pollutants causally linked to DNA damage and the disruption of this essential cellular function. Consequently, these exposure occasions could increase the risk of cancer (Au et al., 2010; Ruchirawat et al., 2010). Exposure to vinyl chloride may be associated with Raynaud's syndrome, acral sclerodermatous transformations, acroosteolysis (AOL), skin cancer, and cutaneous signs of liver disease (Goodman et al., 2023). Moreover, the occupational exposure to 1,3-butadiene is linked to leukemia and cardiovascular disease (Lin et al., 2020; Chen and Zhang, 2022). Furthermore, current evidence indicates that nonoccupational exposure to 1,3-butadiene may be linked to specific reproductive effects and, notably, to various children developing tumors, autism, and asthma (von Ehrenstein et al., 2014; Hall et al., 2019; Kuang et al., 2021). This study focuses on 1,3-butadiene because of its long-term cancer risk.

CONCLUSION

This study performed an analysis of the average VOC concentrations emitted from the petrochemical industrial estate of Rayong city in Thailand. The results revealed mean levels of vinyl chloride, benzene, and ethylbenzene were significantly different among their mean levels in each sampling site. The total VOC concentrations during the dry season were not significantly different from the wet season in all sites. Moreover, the ambient concentrations of 1,3-butadiene (1.13 ± 1.06 to 1.49 ± 1.91 µg/m³) in the industrial estate of Rayong city exceeded the annual standard (0.33 µg/m³) set by the Pollution Control Department (PCD). Although the level of vinyl chloride (0.60 ± 0.63 to 1.24 ± 0.43 µg/m³) and benzene (0.03 ± 0.03 to 0.87 ± 1.64 µg/m³) remained below the particular annual standards, their continued distribution in the atmosphere requires consideration regarding potential human health effects, specifically increased cancer risk. The main effect of meteorological conditions on VOCs might be air temperature and relative humidity. The PCA evaluated the sources of VOCs in the industrial estate in Rayong City, which were classified as sources from the synthetic rubber and thermoplastic resins industry, wastewater treatment, vehicle exhaust, industrial solvent usage, and the petrochemical industry, including slurry, open equipment, vessels, and raw material in PVC industrial emissions. Moreover, the highest CEQ value, which contained high levels of carcinogenic VOCs, might be associated with the petrochemical industries primarily producing plastic resins or polymers and wastewater treatment. However, both non-carcinogenic and carcinogenic risks associated with VOCs indicated no adverse impact on human health. The conclusion clarified that health risks assessed account for exposure duration, frequency, and toxicological potency, which moderate the potential health impact. Elevated concentrations require the risk of dose accumulation from exposure conditions to cause significant adverse health effects. This study focuses on 1,3-butadiene because of its long-term cancer risk.

The study has several limitations. Geographic coverage was restricted to only three monitoring sites, and the assumptions used in the risks modelling may have introduced data gaps. Future studies should expand monitoring to additional areas, incorporate personal exposure assessments, refine seasonal source apportionment, and investigate the potential synergistic health effects of combined VOC exposures. Moreover, optimizing air quality in industrial areas requires a synergistic approach encompassing continuous monitoring, implementation of targeted source controls (with emphasis on high-risk compounds, e.g., 1,3-butadiene), and strategic health risk communication directed at informing relevant policymakers and stakeholders.

ACKNOWLEDGEMENTS

The authors are grateful to the Faculty of Science, Energy, and Environment, King Mongkut’s University of Technology North Bangkok. King Mongkut's University of Technology North Bangkok funded this research under Contract no. KMUTNB-68-BASIC-48. The authors would like to thank Maptaphut City municipality and Thailand’s Pollution Control Department (PCD) for providing VOCs data.

AUTHOR CONTRIBUTIONS

Susira Bootdee: Conceptualization (Lead), Methodology (Lead), Data Curation (Lead), Data Analysis (Equal), Investigation (Lead), Resources (Lead), Writing – Original Draft (Lead), Writing – Review & Editing (Lead), Visualization (Lead), Supervision (Lead), Project Administration (Lead); Suganya Phantu: Data Curation (Supporting), Visualization (Supporting), Statistical & Data Analysis (Equal). All authors have read and approved the final manuscript.

CONFLICT OF INTEREST

The authors declare that they hold no competing interests.

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