Evaluation of BTEX Pollution and Health Risk for Sustainable Use of a Typical Chemical Pesticide Industrial Site

Abstract

BTEX (benzene, toluene, ethylbenzene, and xylenes) are widely used in pesticide manufacturing industries. Due to their high volatility and toxicity, BTEX compounds often leak during production, storage, and transportation, posing significant threats to human health and the environment. In this study, soil and groundwater samples at a chemical pesticide industrial site in southern China were collected and analyzed. Soil concentrations ranged from 0.05–142 mg/kg for benzene, 0.05–315 mg/kg for toluene, 0.05–889 mg/kg for ethylbenzene, 0.05–2800 mg/kg for m-&p-xylene, and 0.05–668 mg/kg for o-xylene. Groundwater concentrations were 0.7–340,000 μg/L for benzene, 0.9–4070 μg/L for toluene, 0.5–1900 μg/L for ethylbenzene, 1.6–6000 μg/L for m-&p-xylene, and 0.6–1500 μg/L for o-xylene. While the average concentrations were relatively low, there were numerous locations where BTEX levels significantly exceeded national soil and groundwater standards. Despite the minimal health risks from soil BTEX pollution, utilizing groundwater for drinking or bathing could result in unacceptable cancer and non-cancer risks. These findings underscore the urgent need for remediation efforts, particularly concerning benzene contamination in groundwater, to ensure the sustainable utilization of the industrial site in question.

1. Introduction

BTEX compounds include benzene, toluene, xylene, ethylbenzene, and styrene, which are widely used in petrochemical, coal chemical, and pesticide manufacturing industries [1,2]. Due to their high volatility and toxicity, these compounds are prone to leakage during production, storage, transportation, and handling, leading to widespread BTEX pollution in the environment [3,4].

The toxicity of BTEX is significant, posing serious threats to human health and the ecological environment [5,6,7]. BTEX can enter the human body through inhalation, skin contact, and ingestion, causing damage to the central nervous system, liver, and kidneys [4,8,9]. The toxicity of benzene is particularly notable; long-term exposure to benzene environments can lead to hematopoietic system damage, causing severe diseases such as leukemia and aplastic anemia [8,10,11]. Toluene primarily affects the central nervous system, causing symptoms such as headache, dizziness, insomnia, and memory loss, and severe cases can lead to neurasthenia syndrome [12,13]. The toxicity of xylene and ethylbenzene to the human body should not be overlooked either, as long-term exposure can cause liver and kidney damage, as well as neurological dysfunction [14,15,16]. The International Agency for Research on Cancer (IARC) classifies benzene as a Group 1 carcinogen [17,18], highlighting its high risk to human health.

Stricter environmental policies, industrial upgrades, and land transfer demands have driven industrial enterprises to shut down or relocate, leaving behind numerous contaminated sites [19]. As the use of industrial sites shifts from industrial land to residential or commercial land, the monitoring and risk assessment of BTEX pollution become particularly important. The residual pollution of shut-down sites directly relates to the health and environmental safety of future users [20]. BTEX compounds have high mobility and persistence in the environment; once they enter the soil and groundwater, they are difficult to eliminate quickly through natural attenuation. Therefore, detailed pollution monitoring before site development is crucial to clarify the types, concentrations, distribution, and potential risks of pollutants, which is a prerequisite for ensuring the health and environmental safety of future site users [20,21,22].

Research on BTEX pollution has accumulated substantial findings both domestically and internationally. Internationally, the United States Environmental Protection Agency (EPA) and IARC have extensively studied the toxicity and carcinogenicity of BTEX compounds, formulating stringent environmental quality standards and risk assessment methods [17,23]. European countries also place great emphasis on the governance of BTEX pollution, adopting various measures to reduce industrial emissions and remediate contaminated soil and water sources [24,25,26]. In China, with the continuous strengthening of environmental protection policies, certain progress has been made in the governance of BTEX pollution. In recent years, the Chinese government has issued a series of policy documents requiring enhanced monitoring and remediation of industrially polluted sites, particularly those transitioning to residential or commercial use, which must undergo rigorous environmental assessment and risk management [27,28]. However, relevant information about BTEX contamination, especially for the pesticide industry in China, is still scarce.

This study conducts BTEX pollution monitoring and risk assessment at a chemical pesticide enterprise site in southern China, providing the scientific basis and data support for subsequent environmental remediation, and has important practical significance. The research findings will help formulate scientific pollution remediation schemes, ensure environmental safety after the site is converted to residential or commercial use, and promote the improvement and implementation of contaminated site management policies.

2. Materials and Methods

2.1. Study Area

The industrial site with the layout shown in Figure 1 is located in southern China. The main products include methamidophos, glyphosate, spermidine, methyl parathion, dimethoate, chlorpyrifos, quizalofop, imidacloprid, fipronil, sufosfamide 203, trichlorfon, chlorobenzene, and alkyl dipropyl ethers. The primary raw materials are O,O-dimethylphosphorochloridothioate (methyl chloridate), ammonia water, toluene, sodium p-nitrophenolate, soda ash, xylene, benzene, chlorine, diphenyl ether, and industrial yellow phosphorus. The company was entirely relocated in 2007.

The region where the industry site is located is dominated by the East Asian monsoon. The annual average temperature is between 15.2 °C and 16 °C, with annual precipitation of 1000–1100 mm. According to the survey data, the soil layers from top to bottom on the site, based on their physical and mechanical properties, are filled soil, silty clay, silty clay, silty clay mixed with silt, silt, silty clay mixed with silt, silt, silty clay.

2.2. Sample Collection and Analysis

2.2.1. Sample Collection

Based on a systematic analysis of previously collected data, combined with an assessment of pollution differences between the production and living areas of the industrial site, the investigation area was divided into key investigation areas, general investigation areas, and peripheral investigation areas. The sampling grid used was primarily 20 m × 20 m in key areas, while general areas (such as office, living, and peripheral zones) had a reduced sampling density with a grid of 40 m × 40 m. The sample locations were at the center of each grid but subjected to adjustments based on professional judgment, visual and olfactory inspection, and on-site rapid detection methods. Groundwater monitoring points were positioned along the groundwater flow direction, as shown in Figure 1.

The sampling depth design for soil and groundwater was based on geological survey conclusions, with soil samples collected down to 18 m below the industrial site. In principle, soil samples were taken every 1–1.5 m within the sampling depth range, with additional samples taken if unusual soil color or odor was detected (using on-site detection equipment to assist in determining sampling locations and depths). For zones A, B, C, D, E, F, G, and K, the average moisture contents are 28.5%, 28.4%, 28.5%, 30.0%, 28.0%, and 30.6%, respectively. The corresponding pH values are 7.92, 7.43, 7.79, 8.21, 8.27, 8.11, 8.17, 8.22, and 7.97. Groundwater monitoring wells were placed in conjunction with soil sampling, with well depths allowing for contact with water-bearing layers of approximately 2 m deep. The pH of groundwater was 7.18 ± 0.41.

Quality control measures were implemented throughout the entire process of soil and groundwater sampling, preservation, and transportation. The main quality control measures included providing specialized training for sampling personnel to ensure they are familiar with production processes, proficient in sampling techniques, and knowledgeable about relevant safety operations and handling procedures; ensuring sampling tools and equipment are kept dry and clean to prevent contamination and loss of samples; immediately labeling containers after samples are placed inside; conducting on-site checks after sampling, including the verification of sampling records and sample labels; and ensuring that during sample transportation, containers are not inverted or placed upside down to prevent breakage, wetting, and cross-contamination. Samples were transported promptly to the laboratory for analysis under refrigerated conditions (4 °C) in a dark environment.

2.2.2. Laboratory Testing and Quality Assurance

Purge and Trap-Gas Chromatography-Mass Spectrometry were applied for the determination of BTEX in samples following the EPA Method 8260C [29].

Major Instruments and Equipment: Agilent 7890A/5975C Gas Chromatography-Mass Spectrometer (GC-MS) (Santa Clara, CA, USA); Chromatography column: DB-VRX (60 m × 0.25 mm × 1.4 μm); Teledyne Tekmar Atomx Purge (Santa Clara, CA, USA) and Trap-Automated Sampler with Vocarb 3000 purge and trap column, and Teledyne Tekmar Aquatek 70 automated sampler (Mason, OH, USA).

Purge and Trap Program Parameters: Purge time: 11 min; purge flow rate: 40 mL·min⁻¹; purge temperature: 25 °C; desorption temperature: 250 °C; desorption time: 2 min; desorption flow rate: 300 mL·min⁻¹; thermal desorption line cleaning time: 2 min; cleaning temperature: 280 °C; cleaning flow rate: 300 mL·min⁻¹

GC-MS Parameter Conditions: Chromatography column: DB-VRX (60 m × 0.25 mm × 1.4 μm); split ratio: 10:1; constant pressure: 30 psi; injection port temperature: 200 °C; MS interface temperature: 255 °C; ion source temperature: 230 °C; scan range: 15–550 atomic mass units; solvent delay time: 3 min; the GC temperature program is as follows: start at an initial temperature of 45 °C and hold for 10 min, then increase the temperature at a rate of 12 °C per minute to 190 °C and hold for 2 min, and finally increase the temperature at a rate of 6 °C per minute to 225 °C and hold for 1 min.

Quality assurance and quality control measures in the laboratory included blank tests, parallel sample spiking tests, and surrogate spiking tests, with the accuracy and precision of the data required to meet the following criteria: (1) Blank Tests: for each batch of samples (20 samples per batch), at least one full procedural blank and laboratory blank should be performed, with target compound concentrations below the detection limit; (2) Blank Spiking: at least 5% of each sample batch should undergo blank spike recovery tests, with recovery rates between 70% and 130%; (3) parallel sample testing: at least 5% of each sample batch should undergo parallel sample testing, with relative deviations of duplicate results within 100 ± 20%; (4) surrogate spiking recovery testing: at least 5% of each sample batch should undergo surrogate spiking recovery tests, with recovery rates between 70% and 130%. LOD and LOQ were defined as the concentrations corresponding to signal-to-noise ratios S/N = 3 and S/N = 10, respectively. The LOD for BTEX in soil and groundwater are 0.05 mg·kg⁻¹ and 0.5 μg·L⁻¹, respectively. No BTEX were detected in the method blanks. The recovery rates for spiked blanks ranged from 74% to 123%, while the recovery rates for surrogate spikes ranged from 70% to 117%. The relative deviations, defined as (c1 − c2) × 2/(c1 + c2) × 100%, where c1 and c2 are the measured concentrations of the two parallel samples of parallel samples, were within 20%.

2.3. Health Risk Assessment

The USEPA health risk assessment method was employed with both carcinogenic and non-carcinogenic effects of pollutants considered [30]. Carcinogenic risk is usually expressed as a risk value (Risk), representing the probability of cancer occurrence in an exposed population, calculated as follows:

RISK = CDI × SF when CDI × SF < 0.01

(1)

RISK = 1 − exp(CDI × SF) when CDI × SF > 0.01

(2)

Non-carcinogenic risk is described using the hazard index (HI):

HI = CDI/RfD

(3)

where CDI is the chronic daily intake, mg·kg⁻¹·d⁻¹; SF is the slope factor for carcinogens, kg·d·mg⁻¹; RfD is the reference dose for the pollutant, mg·kg⁻¹·d⁻¹. The total health risk from exposure to multiple pollutants is cumulative. The calculation of CDI considers ingestion of soil, dermal contact with soil particles, inhalation of soil particles, drinking water and baths. The formulas are as follows:

CDI_ingest = c × IR × EF × ED × 10⁻⁶/(BW × AT)

(4)

CDI_derma = c × SA × ABS × AF × EF × ED × 10⁻⁶/(BW × AT)

(5)

CDI_inhale = c × InhR × EF × ED/(BW × AT × PEF)

(6)

CDI_drink = c × U × EF × ED/(BW × AT)

(7)

CDI_bath = c × SA × PC × ET × EF × ED × 10⁻³/(BW × AT × PEF)

(8)

where c is the pollutant concentration in soil or groundwater, mg·kg⁻¹ or mg·L⁻¹; IR is the soil ingestion rate, mg·d⁻¹; SA is the skin surface area exposed, cm²·d⁻¹; ABS is the dermal absorption factor, unitless; AF is the soil-to-skin adherence factor, mg·cm⁻²; InhR is the inhalation rate,m³·d⁻¹; PEF is the particle emission factor, m³·kg⁻¹; EF is the exposure frequency, d·a⁻¹; ED is the exposure duration, a, BW is the average body weight of the exposed population, kg; AT is the average exposure time, d; U is the daily water intake, L·d⁻¹, PC is the skin permeability coefficient, cm·h⁻¹; and ET is the exposure time per event (bath time), h.

3. Results

3.1. BTEX in Soil

The site soil analysis revealed the presence of benzene, toluene, ethylbenzene, xylene and styrene, with benzene having the highest detection rate (defined as the ratio of the number of samples in which a particular pollutant (e.g., benzene) is detected to the total number of samples tested) of 20%, followed by o-xylene at 17%, and styrene with the lowest detection rate at 0.16% (Figure 2a). This high detection rate of benzene and xylenes can be attributed to their historical use as primary raw materials at the site before production ceased. For ethylbenzene, m- and p-xylenes, and o-xylene, the highest detection rates and concentrations were found in the peripheral greenbelt area (Zone K). Figure 2b presents the average concentrations of BTEX in soil across different zones. The highest average concentrations for each compound are as follows: Benzene is most concentrated in Zone C at 16.8 mg/kg, while Toluene reaches its peak in Zone E at 57.6 mg/kg. Both Ethylbenzene and m-xylene and p-xylene all have their highest averages in Zone K, with concentrations of 47.5 mg/kg and 115 mg/kg, respectively. Additionally, o-xylene also peaks in Zone K at 37.5 mg/kg. Styrene, however, is most concentrated in Zone A, with an average of 0.5 mg/kg.

The maximum benzene concentrations in Zones A, C, and E (72.5, 593, and 142 mg/kg, respectively) exceed China’s soil quality standard for construction land (40 mg/kg as the risk intervention value for benzene in Type II land) [31], indicating a potential unacceptable health risk. The highest benzene concentrations in Zones D and G (36.9 and 13.8 mg/kg, respectively) also exceed the standard for Type I land (10 mg/kg), suggesting potential health risks if the site is used for residential purposes. The maximum benzene concentration in Zone F (4.19 mg/kg) surpasses the risk screening value for Type II land (4 mg/kg), and the maximum concentration in Zone K (1.24 mg/kg) exceeds the risk screening value for Type I land (1 mg/kg), indicating potential health risks in these areas as well.

The highest toluene concentration at the site was found in Zone A (48.8 mg/kg), significantly below the risk screening value for Type I land (1200 mg/kg), indicating a low health risk from toluene. However, the maximum ethylbenzene concentrations in Zones A, E, and K (674, 520, and 889 mg/kg, respectively) greatly exceed the risk intervention value for Type II land (280 mg/kg), posing unacceptable health risks. In Zone F, the highest ethylbenzene concentration (67.2 mg/kg) surpasses the risk screening value for Type II land (28 mg/kg) but remains below the risk intervention value for Type I land (72 mg/kg), indicating a potential health threat. Other zones (B, C, D, and G) show maximum ethylbenzene concentrations (0.09, 0.42, 1.39, and 0.57 mg/kg, respectively) below the risk screening value for Type I land (7.2 mg/kg), indicating negligible health risks.

The highest m- and p-xylene concentrations in Zones A, E, and K (1289, 686, and 2800 mg/kg, respectively) far exceed the risk intervention value for Type II land (570 mg/kg), indicating unacceptable health risks. In contrast, the highest m- and p-xylene concentrations in Zones B, C, D, F, and G (0.63, 0.31, 3.67, 71.8, and 0.54 mg/kg, respectively) are well below the risk screening value for Type I land (163 mg/kg), suggesting minimal health risks. The highest o-xylene concentration in Zone K (668 mg/kg) exceeds the risk intervention value for Type II land (640 mg/kg), indicating a potential health risk. Zone A’s highest o-xylene concentration (634 mg/kg) is close to the control value, posing a serious health threat. Other zones show much lower o-xylene concentrations (0.07–42.6 mg/kg), indicating low health risks.

Styrene concentrations at the site are very low, with a maximum of only 0.5 mg/kg, significantly below the risk screening value for Type I land (1290 mg/kg), indicating no health risk.

3.2. BTEX in Groundwater

In the site’s groundwater, benzene, toluene, ethylbenzene, and xylene were detected, with the exception of styrene (Figure 3). Benzene had the highest detection rate at 61%, with a maximum concentration of 340 mg/L, followed by toluene at 29%, though its maximum concentration was significantly lower at 4.07 mg/L. The highest concentration of m- and p-xylenes reached 6 mg/L.

The benzene concentration in the site’s groundwater (173.3 ± 68.4 mg/L) is 1444 times higher than the Chinese Class IV groundwater standard (≤120 µg/L) [32] and 347,000 times higher than the Class I standard (≤0.5 µg/L). This severe exceedance indicates a significant health risk if the groundwater is used for drinking purposes.

Toluene’s concentration in groundwater, although much lower than benzene, still reached 0.86 ± 1.48 mg/L. While this is below the Chinese Class IV standard (≤1400 µg/L), it exceeds the Class III standard of 700 µg/L and is 1720 times higher than the Class I standard (≤0.5 µg/L), indicating a substantial health risk if consumed directly. The ethylbenzene concentration was 0.33 ± 0.70 mg/L, exceeding the Class III standard (≤300 µg/L), and is 11 times the Class II standard (≤30 µg/L) and 660 times the Class I standard (≤0.5 µg/L).

China’s groundwater quality standards do not specifically address m- and p-xylenes or o-xylene individually but do set a standard for total xylenes [32]. The detected concentrations of m- and p-xylenes and o-xylene were 0.90 ± 2.00 mg/L and 0.29 ± 0.60 mg/L, respectively, both exceeding the total xylene Class II standard (≤100 µg/L), with m- and p-xylenes exceeding the Class III standard (≤500 µg/L) by 80%. Notably, apart from styrene, which was not detected, the maximum concentrations of benzene, toluene, ethylbenzene, and xylenes in this site far exceed the Class IV standard, indicating severe BTEX contamination, rendering the groundwater unsuitable as a drinking water source.

3.3. Cancer Risks

Benzene, a well-known carcinogen, was detected at significant levels in both soil and groundwater at the site, warranting a detailed carcinogenic risk assessment. Other BTEX compounds were not considered for this analysis due to the lack of specific slope factor (SF) data. The assessment considered various exposure scenarios over different durations of work or residence (5, 10, 20, and 30 years). Generally, a carcinogenic risk between 10⁻⁴ and 10⁻⁶ is deemed acceptable, while a risk below 10⁻⁶ is considered negligible.

Based on previous studies [33,34,35], we utilized the following parameters for the risk calculation: an ingestion rate (IR) of 100 mg/day, skin surface area (SA) of 200 cm²/day, absorption factor (ABS) of 0.1, adherence factor (AF) of 0.07, inhalation rate (InhR) of 20 m³/day, particle emission factor (PEF) of 1.32 × 10⁹ m³/kg, exposure frequency (EF) of 300 days/year, average body weight of 65 kg, averaging time (AT) of 70 years × 365 days/year, skin permeability coefficient (PC) of 0.01 cm/h, and exposure time (ET) of 0.25 h/day. The carcinogenic risk from benzene exposure was calculated based on these parameters and the measured concentrations in soil and groundwater. The results indicate that the carcinogenic risk associated with benzene exposure increases with the duration of work or residence at the site (

Table 1. Cancer risks of people who work or live in the studied site for different durations.

Environmental Media	Exposure Route	Work Time or Residence Time, Years
		5	10	20	30
Groundwater	Drink	5.21 × 10−4	1.04 × 10−3	2.08 × 10−3	3.13 × 10−3
	Bath	9.77 × 10−6	1.95 × 10−5	3.91 × 10−5	5.86 × 10−5
Soil	Ingest	3.76 × 10−9	7.52 × 10−9	1.50 × 10−8	2.26 × 10−8
	Dermal contact	5.79 × 10−10	1.16 × 10−9	2.32 × 10−9	3.47 × 10−9
	Inhale	5.70 × 10−13	1.14 × 10−12	2.28 × 10−12	3.42 × 10−12

). Specifically, benzene concentrations in groundwater were significantly higher than acceptable standards, leading to carcinogenic risks exceeding the 10⁻⁴ threshold when used as a drinking source. In contrast, soil exposure, primarily through ingestion, posed a negligible carcinogenic risk, with values around 10⁻⁹, which are considered insignificant.

3.4. Non-Cancer Risk

Figure 4 illustrates the exposure concentrations of BTEX compounds through various exposure pathways. The exposure to BTEX due to groundwater contamination is dominated by benzene, which accounts for 95% of the total BTEX exposure. This dominance is attributed to the significantly higher concentration of benzene in groundwater compared to other BTEX compounds. In contrast, soil contamination shows a different profile: xylenes (including o-, m-, and p-xylenes) contribute the most (61%), followed by ethylbenzene (19%), benzene (14%), and toluene (6%). Styrene concentrations in both groundwater and soil are negligible and thus can be disregarded.

Figure 5 presents the non-carcinogenic risks associated with BTEX exposure through different pathways based on the reference dose (RfD) values of 4 × 10⁻³, 8 × 10⁻², 1 × 10⁻¹, and 2 × 10⁻¹ mg/kg/day for benzene, toluene, ethylbenzene, and xylenes respectively [36]. The RfD for benzene is significantly lower than for other BTEX compounds, being only 1/20 to 1/50 of their values. Consequently, benzene is the primary contributor to non-carcinogenic risk in all exposure pathways.

The non-carcinogenic risk from drinking water exceeds a hazard quotient (HQ) of 1 even with just five years of exposure, indicating that the groundwater is unsuitable as a drinking water source. Bathing in the contaminated water also presents a significant risk, surpassing an HQ of 1 after 30 years of exposure, suggesting that even occasional use of this water for bathing should be avoided over the long term. Although soil contamination poses a lower non-carcinogenic risk (less than 6.4 × 10⁻⁴), the risk increases significantly with prolonged exposure and should not be ignored.

4. Discussion

4.1. Factors Influencing BTEX Pollution Levels

In this study, the highest BTEX concentrations were not consistently found in production areas. Zone K exhibited very high BTEX levels, likely due to its soil being rich in organic carbon from surrounding vegetation [37]. In contrast, the industrial site had relatively low organic carbon content due to a lack of vegetation. It has been established that higher soil organic carbon enhances the adsorption of BTEX compounds [38,39], which explains the elevated BTEX levels in Zone K. Additionally, Zone K’s proximity to the pesticide production area (Zone A), where related substances are used as raw materials, contributes to this contamination. The similarity in pollutant profiles between Zone A and the adjacent office and residential area (Zone F) indicates the migration of pollutants. However, Zone F’s lower soil organic carbon content (0.3–0.71%, measured in this study) results in significantly lower BTEX concentrations compared to Zone K. The packaging and warehouse area (Zone E) also exhibited notable BTEX pollution, indicating the impact of inadvertent leaks during storage on soil contamination [40,41].

The pollution levels of BTEX compounds in soil are influenced not only by emissions but also by the volatility of each compound [42]. Generally, less volatile BTEX compounds tend to have higher residual concentrations in soil. Assuming similar emission levels, soil concentrations typically follow the trend of xylene > ethylbenzene > styrene > toluene > benzene. However, styrene’s minimal use as a primary raw material leads to the lowest emissions and residual soil concentrations. The intermediate production area (Zone C), where benzene is used as a raw material, exhibits significantly high benzene soil content due to substantial emissions during production [36].

The observed trend that less volatile BTEX compounds tend to have higher residual concentrations in soil aligns with the known environmental behaviors of these chemicals. Volatile organic compounds (VOCs) like benzene tend to evaporate quickly, reducing their soil concentrations over time [43], whereas less volatile compounds such as xylenes and ethylbenzene persist longer in the soil environment [44]. The migration of pollutants from industrial areas (Zone A) to adjacent zones (e.g., Zone F) underscores the importance of considering the spatial distribution of soil contamination in environmental risk assessments. Effective zoning and land use planning are crucial to prevent human exposure to contaminated soils, especially in areas intended for residential use [45]. Furthermore, the storage and handling of chemicals, as evidenced by the contamination in Zone E, should be rigorously controlled to prevent leaks and spills that contribute to soil pollution. Implementing best practices for chemical storage and emergency response plans can significantly reduce the risk of soil contamination [46].

There is a certain consistency in the detection of BTEX compounds in both soil and groundwater. Styrene had the lowest detection rate, yet the concentrations showed some variation. Xylene had higher concentrations in soil, whereas benzene had the highest concentration in groundwater. This could be attributed to benzene’s higher solubility in water compared to other BTEX compounds, coupled with its frequent use as a raw material, leading to substantial emissions. The residual concentrations of BTEX compounds in groundwater align with their respective solubility in water, indicating that the persistence of BTEX compounds in groundwater is possibly controlled by their solubility.

4.2. Implications for Remediation Strategies and Sustainable Use of the Industry Site

This study highlights significant environmental and public health concerns due to soil contamination by BTEX compounds at the investigated site. Benzene, a known human carcinogen, poses serious health risks even at low concentrations [47]. The elevated benzene levels in Zones A, C, and E suggest that these areas should be prioritized for remediation to mitigate potential health risks. Ethylbenzene and xylenes, although less hazardous than benzene, still pose substantial health risks, particularly at high concentrations. Chronic exposure to ethylbenzene can cause various health issues, including respiratory problems and effects on the central nervous system [5]. The high concentrations of ethylbenzene and xylenes in Zones A, E, and K necessitate targeted soil remediation efforts.

The significant levels of benzene in groundwater present a critical health risk, particularly if the water is used for drinking or bathing. While the soil ingestion pathway poses minimal risk, the potential for benzene volatilization and subsequent inhalation is a major concern. However, the study did not account for atmospheric benzene exposure, which might be significant due to benzene’s volatility. Assuming equilibrium between benzene in groundwater and the atmosphere, and using benzene’s Henry’s law constant at 25 °C (1.8 × 10⁻³ mol·m⁻³·Pa⁻¹) [48], the potential benzene concentration in air could reach 246 µg/m³. This exceeds China’s indoor air quality standard for benzene (30 µg/m³) [49] by 8.2 times, suggesting a considerable carcinogenic risk through inhalation.

The findings underscore the importance of comprehensive remediation strategies to address BTEX contamination, particularly benzene. Even for non-drinking purposes such as bathing, the carcinogenic risk approached 10⁻⁵, highlighting potential health hazards with prolonged exposure. The persistence and mobility of benzene in groundwater necessitate immediate and effective remediation efforts due to its high toxicity. The presence of toluene, ethylbenzene, and xylenes in groundwater, while less hazardous than benzene, still presents substantial health risks at the detected concentrations. The high concentrations detected necessitate comprehensive groundwater remediation strategies.

The relationship between BTEX compound solubility and their concentrations in groundwater provides valuable insights into their environmental behavior. Benzene’s relatively higher solubility compared to other BTEX compounds explains its higher concentrations in groundwater, aligning with previous research findings on the solubility and persistence of VOCs in groundwater [46]. This information can guide the development of targeted remediation approaches with pollutants of high solubility being considered in priority when dealing with groundwater pollution.

When examining different exposure pathways, drinking water emerges as the primary route of exposure, followed by bathing, ingestion, dermal contact, and inhalation. In drinking and bathing pathways, where benzene is the predominant BTEX compound, the non-carcinogenic risk is almost entirely attributable to benzene. Even though other BTEX compounds are present, their higher RfD values mean their contributions to non-carcinogenic risk are relatively minor. For other exposure pathways, benzene still contributes to 86% of the non-carcinogenic risk despite not having the highest exposure concentration. This is because the exposure concentration of xylenes, the most abundant BTEX in soil, is offset by their much higher RfD. It is important to note that exposure through drinking and bathing can be avoided by using other clean water sources, suggesting that more attention should be given to the other exposure pathways that are less controllable. In the meantime, unlike soil pollution, groundwater could be transported, polluting the groundwater in adjacent areas and threatening the health of people residing near around.

Overall, the primary concern at this site is groundwater contamination, particularly with benzene. Immediate action is required to address this contamination to protect public health. The high non-carcinogenic risk associated with benzene exposure, especially through groundwater, underscores the need for immediate remediation strategies. It is also critical to implement continuous monitoring and stringent control measures to mitigate health risks.

5. Conclusions

This study conducted a thorough assessment of BTEX pollution at a former chemical pesticide industrial site in southern China, revealing significant contamination in both soil and groundwater. The highest concentrations of benzene, ethylbenzene, and xylenes in several zones exceeded Chinese soil quality standards, indicating serious environmental and health risks. Benzene, a known carcinogen, poses a particularly high risk, and groundwater analysis showed benzene levels far above safe drinking water standards. These findings highlight the urgent need for effective pollution control and remediation measures to ensure the safety of future site users.

The results of this study emphasize the critical need for rigorous remediation efforts to address BTEX contamination at former industrial sites. Effective land use planning and zoning, along with continuous monitoring, are essential to mitigate health risks. Policymakers should enforce stricter environmental regulations and develop comprehensive guidelines for assessing and remediating contaminated sites. The findings provide a scientific basis for targeted remediation plans and underscore the importance of protecting public health and the environment in the redevelopment of such sites.