The study assessed the volatile organic compound (VOC) pollution characteristics in a chemical site in Weinan, China. The results indicated that chloroform, benzene, trichloroethylene, 1,2-dichloroethane, ethylbenzene, 1,2-dichloropropane, and 1,2,3-Trichloropropane exceeded the soil standard limit for soil contamination of development land (GB36600, PRC). Using pollution index, ambient severity, and correlation coefficient revealed industrial production and relocation activities as sources of VOCs contamination in the site. The carcinogenic risk assessed by human exposure to site VOCs through ingestion, respiration, exposure, etc., exceeded the potentially acceptable level (1.0 × 10−6). 1,2,3-trichloropropane has the highest carcinogenic risk across all pathways, regions, and populations. The long-term exposure and emission of VOCs in the investigated sites could likely pose an adverse health risk to site staff and the surrounding sensitive groups. Therefore, it is necessary to carry out strict investigation and evaluation of the site, and timely repair and control to protect the water, soil, and air environment and to avoid the long-term cumulative exposure risk to human health caused by VOCs emission.
The acceleration of urbanization has led to the relocation of existing urban industrial sites. Thus, many vacated industrial sites that need redevelopment also require remediation of contamination [1,2]. According to incomplete statistics, over 1 lakh high-pollution plants have been shut down or relocated in the past decade in China. Statistically, the main soil pollutants in China’s contaminated sites are volatile organic compounds (VOCs) and semivolatile organic compounds (SVOCs), which include benzene, chloroform, toluene, carbon tetrachloride, tetrachloroethylene, and dichloroethane. Moreover, most of them are cumulative, diverse, toxic, and carcinogenic [3,4].
As the precursors of ozone and secondary organic aerosols , VOCs are ubiquitous in the atmosphere and the majority of them have been proved to be detrimental to human health. VOCs in the environment was formed by natural and anthropogenic factors. As precursors of ozone and secondary organic aerosols, natural emissions contribute 91.9% of total VOCs on a global scale. But in human-inhabited areas, anthropogenic factors are comparable to natural factors [6,7], such as vehicles, landfills, liquefied petroleum gas/natural gas, biomass/biofuel combustion, industrial production, catering, building materials, and decoration [8,9]. A large number of VOCs potentially have carcinogenic effects on the human body, which is considered to be a more serious problem than other health-related effects. The main effects of VOCs on human health are usually related to the central nervous and hematopoietic systems [10,11]. Many studies have shown that VOCs-polluted soil environment in industrial site soil enters the human settlement environment through precipitation, runoff, and volatilization. In turn, it affects the central nervous system, blood, immune system, and skin of the human body through diet, respiration, contact, etc. [12,13]. Scholars have conducted research on the pollution status and sources of ambient VOCs in different regions. They found that sufficient sunlight and good air diffusion conditions in spring and summer are more conducive to photochemical reaction, combustion, and VOCs diffusion . Therefore, the concentration in autumn and winter is higher than in spring and summer . Xiang and Han  found that the concentration of VOCs in farmland around Shanghai industrial zone in China was higher than that in Beijing and Ningbo, China, but lower than that in Taiwan, China, and Aliaga, Turkey. Hu et al.  studied the emission characteristics of VOCs in different functional areas in Hefei, China, and found that the detected concentration of VOCs in traffic areas was the highest, followed by industrial areas, development areas, and residential areas, indicating that vehicle exhaust is one of the main sources of high concentrations of VOCs in the air.
Several countries have conducted studies on VOCs contamination and potential hazards to human health in urban chemical sites soil or near-surface air [18,19]. The United States “Federal Positive Risk Assessment: Management Procedures” first proposed a four-step research system for health risk assessment in 1983. Subsequently, other countries had improved the assessment of legal and technical guidelines and constantly deepening and perfecting the various types of potential pollutants, exposure pathways, and risk assessment methods [20,21]. China’s research on the health risk assessment of VOCs in the environment started relatively late, and in the early stage of the research, it mainly used foreign advanced assessment theories and methodologies for reference. Zhang et al.  analyzed and evaluated the compositional changes and health risks of VOCs during the remediation process of a closed pesticide and chemical plant. Zhao et al. [23,24] studied the most serious VOCs pollution during site excavation during the restoration of a site in Zhenjiang, which is closely related to the original production process and by-products. Through the research by many scholars on the types of pollutants, exposure routes, and risk assessment index systems in different environmental media, China has formed a relatively systematic assessment system and standardized the technology, methods, and content of site environmental risk assessment (Series standard HJ25). For example, Nie  used China HJ25.3 to evaluate the health risk status of a chemical plant in the south, and found that harmful VOCs in the workshop, raw materials, and product areas entered the environment through respiration, skin contact, and soil steaming heat, and had high cancer risk.
Numerous studies have shown that the characteristics and risks of VOCs caused by the remediation of contaminated sites have become the focus of environmental concerns . Restoration of contaminated industrial sites, regardless of whether this includes on-site or off-site types of repair, generally requires digging of the polluted soil. During the excavation of the contaminated soil, large amounts of VOCs may be released into the atmosphere, thereby exposing the operating staff to hazards. As an important source and sink of VOCs, it is of great significance to study the content, distribution, diffusion characteristics, and risks of VOCs in soil . However, in the early stage of the investigation, the research on the distribution of VOCs in the site soil and health risk assessment is not enough. In order to explore the characteristics of the site soil VOCs and the health risks for the surrounding sensitive bodies, and to provide scientific guidance for the restoration and health protection of similar polluted sites, this study was carried out in a chemical site, in Weinan City, China, 2018.
2 Materials and methods
2.1 Study area, sampling, and analysis
The study was based on a closed chemical plant (site) in Weinan, China, with an area of 92,000 m2 [28,29]. The site was surrounded by Weihe River, Youhe River, sensitive residential areas, schools, and major traffic ways. The site was a concentration area of small enterprises for production such as pesticides, chemicals, and building materials. Finally, the company’s leading product was fumaric acid. The chemical site was mainly divided into the pesticide production area (P), the food additive production area (F), the benzene purification and storage area (B), product storage area (S), living area (L), office area (O), and wastewater treatment area (W) (Figure 1). In the future, the site will be planned for residence and park.
The soil environment of the chemical site was investigated from August to October 2018. According to Chinese technical guidelines for monitoring during risk control and remediation of soil contamination of land for construction (HJ25.2), and comprehensive zoning arrangement method and system arrangement method, a total of 36 soil sampling points were arranged, and the maximum sampling depth was 10 m. Soil samples were taken at every 0.5 m for a depth of 0–3.0 m, and at every 1.0 m below 3.0 m. A total of 65 soil samples were collected. A drilling rig (QZ-50G produced by JIEKE, China) was used to drill the soils at different depths. All samples were stored in a dedicated brown bottle to keep the soil fresh (at 4°C), and sent to the laboratory for analysis immediately. To check if the whole process of sample collection and analysis was contaminated, two blank samples (with 10 mL of collective modifier and 2.0 g quartz sand) were also collected.
The VOCs of the chemical site soil was detected by the headspace-gas chromatography-mass spectrometry (GC-MS) method. The soil was extracted by shaking with methanol solution (150 times/min, 10 min), then quartz sand, 10 mL of matrix modifier, 100 µL of methanol solution, and 2.0 µL of internal standard (chlorobenzene) and substitutes were added to the extract and then allowed to stand after shaking (150 times/min, 10 min). The extract was assayed on a VF-624MS column (60 m, 0.25 mm) on a GC-MS (Agilent 7890B-5977A, USA). The results showed that the detection components of the blanks of the whole process were lower than the detection limit (0.8–4 μg/kg). The samples with not less than 10% of the total were randomly selected for parallel analysis, and the calculated relative deviation was lower than 13.8% (no more than 10% of the total matrix spiked sample, the recovery of matrix peaked between 93.4% and 108.8%) .
2.2 Data analysis method
The pollution index (PI) was used to evaluate the degree of VOCs in chemical sites, which also remains to be the first step to know VOCs pollution levels. The equation for calculating PI was the ratio of VOCs measured concentrations of the soil divided by the value of environmental quality risk control standards for soil (GB36600). According to the document, the variation in PI could be defined as follows: PI ≤ 1 (non-pollution), 1 < PI ≤ 2 (minor pollution), 2 < PI ≤ 3 (light pollution), 3 < PI ≤ 5 (medium pollution), and PI > 5 (heavy pollution) .
As an important method for organic contaminants evaluation, the ambient severity (AS) method is introduced into the VOCs evaluation of soil of the chemical site. The potential risk from the VOCs was evaluated using the AS method, which could be calculated with the equation :
where is the ambient severity (AS) for the compound i in the soil; is the measured concentration of compound i, and is the target value for compound i, which can be defined as the risk screening values for soil environmental quality risk control standard for soil contamination of development land in China (GB 36600). It is assumed that the potential risk posed by each VOC to humans has a linear relationship with its AS value , and that the total ambient severity (TAS) is the sum of the AS values for each compound, that is .
Human health risk assessment of contaminated sites is used as a means of pollution assessment [35,36]. Human health risk assessment is a quantitative method for quantifying the adverse effects of human exposure to VOCs from a contaminated environmental medium (e.g., soils and sediments). There are six pathways for adults and children to become exposed to soil VOCs: ingestion, inhalation, dermal absorption, inhalation of gaseous pollutants from the surface and underlying soil in outdoor air, and inhalation of gaseous pollutants from the underlying soil in indoor air (HJ 25.3) . Carcinogenic risk (CR) is defined as the probability of an individual developing any type of cancer throughout a human life due to exposure to carcinogens. For VOCs, the sum of CR values of different organic compounds is called total carcinogenic risk (TCR). CR and TCR are calculated by the formula:
where ADI is the average intake, SF is the carcinogenicity slope factor, and other parameters are obtained from the study area and US EPA guidebook [38,39]. Risks ≤1.00 × 10−6 are considered ignorable. Conversely, risks lying >1.00 × 10−6 are generally considered unacceptable lifetime carcinogenic risk.
The Hazard Quotient (HQ) is calculated as the ratio of the ADI and the reference dose (R fD) for a given contaminant (equation (4)) . The HQ characterized the level which the human body is harmed by exposure to a non-carcinogenic pollutant through a single route. The sum of the HQ values of all the metals in the soil, called hazard index (HI), was used to assess the overall noncarcinogenic effects posed by multiple contaminants (equation (5)).
If the HI value is <1, the exposed individual is unlikely to experience obvious adverse health effects; if the HI value is >1, there could be a risk of noncarcinogenic effects.
3 Results and discussion
3.1 Concentration, composition, and distribution of VOCs
Seven VOCs were detected in soil samples from chemical sites: chloroform (CH), benzene (B), trichloroethylene (TH), 1,2-dichloroethane (1,2-DE), ethylbenzene (EB), 1,2-dichloropropane (DP-1,2) and 1,2,3-trichloropropane (1,2,3-TH), and had a relatively high detection rates (>23%) (Table 1), which indicated that the VOCs in the soil environment were mainly benzene series and halogenated hydrocarbons. The results were basically consistent with those obtained in the similar sites investigation from Zhang and Kyab [41,42]. The total concentrations of the seven VOCs ranged from 0.19 to 50.98 mg/kg, with an average of 14.05 mg/kg. The EB concentrations in chemical site soil were detected from ND (not detected) to 38.15 mg/kg. The mean of CH, B, EB, and 1,2,3-TH were 0.42, 2.28, 12.74, and 0.47 mg/kg, respectively, and were all higher than the Chinese soil environmental quality risk control standards. On the whole, VOC concentrations varied significantly across the functional areas. The average concentrations of the VOCs in different functional areas were in the order: P > B > F > W > other areas. Obviously, the production and raw material areas were higher than other areas .
|Chemical site ( n = 37)|
|Detection rate (%)||43||29||43||23||20||85||57||—|
|Pesticide production area ( n = 27)|
|Food additive production area ( n = 9)|
|Benzene purification and storage area ( n = 19)|
Note: ND, not detected; SD, standard deviation; CV, coefficient of variation; —, no available data.
Figure 2 showed the composition of VOCs in the soils in different functional areas of the chemical site. The average concentrations of the seven VOCs at different depth of soil decreased in the order: EB ≫ B ≫ 1,2-DP > 1,2,3-TH > CH > TH > 1,2-DE, while B and EB also produced fumaric acid, the main raw material [44,45]. Particularly, the content of EB in the soil of P area was up to 83% of the total VOCs, and the content of B in the soil of B area was up to 62%. In addition, 1,2,3-TH was detected in all functional areas of the site (except the L area), indicating that the production process of pesticides was backward at the beginning of the site’s use, and the by-products were not properly disposed of, which eventually led to the spread of pollutants .
The vertical distribution of VOCs in soils was very different between functional areas [23,47]. The VOCs were mainly distributed in three production core functional areas such as P area, B area, and F area, whereas only a few samples in O, L, and S area detected. The highest concentration of 1,2,3-TH was distributed at 1.0–2.0 m in the P area (Figure 3 P(b)), and was also detected at 0–3.0 m in the adjacent F area (Figure 3 F(b)). The CH and 1,2-DE were concentrated in the range of 0–10 m soil depth in the pesticide production area, and the maximum value occurred at the depth of 1.0–2.0 m. Similarly, the maximum value of 1,2-DP was observed at 3.0–4.0 m, and the B and EB were mainly distributed in the range of 0.5–4.0 m. The EB pollution extended to 10 m or even deeper in soil layers in the P area, and the highest concentrations were found at 7.0 m depth. These results indicated that the VOCs in the soils of the chemical site were directly related to the production of pesticides and food additives, and were concentrated in the production area both horizontally and vertically. At the same time, it was also the core area of production and sewage disposal in the site. Leaks may have occurred during the dismantling of the sunken raw material tank, which extended to the deep soil along with the sewage facilities and even had an impact on the groundwater environment .
3.2 Pollution characteristics of VOCs
According to results (Table 2) of all the 65 samples of chemical site soil, 23% CH, 12% 1,2-DE, 18% B, 37% EB, 38% 1,2,3-TH, and less than 10% TH and 1,2-DP respectively, have a PI > 1, suggesting contamination from these VOCs. Only in the P area, there were about 41% CH, 19% 1,2-DE, 15% TH, and 4% 1,2-DP with its PI from 1 to 5, indicating that soil was somewhat contaminated based on the above index. Meanwhile, the high PI of EB was about 15% and about 74% from 1 to 5, and about 15% of B above 5. In the B area, the PI of B was about 5%, above 5 and 21% from 1 to 5, which was similar to the B result in the B area. This shows that both the production areas were under B contamination, and 14% of samples could be categorized as heavily contaminated by B . In addition, the proportion of IP value of 1,2,3-TH higher than 5.0 in pesticide production area and sewage treatment area accounted for 78% and 50% respectively, which further proved that these areas soil was seriously polluted by 1,2,3-TH. The result was consistent with the site’s utilization history, production process, raw material, and by-product characteristics, etc.
|Functional areas||PI||Ratio (%)|
The AS of chemical site soil VOCs was evaluated (Table 3) based on the detection rate and the results of the above organic pollution assessment. The AS for the VOCs were universal above 1.0, which indicates that the concentration of VOCs was higher than the target value for the compound, and had a potential impact on human health and environment. Obviously, the highest TAS value was 83.6 in the pesticide production area, it was necessary to attach high importance to the impact of its pollution on human health. Although the AS of other functional areas VOCs is less than 1.0, the maximum TAS was above 1.0, and hence attention should be paid to its impact on human health. Out of the seven VOCs, the main impact came from 1,2,3-TH, B, and CH, with the maximum AS of 71.8, 12.3, and 4.9, respectively.
|Functional area||Ratio (%)||TAS|
To investigate the common characteristics of VOCs in the chemical site, correlation analyses between VOCs were calculated. This analysis could effectively reveal the relationships among parameters and understand the sources of chemical components. Correlations between the CH, 1,2-DE, B, TH, 1,2-DP, EB, and 1,2,3-TH were significant at p < 0.01 level as shown in Table 4. This suggests that they had a common origin or similar chemical behavior. Obviously, the sources of soil pollution are possibly the production of pesticides food additives, and wastewater treatment. This result means that VOCs in the soil not only entered the atmospheric environment through emission but also infiltrated into the deep soil and even polluted the groundwater environment [49,50].
Note: ** and * correlation is significant at the 0.01 and 0.05 levels, respectively.
3.3 Health risk assessment of VOCs
The carcinogenic (CR) and hazard quotient (HQ) of seven VOCs in the chemical site soils due to six exposure pathways are shown in Table 5. The results imply that the CR and HQ of human exposure to CH, 1,2-DE, B, TH, 1,2-DP, EB, and 1,2,3-TH in the chemical site soils were high and exceeded the acceptable risk level, with the TCR values of all being above 1.00 × 10−6, and also exceeded the acceptable risk range of US EPA carcinogens (1.00 × 10−6 to 1.00 × 10−4) and the 1.00 × 10−4 limit of Australia and the Netherlands [51,52]. The TCR for humans exposed to CH, 1,2-DE, B, TH, 1,2-DP, EB, and 1,2,3-TH were 3.82 × 10−4, 1.28 × 10−4, 1.45 × 10−3, 1.88 × 10−5, 2.30 × 10−4, 2.16 × 10−3, and 3.78 × 10−5 respectively. The CR of VOCs in the following order: CRiiv1 > CRois > CRiov2 > CRdcs > CRpis > CRiov1, suggest that ingestion and inhalation were the main exposure pathway. Similarly, the HQ of different exposure pathways are in the following order: HQiiv1 > HQiov2 > HQpis > HQois > HQdcs > HQiov1. The HI of all VOCs were above 1.0, and the HI of VOCs descended in the following order: 1,2,3-TH > B > 1,2-DP > TH > EB > CH > 1,2-DE [35,53].
|CRois||5.49 × 10−8||4.96 × 10−8||3.56 × 10−7||5.28 × 10−28||2.20 × 10−8||6.13 × 10−7||2.74 × 10−5|
|CRdcs||2.09 × 10−8||1.89 × 10−8||1.35 × 10−7||2.01 × 10−28||8.37 × 10−9||2.33 × 10−7||1.04 × 10−5|
|CRpis||6.93 × 10−7||6.26 × 10−7||8.58 × 10−7||8.00 × 10−8||1.04 × 10−7||2.37 × 10−6||—|
|CRiov1||2.39 × 10−9||2.16 × 10−9||5.58 × 10−9||2.76 × 10−10||3.58 × 10−10||8.17 × 10−9||—|
|CRiov2||1.40 × 10−6||4.65 × 10−7||5.31 × 10−6||6.86 × 10−8||8.41 × 10−7||7.89 × 10−6||—|
|CRiiv1||3.80 × 10−4||1.26 × 10−4||1.44 × 10−3||1.86 × 10−5||2.29 × 10−4||2.14 × 10−3||—|
|HQois||6.81 × 10−3||6.15 × 10−3||6.22 × 10−2||8.82 × 10−2||2.61 × 10−4||2.14 × 10−2||8.78 × 10−3|
|HQdcs||2.23 × 10−3||2.01 × 10−3||2.04 × 10−2||2.89 × 10−2||8.55 × 10−5||7.02 × 10−3||2.87 × 10−3|
|HQpis||5.83 × 10−3||5.26 × 10−3||6.95 × 10−2||1.85 × 10−1||4.93 × 10−2||1.80 × 10−2||9.82 × 10−1|
|HQiov1||2.01 × 10−5||1.81 × 10−5||4.52 × 10−4||6.37 × 10−4||1.70 × 10−4||6.19 × 10−5||3.38 × 10−3|
|HQiov2||1.18 × 10−2||3.91 × 10−3||4.30 × 10−1||1.59 × 10−1||3.99 × 10−1||5.98 × 10−2||1.88 × 101|
|HQiiv1||3.20 × 100||1.06 × 100||1.17 × 102||4.31 × 101||1.08 × 102||1.63 × 101||5.10 × 103|
|TCR||3.82 × 10−4||1.28 × 10−4||1.45 × 10−3||1.88 × 10−5||2.30 × 10−4||2.16 × 10−3||3.78 × 10−5|
|HI||3.22 × 100||1.08 × 100||1.17 × 102||4.36 × 101||1.09 × 102||1.64 × 101||5.12 × 103|
Human health risk assessments showed that the TCR and HI values were above 1.00 × 10−6 and 1.0, respectively, indicating an unacceptable threat for human health from the 7 VOCs in the chemical site soil samples (Figure 4). The TCR values for soil VOCs in the functional areas of chemical site were as follows: P > B > F > W > O > other areas, and HI values were as follows: P > F > B > W > O > other areas. The highest maximum TCR and HI values of VOCs for humans was in the P area soils (4.60 × 10−3 and 5.42 × 103) and the lowest was in the O area soils (2.79 × 10−6 and 6.98 × 10−2), respectively. Compared with different areas, both TCR and HI values for areas in the study were all above threshold values (except HI for W and O area), reflecting that VOCs impact on human health cannot be ignored. Thus, sufficient attention should be paid to the chemical site soil pollution before the development . Moreover, highly toxic substances were often associated with high health risks .
It is noteworthy that the CR value of 1,2,3-TH contributed over 90% to the TCR value in the W and O areas, and the B and EB also contributed at least 78% to the TCR value in the P, F, and B areas. The VOCs 1,2,3-TH, B, and EB may pose a higher lifetime carcinogenic risk to humans via exposure pathways compared with 1,2-DP, 1,2-DE, TH, or CH. Similarly, 1,2,3-TH and B are the largest contributors to the HI value of the chemical site. It is noteworthy that the TCR and HI values of the P area were significantly higher than other areas in the chemical site, and all seven pollutants have a certain contribution (Figure 4).
It was obvious that the TCR and HI produced by VOCs in the soil of each functional area through various exposure pathways were different (Figure 5). The TCR values of W and O areas were due to the exposure pathways, ingestion (67 and 72%) and dermal adsorption (26 and 28%). Affected by heavy VOCs pollution in chemical site subsoil, VOCs contribute 75% or even 97% of lifetime carcinogenic risk through the inhalation of gaseous pollutants from the underlying soil in indoor air route compared to other exposure pathways. In addition, except for the above pathways, inhalation and inhalation of gaseous pollutants from the surface and underlying soil in outdoor air were also important pathways leading to noncarcinogenic risk [25,55]. Therefore, it was necessary to take measures to control the diffusion of VOCs from the soil of chemical plants into the air, and personnel should wear professional protective clothing when working. Comprehensive protection of personnel safety and avoiding direct contact with contaminated soil, and minimize the impact of site operations on workers’ health .
The site investigated were closely related to production activities. Seven VOCs were detected in the soil, and their parameters exceeded the standard limit of the soil. VOCs enter the human body through particulate matter via the respiratory system and skin contact in different ways, thus posing a non-negligible health risk to the site population. Furthermore, these pathways were associated with unacceptable carcinogenic and noncarcinogenic risks. Therefore, it is strongly recommended that when investigating, excavating, and repairing the site, the staff should wear protective clothing, wash their hands, and bathe frequently to ensure personal safety. In addition, it is recommended that the government strengthen the construction of legislation and standards for the supervision of industrial site restoration and development, to ensure that industrial sites are first investigated and evaluated, then restored and managed, and finally green development is carried out. Always attention should be paid to site production safety and population health throughout the process.
We are grateful for the reviews and support that this manuscript received from the reviewers and editor.
Funding information: This research was funded by the Technology Innovation Center for Land Engineering and Human Settlements, Shaanxi Land Engineering Construction Group Co., Ltd and Xi’an Jiaotong University (2021WHZ0094), Shaanxi Province Enterprise Innovation Striving for the First Young Talents Support Program Project (2021-1-2), Shaanxi Provincial Land Engineering Construction Group Internal Research Project (DJNY2021-24), and Institute of Land Engineering and Technology, Shaanxi Provincial Land Engineering Construction Group Internal Pre-research Project (2020-NBYY-23).
Author contributions: Yan Li proposed the framework of the study, performed all the statistical analyses, and drafted the manuscript. Bo Yan collected and analyzed the samples, interpreted the results, and brought out the environmental problems in the investigated site. All authors carried out the site investigation, revised, and approved the final manuscript.
Conflict of interest: The authors state no conflict of interest.
Ethical approval: The conducted research is not related to either human or animal use.
Data availability statement: All data generated or analysed during this study are included in this published article (and its supplementary information files).
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