A comprehensive study on the spatial and temporal variation of BTEX and asbestos in the northwest of Iran: Human risk assessment

Our plain-English summary of A comprehensive study on the spatial and temporal variation of BTEX and asbestos in the northwest of Iran: Human risk assessment, by E. Zarezadeh, A. Jonidi Jafari, M. Gholami, et al (Heliyon, 2024).

The study

• Authors: E. Zarezadeh, A. Jonidi Jafari, M. Gholami, M. Farzadkia, E. Ashouri, A. Shahsavani, M. Kermani, P. Nakhjirgan
• Journal: Heliyon
• Published: 2024;10(11):e31640
• Cited by: 1 article, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Substances like asbestos and other air pollutants, such as BTEX (benzene, toluene, ethylbenzene, and xylene), are hazardous compounds due to their adverse effects on human health. This study aims to investigate the levels, seasonal variations, spatial distribution, potential sources, and associated health risks associated with BTEX compounds and asbestos fibers in the ambient air of Tabriz. Air samples were taken at 16 different locations during the 2020-2021 period. Glass containers with charcoal were used for sample collection, and the BTEX content was determined using the GC-FID method. Phase-contrast microscopy (PCM) analysis was conducted with a low-volume peripheral pump for asbestos fiber sampling. The results showed that the average concentration of ∑BTEX was 37.94 and 27.98 μg/m3 in autumn and spring, respectively. The same parameter was 2.26 and 1.68 f/L for asbestos in the autumn and winter, respectively. The contribution of BTEX to ozone formation potential (OFP) in the research area showed that xylene and toluene were the major contributors to ozone production in different seasons. The risk of exposure to benzene compounds was 24 × 10-4 in children and 55.9 × 10-4 in adults, while the risk of exposure to ethylbenzene was 3.78 × 10-4 in children and 3.25 × 10-4 in adults. The estimated lifetime cancer risk was found to be the highest for benzene, followed by ethylbenzene. The estimated cancer risk for benzene and ethylbenzene exceeded the threshold values set by EPA, which signals a significant carcinogenic risk due to exposure to these substances in the ambient air of Tabriz. According to the EPA guidelines, the low carcinogenicity risk levels are between 10-4 and 10-6. According to the findings for the exposure to asbestos fibers, the maximum values of excess cancer risk (ECR) and estimated lifetime cancer risk (ELCR) were observed in the 16-30 age range across all locations, suggesting increased exposure to asbestos fibers compared to other age groups.

© 2024 The Authors.

In plain English

The authors measured BTEX chemicals (benzene, toluene, ethylbenzene and xylene) and airborne asbestos fibers in the outdoor air of Tabriz, Iran, and estimated the resulting health risks. They collected 128 samples (64 for BTEX and 64 for asbestos) at 16 stations across the city over the four seasons of 2020–2021. Asbestos fibers were counted by phase-contrast microscopy, and the analysis did not distinguish fiber types. Average asbestos levels were 1.68 f/L in winter, 1.90 in spring, 1.93 in summer and 2.26 in autumn, with an overall average of 1.94 f/L. The highest station, Qoom Tapa, averaged 3.81 f/L. Estimated asbestos cancer risk was highest for the 16–30 age group and fell between 1 × 10−4 and 1 × 10−6. For benzene, estimated cancer risk was 24 × 10−4 in children and 55.9 × 10−4 in adults. The authors concluded that benzene and ethylbenzene posed a significant cancer risk. They noted that only 16 sites were sampled, and that their asbestos risk method may overestimate risk and ignores smoking and lifestyle.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Environmental air-monitoring study across seasons and locations, with a calculated (modelled) human health risk assessment
• Who was studied: Outdoor (ambient) air at 16 sampling stations in Tabriz, northwest Iran (over two million residents), sampled in four seasons during 2020–2021. Risks were estimated for children and adults (BTEX) and for age groups 0–2, 2–6, 6–16 and 16–30 years (asbestos).
• Exposure: Environmental airborne asbestos fibers counted by phase-contrast microscopy (PCM), without distinguishing fiber types, plus BTEX compounds (benzene, toluene, ethylbenzene, o-xylene, p-xylene) collected on charcoal tubes and analysed by GC-FID
• Main results:
  • Average asbestos fiber concentrations by season were 1.68 (winter), 1.90 (spring), 1.93 (summer) and 2.26 f/L (autumn)
  • Overall average asbestos fiber concentration across the study period was 1.94 f/L
  • Qoom Tapa Station had the highest annual average asbestos concentration, 3.81 f/L
  • The 16–30 age group had the highest asbestos exposure concentration (EC) and lifetime cancer risk (ELCR) values at all sites
  • The estimated asbestos carcinogenicity risk fell between 1 × 10−4 and 1 × 10−6, the range the authors cite as the EPA target level
  • Estimated cancer risk (ELCR) from benzene was 24 × 10−4 in children and 55.9 × 10−4 in adults
  • Estimated cancer risk from ethylbenzene was 3.78 × 10−4 in children and 3.25 × 10−4 in adults
  • The non-cancer hazard quotient for benzene was above 1 for both children (4.24) and adults (9.26)
  • Seasonal average total BTEX was highest in autumn (37.94 μg/m3 in Table 2) and lowest in spring (27.98 μg/m3)
  • The toluene-to-benzene ratio ranged from 4.8 to 6 over the year, which the authors interpreted as indicating mainly industrial sources
• The authors' conclusion: The authors concluded that estimated cancer risks for benzene and ethylbenzene exceeded WHO and EPA threshold values, suggesting a significant cancer risk from these compounds in Tabriz's ambient air.
• Limitations the authors state:
  • Sampling at only 16 locations may not adequately reflect changes in pollution across the city
  • The simple, conservative method used for asbestos cancer risk tends to overestimate risk
  • The analysis did not distinguish between types of asbestos fibers
  • Confounders for age-specific risks, such as smoking and lifestyle, were not considered

Topics

Medical terms in this study, explained in our Lexicon: Carcinogenic.

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