The Concentration of BTEX in the Air of Tehran: A Systematic Review-Meta Analysis and Risk Assessment

Abstract

In the current study, the concentration of some pollutants which are categorized as volatile organic compounds (VOCs), including benzene (B), toluene (T), ethylbenzene (E), and o-xylenes (o-X), in the air of Tehran was evaluated by the aid of a systematic review and meta-analysis approach. Also, the health risk for the exposed population was estimated using the recommended methods by the Environmental Protection Agency (EPA). The rank order based on their concentration in BTEX was benzene (149.18 µg/m³: 31%) > o-xylene (127.16 µg/m³: 27%) > ethylbenzene (110.15 µg/m³: 23%) > toluene (87.97 µg/m³: 19%). The ratio B/T in this study was calculated as 1.69, repressing that both stationary and mobile sources of emission can be considered as the main sources for benzene and toluene. Moreover, strong photochemical activity in Tehran was demonstrated by the high ratio of E/o-X. Meta-regression indicates that the concentration of BTEX has insignificantly (p-value > 0.05) increased over time. The BTEX compounds based on the target hazard quotient (THQ) were ordered as benzene > o-xylene > ethylbenzene > toluene. Percentile 95% of THQ due to benzene (4.973) and o-xylene (1.272) was higher than a value of 1. Percentile 95% excessive cancer risk (ECR) for benzene (1.25 × 10⁶) and ethylbenzene (1.11 × 10⁶) was higher than a value of 1.00 × 10⁶. The health risk assessment indicated that the population of Tehran are at considerable non-carcinogenic and carcinogenic risks.

Figure 1

The selection process of articles and inclusion.

Figure 2

Forest plot of concentration (ppb) of benzene (a), toluene (b), ethylbenzene (c), and o-xylene (d) in the ambient air of Tehran. ES: effect size, CI: Confidence interval.

Figure 3

The percentage of BTEX in the ambient air of Tehran.

Figure 4

TTHQ of BTEX in ambient air due to inhalation exposed population.