Volatile organic compounds (VOCs), particularly toluene, are major contributors to indoor air quality degradation in residential settings, yet comprehensive assessment of global residential toluene concentrations remains limited. This systematic review and meta-analysis aimed to: (1) quantify pooled toluene concentrations in residential indoor air, (2) examine temporal trends, and (3) identify factors influencing concentrations. Following PRISMA 2020 guidelines, we systematically searched PubMed, ScienceDirect, and SpringerLink databases through April 13, 2023. Studies quantitatively reporting toluene concentrations in residential indoor air were included. We conducted random-effects meta-analysis, temporal trend analysis, and moderator analyses for geographical region, smoking status, and season. Health risk was assessed using hazard quotient (HQ) calculations. Twenty-three studies met inclusion criteria (from 444 initially identified). The pooled toluene concentration was 27.13 µg/m3 95% CI: 20.05 – 34.20 µg/m3, showing a statistically significant decreasing temporal trend (β = -0.034, p = 0.004). Rural areas exhibiting significantly higher levels than urban areas (p < 0.001). Smoking status and seasonal variations showed no significant impact. The non-cancer health risk (HQ) values were low (< 1) for all of the studies (mean HQ = 3.10 × 10⁻4), and publication bias was detected. Residential toluene concentrations have declined over the past two decades but vary significantly by geographical region. Current exposure levels appear to pose minimal acute health risks, though publication bias warrants cautious interpretation. Standardized sampling methodologies and larger sample sizes are needed for improved risk assessment. Table of Contents (TOC) Graphic
Rostami et al. (Mon,) studied this question.