A Monte Carlo simulation and meta-analysis of health risk due to formaldehyde exposure at different seasons of the year in various indoor environments.

Formaldehyde is considered as a significant contaminant. This study aimed to perform comprehensive research with systematic review, health risk estimation, meta-analysis, and Monte Carlo simulation to evaluate exposure to formaldehyde at different seasons of the year in various indoor environments. A systematic literature review was initially performed. The essential information was extracted and associated health risks were calculated. Subsequently, the data were analyzed. The values for non-carcinogenic and carcinogenic risks in 96.97 % and 78.79 % of studies conducted in residential areas exceeded the permissible limits, respectively. Additionally, these values in 16.67 % of studies performed in educational settings were higher than the permissible limits. No studies in vehicles reported values above the acceptable thresholds. Also, the risk values in residential and educational places in summer were higher compared to other seasons. While in vehicles, these values in winter were greater. In the meta-analysis, the maximum pooled non-carcinogenic and carcinogenic risks were 3.69 and 2.02 × 10-4 in residential areas, 0.69 and 1.51 × 10-5 in educational places, and 0.29 and 2.72 × 10-5 in vehicles, respectively. In the Monte Carlo simulation, the highest mean values of non-carcinogenic and carcinogenic risks were 4.40 and 2.41 × 10-4 in residential places, 3.16 and 6.93 × 10-5 in educational places, and 0.29 and 2.78 × 10-5 in vehicles during winter, respectively. Formaldehyde exposure in indoor microenvironments is a crucial health effect globally. Some protective measures include using safe building materials, installing air purification systems, ensuring proper ventilation, maintaining a low to moderate temperature, and delaying occupancy for at least six months following renovation.