Global comparative of cancer and non-cancer risk of inhalation exposure to formaldehyde in the outdoor environments, 1997–2024: a Monte Carlo simulation and meta-analysis survey

Formaldehyde is one of the most common compounds in outdoor environments. The current research aimed to conduct a comprehensive investigation through systematic review, health risk assessment, meta-analysis, and Monte Carlo simulation to assess the risks of inhalation exposure to formaldehyde in outdoor environments among different nations. A systematic search was conducted in five digital databases. Following the selection of proper studies, key data were extracted by the reviewers. The method for quantitative risk assessment designed by the United States Environmental Protection Agency (USEPA) was utilized to estimate both cancer and non-cancer risks linked to inhalation exposure to formaldehyde. A meta-analysis was carried out to compute the pooled values of cancer and non-cancer risks. Additionally, Monte Carlo simulation was applied to analyze the distribution of environmental inhalation exposure to formaldehyde. Non-carcinogenic risk in 3 out of 40 studies (7.50 percent) was greater than the permissible limit recommended by the USEPA. On carcinogenic risk, 36 out of 40 studies (90.0 percent) showed uncertain risk and 4 out of 40 studies (10.0 percent) displayed actionable risk. The results showed that inhalation exposure to formaldehyde may be associated with non-carcinogenic consequences, whereas an association with moderate to high carcinogenic risks has been documented. Also, the results disclosed that the probability of risks due to inhalation exposure to formaldehyde was greater in summer compared to other seasons. These results indicate the need to reduce formaldehyde emissions from the standpoint of their carcinogenic risk, particularly in the warm season.