Humans could be exposed to formaldehyde, a by-product of drinking water disinfectants, by both oral intaki and inhalation. The guideline value of formaldehyde in drinking water was established by WHO in 1992, and the guideline for air quality was also published by WHO in 2000. However, the inhalation exposure was not incorporated into WHO drinking water guideline establishment. In this article, we re-evaluated oral toxicity and inhalation toxicity studies in addition to the latest information, and calculated Tolerable Daily Intake (TDI) via oral administration and tolerable air concentration via inhalation. Then, the human health risk of formaldehyde was assessed via an oral administration and via an inhalation, separately.
For oral administration, TDI for general toxicity was calculated an 0.15 mg·kg-1·d-1 from NOAEL of 15 mg·kg-1·d-1, divided by uncertainty factor (UF) of 100 because of the lack of oral carcinogenicity. A 10% benchmark dose of 0.3 mg·m-3 in general inhalation toxicity and a NOAEL of 2.5 mg·m-3 in inhalation carcinogenicity were selected as the starting points for calculation of tolerable air concentration. The tolerable air concentrations based on general toxicity and carcinogenicity study were calculated as 0.037 mg·m-3 divided by UF of 8 and 0.031 mg·m-3 divided by UF of 80, respectively. Based on the above TDI or tolerable air concentrations, we assessed the risk of formaldehyde in drinking water, using two exposure scenario, and concluded that the detected levels of formaldehyde in the recent national investigation reports might not affect to human health.
