Objective To investigate formaldehyde concentrations in the indoor air of kindergartens in Wulong District, Chongqing, China, and to assess the carcinogenic risks.

Methods In 2019, we randomly selected 13 urban kindergartens and 13 township kindergartens in Wulong District, along with 5 children's residences each, and measured the concentrations of formaldehyde in the indoor air of kindergartens and residences. The carcinogenic risk of air formaldehyde was estimated by the health risk assessment method.

Results The median concentration of indoor formaldehyde in the kindergartens was 0.029 (0.024~0.122) mg/m³. Urban kindergartens had a significantly higher median formaldehyde concentration than township kindergartens (0.0470.029~0.183 mg/m³ vs 0.0250.018~0.034 mg/m³, P < 0.05). The mean formaldehyde concentration in the children's residences was 0.014 (0.011~0.022) mg/m³. There was no significant difference in the formaldehyde concentration between the urban and township residences of children (0.0140.013~0.038 mg/m³ vs 0.0110.008~0.019 mg/m³, P>0.05). The indoor formaldehyde concentration was below the national regulatory limit in 8 (61.54%) urban kindergartens, 11 (84.62%) township kindergartens, and all children's residences. The carcinogenic risk of formaldehyde was 2.29×10^-5 for urban children, 1.46×10^-5 for township children, and 1.88×10^-5 for total children in Wulong District.

Conclusion The concentration of formaldehyde in the indoor air of kindergartens in Wulong District can cause a certain health risk, which should be paid attention to.