Indoor air toluene exposure and its influencing factors in family houses of primary school students in Lanzhou

Background Indoor environment safety is related to people's health. In recent years, indoor pollution of benzenes has been increasingly serious. Toluene, a common indoor benzenes pollutant, is very harmful to human health. However, there are few studies on the influencing factors of indoor toluene concentration.

Objective This study investigates toluene contamination in residences in Lanzhou City and its influencing factors.

Methods Two primary schools nearest to the two environmental monitoring stations in Lanzhou were selected as study sites, and 60 students from the two schools were selected as study subjects and completed a questionnaire on indoor environment from August to November 2018 (non-heating season). The indoor benzene, toluene, and xylene concentrations in their residences were measured from August to November 2018 (non-heating season) and from January to March 2019 (heating season). Paired t-test was employed to compare the differences in indoor benzene, toluene, and xylene concentrations between heating and non-heating periods, single factor analysis for the differences in indoor toluene concentrations under different room characteristics between heating and non-heating periods, and multiple linear regression analysis for potential influencing factors of indoor toluene.

Results The mean concentrations of benzene, toluene, and xylene in non-heating period were 0.009, 0.009, and 0.003 mg·m^-3, respectively, and all were qualified according to the national indoor air quality limits. The mean concentrations of these chemicals in heating period were 0.008, 0.283, and 0.001 mg·m^-3, respectively; the indoor toluene concentration of two residences exceeded relevant national limit, and the unqualified rate was 3.5%; benzene and xylene were both qualified. The paired t-test results showed significant differences in indoor toluene and xylene concentrations between heating and non-heating seasons (t=5.283, P=0.023; t=12.700, P=0.001), except indoor benzene (t=0.213, P>0.05). The results of single factor analysis showed that the indoor toluene concentrations in heating period were higher in residences on floor ≤ 7, renovated in recent five years, and with indoor molds than those on floor >7, not renovated, and without molds (P < 0.05), but not different among those categorized by cumulative time of residence in use, residence proximity to driveway, indoor carpet, air conditioning, frequency of opening windows, and frequency of home cooking per week (P>0.05). The results of multiple linear analysis showed a positive correlation between indoor molds and indoor toluene concentration in heating season (b=2.968, P=0.003); the relationships between other variables and indoor toluene concentration were not significant (P>0.05). In non-heating season, both single factor and multiple linear analyses revealed no relationships between the above indicators and indoor toluene concentration (P>0.05).

Conclusion Slight residential benzenes pollution in Lanzhou is found in the study, and the increase of indoor toluene concentration is related to a moldy house.