Higher indoor PM2.5 concentration of cadmium (Cd) and thallium (Tl) is related to domestic smoking

Indoor air pollution is estimated to be greater in indoor than in outdoor environment. Tobacco smoke may significantly contribute to indoor air pollution and domestic smoking is correlated to indoor airborne particulates with aerodynamic diameter<2.5µg (PM2.5). Heavy metals, such as Cd and Tl, are present in tobacco and dispersed in the environment by tobacco combustion. In the context of RESPIRA Project, we performed outdoor/indoor measurements of PM2.5 by gravimetric sampling in 73 houses in the Mediterranean Area of South Italy. Gravimetric Teflon filters were analyzed for PM metal content by inductively coupled plasma (ICP) optical emission spectrometry and ICP mass spectrometry for obtaining Cd and Tl concentration. The presence/absence of smokers in each dwelling was investigated by a questionnaire fulfilled by householders. The relationships of indoor/outdoor concentrations were not significant for both Cd and Tl. Conversely, the indoor Cd/Tl correlation was highly significant (R2=.812, p<.0001) showing that both metals in indoor PM2.5 have a common indoor source. Higher concentration of PM2.5 such as of Cd and Tl was associated to the presence of smokers at home: PM2.5 was (median and interquartile range) 24.2 µg/m3 (16.9-41.5) for smoker and 15.7 (10.9-22.5) for non-smoker houses (p<.0001); Cd was 0.148 ng/m3 (0.081-0.449) and 0.032 (0.028-0.080) respectively (p=.0002); Tl 0.069 ng/m3 (0.042-0.146) and 0.020 (0.008-0.042, p<.0001) (Mann-Whitney U-test for nonparametric data). These results suggest that the levels of cadmium and thallium in PM2.5 are markers of third-hand smoking RESPIRA Project was funded by Operational Cross-border Program Italy-Malta 2007-13 code A1.2.3-72.