Lack of correlation between cigarette mainstream smoke particulate phase radicals and hydroquinone yield

Evidence suggests that when compared with non-smokers, cigarette smokers are exposed to an increased burden of free radicals from both the vapor phase and particulate phase of the cigarette smoke aerosol. In this study, primary emphasis was placed on the free radicals found in the particulate phase. Published reports hypothesize that the particulate phase free radicals of cigarette mainstream smoke (MS) condensate consist of a hydroquinone/semiquinone/quinone shuttle. However, our results do not suggest that there is a positive correlation between the smoke yield of hydroquinone and the presence of particulate phase free radicals. First, 10-fold reductions in MS hydroquinone yield were obtained when KNO3 was applied to the surface of tobacco of an American blended cigarette. Surprisingly, there was no significant corresponding change in the yield of particulate phase radicals. Second, in experiments testing MS from low and high hydroquinone-yielding tobaccos there was no consistent corresponding relationship between hydroquinone and particulate phase radical yields. In one series of blends there was at best an inverse relationship between hydroquinone and particulate phase radical yields. In contrast with the published literature, we conclude that the particular compound or compounds driving particulate phase free radical formation are currently unknown. An additional experiment reported here suggested that components of the water soluble extract of burley tobacco may be driving the formation of particulate phase free radicals.