The amount retained in ash can be understood from a review of available literature. Cadmium is always reported as being more volatile than lead during thermal treatments. In tobacco it is primarily present

bound to organic material and is therefore mobilized at relatively low temperature. Lead and arsenic are present in a large part as inorganic, non-volatile compounds and can readily form such compounds upon tobacco combustion, notably by reaction with calcium. This explains the observed differences in the amounts found in ashes (Cd 20–30%, Pb and As 50–70%). The transfer to selleck screening library sidestream smoke can also be understood from published information. The fact that approximately 40–55% of cadmium present in a cigarette is exhausted to sidestream smoke and collected with the particulate matter is consistent with the formation of CdCl2, where cadmium is in the Cd(II) oxidation state, as expected from speciation

studies [108]. Lead can also be chlorinated, but a much lower transfer is observed. This is likely because less lead is volatilized, although the extent of the difference in sidestream transfer between lead and cadmium could be associated with the presence of a volatile cadmium derivative. In mainstream smoke, both lead and cadmium are find more expected to be present as oxides or chlorides, all derivatives in the particulate matter at filter level. Overall, the transfer of lead and cadmium to mainstream smoke should not be very different. The fact that cadmium

is selectively retained by activated carbon in a cigarette filter, while lead is not, shows that some reactions remain unaccounted for and suggests that a large part of the cadmium (and not lead) is present as a gas-phase species, even at temperatures approaching ambient. This species is unlikely to be CdCl2, first because the same retention would be observed with lead (PdCl2 and CdCl2 share similar physical properties) [109], but also because both metal di-chlorides have been shown to be only present in the particulate matter below 150 °C [115]. PbCl4, absent from high temperature chlorine reaction products, is not expected to be found in smoke [109]. A remaining possibility is the reaction of cadmium with radicals. Primary radicals, mostly carbon-centered such as alkyl radicals, are formed by tobacco decomposition for in the hot zone. These very reactive species can further react to yield secondary radicals, some carbon-centered like acyl or alkylamino radicals, but most oxygen-centered [118]. Primary radicals do not react in totality and, in fact, both methyl and ethyl radicals were observed as important radical species in mainstream smoke at filter exit. The yield of carbon-centered radicals from the reference cigarette 2R4F smoked with the ventilation blocked was estimated at 265 nmole/cig. [119]. Gas-phase reaction of cadmium with short hydrocarbon radicals can yield organometallic derivatives. Indeed a well-studied and documented example is the reaction with methyl radicals.