7 and Fig. 8. Separate regressions were made for samples with activated carbon in the filter 5-FU and samples without any activated carbon. The calculated slopes and the associated standard error are reported in Table 7. To further ensure that the observed selective filtration of cadmium can really be attributed to the presence of activated carbon in the market survey samples, we prepared a specific set of prototypes,
as described in Section 2, differing only in the presence or not of activated carbon in the filter. These prototypes were smoked under HCI machine-smoking regime and the 3 selected elements Cd, Pb, and As were measured. The means and standard error of the mainstream smoke yield of each element are presented in Table 8, expressed both on a per-cigarette basis and normalized to the nicotine yields. The results obtained for cadmium, arsenic and lead in mainstream smoke demonstrate that a selective retention of cadmium is occurring in activated carbon filters, while it is not the case for arsenic and lead. This phenomenon is possible only if cadmium is present to some degree in the gas-phase of mainstream smoke  and . After reviewing the results obtained for cigarette
fillers and mainstream smoke, Bortezomib price the discussion focuses on possible explanations for the differences in filtration observed in the case of cadmium. The observed cadmium levels obtained from a large set of worldwide commercial samples are consistent with previously reported distributions for smaller, single-country data sets , , ,
,  and , as well as with the levels reported for 755 samples of Burley, flue-cured and oriental tobacco leaves collected in 13 countries during the period 2001–2003 . The distribution of lead levels measured from 568 samples in the present study is consistent with the distributions of smaller datasets recently reported for single countries , , , , , , , , , ,  and , but substantially lower than the distributions given in older reports  and ; this is essentially linked to the appearance of unleaded gasoline in the eighties. The distribution of arsenic levels through is in line with the results obtained from smaller datasets of commercial products from single countries ,  and , and the mean of 400 ng/g obtained from 1431 samples of Burley, flue-cured and oriental tobacco leaves collected in 20 countries during the period 2002–2004 . The observed cadmium levels in mainstream smoke generated under ISO and HCI machine-smoking regime are consistent with data obtained for smaller datasets , , , , ,  and ; the present data are much narrower in range than the historical results provided in an early review . The ranges and median values for cadmium smoke yields expressed per mg nicotine are slightly higher under the more intense smoking regime.