A new study shows that the concentration of polycyclic aromatic hydrocarbons (PAHs) in smokeless tobacco products (STPs) can differ by as much as 60 fold, with the highest levels in moist snuff, and dry snuff and soft pellets; the lowest levels were in snus. Higher levels can be explained by the use of of fire-cured tobaccos in the products. The source of the trace amounts of PAHs in snus and other products using non-fire-cured tobaccos was previously unknown. The results of this study indicate the source to be environmental pollution, such as car exhausts and agricultural and wood fires.
Scientists at British American Tobacco and the University of Louisville analysed 70 contemporary STPs, representing 80-90% of market share in Sweden and the USA, including chewing tobacco, dry and moist snuff (dipping tobacco), hard and soft pellets, plug, and loose and portion snus, for 21 PAHs.
PAHs are produced during the incomplete burning of organic material such as coal, oil, gas, wood, and tobacco. They do not occur naturally in plants such as tobacco, but can be created during the drying (curing) process, for example, if the tobacco leaf is exposed to exhaust gases from heat sources that rely on burning wood, this can increase PAH level. Fire-cured tobaccos, whose production involves direct contact of the tobacco leaf with wood smoke, contain particularly high concentrations of PAHs.
The US Food and Drug Administration, has identified 15 PAHs as harmful or potentially harmful constituents in tobacco, and one, benzo(a)pyrene (B[a]P), is a known human carcinogen. This comprehensive analysis did not find seven of the FDA-specified PAHs in any of the STPs tested. However, it provided benchmark quantitative information on the PAHs in contemporary STPs used in Sweden and the USA.
In this study, PAHs were found in all STPs tested, but there were significant differences in the total and individual PAH concentrations in the different product styles. Substantially higher levels of total PAHs (10-60 fold) were found in moist and dry snuff and soft pellets than in the other STPs.
To establish the sources of PAHs in STPs, the researchers looked at ratios of different PAHs, which have previously been shown in a number of environmental and food matrices to differ according to source. Analysis confirmed that the use of fire-cured tobaccos in the snuffs and soft pellet were the major source of PAHs in these products - suggesting this method can be used as a diagnostic tool to identify the source of PAHs in STPs.
Analysis also indicated, for the first time, a variety of contributors to the trace levels of PAHs in snus and other STPs. For example, lower temperature petrol-based sources (such as car exhaust fumes) and higher temperature combustion sources (such as agricultural or wood fires) appeared to be important contributors to PAHs in snus. The researchers note that such environmental pollution could be difficult to avoid.
'Data from this research will help scientists and regulators understand the diversity of tobacco products and the substantial differences in toxicant levels between these STP categories,' says Kevin McAdam, lead author of the study and Principal Scientist at British American Tobacco. 'Moreover, the use of the diagnostic analysis of PAH ratios represents a valuable tool for understanding where PAH contamination of STPs arises'.
Additionally, the study identified strong correlations between B[a]P and all the other PAHs except the naphthalenes. As there are well established methods for determining B[a]P in tobacco, this finding suggests that B[a]P could be used as a good surrogate marker for many PAHs in STPs.
The study was published in Chemistry Central.