Minerals, Tobacco and Smoking-Related Disease

As much as 8% (by dry weight) of commercial tobacco is mineral, and the view that minerals are inert, playing no more than a passive role in smoking-related disease, is challenged. An inventory of minerals in tobacco is presented and an interpretation of their sources given. Using elemental abundances the relative contributions of natural and anthropogenic sources to the commercial product is quantitatively modelled relative to average crustal abundances. A framework is presented for investigating the potential ways in which minerals with, or acquire, toxic properties behave in the smoking environment. In order to represent a potential hazard any mineral (or mineral reaction product) with suspected toxic properties must partition into smoke and be respirable. For inhalation a significant proportion of the particles must be smaller than 10 microns. Three categories of potential hazard are recognised: 1. Minerals with intrinsic toxic properties. Quartz can amount to 1% or more in some cigarettes and is defined as a human carcinogen by the IARC. It is not likely to represent a hazard as its grain size is probably too coarse to be respirable. However talc, also a Type 1 carcinogen when it is contaminated with asbestos, is a common constituent of cigarette paper and may be of respirable size. Some other minerals also fall into this category. 2. Minerals that generate toxic products on combustion. Examples are the biominerals calcium oxalate monohydrate (whewellite) and dihydrate (weddellite), which amount to about 5 wt% of popular UK brands. These minerals decompose at tobacco combustion temperatures yielding large quantities of carbon monoxide. A substantial fraction of the CO budget of UK cigarettes may derive from this source. 3. Minerals that acquire toxic properties on combustion. Little is known about free radical generation on mineral surfaces during tobacco combustion, but the devolatilisation of calcic phases (carbonates and oxalates) creates oxide particles with surfaces highly adsorbent to polycyclic aromatic hydrocarbons (PAH). Calcic mineral particles are two orders of magnitude more abundant in smokers' lungs compared with non-smoking controls in residents of Vancouver. Such particles may thus be potential agents for the delivery of PAH carcinogens, including benzo(a)pyrene, to the lungs. None of the potential hazards listed above has yet been properly evaluated.