H/T MikeF and Rose for comments on tobacco ‘tar’ studies. The Production of Tumors by Tobacco Tars (1941) described how tars were condensed from tobacco in a still, and then painted onto various laboratory animals to produce tumours. It also provided a helpful cross-section of the still used to prepare distillates:
I couldn’t help but notice that there was an asbestos gasket at the top of the steel pipe in which the tobacco was heated, over which gases or vapours ascending out of the pipe at the top would have passed. There was also an asbestos cover and an asbestos board included in the contraption, which was placed inside a garbage can.
They didn’t know in 1941 that asbestos is a Group 1 carcinogen (carcinogenic to humans):
Quartz, mica, and asbestos are all examples of network covalent crystals that have the formula SiO2. The difference between them is in their lattice structure. Quartz forms a three-dimensional lattice with Si and O at the lattice points. Mica has a two-dimensional crystal lattice with Si and O at the lattice points. This two-dimensional lattice gives mica its flat surface. Flat mica molecules are held together with weak dispersion bonds that allow mica to be peeled apart.
Asbestos has a one-dimensional lattice of Si and O. It has a needle-like structure that appears as threads when asbestos molecules are pulled apart from one another. Asbestos is found in natural deposits. Asbestos is a known carcinogen. In slides taken at the Gray’s Freshwater Biological Institute in Minnesota, normal cells are punctured by the needle-like asbestos macromolecules, leaving damaged cells that reproduce cancer cells.
Because of the high melting point and soft, fiber-like structure of asbestos, it has been used in fire-proof suits, as insulation, as roofing material, in floor tiles, in pipe wrap, in automobile brake pads, to sound-proof ceilings and walls, and as fire-proof material in wire supports for ring stands in chemistry labs. In 1989, the Environmental Protection Agency ordered a ban on most of these uses of asbestos. Efforts are taking place to rid buildings, such as schools, of loosely sprayed asbestos insulation. The removal of asbestos must be carefully controlled to prevent exposure from airborne particles. It was interesting to be at Breck School last summer to see asbestos being removed from the school. The entire area was closed off with plastic. Huge ventilation pipes were installed, and the people doing the removal dressed in “space” suits with respirators. Instruments to monitor air quality during the removal process were carefully watched.
And since mica has the same chemical formula as asbestos – SiO2 -, it seems plausible to suppose that the “expanded mica” insulation around the still is really asbestos by another name, and equally carcinogenic.
What about the chrome and aluminium and steel components of the still? Might they be carcinogenic? And what about the soot that was likely to be produced by heating tobacco to 800° C?
I also noticed this passage:
Effect of fractions of tar on rabbits. — Each of 5 fractions and the residue was tested. Two cubic centimeters of benzene were added as a solvent to each gram of substance. All rabbits used were white. All except 2 of the rabbits were painted for at least i86, and most for 2oo days. One in the i4o-i8o° C. series died at 96 days and one in the residue series died at i47 days, both without tumors.
So the condensed tar was dissolved in benzene, presumably to make it easier to paint onto the mice or rabbits. Coal tar in the control group was also dissolved in benzene. I wonder if benzene is a carcinogen?
Group 1 carcinogens are “carcinogenic to humans”. Included among known Group 1 carcinogens are:
Asbestos (all forms) and mineral substances (such as talc or vermiculite) that contain asbestos
Chromium (VI) compounds
Iron and steel founding (workplace exposure)
Soot (as found in workplace exposure of chimney sweeps)
Well, the still probably doesn’t produce much in the way of aluminium or iron, but apart from that, more or less everything it’s made of is carcinogenic. And if the carcinogenic still wasn’t enough, carcinogenic benzene was liberally added to the tobacco condensate tar.
It’s amazing, with such a confection of multiple carcinogens being painted on the lab animals, that while papillomas and tumors were produced, no proven carcinomas were produced in the rabbits in this 1941 study.
Most likely, asbestos and benzene and chromium compounds weren’t known to be carcinogenic in 1941, otherwise this particular still would never have been used. If high temperature glass had been used to make the entire still and condenser, there would have been no contamination by carcinogens (assuming glass isn’t carcinogenic). Has that ever been done? As it stands, given the degree of carcinogen contamination, this 1941 study would seem to be entirely without value.
Anyway, alcohol (ethanol) is, like asbestos, yet aother Group 1 carcinogen. The following video shows how cancer tumours develop in a glass of beer in the space of a few minutes.
I reckon the trick to avoiding getting cancer is probably to avoid swallowing the tumours.