I need to find more collaborating evidence but this paper from Canada means that we are in the home straight that passive smoking does not cause lung cancer (LC).
The World Health Organization (WHO) and its cancer subsidiary the International Agency for Research on Cancer (IARC) in their zeal to prove active smoking causes lung cancer have in my opinion also proved that passive smoking does not cause lung cancer in non smokers.
The basic theory is that one of the by products of active smoking, from the burning of tobacco is benzo(a)pyrene (BAP) a 5 ring benzene molecule. When ingested onto the lungs causes a genetic mutation called a guanine to thymine (G to T) transversion of the Transprotein 53 (p53) gene. The purpose of the p53 is to to regulate the cell cycle and to act as a tumour suppressor. This paper (1) by Hainaut and Pfeifer is cited by the WHO/IARC.
So therefore to prove that non smokers contract lung cancer they have to be tested for the G to T mutation. In fact some do, about 10% of non smokers who have LC have this mutation. I have calculated that the incidence rate in the UK would be 1.31 per 200,000 people, about 393 people a year. To put this into perspective crossing the road or driving a car is 7.5 times more deadly.
BUT, BUT, BUT.
I have recently discovered that some non smoking coal miners exposed to Argon also have the G to T transversion, although not highly elevated numbers. (2)
However what is most devastating is the omnipresence of BAP in our day to day lives. BAP is produced by solid fuels (coal, wood, dung) barbeques, burnt toast, and crucially car exhausts. Benzene is a constituent every time we fill up our cars.
On solid fuels this paper says “..solid fuels have been associated with lung diseases. Delgado et al in Mexico City studied 62 patients with lung cancer, mainly adenocarcinoma (72%). They suggested that in 39% of the patients, wood smoke exposure was the etiologic factor.
The authors looked for the presence of p53 mutation, phospho-p53, and the protein MDM2 in Western blot assays from blood samples in their 62 patients with lung cancer and in a group of 18 control subjects, which included patients with obstructive lung disease. The abnormalities in the above markers were similar in those patients in whom wood smoke was the etiologic factor and in the group of patients with a significant history of tobacco use.” (3)
That is solid fuel fires what about petrol (gasoline) and how much BAP is pumped out by cars? This paper from Health Canada gives us a clue.
It starts by saying “Anthropogenic sources include the combustion of fossil fuels, coke oven emissions and vehicle exhausts.4,5 Based on an inventory of Canadian emissions,2 it has been estimated that 19 000 to 22 000 kg are emitted annually from anthropogenic sources (i.e., industrial processes, fossil fuel combustion and transportation).”
It goes on to say ”
In a recent review, it was reported that atmospheric concentrations of BaP in summer in urban centres average 3.6 ng/m3 (standard deviation 4.0).11 In winter, concentrations are higher (mean 7.1 ng/m3; standard deviation 5.1), probably because of the contribution from industrial and domestic heating, which uses fossil fuels.
Significant amounts of BaP are inhaled in tobacco smoke. The amount of BaP per cigarette is between 18 and 50 ng”
You may have read my previous post that non smokers breathe in between 1% and 0.001% of that of smokers. (5)
Smoky bar BAP inhalation will be (ng/m3)
0.18 to 0.5 while in urban centres it is 3.6 to 7.1.
Therefore if BAP is a cause of lung cancer then non smokers are between 7.2 to 39.44 times just as likely to contract the p53 mutation form of lung cancer from breathing in car exhaust fumes than from the most concentrated of second hand cigarette smoke.
I conclude that few if anyone has contracted lung cancer from inhaling second hand tobacco smoke.