Diesel exhaust fumes cause cancer

NAIROBI: On Friday January 15, I spend nearly one hour at the GPO bus stop in Nairobi's central business district as I had chosen to use public transport. Sitting there, I felt chocked and suffocated by the thick black smoke coming from stationary vehicles that had their engines running as they waited to fill up with passengers. 

I then remembered that in June 2012, World Health Organisation (WHO) experts concluded that diesel engine exhaust fumes can cause cancer in humans. They said the fumes belong in the same potentially deadly category as asbestos, arsenic and mustard gas.

The International Agency for Research on Cancer (IARC), part of the WHO, announced that it had reclassified diesel exhaust as a 'definite carcinogen' thus putting it in its highest category (Category 1).

In other words, IARC's expert panel assessed all the available scientific evidence and decided that exposure to diesel exhaust fumes can, and does, cause cancer in humans – specifically lung cancer (although there is weak evidence that these fumes are also linked to bladder cancer).

But what does this mean in practice? Is this something the general public should be worried about? How exactly do diesel exhaust fumes cause cancer?

When diesel burns inside an engine it releases two potentially cancer-causing things: Microscopic soot particles, and chemicals called 'polycyclic aromatic hydrocarbons', or PAHs. There are three possible ways these can cause cancer:

Inhaled PAHs could directly damage the DNA in the cells of our lungs – leading to cancer. The soot particles can get lodged deep inside the lungs, causing long-term inflammation which can increase the rate at which cells divide. So if any nearby lung cells pick up random mutations, this inflammation could, theoretically, make them more likely to grow and spread.

According to the IARC: "Diesel exhaust may be carcinogenic by a combination of these effects – we know the particles are coated with the PAHs, delivering them deep into the lungs where they get stuck and, potentially, cause damage. We however, don't know for certain which of these mechanisms is most important in practice."