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IARC: air pollution is carcinogenic

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Does outdoor air pollution cause lung cancer deaths? IARC says it does. It is an historical day for epidemiology, toxicology and public health – this 17th of October – since the greatest world authority on carcinogenic agents presented in Paris the results of monograph n. 109 about outdoor air pollution. Classified as Group 1, i.e. carcinogenic for humans, outdoor air pollution is now considered as dangerous as vinyl chloride, asbestos, formaldehyde or ionizing radiations.

IARC had already classified as carcinogenic some smog components, like diesel emissions and benzo(a)pyrene. But this time the whole outdoor air pollution – the mix of traffic combustions, heating and industrial emissions – is in Group 1. A decision that will certainly have relevant scientific and political consequences. “Classifying outdoor air pollution as carcinogenic to humans is an important step,” stresses IARC Director Dr Christopher Wild. “There are effective ways to reduce air pollution and, given the scale of the exposure affecting people worldwide, this report should send a strong signal to the international community to take action without further delay.”

Mostly lung, but also bladder cancers

Monograph n. 109 collected an impressively huge amount of data and studies that eventually convinced the international expert panel to take the non-easy decision. Therefore, we can reasonably affirm that outdoor air pollution exposition increases the risk for lung and bladder cancer. The individual risk is not quantitatively comparable to tobacco smoke, which remains the principal killer, but those who considered smog as the lesser evil of development now will have to change their mind. It is not just small particulate, polycyclic aromatic hydrocarbon (PAHs), ozone and nitrogen dioxide that increase the risk for respiratory diseases, hearth failure and other problems like low birth-weight (as just confirmed by a study on Lancet): now we can assert with relative certainty that a significant part of lung cancers are caused by these environmental expositions.

According to World Health Organization, this means 223,000 deaths worldwide, plus 3 million deaths approximately for all other PM2.5 correlated diseases - half of whose are ascribable to heavy pollution by coal, traffic and biomass (mostly firewood) in China and South-East Asia.  

The poisons identikit

A recent report of the European Environmental Agency (EEA, 2012) pointed out PM and ozone as the most problematic pollutants in Europe. We still know too little about PM: according to IARC volume Air Pollution and Cancer (available as e-book on the agency website), typically only 20% of organic PM is identified at molecular level. Levels are determined mostly by local point emissions, but also, to a small degree, by intercontinental transportation”. Extremely critical pollutants are also benzo(a)pyrene, lead (in certain areas) and benzene. De facto, 90-95% of urban European population is exposed to PM2.5 levels higher that those recommended by WHO air quality guidelines, 81% to correspondent PM10 levels, more than 97% to ozone and 94% to benzo(a)pyrene, always in concentrations higher than WHO thresholds. Actually, depending on the pollutants, distributions can be more or less uniform. Secondary species concentrations (such as sulphates, ozone, organic acids) are relatively uniform on the territory. On the contrary, primary pollutants (like carbon monoxide, polycyclic aromatic hydrocarbon and black carbon) have very high concentrations in road canyons and generally up to 200 meters of most trafficked roads.

Indoor, the situation is not much better: on the contrary, in certain conditions concentrations can be quantitatively and qualitatively much more critical than outdoor. According to IARC revision, in fact, almost 100% of a nonpolar atmospheric gas (like benzene, toluene, xylene) is transported indoor and persists in time. On the other side, polar compounds, hydro-soluble gases (for example formaldehyde, hydrogen peroxide or nitrogen acid) penetrate the building with minor efficiency and have high decaying factor indoor. Concentration of organic matter particles are often much higher than outdoor. 

Hence, the ten thousand litres of air that we inhale every day mark a heavy trail on our health.  Even in terms of DNA mutations, often the fatal trigger of lung cancer.

The biomass issue

Concerning to pollution damages causes, traffic is responsible between 20 and 40%, with diesel accounting heavily (as IARC recently assessed). The biomass contribute, however, should not be underestimated, and it is certainly heavier worldwide than industrial and traffic combustions, which take place in controlled conditions. Traditional biomass represents 10% of primary energy consumption worldwide, with 2.7 billion of people using firewood for cooking or heating. It is not by accident if it ranks among the first burden of disease at planetary level, with 2 million premature deaths yearly for acute lower respiratory tract infection, chronic obstructive pulmonary disease and lung cancer.

“Even though the majority of biomass fuels have no contaminants” states the IARC report, “a fuel fraction converts into incomplete combustion products. Biomass combustion smoke contains thousands of chemical substances and many of them have documented inflammatory and carcinogenic effects (benzene, butadiene, formaldehyde).

Who might think biomass pollution only concerns emerging countries or isolated countryside is mistaking. One of the paradoxical effects of the on-going economic crisis is the return of “wild” firewood combustions also in urban contexts. Dimosthenis Sarigiannis of Aristotle University of Thessaloniki, recently documented this situation for his city, ground by the terrible Greek recession that questionable austerity measures are trying to solve. Since the Greek government increased taxes on fuel oils for heating, in 2012 (from 0.90 cents to 1.30 euro per litre), people started using firewood from any provenience (from trees to old furniture). The result was a drastic increase of PM pollution in the winter (while in the summer it decreased for the traffic reduction), with picks of 200 micrograms per cubic metre in Thessaloniki (but similar data were collected in Athens and other cities).

During the last conference of the Environmental Health and Economcs Network (EHEN) of WHO, Sarigiannis quantified in 2 billion of euro the possible savings for avoidable deaths and diseases if Greece moved from firewood heating to a less polluting fuel like gas.

How many years o life (and money) spared

More in general, according to a recent study conducted with costs/benefits analysis by Mike Holland (member of EHEN) all over Europe, the present conditions of air pollution will be responsible of 4.28 million of years of life lost (YLL) annualy (which corresponds to about 8 months loss of healthy life expectancy on average for every citizen), that might reduce to 3.53 million, if all the measures nowadays available for reducing pollutants were applied.

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