Benzene in air increases cancer risk. What's the state of our air then?
Benzene is a major carcinogen found in air and can even be deadly at high concentrations. I look into the data at what levels it is dangerous and what's our air quality like.
TLDR:
Benzene today is rather well controlled, and despite ubiquitous background presence of <5 PPB across Europe and US, it is unlikely to cause increased cancer risk at that level.
It can also have a less documented impact on reproductive health, however, current evidence does not show significant risk increases at those background concentrations.
It is very dangerous at breakout concentrations and in leak scenarios and can be instantly deadly.
Why benzene?
The day has come to write the second installment of the Molecular Spec blog! Today I look at air quality and specifically at benzene - one of the major contaminants in our air.
Two separate situations made me look into it at more depth:
a visit to an industrial manufacturer where they were monitoring ambient air for benzene contamination with a view to prevent leaks and contamination using large metal shelf-like devices costing tens of thousands;
frequent visits to a chemical lab where any sample we would run had benzene as a background molecule in the surrounding air despite overall a pretty good ambient air quality.
Personal photo from a lab
What is benzene and why is it dangerous?
Benzene has perhaps one of the more famous chemical structure symbols with its alternating single double bonds in a perfectly drawn structure. It is made of carbon and hydrogen molecules.
Benzene occurs naturally as a component in petroleum and natural gas condensate. Combustion processes and wood fires result in increased concentrations of benzene in air (source) - so that includes cars, fossil fuel burning facilities and most things related to gasoline.
Benzene is also widely used in chemical manufacturing as a manufacturing agent covering products such as drugs, dyes, coatings, adhesives, insecticides, and plastics. It gets released by tobacco and incense smoke, with data out there that being in a closed room with either of those smoke sources, pushes the concentration above the safe exposure limits!
Interestingly, benzene is still allowed to be mixed into gasoline for improved performance. In the EU this is limited to 1% of volume since 1998 and in the US it should be below <0.6%.
Once inside our body, it either gets metabolised and leaves the body through urine or is exhaled. If the concentrations are higher, it gets metabolised and this is where the risks kick in - the results of its metabolism can accumulate in bone marrow (paper), then resulting in increased cancer risk, leukemia in particular.
I think it is probably fair to name benzene as the highest danger carcinogen in air. It is well illustrated in the following study of contamination inside newly refurbished university buildings in China (paper). Despite a wide range of volatile organic compounds (VOCs) being present after refurbishment, all the increases in cancer risk were attributed to benzene exposure or exposure to its derivative ethylbenzene (this did not include formaldehyde though, another significant carcinogenc especially in indoor air).
The above finding is important to appreciate given that standard home air quality detectors tend to measure only the total VOCs concentrations. Many VOCs are completely harmless, such as smells from food, thus identifying the exact molecules in the overall VOC reading is essential - especially if it could be benzene.
Lately evidence has also emerged that benzene can affect the reproductive system. Benzene exposure has been found to affect sperm quality and lead to damage to testicles. Research showed that 50 PPM exposure damages testes in mice, while 10 PPM showed no damage (paper). There are also papers on the damaging impact of benzene on ovaries, although the doses there were rather high at 2000 PPM+ (paper). Remarkably there is research showing that resveratrol (popularised by David Sinclair) can alleviate and reverse the effects of benzene, as tested in pig ovaries (paper)
The reproductive system changes is a much broader topic - I might need to cover this in a separate blog post. The research community is also not in full agreement on what’s going on. The discussion rages from claims that the West has seen near 50% declines in sperm count, while the NYT is writing that such a conclusion is entirely wrong. But if there really is something there - and my intuition is at least not to dismiss it outright - it could be a broad range of various toxic chemicals we should look at. With benzene potentially in the mix but not the only culprit - there’s phtalates, PAHs, other BTEX (benzene, toluene, ethylbenzene, xylene) compounds, PFAS (Per- and polyfluoroalkyl substances, covered in the previous post), bisphenol A.
Returning to the numbers, the safe levels as per regulations are <5 PPB in air in the EU. The US has occupation limits at 1 PPM and a drinking water limit of 5 PPB. China’s occupational limit is 1.9 PPM. Benzene can be very dangerous though - a concentration of 20,000 PPM is fatal within minutes. CDC sets the IDHL (The Immediately Dangerous to Life or Health) value at 500 PPM.
At what levels is benzene present in the air?
We actually start smelling benzene at 1.5 to 4.7 PPM in air (CDC source), which is way above the permissible limit in the EU and above the occupation limits across the continents. Thus if you smell a sweetish smell and it could be benzene, best to get out of there!
The above map from European Environment Agency from 2018 largely shows the numbers we want to see. Only a handful of locations were above EU’s treshold of 5 PPB: one spot in Czech Republic, one at the French-German border, a few around Athens, Greece, and Sofia, Bulgaria.
In the US the data is very similar broadly in the range of 1-5 PPB across various states (EPA).
What’s the danger?
Since benzene is closely related to gasoline and combustion, it is reassuring to see that concentrations at the pump do not exceed the permissible levels. A study of 33 samples at the pump in the US showed just one sample above the safe levels and measuring 55 PPB (paper).
The risk increases if one lives around a cluster of gas stations (paper) or near certain facilities such as refineries, where levels of 31 PPB average throughout the whole year were recently measured in Louisiana (article).
However, in industry, very high cancer risks remain - in China’s printing plants, up to 40% of workers depending on their job roles within the plants were assessed at very high cancer risk (paper). I think this well illustrates the danger of benzene and the need to continuously monitor it - because if there is a leak or a high concentration source, the damage is near certain. For instance a leak in Brazil in 2013 led to benzene being present in groundwater and food and was assessed to result in an equivalent of 100-200 new cancer cases per 1m population.
Worth noting a recent study in California which discovered that gas stoves leak benzene when off. It gained quite a bit of press. Having a leaky stove can expose people to 4-10 PPB levels of benzene, which is above safe levels:
Source: paper
Lastly, one needs to answer the question “does the permissible level of contamination of say 1 PPB in the background a year can have impact over a period of many years”? A 3 year study of different European locations showed a large (10x) jump in concentrations during winter, likely due to emissions from heating facilities, however, the levels remaind broadly around 1 PPB level and not more than 6 PPB (p9, paper), with the cancer risk assessed very low. Only at higher levels are long term exposures a concern - e.g., 0.5-1 PPM (500 PPB to 1000 PPB) over longer periods showed increased risk in leukemia (paper).
What’s next?
Benzene seems broadly under control, but in cases of leaks it can still cause great harm. As with all contaminants we must be able to measure it - once we measure, we can take action and control it. I just wished that one day consumer-friendly and affordable measurement solutions existed. Today one needs highly sophisticated and expensive instrumentation (as we offer at Volatile AI among others). What’s more, it often requres a full chemical lab to measure it.
As benzene is under control, our air quality is constantly under pressure from various factors: the topics of today include formaldehyde, PAHs, NOx compounds - perhaps that’s for a future blog? What other contaminants are you concerned about when it comes to air quality?