Intelligence, Cancer, and Eyjafjallajökull

ResearchBlogging.orgThis seems to have become unofficial volcano week, here at ScienceBlogs. If you haven't been following the coverage of the Eyjafjallajökull eruption at Erik Klemetti's Eruptions blog, you should consider doing so. Also, Dr. Isis has a post on how the eruption has fouled up all nuclear imaging plans at her place of research, and Ethan explains how volcanic lightening works.

Our benevolent overlords have further commented: "Eyjafjallajökull's ill temper has been an unexpected object lesson in the complexity and interconnectedness of our environment, technology, and social networks." To that I say: yes! But what about cognition and intelligence?

You say: what do cognition and intelligence have to do with the volcano? I say: everything. Kind of. Let's start at the beginning.

Put most simply, a teratogen is something in the environment that messes with a developing fetus. Specifically, teratogens are environmental agents that are relatively harmless to an adult, but that can result in birth defects and developmental disorders of varying severity in the child. It was once thought that, for mammals, the uterus completely protects the fetus from the external world. Then in the 1960s, it became painfully clear that this was not the case. Doctors had been prescribing thalidomide as a sedative drug since the 1950s, but more than 10,000 children in 46 countries were born with deformities as a result. Luckily, some clever physicians realized there was a link between these birth defects and maternal thalidomide use, and by 1961 it was no longer prescribed. Now, we know that many environmental agents have teratogenic effects.

In the 18th century, higher rates of skin cancer were observed in roofers who were exposed to soot. In 1947, a relationship between coal tar and lung cancer was established. Soon after, it was discovered that it was polycyclic aromatic hydrocarbons (PAHs), specifically, in coal and soot that was responsible for the cancer's development. By 1983, the International Agency for Research on Cancer had identified thirty PAHs that were carcinogenic, and in 1997 the United States Environmental Protection Agency identified sixteen PAHs as "highly toxic." There are over 200 unique PAHs present in cigarette smoke.


Figure 1: A few typical PAH molecules. Source.

"Hydrocarbon" refers to the fact that these molecules are composed of carbon and hydrogen atoms. "Polycyclic" means that these molecules are collections of rings of carbon atoms, and "aromatic" refers to the kinds of chemical bonds that exist between the atoms.

A study was just published online in the journal Environmental Health Perspectives concerning the relationship between these airborne carcinogens and intelligence, especially with respect to prenatal exposure. Are PAHs significantly teratogenic?

So, a group of researchers wanted to investigate the relationship between prenatal PAH exposure and intelligence at age five. A cohort of 505 pregnant, healthy, non-smoking women were recruited in Krakow, Poland between 2001 and 2006. They were all at least 18 years old when they entered the study, had no history of illicit drug use, no diabetes, no hypertension, and had lived in Krakow for at least one year prior to enrolling in the study.

First, each woman participated in a 45 minute questionnaire. Then, each woman's air was continuously monitored for 48 hours at some point during the second or third trimester. They were given small backpacks to carry around with them that continuously monitored the air, and they were instructed to keep it next to their beds at night. After delivery, a sample of (umbilical) cord blood and of venous blood was taken from the mother, to measure the concentration of PAHs in the blood. Then, after the children reached five years of age, they were given a handful of standardized intelligence tests. 214 children were included in the study.

What they found was that higher prenatal exposure to PAHs was associated with decreased scores on the standardized intelligence tests, after controlling for potentially confounding variables; the average decrease was 3.8 IQ points. The results suggest that prenatal airborne PAH exposure negatively affects childrens' intelligence by age 5, and has potential implications for future academic achievement.

Polycyclic aromatic hydrocarbons (PAHs) are air pollutants that are produced by the incomplete combustion of organic materials. Most environmental PAHs are anthropogenic - that is, produced by humans - such as from coal burning power plants, diesel- and gas-powered vehicles, and home heating systems. PAHs are also present in tobacco smoke as well as in charred foods.

But I was particularly interested to learn about the natural sources of PAHs, so I did some digging. Forest fires are an important source of PAHs, and so are VOLCANIC ERUPTIONS!! It may be that humans are a bigger source of PAHs than volcanoes. But lately, in case you hadn't noticed, there've been a lot of polycyclic aromatic hydrocarbons in the air around Iceland.


Figure 2: The ash plume from the 2010 Eyjafjallajökull eruption. (From this post at the Eruptions blog).

The ash cloud was expected to have reached North America sometime this past Monday. It should be noted that some reports say that there isn't much to worry about with respect to this eruption, health-wise. Even still, the effects of this (and other) eruptions are sure to be widespread and we may indeed not realize or predict what the long-term effects may be.

Who wants to start distributing air quality backpacks to pregnant women in Iceland? Nothing like a little opportunistic science!

Susan Claire Edwards,, Wieslaw Jedrychowski,, Maria Butscher,, David Camann,, Agnieszka Kieltyka,, Elzbieta Mroz,, Elzbieta Flak,, Zhigang Li,, Shuang Wang,, Virginia Rauh,, & Frederica Perera (2010). Prenatal Exposure to Airborne Polycyclic Aromatic
Hydrocarbons and Children's Intelligence at Age 5 in a
Prospective Cohort Study in Poland Environmental Health Perspectives : 10.1289/ehp.0901070

SkupiÅska K, Misiewicz I, & Kasprzycka-Guttman T (2004). Polycyclic aromatic hydrocarbons: physicochemical properties, environmental appearance and impact on living organisms. Acta poloniae pharmaceutica, 61 (3), 233-40 PMID: 15481250

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Interesting entry. It's good to read about some Polish researches on foreign blogs.