From the water we drink to the air we breathe, the Earth systems on which humanity depends are polluted by the industrial activities on which we rely. Anthropogenic chemicals have been detected all over the planet, in organisms more than 10,000 meters below the ocean’s surface and in foods within the reach of a grocery store shopper. As persistent pollutants cycle through ecosystems and food webs, they move continuously into and out of our bodies and our lives.
Human-made chemical markers in the geologic record have been used to identify a new epoch in Earth’s history: the Anthropocene. Yet the so-called “Age of Humans” is a recent phenomenon in geologic time, and some pollutants have much deeper origins.
Pollutants such as polycyclic aromatic hydrocarbons (PAHs) are produced by fossil fuel processing and gasoline and diesel combustion by humans, but they also occur naturally in smoke from burning organic materials and in fossil bitumen that seeps through Earth’s surface. Given the variety of health problems associated with high and/or chronic levels of PAH exposure, such as cancer, reproductive and developmental impairments, and organ damage, it’s even been suggested that PAH exposure was a human selective pressure in our evolution as a species.
Did ancient people have PAH-related health risks as we do today? This is an interesting question – not only for its broader temporal perspective on current health issues, but also for the innovative methodology needed to address it.
When we first posed this question, our focus was on PAH exposure as a possible factor in the health decline of native inhabitants the California Channel Islands. We showed that toxic PAHs were present in the fossil bitumen that were used to make water bottles for at least 5000 years, and found skeletal evidence of decreasing head size – an observed effect of fetal PAH exposure – as bitumen use increased over millennia.
However, as a guiding principle of toxicology, the difference between a poison and a remedy is the size of the dose. In our new latest study, we employed methods of toxicology and experimental archaeology to estimate the daily exposure doses of PAHs that someone who made or drank from one of these ancient water bottles could have experienced.
We replicated these bottles with traditional materials and techniques, guided by archaeological and ethnohistoric evidence, and tested PAH concentrations in the air above the bitumen as it melted and in water and oil stored in a replicated bottle for different periods of time. We analyzed and interpreted our results according to modern safety standards for PAH exposure established by the U.S. Environmental Protection Agency.
Interestingly, the water stored in the bitumen-coated bottle showed levels of PAH contamination that were unlikely to pose a hazard to human health – even after two months of storage! Yet the PAH concentration in the air sampled as the bitumen melted (which would have been done for many purposes, not just water bottle manufacture) was significantly higher than the EPA’s limit for inhalation, when calculated with potency equivalence to benzo(a)pyrene (140 vs. 2 ng/m3). Furthermore, the concentration of naphthalene in the air sample (4.4 μg/m3) was higher than the EPA’s reference dose (3 μg/m3), as well as the concentration reported for cigarette smoke (2.7 μg/m3).
Although it appears that PAH exposure from water stored in bitumen-coated bottles was a minor health risk for the people who used them, we cannot rule out the possibility of its contribution to adverse health effects from the manufacturing process – or from the many other uses of bitumen by the ancient Channel Islanders.
In order to pursue this question further, we will continue with this integrative approach that we have termed “paleotoxicology”, aided by recent technological advances that allow for high resolution measurements of organic pollutants (as well as toxic metals such as lead and mercury) of different substances. In so doing, we aim to enrich our understanding of human health in the past as well as the present, and the challenges for planetary health in the future.