Archaeologists have long been puzzled by the apparent decline in the overall health of Paleoindians living in and around the Channel Islands off the coast of Southern California. A new study in the journal Environmental Health suggests that a possible cause may have been the use of bitumen to seal ancient water bottles. The study “Ancient water bottle use and polycyclic aromatic hydrocarbon (PAH) exposure among California Indians: a prehistoric health risk assessment,” re-created the ancient water bottles and then used them to store both water and olive oil to determine their health risks.
The Channel Islands are unusual in North American archaeological history in that a relatively continuous record of human skeletal remains have been unearthed, covering a period from about 13,000 years ago up to the present day. The Chumash, the descendants of these Paleoindians, still live in the area. Just recently, on June 8th, archaeologists discovered a massive Chumash burial ground, containing thousands of graves, near the Santa Ynez Mission, which lies near the coast across from the Channel Islands.
Scientists studying the skeletons found that, beginning about 5,000 years ago, they began to exhibit reduced bone quality, shorter lengths and smaller skulls, and increasing tooth decay. Given that any number of things, from malnutrition to infectious diseases, can cause these symptoms, researchers have proposed different hypotheses, including overpopulation of the islands, but all of these theories do no take into account the gradual decline over so long a period of time. From about 7,500 years ago up to the historical period, the average height of the Channel Island Indians shrank four inches. In 2011, in the journal Environmental Health Perspectives, a team led by Sabrina Sholts, an anthropologist at the Smithsonian’s National Museum of Natural History, noted that while “On San Miguel Island, bitumen occurs in man-made objects between 10,000 and 7,500 years old,” its use “becomes more prevalent with the development of bitumen-sealed water-bottle baskets about 5,000 years ago.”
Bitumen, also known as asphalt or pitch, seeps naturally to the surface around the Channel Island region and some pools, such as the La Brea Tar Pits, are famous for becoming death traps to ancient mammals such as saber-toothed tigers. Submarine seepage in the channel produces tar balls, which frequently wash ashore. Consuming asphalt, which may contain a wide assortment of PAHs (a large group of chemical compounds generally formed through the incomplete combustion of organic matter), can be harmful and lead to reproductive and development impairments, increasing risk of cancer, and organ failure.
The Indians in the Channel Islands used the bitumen in many ways: medicinally, ritually, and as a sealant for the innovative plank canoe known as the tomol, but its use in sealing water bottles caught the attention of Sholts and her team. In this new study, the team “replicated prehistoric bitumen-coated water bottles with traditional materials and techniques of California Indians” by weaving a bottle-shaped basket and then mixing and boiling bitumen and pine pitch and applying that over it. They then filled the bottles with water or oil to determine the potential leaching and thus the health risks.
Interestingly, the study found that the contamination level was so low that the “water stored in bitumen-coated water bottles was not a significant source of PAH exposure.” Although it may not have been the water bottles alone, the evidence that the Channel Island Indians were exposed to high levels of PAHs was still strong. Bitumen became an important part of their economy and culture, so much so that cakes of the material were “always kept on hand” by the Chumash and it was traded extensively with other Indians. Over time the Channel Island Indians began to rely on fish and shellfish as a greater part of their diet, which in that area have high levels of PAHs because of the heavy seepage of bitumen underwater. Although it could not find a conclusive link, the study argues that “sub-lethal PAH exposure remains a possible factor in the health decline over time previously observed among the prehistoric coastal Chumash.”
In the past 50 years, the worldwide use of fossil fuels on a massive scale has made PAH exposure a significant health threat to human populations. The study raises the possibility that some of these effects may become apparent only after the passage of hundreds of years, the price future generations may have to pay for the environmental destruction of today.