Scientists make water bottles the old-fashioned way to see if they were toxic to early Californians
Kevin Smith processes bitumen in the traditional method of Native California Indians for use as a coating for woven water bottles. Samples of air were taken and analyzed for pollutants. (Credit: Nicholas Radtkey, UC Davis, and Sabrina Sholts, Smiths
If the ubiquity of pollutants in modern life has you yearning for the simpler ways of California’s early residents, an unusual scientific experiment may prompt you to reconsider.
After constructing water vessels using the methods of prehistoric people who lived on the Channel Islands, researchers found that their 5,000-year-old manufacturing process polluted the air with chemicals that the Environmental Protection Agency classifies as dangerous.
The findings, published Friday in the journal Environmental Health, demonstrate that human exposure to harmful chemicals is nothing new.
“Throughout human history,” the study authors wrote, pollutants “have been an ever-present health hazard.”
The ingredient that might have harmed the health of Native Americans is called bitumen. It is a form of raw petroleum that was quite handy in the days before glue and plastic. The sticky substance was both adhesive and water-repellant, making it useful in items including bottles and boats. Anthropologists believe some people may have even chewed it like gum.
Ancient people in California, Mexico and the Middle East have been using bitumen for up to 70,000 years. But scientists weren’t sure whether this would have been hazardous to their health.
There were good reasons to be suspicious. Some of the chemicals we encounter today through exposure to petroleum-based products like plastics and fossil fuels may cause cancer or lead to other health problems.
Sabrina Sholts, an anthropologist from the Smithsonian Institution, and her colleagues had previously analyzed chunks of raw bitumen collected from the La Brea Tar Pits in Los Angeles and the Channel Islands, off the coast of Santa Barbara. In that study, they found that the bitumen contained chemicals known as polycyclic aromatic hydrocarbons, or PAHs. According to the EPA, 16 of these are high-priority pollutants.
Would the same have been true in prehistoric days? To find out, Sholts and her team needed to do some role-playing.
What followed was a foray into experimental archaeology. Team members used historical records to figure out exactly how water bottles were made by the island residents. Then they replicated their methods exactly, weaving rush plants into bottles and coating them with bitumen that was melted down with hot pebbles inside an abalone shell.
While melting the bitumen, the team measured chemicals in the air above the mixing dish to see if the laborers would have inhaled any pollutants.
When the containers were finished, the researchers filled one with water and let it sit for two months, taking samples every so often to see whether toxins were leaching into the water over time.
They did the same experiment with oil. While anthropologists don’t think the island residents used oil, they did eat oily fish that could have been kept in bitumen-coated vessels or eaten on bitumen-coated plates.
The researchers found that harmful chemicals did leach into both the water and the oil. Although higher concentrations were found in the oil, in neither case were the pollutants high enough to present a serious health risk, according to EPA standards.
The air samples, however, revealed that the bitumen-melting process produced unhealthy concentrations of PAHs, such as naphthalene. People who stood over melting bitumen would have breathed in the same concentration of naphthalene that’s produced by about 1.5 cigarettes. That exceeds the EPA’s safe limit, which means that anyone who used bitumen to make bottles or boats might have been harmed by breathing contaminated smoke.
Sholts said that while the level of exposure probably wasn’t high enough to cause significant health decline in most people, the study results tell only part of the story.
Anthropologists believe that the island residents used bitumen as body paint, as casts for injuries, and as a general, all-purpose glue. Some of these uses may have resulted in dangerous levels of PAH exposure, Sholts said.
The study shows that chemicals we think of as modern toxins have actually been around for thousands of years, said Patricia Lambert, a biological anthropologist at Utah State University who was not involved in the work.
“Exposure to toxic levels of PAHs may well have occurred long before the age of automobiles,” she said.
Eric Bartelink, a bioarchaeologist and forensic anthropologist at Chico State University who studies prehistoric Californians, agreed with the study authors that bitumen probably didn’t play a role in the demise of the islanders.
Even so, he said the work will probably inspire other anthropologists to pay more attention to environmental risks in the populations they study.
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