TAR ON THE BEACHES OF SOUTHERN CALIFORNIA MAY HAVE AFECTED CHUMASH HEALTH

Because I winter in Southern California, I'm well aware of the tar that comes up on the beach. I always thought it was from the tankers off shore but this article says these clumps of a sticky black substance with a texture halfway between molasses and rubber have been there since prehistoric times. Could these tar balls - collected by humans for thousands of years - provide evidence that our long-standing relationship with hydrocarbons was toxic from the outset?

Long before we started asphalting roads, prehistoric people around the world used bitumen, which seeps from the ground naturally in places. Archaeological finds suggest that California's prehistoric locals, the Chumash people, eagerly collected the tar balls. They used them to caulk the seams of ocean-going craft and waterproof woven baskets to make drinking vessels, as well as for making casts for broken bones and poultices for sore joints. Some Chumash even chewed bitumen like gum.

We now know that bitumen can be a source of polycyclic aromatic hydrocarbons (PAHs) - pollutants that have been linked to a number of health problems. To find out whether California's tar balls had the potential to damage the Chumash's health, Sebastian Wärmländer of Stockholm University in Sweden and colleagues analyzed samples taken from Californian beaches and from the La Brea tar pits in Los Angeles. They found the tar contained 44 PAHs, including many known carcinogens.

Wärmländer's team then turned to the Chumash's bones to see whether the tar balls had had an effect on their health. Most symptoms of health problems caused by PAHs reveal themselves in the flesh, but studies have suggested that mothers who are exposed to PAHs during pregnancy give birth to smaller than average babies, who become shorter than average adults.

Wärmländer and his colleagues measured 269 adult skulls from burials made between 6500 BC and AD 1780 on Santa Cruz and Santa Rosa islands off California's coast. They found that, over the generations, the skulls of men decreased from 3370 cubic centimeters to 3180 cm3. The women's skulls decreased from 3180 cm3 to 2980 cm3. Previous studies have shown femur length declined over this period too.

The decreasing stature of the Chumash suggests declining health, says Wärmländer's team. This has been suggested before, but this is the first time bitumen has been considered as a contributor to this decline.