Synchrotron reveals tales told by old bones
Saskatoon - The old saying “reading the bones” is being given a new twist for a group of people who lived on the island of Antigua over 200 years ago using the Canadian Light Source (CLS) synchrotron.
Treena Swanston, a post-doctoral fellow at the University of Saskatchewan (U of S) and Tamara Varney, an archaeologist at Lakehead University in Thunder Bay are working with staff scientists at the CLS, Swanston’s supervisor U of S Professor David Cooper, and Antigua’s national park service to shed light on life on the Caribbean island using the presence of trace amounts of lead and strontium as clues, using the CLS to hunt for the presence of these elements in tiny shards of bones from sailors and others interred in a Royal Navy cemetery in the late 1700s to early 1800s. The work is published online in the Journal of Archaeological Science.
Many people might find it surprising that bone, in addition to being formed as we grow or healing after breaks, is constantly being rebuilt and recycled by the body. As new bone is laid down, there is the chance that metals in the body will be incorporated along with the usual calcium and phosphorous. The presence of those other metals can yield important insights into a person’s diet, what they did for a living, what medicines they might have used, and even how long they might have lived in a particular place. The challenge for researchers is to prove that the traces they are finding were incorporated into a person’s bones while he or she was alive and not the result of post-mortem contamination.
“We used the synchrotron to determine if the trace elements we were interested in were being taken up by the bone during life,” explains Swanston. “We were able to compare maps of elements with the bone histology to differentiate between contamination and biogenic uptake.” The bones used in the study were collected by Professor Varney, working with National Parks Antigua, from a cemetery that was threatened by a nearby development. To see if the synchrotron could differentiate between something deposited while the bone was being grown and not by contamination, the team decided to focus on two metals: lead, notorious for how it can hang around in the body, and strontium, an element that can also substitute for calcium in bone.
“Our other chemical analyses had indicated elevated levels of lead, but we couldn’t say if it was coming from contamination from the soil,” says Swanston. “Lead was very common in these people’s lives; used in everything from eating utensils to containers for storing water (Antigua has no sources of fresh water other than collecting rain in cisterns).”
Samples of bone scanned at the CLS showed concentrations of lead that could be matched with the micro-architecture of bone in conventional photographs of the same specimen. When the researchers looked at scans for strontium they found similar results. While neither a nutrient nor a toxic substance, strontium is interesting because people are exposed to it through their diet. Relative amounts of strontium could be an indicator of where a person came from – such as England or Africa – with evidence of episodes of strontium concentration even being a clue to what a person was doing, like spending time at sea as a sailor, or working on a sugar plantation.
“The interesting thing about this Royal Navy cemetery is that it wasn’t segregated like other cemeteries of the time would have been,” notes Swanston. “So we also gain a social dimension that lets us look at the different ancestries and social determinants of health.”
The team is now expanding their research, looking to identify other metals that can be correlated in the same way in bones from this cemetery and others that provide further insights into the lives – and deaths – of their residents.
Reference: Swanston, T., Varney, T., Coulthard, I., Feng, R., Bewer, B., Murphy, R...Cooper, D. (2012) Element localization in Archaeological Bone using Synchrotron Radiation X-ray Fluorescence: Identification of Biogenic Uptake. Journal of Archaeological Science, DOI:10.1016/j.jas.2012.01.041