Monday Mourning

“You’re saying strontium is incorporated into a person’s bones and teeth, much like calcium.”

“Right.”

“And calcium in the human skeleton is replaced on roughly a six-year cycle.”

“Yep.”

“So, like skeletal Ca, skeletal Sr reflects an individual’s diet over the last six years of life.”

“Six to ten,” Art said.

“But Ca levels don’t change in tooth enamel as they do in bone. Once laid down, enamel is stable.”

“And the same is true of Sr. So dental enamel continues to reflect the average dietary Sr isotope composition ingested when the tooth was formed.”"

"“So if someone relocated from the place in which she was living when her teeth were forming, that individual’s dental and skeletal Sr levels would differ. If she stayed put, those levels would remain similar.”

“Precisely. Enamel values suggest place of birth and early childhood. Bone values suggest place of residence during the last years of life.”

A thought stopped me in midscribble.

“Doesn’t our food come through national and international networks these days?”

“We drink local water, at least most of the time.”

“True. Tell me what you did with my specimens.”

“After removing all extraneous materials, we ground them. Then we separated out the Sr by ion-exchange chromatography, analyzed the purified Sr using thermal ionization mass spectrometry, and collected the Sr ratios by multicollector dynamic analys—”

“Art.”

“Yes?”

“What did you find?”

“One of your three saw a bit of the world.”

22

“GO ON.”

“First, let’s talk teeth. Two of your individuals overlap in their dental Sr values.”

“Which two?”

Paper rustling.

“Let’s see…38426 and 38427. For them I’d expect a childhood diet with an average Sr value of plus ninety to plus one hundred five. But 38428 is statistically distinct. The Sr isotope composition of that individual’s dental sample suggests a childhood diet with an average Sr value of plus fifty to plus sixty.”

“Meaning 38428 was not born in the same region as the other two?”

“Correct.”

“Can you tell where she’s from?”

“That’s where it gets interesting. Last year we had a case of jumbled remains from a barrel found in some hophead’s basement in Detroit. Police knew the victims were business associates of the drug dealer who owned the house, but wanted the bones sorted into individuals. None had dental work, all were black, in their mid-twenties, and about the same size. One of the three was born in north-central California, one was from Kansas, and the other was local Michigan talent.

“We didn’t have control groups from the three areas in question, so we had to infer the isotope composition of the dietary Sr from the bedrock geology in each region, then work back to the various bones in the barrel. You still there?”

“I’m here.”

“Someone who spent their childhood in north-central California should have Sr values in the range of plus thirty to plus sixty.” Rustle. “That’s exactly where 38428 falls.”

For a moment I was taken aback.

“Meaning my girl’s from California?”

“Meaning she could be. If you have no other ideas, it’s as good a starting point as any. Of course, she could be from another region with similar bedrock geology.”

“And my other unknowns?”

“A couple of years back we had a case involving commingled remains recovered from a common grave in Vietnam. The army had IDs for the two soldiers, but wanted the bones separated into individuals. One soldier had grown up in northeastern Vermont. The other was from Utah.”

Art gave me no chance to interrupt.

“A study of the Sr isotope composition of the groundwater near St. Johnsbury in Vermont suggested values in the range of plus eighty-four to plus ninety-four. The teeth from one of the soldiers produced Sr values smack-dab in that range.”

“The Vermonter.”

“Yes. The teeth of 38426 and 38427 produced identical values.”

“Meaning these girls were from Vermont?”

“Not so fast. The same rock formations extend across the border into Quebec. What I’m suggesting is that the Sr values of your other two girls are consistent with what I’d expect from people born in the region where the remains were found.”

“The Montreal area.”

“Yes. Now let’s talk bones. For 38426 and 38427, the Sr values in their teeth are similar to the Sr values in their bones.”

“Suggesting they didn’t stray too far from home.”

“Right. But 38428 is a different story.”

I waited.

“Her skeletal Sr values are higher than her dental Sr values. What’s more, her skeletal Sr values are very similar to the skeletal Sr values for 38426 and 38427.”

“The Quebec stay-at-homes.”

“Yes.”

I took several moments to digest that.

“You’re suggesting 38428 was raised in one place, but spent the last few years of her life in another.”

“Looks that way.