Can't edit previous comment but - I tracked down the actual study, the soil was indeed from graves (right under the sacrum where the bowels were) and was compar

Can't edit previous comment but - I tracked down the actual study, the soil was indeed from graves (right under the sacrum where the bowels were) and was compared to control samples by the head or feet of the grave. The friars were buried with clothes, the laypeople in shrouds so similar deal and the sites were a few hundred meters apart so about as well controlled as you could expect, I reckon.