Potential dietary, non-metabolic accumulation of arsenic (As) in seaweed-eating sheep's teeth: Implications for archaeological studies

Evaluating the extent of an individual's exposure to arsenic, (potentially) indicative of proximity to smelting activities, poisoning, or dietary history, has proven difficult in archaeological contexts due to uncertainties surrounding how arsenic biogenically accumulates in the tissues commonly found at archaeological sites such as bone and tooth, in addition to issues of diagenesis. In this study, teeth of modern sheep naturally exposed to high amounts of arsenic by means of seaweed in their diet are compared to the teeth of a less exposed 'control group' of modern sheep consuming predominantly grass. Through analysis of total arsenic and other element concentrations in samples of enamel, cementum and dentine by hydride generation atomic fluorescence spectrometry (HG-APS), as well as by bioimaging of radial tooth sections of sheep molars by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), this research demonstrates that in teeth of sheep exposed to dietary arsenic, arsenic predominantly accumulates in the infundibulum and occlusal dentine. The major route of uptake of arsenic in these teeth is therefore likely not by ingestion and metabolisation during growth of the tooth, as is thought to be the case for lead and barium, but rather due to direct surface contact, potentially even occurring during mastication. The implications of this type of in vivo chemical alteration of teeth for archaeological trace element studies are explored.