Reuse of ESR-irradiated tooth enamel for amino acid geochronology: assessing the impact of gamma irradiation

Abstract Hominin and faunal fossil collections are valuable scientific resources for investigating past populations, making it critically important to preserve these rare materials and prioritise minimally destructive methods. Electron spin resonance (ESR) dating of tooth enamel typically requires laboratory irradiation of powdered subsamples; however, the effects of this treatment on organic biomolecules, and therefore their potential reuse for amino acid geochronology (AAG), remain largely unknown. This study investigates the impact of gamma irradiation on amino acids within tooth enamel, and its implications for reuse of leftover ESR-dated enamel for AAG from two palaeolithic sites: Hortus, southern France and Belle-Roche, Belgium (maximum laboratory gamma dose of 1500 and 3000 Gy respectively). Our results show that laboratory irradiation induces negligible racemisation in selected amino acids, although significant correlations between dose and D/L values emerge at higher doses (> 1200 Gy). This demonstrates that while low-level gamma irradiation (e.g. <500 Gy) does not substantially compromise the chemical integrity of amino acids in enamel, higher doses may alter racemisation patterns, potentially affecting AAG interpretation. Consequently, this supports cautious reuse of irradiated ESR powders, preferably those exposed to low laboratory doses, enabling effective reuse of finite fossil tooth enamel resources.