Hidden dangers? Investigating the impact of volcanic eruptions and skeletal fluorosis in medieval Iceland

Volcanic emissions are known to be a serious source of pollution to humans and animals. This study aimed to examine the possible health burden of fluoride (F) exposure from volcanic eruptions in the past. Osteological analyses were performed on 186 skeletons from seven sites across Iceland with the aim of identifying skeletal changes potentially associated with osteofluorosis. Additionally, ion selective electrode (ISE) was used to investigate possible correlations between skeletal lesions and bone fluoride concentrations in a subset of skeletons (n = 50) from two of these sites, Skriðuklaustur in Fljótsdalur and Skeljastaðir in Þjórsárdalur. The results showed that pathological markers or skeletal changes increased according to age across all investigated time periods and geographical regions but likely not due to significant fluoride exposure. The fluoride concentration range was 223–4370 ppm (mean = 2324 ± 1067 ppm) at Skriðuklaustur (n = 36) while at Skeljastaðir (n = 14), the range was 223–3030 ppm (mean = 1366 ± 937 ppm). The pathological changes noted in this study are thus more likely to relate to the environment, population dynamics, culturally mediated behaviours and increasing urbanisation than serious fluoride contamination. Therefore, volcanic emissions appear to have only substantially affected those living within the closest vicinity of actual eruption events. It may be vital to not only consider the severity of the immediate effects of volcanic pollution but also to reinforce socioeconomic circumstances and disaster preparation in regions with environmental hazards.