Geographic origins of the population sample
Isotope data are summarised in Table 1 (for more detailed results, see OSM1) and strontium and oxygen isotope values are plotted against each other in Figure 5. A strontium ratio of 0.714 or higher was originally thought to reflect individuals who spent their childhood outside the Peak District (Evans et al. Reference Evans2023) but as this accounted for an unusually high proportion of the population sample (seven of 17), additional analysis of regional minerogenic soils was undertaken (see O’Regan et al. Reference O’Regan2023). This demonstrated that 87Sr/86Sr values of 0.714 and above are more widely present within the Peak District biosphere than hitherto suspected (O’Regan et al. Reference O’Regan2023: 2). It therefore seems most parsimonious to conclude that these high 87Sr/86Sr values are consistent with a childhood in the Peak District, while strontium values alone do not indicate any in-migration.
Summary results of isotopic analyses (for detailed results see OSM1). Sites are presented in chronological order.
Table 1 Long description
A table summarizing isotopic analyses across different samples. The table has six rows and seven columns. The columns are labeled Sample, Sample size, 87Sr/86Sr range, δ18O range (‰), δ18O mean (‰), Pb range (ppm), and Pb mean (ppm). The row labels are Eldon, Hole, Wigber Low, Joule Yard, and Spital Field. Each row provides specific values for each column. For example, the Eldon sample has a sample size of 2, an 87Sr/86Sr range of 0.7153–0.7162, a δ18O range of 16.1–16.3, a Pb range of 0.66–4.29, and no values for δ18O mean and Pb mean. The Wigber Low sample has a sample size of 5, an 87Sr/86Sr range of 0.7106–0.7158, a δ18O range of 17.1–18.4, a δ18O mean of 17.8, a Pb range of 2.0–69.1, and a Pb mean of 24.9. The Joule Yard sample has a sample size of 5, an 87Sr/86Sr range of 0.7114–0.7150, a δ18O range of 17.2–17.9, a δ18O mean of 17.6, a Pb range of 25.5–54.1, and a Pb mean of 33.6. The Spital Field sample has a sample size of 5, an 87Sr/86Sr range of 0.7098–0.7136, a δ18O range of 17.1–18.2, a δ18O mean of 17.7, a Pb range of 25.2–68.4, and a Pb mean of 33.6.
Strontium and oxygen isotope values among the population sample (figure by H. O’Regan, J. Evans & A. Bloxam).
Two individuals possessed both elevated 87Sr/86Sr and depleted δ18O values, which may indicate that they spent their childhood in a different region. These are the two Iron Age individuals from Eldon Hole (ELD-01: 87Sr/86Sr, 0.715; δ18O, 16.1‰; ELD-02: 87Sr/86Sr, 0.716; δ18O, 16.3‰; Figure 5). Outside the Peak District biosphere, the high 87Sr/86Sr values of these individuals are found in south-west England or northern Scotland (Evans et al. Reference Evans2023), though the low δ18O values suggest a potential origin in a colder climate. A Scandinavian origin is possible, as the values are similar to a small group of individuals buried in the Weymouth Viking-age mass grave (Evans et al. Reference Evans2018; Figure 5 & OSM1).
Among the early medieval sample (seventh–eleventh centuries; Wigber Low and Joule Yard; n = 10), one individual has isotope values consistent with a childhood outside the Peak District. Burial 7 at Wigber Low (sample WIG-05) contained the remains of a male, aged approximately 45 years, interred without grave goods. The elevated 87Sr/86Sr and δ18O values of this individual (0.715 and 18.4, respectively) indicate a potential origin from western Britain (Figure 5, OSM1). The movement of people from west to east has been noted in northern Britain from the fifth–seventh centuries (Morez et al. Reference Morez2023: 10); and western British origins have also been identified for females buried in poorly furnished or unfurnished graves in seventh-century central-eastern England (Hamerow et al. Reference Hamerow2024: 499). In the later medieval sample (late eleventh–early sixteenth centuries; Spital Field; n = 5), all individuals have 87Sr/86Sr values below 0.714, consistent with regularly encountered Peak District levels, although two individuals have δ18O values that could potentially indicate a more westerly origin (SPF-SK009, 18.2‰; SPF-SK011, 18.0‰; Figure 5 & OSM1).
Lead isotope values for the sample population are presented in Figure 6, using ratios of 207Pb/206Pb and 208Pb/204Pb. With one exception, the individuals plot within the Peak District range. The young male from burial 1 at Wigber Low (sample WIG-01) has lead isotope values that fall more within the Yorkshire Pennines range but there is some isotopic overlap with the Peak District (OSM2, Figure S1) and his strontium and oxygen levels are typical of childhood in the Peak District (Figure 5). The Iron Age individuals from Eldon Hole possessed lead isotope values indicative of local Peak District contamination, despite likely originating from outside the region (Figure 6).
Lead isotope and concentration values among the population sample (figure by A. Bloxam, J. Evans & H. O’Regan).
Social dynamics of lead production
Current literature suggests that lead concentrations in human teeth above 0.6–0.7ppm are indicative of anthropogenic activities; while values below 0.5ppm reflect natural ‘background’ levels (Moore et al. Reference Moore2021: 847). Only the Iron Age adult from Eldon Hole had a value that accords with the notional natural background (ELD-01; 0.66ppm). The other individual from this site, a child (ELD-02), had a value of 4.29ppm, showing exposure to anthropogenic lead pollution from ore or lead-working (Figures 7 & 8). This could indicate the movement of a family into the area to exploit mineral resources, or into a community where some lead extraction took place. All but one of the medieval individuals had lead concentrations of more than 10ppm (Figure 7), indicating substantial anthropogenic lead exposure in childhood. Four individuals (27%) had levels over 40ppm; 10 (66%) ranged between 15 and 40ppm; and one (7%) measured 2ppm (Figure 7). Examination of the three cemetery populations chronologically, in comparison with cemetery populations across Britain, provides different perspectives on the social and environmental dynamics of lead production.
Radiocarbon date-ranges and lead concentrations (ppm) among the population sample. Median lead concentrations in studied medieval populations are shown by the dashed lines: fifth–seventh centuries (green); eighth–eleventh centuries (purple); twelfth–fifteenth centuries (orange) (data from Montgomery et al. Reference Montgomery2010; Millard et al. Reference Millard and Zuckermann2014; Moore et al. Reference Moore2021) (figure by H. O’Regan, C. Fear & A. Bloxam).
Comparison of lead concentrations (ppm) in human tooth enamel between cemetery samples (left) and between males and females in the population sample (right) (figure by H. O’Regan, C. Fear & A. Bloxam).
The Wigber Low sample shows distinct variations in lead concentrations, possibly linked to gendered roles and social status (Figures 7 & 8, OSM1). The local males had the lowest exposure (WIG-01, 10.9ppm; WIG-03, 2ppm), and may not have been personally involved in lead production but may have benefited from its control. The male from the unfurnished grave (WIG-05), possibly an immigrant to the area, had a lead level of 29.5ppm. The two females both had lead levels higher than the local males (WIG-04, 69.1ppm; WIG-06, 13.2ppm), possibly reflecting ore processing when children, although the female (WIG-06), furnished with more grave-goods, has a much lower concentration. The male, WIG-03, buried with a sword, possessed a level of lead exposure similar to those from Iron Age and Roman cemeteries in non-lead-producing regions of Britain (Figure 9). The lead concentrations of individuals WIG-04 and WIG-05, however, have been found only in the lead-producing centre at Castleton and in populations from Industrial Revolution-era (post-1750s) Coventry and Chelsea, London (Figure 9, OSM3; Millard et al. Reference Millard and Zuckermann2014).
Lead concentrations (ppm) from individuals included in this study compared with individuals from other sites in Britain. N: Neolithic; BA: Bronze Age; IA: Iron Age; R: Roman; EM: early medieval; M: medieval; PM: post-medieval (figure by H. O’Regan, C. Fear & A. Bloxam).
Demonstration of a direct relationship between high lead levels in childhood tooth enamel and high lead levels in the blood, resulting in lead poisoning, has proven complex (Moore et al. Reference Moore2021: 853). A recent study shows an association between high levels of lead in tooth cementum (formed in adolescence to adulthood) and earlier age at death in modern individuals, suggesting that “Pb over even just a few years in childhood trended towards a negative association with age at death”, but this is not a direct correlation, only a “direction of association” (Farmer et al. Reference Farmer2024: 7). Tentatively, therefore, the deaths of the females from Wigber Low (WIG-04 at 17 years and WIG-06 at 17–25 years) could reflect this ‘direction of association’. Both were seemingly co-located with children aged around two (WIG-04) and five years old (WIG-06).
The comparatively lower lead levels (below 13.5ppm) in the local males, both furnished with weapons (WIG-01, WIG-03), and the female buried with a crystal ball (WIG-06), could reflect legacy landscape lead pollution from Roman production in the region, while the high levels of lead in the male from the unfurnished grave (WIG-05) and the younger female (WIG-04) may identify lower-status households, producing lead for estate owners. The involvement of the Wigber Low community in smelting lead during the mid-seventh century seems to corroborate the hypothesis that increased wealth for local elites coincided with renewed demand for the metal in Christian monumental building (Loveluck Reference Loveluck, Bintliff and Hamerow1995: 90; contra Brown Reference Brown2024).
The slightly later Joule Yard population from Castleton demonstrates an increase in levels of production and consequent lead exposure. All five sampled individuals had lead concentrations above 25ppm, three between 30 and 54ppm (Figure 7). One individual was aged 17–23 years at death, the others were 30–55. These high lead concentrations, mostly during the 680s to 880s (Figures 4 & 7), may indicate a specialist community of lead-mining and smelting families at Castleton. The levels of lead ingested as children suggest a living environment that was highly contaminated by the mid-eighth century. At Wigber Low, from c. 625–685, only those likely undertaking ore processing or smelting were heavily contaminated but by 680–750 the whole population sample at Joule Yard in Castleton, 48km to the north, showed high lead levels. The beginning of a rise in lead pollution in the mid-eighth century is evident in the peat-core from Lindow Moss (Cheshire), approximately 50km west of Castleton; this may also reflect the onset of larger-scale Peak District production, although the spacing of radiocarbon dates along this core gives wide error margins post AD 500, and the predominant wind directions would take Peak District pollution south/south-east, away from Lindow Moss (Le Roux et al. Reference Le Roux2004: figs. 2 & 5; Loveluck et al. Reference Loveluck2020: 478–81).
The lead concentrations in eight individuals from Repton in the Trent Valley (Derbyshire) provide a comparison for Joule Yard, deriving from a population believed to be contemporaneous with a Viking over-wintering camp in 873–874 (Jarman et al. Reference Jarman2018). Four teeth were sampled from inhumation graves and another four from a collection of disarticulated charnel. The lead levels among the individuals from the charnel (two males, two females) range from 4.7ppm to 31.64ppm, with the females having the highest values (females: 20.19 & 31.64ppm; males: 4.7 & 13.76ppm; Figure 10: Repton a; Budd et al. Reference Budd2004: 51, tab. 2). Concentrations in samples from the individual graves were much lower, with a range of 0.4–0.51ppm for three males and a value of 29.5ppm for one juvenile (Figure 10: Repton b). These levels overlap with the lower concentrations observed at Wigber Low but reach their peak at the base of the range of values obtained for Joule Yard (Figure 10). Both females, one male and the unsexed juvenile at Repton had significant exposure to lead in childhood, yet the level of exposure was less than that seen in WIG-04 and almost all the Joule Yard population. One of the lowest values in the Repton sample (0.51ppm) derives from a double burial that included a Thor’s hammer and sword (G 511), echoing the findings from Wigber Low, where the lowest lead concentration comes from the male buried with a sword (WIG-03).
Lead concentration (ppm) ranges from this study and other British sites, alongside the population from Sala, Sweden. N: Neolithic; BA: Bronze Age; IA: Iron Age; R: Roman; EM: early medieval; M: medieval; PM: post-medieval (figure by H. O’Regan, C. Fear & A. Bloxam).
Among the later medieval population at Castleton, all the sampled individuals from Spital Field had lead concentrations between 25 and 68ppm. This, again, reflects childhood in a heavily lead-contaminated environment, and probably membership of lead-mining/smelting households. The only female within the sample has the lowest lead level of the group (although this was still high at 25.2ppm) and she died aged 18–21 years, while the males have higher lead levels but appear to have lived longer. The three females included in this analysis (WIG-04, WIG-06, SPF-SK009) all died between the ages of 17 and 25 and both females from Wigber Low were buried close to young children. Pregnancy remobilises lead that has been deposited within bone (World Health Organization 2010: 27), which may make both mother and fetus more vulnerable to lead poisoning. The high proportion of grave memorials for children at the silver-lead mine/smelting settlement and mint at Melle, dating from the eighth–ninth centuries, may also hint at the impact of lead working but skeletal remains have yet to be analysed (Bourgeois et al. Reference Bourgeois2009: 28).
The two individuals with the highest concentrations of lead at Spital Field have near-identical radiocarbon dates, calibrated to the late twelfth–thirteenth centuries (R-combined: 1175–1270) (Figure 7). Perhaps not coincidentally, the highest levels of Peak District lead production recorded in the Pipe Rolls occurred between the mid-1180s and 1215 (Loveluck et al. Reference Loveluck2020: 486, OSM5: 42). The highest lead-pollution levels in the north-west-facing Colle Gnifetti ice-core (Swiss-Italian Alps) and varved lake-sediment cores from Sweden were also reached at c. 1200 and are attributed to predominantly British pollution sources in both records (Brännvall et al. Reference Brännvall1999: 4392–94; Loveluck et al. Reference Loveluck2020: 476). Levels of lead pollution also reached a medieval zenith by c. 1150 within the wider medieval error margins of the Lindow Moss peat core (Le Roux et al. Reference Le Roux2004: 509).
The 87Sr/86Sr and δ18O isotope results presented here indicate little immigration among the early- to late-medieval populations in the Peak District, where lead production was seemingly a long-term, inherited tradition. In other silver-lead-producing regions, greater levels of inward migration by adolescents and adults resulted in a different pollution profile. For example, lead concentrations among workers buried in two cemeteries (Sala a and b) at the sixteenth-century lead-silver mines at Sala, Sweden, show much lower lead levels in one of the cemeteries (Sala a in Figure 10), compared with the population of the Peak District (OSM3). The Sala mines received significant prisoner-forced labour, bringing in individuals who had spent their childhoods outside landscapes contaminated by lead pollution, and this is probably reflected in the cemetery population with lower enamel lead concentrations (Price et al. Reference Price2017: 5, 11, tab. 1).