Effects of acidification on the isotopic ratios of Neotropical otter tooth dentin

Acidification does not alter the stable isotope composition of bone collagen

In this study, we compared the elemental and isotopic composition of modern and ancient bone samples pre-treated using different demineralization agents with acidic and neutral pH. The purpose of our research was to examine if demineralization using a mineral acid such as hydrochloric acid (HCl) significantly alters the δ ¹⁵N and δ ¹³C values of bone collagen. Evidence from the elemental and amino acid composition of the samples were incorporated alongside isotopic compositions to provide a holistic view of the effect of demineralization agents on the composition of bone collagen. The stable isotope compositions of collagen extracts were also compared against equivalent whole bone samples to assess whether whole bone has a stable isotope composition that is comparable to collagen demineralized with a neutral agent. Our results demonstrate that bone demineralization using either ethylenediaminetetraacetic acid (EDTA) or HCl yields collagen extracts with stable isotope compositions that are not significantly different, indicating that mineral acid does not alter δ ¹⁵N and δ ¹³C values of bone collagen. The results comparing whole bone and extracted collagen stable isotope compositions indicate that whole bone cannot be used as an effective replacement for bone collagen due to the significantly different stable isotope compositions between these sample materials. In ecological and archaeological studies performing stable isotope analysis on bone, sample pre-treatment to isolate collagen is a necessity to obtain the most reliable and reproducible isotopic measurements.

Integrating fish scale and bone isotopic compositions for 'deep time' retrospective studies

Isotopic studies of archived fish scales have tremendous potential to develop long-term retrospectives that provide important insights into how humans have altered aquatic ecosystems. However, fish specimens in museum archives and other repositories typically date to time periods when the impacts of industrial societies may have already caused profound environmental changes. Archaeological fish bones offer an opportunity to bridge this key temporal gap by providing samples spanning from the recent past to as far back as the Pleistocene. Collagen is the primary protein component of both fish scale and bone, but the comparability of isotopic compositions from these tissues has not been established experimentally. To lay the framework for integrating isotopic datasets from these tissues, we compare δ¹³C and δ¹⁵N of bone and scale collagen, as well as other tissues, from fish with life-time controlled diets. Results show that while there is no difference in δ¹³C between scale and bone collagen, there may be a very slight but meaningful inter-tissue offset in δ¹⁵N (<0.3‰). We discuss potential sources of δ¹⁵N variation in scale and bone collagen measurements. Because there is no difference in scale and bone δ¹³C, and the observed offset in δ¹⁵N is very small (less than analytical uncertainty in many studies), our findings demonstrate that collagen isotopic compositions from these tissues should be directly comparable when integrating datasets from modern and ancient samples to build more powerful, millennium-scale isotopic times series. In linking isotopic compositions of collagen from modern, historical (scales), and archaeological (bones) fish, our findings open the way for more nuanced contextualization of how ecosystems functioned prior to large-scale exploitation and how they have responded to mounting anthropogenic pressures in the intervening centuries.