249-14 The Problem with Paraffin: Does Paraffin Dipping Alter Freshwater Mussel Periostracum δ13C and δ15N values?

Session: Emerging Contaminants: Geochemical Insights and Impacts on Human and Environmental Health

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The dietary ecology of freshwater mussels (Unionida) is poorly understood, handicapping our understanding of their population biology, the drivers of their global population declines, and how to support their recovery. This critical knowledge gap is due to multiple factors, including limitations in field-based methods for assessing their dietary preferences and feeding strategies. The carbon and nitrogen stable isotopic composition (δ¹³C and δ¹⁵N) in shell periostracum are useful proxies for reconstructing unionid diets and can provide information for recent and historically-collected museum specimens. However, some curatorial practices, such as using a paraffin-xylene solution to coat shells in paraffin wax, may obscure a shell’s original isotope values. Here, we investigated the impacts of paraffin wax dipping and removal on periostracum δ¹³C and δ¹⁵N values. We conducted three tests, each using five shells of both Lampsilis siliquoidea and Obliquaria reflexa. In all tests, we sampled periostracum from the 5th growth year, which is visually distinct, has a large surface area, and is easy to sample. The first two tests evaluated the isotopic impact of shell periostracum being dipped in solutions of either paraffin-xylene or xylene-only. In both cases, we dipped half the shells, with the undipped halves serving as experimental controls. In the third test, we evaluated the efficacy of xylene rinses for removing previously applied paraffin coatings, as well as the differences to δ¹³C and δ¹⁵N values between dipped and dipped-and-rinsed periostracum. To assess the amount of paraffin removed using xylene, we calculated the relative proportion of hydrocarbons collected from each of five rinses. We found that paraffin dipping had no significant impact on periostracum δ¹³C and δ¹⁵N values. However, we found that, in the absence of paraffin, xylene dipping led to small (but significant) changes in δ¹³C values of L. silquoidea and δ¹⁵N values of O. reflexa. We also found that, for both species, 80-95% of paraffin was removed after one xylene rinse. However, xylene rinses altered periostracum δ¹³C and δ¹⁵N values of O. reflexa, but not L. siliquoidea. Fortunately, the magnitudes of all significant shifts were smaller than the intra-annual variation in periostracum δ¹³C and δ¹⁵N. Thus, paraffin-coated shells remain useful for assessing dietary information from historical unionid specimens to support biomonitoring and assessments of today’s declining populations.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-6180

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