Is it necessary to filter bone collagen extracted from modern human remains for stable isotope analysis?

Amelia J. Edwards, Thuan H. Chau, Lyndi Low, Lesley A. Chesson, Gregory E. Berg

SNA International

Studies on archaeological remains have demonstrated that filtering bone collagen does not produce meaningful changes in nitrogen (N) and carbon (C) quality criteria or stable isotope delta (δ) values – if the remains were well preserved. These claims have not been extensively studied for modern human remains. Additionally, the impact of filtration has not been addressed regarding sulfur (S) quality criteria and δ values.

Forty-five human bones were previously sampled, prepared, and analyzed from a variety of modern forensic contexts (i.e., field recoveries, disinterments). The resultant extracted collagen was filtered using pre-cleaned Ezee-filters™ and analyzed pre- and post-filtration. Elemental composition and isotope ratio measurements for N, C, and S were performed using a Thermo Scientific™ EA Isolink CN™ in line with a Delta V Plus™ mass spectrometer.

All elemental metrics passed published quality criteria for bone collagen both pre- and post-filtration. Filtering did not have a statically significant impact on either C:N (3.2 vs. 3.2) or C:S (559 vs. 572) atomic ratios based on paired t-tests. The mean differences for δ¹³C and δ³⁴S values were -0.08 ± 0.34‰ and 0.15 ± 1.11‰, respectively, and were not statistically significant. The mean difference for δ¹⁵N values (0.08 ± 0.13‰) was statistically significant (p = 0.0001) but makes no interpretative difference. 

We conclude that it is not necessary to filter bone collagen extracted from modern human remains for stable isotope analysis of N, C, and/or S. This conclusion is in accordance with prior studies of well-preserved archaeological remains regarding N and C.