Medeiros L, da Silveira Monteiro D, Petitet R, Bugoni L

Effects of lipid extraction on the isotopic values of sea turtle bone collagen

Lipids are known to be a potential source of bias in stable isotope analysis (SIA) because they are depleted in ¹³C compared to ¹²C. Although lipids are usually removed before SIA, there is a lack of standardized analytical protocols for this procedure. Two lipid extraction protocols (chloroform-methanol and petroleum ether) were tested in the humeri of loggerhead sea turtles to establish a standard for processing bone collagen of marine animals in SIA. In both lipid extraction treatments, δ¹³C values were higher than the control, but only lipid extraction with chloroform-methanol showed significant differences. By contrast, the δ¹⁵N values were not affected by lipid extraction treatments with either solvent. It was not possible to develop a mathematical correction because the C:N ratio was not a suitable predictor of lipid content, and there was a weak correlation between Δ¹³C and δ¹³C. These results suggest that lipid extraction should be taken into account in SIA of bone collagen tissues for accurate δ¹³C determination and a single sample allows both δ¹³ and δ¹⁵N determination.

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