Effects of decalcification on bulk and compound-specific nitrogen and carbon isotope analyses of dentin.

RATIONALE: For bulk carbon and nitrogen isotope analysis of dentin, samples are typically decalcified. Since the non-protein carbon in dentin is low, whole sample analysis may produce reliable data. Compound-specific isotope analysis (CSIA) of bone and tooth dentin protein is a powerful tool for reconstructing the flow of carbon and nitrogen in modern and past food webs. Decalcification has also been used to prepare bone and dentin samples for CSIA, but the effects of this process on bulk dentin, amino acid composition, and their specific isotope values are not known. METHODS: The bulk isotope values of raw and decalcified dentin from a sperm whale tooth were measured to determine the effects of decalcification and the accuracy of untreated dentin results. CSIA was also performed on decalcified and raw dentin to examine differences in the amino acid isotope values and molar composition between these two approaches. RESULTS: Analysis of raw dentin yields precise and accurate bulk isotope measurements for this animal. The isotopic values of decalcified samples and raw dentin for individual amino acids were similar, but the average of the isotope value offsets between the two sample types was significant. The presence of inorganic material complicated raw sample processing for individual amino acid isotope values, and may have contributed to the isotopic differences between decalcified and raw samples. CONCLUSIONS: Decalcification is not needed to measure bulk isotope values in dentin from this modern odontocete, probably because the lipid and carbonate concentrations are low and the carbon isotope values of dentin protein and carbonate are similar. This method should not be applied in some cases (e.g., with fossil dentin and modern bone). Decalcification should still be used prior to CSIA since significant matrix issues occur with raw dentin processing and decalcification does not alter the amino acid molar composition or isotopic values of dentin.

Inter-annual variation of persistent organic pollutants (POPS) in an Antarctic top predator Arctocephalus gazella.

Persistent organic pollutants (POPs), contaminants that may bioaccumulate in upper trophic level organisms, were detected in the milk of a top predator, the Antarctic fur seal (Arctocephalus gazella). Multiparous females had significantly lower concentrations of certain POPs (trans-nonachlor, p,p'-DDE, and several PCBs) in their milk than primiparous females, likely due to the annual lactational transfer of the POP burden from mother to pup. Furthermore, there were significant interannual differences in POP concentrations in multiparous females' milk from five breeding seasons between 2000 and 2011. Decreasing trends in concentrations of certain POPs over the recent decade coincide with declining global emissions, yet atmospheric concentrations in the Antarctic are not always consistent with global trends, suggesting that additional factors may contribute to temporal trends of POPs in fur seals. Climate shifts and corresponding availability of krill over the past decade were not consistent with trends observed in POP concentrations in fur seal milk, suggesting that climate may not be a key factor. Additional mechanisms, such as variability in the geographic ranges of individual seals during overwintering migrations are discussed and should be explored further.

Time Trends of Polybrominated Diphenyl Ethers (PBDEs) in Antarctic Biota.

Polybrominated diphenyl ethers (PBDEs) are "emerged" contaminants that were produced and used as flame retardants in numerous consumer and industrial applications for decades until banned. They remain ubiquitously present in the environment today. Here, a unique set of >200 biotic samples from the Antarctic was analyzed for PBDEs, including phytoplankton, krill, fish, and fur seal milk, spanning several sampling seasons over 14 years. PBDE-47 and -99 were the dominant congeners determined in all samples, constituting >60% of total PBDEs. A temporal trend was observed for ∑7PBDE concentrations in fur seal milk, where concentrations significantly increased (R2 = 0.57, p < 0.05) over time (2000-2014). Results for krill and phytoplankton also suggested increasing PBDE concentrations over time. Trends of PBDEs in fur seal milk of individual seals sampled 1 or more years apart showed no clear temporal trends. Overall, there was no indication of PBDEs decreasing in Antarctic biota yet, whereas numerous studies have reported decreasing trends in the northern hemisphere. Similar PBDE concentrations in perinatal versus nonperinatal milk implied the importance of local PBDE sources for bioaccumulation. These results indicate the need for continued assessment of contaminant trends, such as PBDEs, and their replacements, in Antarctica.