Comparing polychlorinated n-alkane occurrence and biomagnification with legacy contaminants in a killer whale food web

Summary

Polychlorinated n-alkanes (PCAs), the largest component of the commercial product chlorinated paraffins, have been used globally in increasing amounts since the regulations of legacy contaminants, such as polychlorinated biphenyls (PCBs). The bioaccumulative potential of PCAs compared to legacy contaminants is inconclusive, with limited data available for PCAs with carbon chain length ≤9 and ≥18, particularly in food webs which include mammalian top predators. Here, we analysed and compared PCAs of different carbon chain length (very-short: PCAs-C6-9 [vSCCPs], short: PCAs-C10-13 [SCCPs], medium: PCAs-C14-17 [MCCPs], and long: PCAs-C18-24 [LCCPs]), 57 legacy contaminants, and total mercury (Hg) in killer whales (Orcinus orca) from northern Norway (n = 59) and a range of fish and marine mammals. We found that legacy organic contaminants dominated in concentration and pattern in marine mammals (54–87%), whereas PCAs and Hg dominated in fishes (58–98%). A species' physiology (poikilotherm or homeotherm) influenced the food web magnification of several contaminants, with estimated trophic magnification factors (TMFs) underestimated in PCAs, and overestimated in PCB-153, p.p’-DDE and Hg, if unaccounted for. PCAs-C6-9 and PCAs-C10-13 had similar and low TMFs for poikilotherms and homeotherms, and similar to PCB-28 (TMF range: 1.9–2.4 [95% confidence interval 0.9–5.7]). PCAs-C14-17 and PCAs-C18-24, had high TMFs in poikilotherms (4.8 [1.3–18] and 4.6 [1.2–18], respectively), and no significant trophic magnification in homeotherms (1.0 [0.5–2.3] and 1.0 [0.4–2.8], respectively), with the opposite pattern for PCB-153 and p.p’-DDE. Our results indicate higher PCA concentrations and biomagnification potential in poikilotherms than homeotherms, which is likely due to lower biotransformation and elimination ability.