Temporal trends of persistent organic pollutants in Svalbard polar bears (Ursus maritimus) in relation to climate-associated changes in feeding habits

Abstract

Persistent organic pollutants (POPs) reach the Arctic ecosystems from lower latitudes mostly via air and ocean currents. They biomagnify through Arctic food webs and reach considerably high concentrations in top predators such as polar bears (Ursus maritimus). Although many of these compounds have been banned or restricted for decades, concentrations of polychlorinated byphenyls (PCBs), organochlorine pesticides (OCPs) and polybrominated diphenyl ethers (PBDEs) in Arctic biota still remain high. Temporal trend studies in Arctic biota help assess the effectivness of bans and restrictions. However, trends of POP concentrations in biota are affected by various factors, including dietary source and climate change. Because of retreating sea ice polar bears can be forced to feed at lower trophic levels or consider terrestrial food sources, potentially leading to a decreased uptake of contaminants. We monitored plasma concentrations of 4 PCBs (CB-118, 138, 153, and 180), 4 OCPs (p,p’-DDE, HCB, β-HCH and oxychlordane), 2 PBDEs (BDE-47 and 153), and 5 OH-PCBs (OH-CB-107, 138, 146, 156, and 187) in female polar bears from Svalbard, Norway, over a 20 year time span (1997-2017). All 306 samples were collected in the spring (April). We examined temporal trends in relation to climate – associated changes in feeding habits by using stable isotope ratios of nitrogen (δ15N) and carbon (δ13C) from red blood cells as feeding proxies representing polar bear winter diet. We found a significant decline of both δ13C and δ15N values over our study period, with a steeper trend for δ13C after 2012, indicating an increasing intake of more terrestrial and lower trophic level prey. BDE-153 and β-HCH concentrations were stable over our study period, ΣPCB, ΣOH-PCB and BDE-47 showed a linear declining trend. For p,p’-DDE, HCB and oxychlordane however, trends only declined until 2010-12 and stalled thereafter. Interestingly, trends of all compounds changed in shape and/or rate when adjusted for changes in winter diet. ΣPCB, HCB, β-HCH and BDE-153 concentrations increased significantly after 2010-12 when adjusted for changes in winter diet. Our findings suggest that a climate – related diet shift leads to lower PCB, HCB, β-HCH, and BDE-153 exposure in the Svalbard polar bears, while p,p’-DDE, oxychlordane and BDE-47 exposure is mainly affected by emissions.