Temporal Trends and Future Predictions of Mercury Concentrations in Northwest Greenland Polar Bear (Ursus maritimus) Hair

Abstract

Hair samples from 117 Northwest Greenland polar bears (Ursus maritimus) were taken during 1892-2008 and analyzed for total mercury (hereafter Hg). The sample represented 28 independent years and the aim of the study was to analyze for temporal Hg trends. Mercury concentrations showed yearly significant increases of 1.6-1.7% (p < 0.0001) from 1892 to 2008 and the two most recent median concentrations from 2006 and 2008 were 23- to 27-fold higher respectively than baseline level from 1300 A.D. in the same region (Nuullit). This indicates that the present (2006-2008) Northwest Greenland polar bear Hg exposure is 95.6-96.2% anthropogenic in its origin. Assuming a continued anthropogenic increase, this model estimated concentrations in 2050 and 2100 will be 40- and 92-fold the baseline concentration, respectively, which is equivalent to a 97.5 and 98.9% man-made contribution. None of the 2001-2008 concentrations of Hg in Northwest Greenland polar bear hair exceeded the general guideline values of 20-30 μg/g dry weight for terrestrial wildlife, whereas the neurochemical effect level of 5.4 μg Hg/g dry weight proposed for East Greenland polar bears was exceeded in 93.5% of the cases. These results call for detailed effect studies in main target organs such as brain, liver, kidney, and sexual organs in the Northwest Greenland polar bears.

What are the toxicological effects of mercury in Arctic biota?

“…If, on the other hand, the terrestrial toxic threshold value of 30 μg/g ww is used then polar bears from East Greenland also exceeded the threshold level. The increases observed in Hg concentration in polar bear hair in recent years indicate that kidney concentrations have increased in some of the northern populations (Dietz et al, 2006a(Dietz et al, , 2011a. The prediction of the northeastern Canadian bears as being at risk of Hg toxicity fits well with the liver and hair data described above and in AMAP (2011).…”

“…If the increases observed in Greenland continue, then the median concentrations will reach this level around 2030 in East Greenland and in Northwest Greenland a concentration of 20 μg/g dw will be reached by 2048, if the observed Hg increases continue ( Fig. 11; Dietz et al, 2011a).…”

“…As polar bear hair has been analyzed extensively over time and across regions, and as the Hg levels relate to effect thresholds, this matrix was used to evaluate circumpolar temporal trends in Hg exposure (Dietz et al, 2011a;Stern et al, 2012). Hair represents a good biomarker of Hg exposure since it accumulates organic Hg from blood and can be collected through minimally invasive sampling methods.…”

“…As for blood, it is not known to what extent these effect levels are applicable to wildlife or polar bears in particular. Dietz et al (2006aDietz et al ( , 2011a reported that Hg concentrations in polar bear hair have increased more than 14-fold since preindustrial times in Greenland, indicating a trend that is likely to involve anthropogenic sources. These increases are in accordance with increases in other hard tissues from high trophic level Arctic species (AMAP, 2011;Dietz et al, 2009).…”

“…Among East Greenland bears, in those sampled between 1973Greenland bears, in those sampled between and 2000Greenland bears, in those sampled between and between 2001Greenland bears, in those sampled between and 2008.3% and 60.5% of cases, respectively exceeded the brain stem effect limit. The finding of Hg concentrations continuing to increase in some regions during the last decades, and the higher Hg levels in the northwestern Greenland and northern Canadian High Arctic populations, gives rise to concern for these populations (Dietz et al, 2011a;Rigét et al, 2011). Finally there are parts of the polar bear brain that contain even higher Hg concentrations (such as the pituitary gland, which has about 6-fold higher concentrations) than the brain stem, where more severe effects may be expected (Dietz et al, 2011b).…”