Hepatic trace element concentrations of breeding female common eiders across a latitudinal gradient in the eastern Canadian Arctic

Highlights

• Many elements were elevated in eiders, but generally below toxicological concern.

• We found significant differences in concentrations of some elements among colonies.

• We did not find a consistent pattern in concentrations with latitude.

Abstract

We examined hepatic concentrations of arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), manganese (Mn), mercury (Hg), rubidium (Rb), selenium (Se) and zinc (Zn) in 10 breeding female common eiders (Somateria mollissima) from each of three colonies across 20° of latitude. Levels of many elements were elevated in eiders, although generally below levels of toxicological concern. We found significant differences in concentrations of As, Rb, Hg, Mn and Se among colonies, but not in a consistent pattern with latitude, and Hg:Se molar ratios did not vary among colonies. Furthermore, overlap in element concentrations from birds at different colonies meant that we could not reliably differentiate birds from different colonies based on a suite of their hepatic trace element concentrations. We encourage other researchers to assess baseline trace element levels on this important, harvested species, as a means of tracking contamination of nearshore benthic environments in the circumpolar Arctic.

Introduction

A variety of trace elements, many of toxicological interest (e.g., cadmium - Cd, mercury - Hg, selenium - Se) are elevated in Arctic wildlife species (Muir et al., 1999, AMAP, 2009). This is attributable in part to long-range transport to Arctic ecosystems from anthropogenic sources (e.g., emissions from industrial activity) in tropic and temperate regions to the south (Bidleman et al., 2003), and in part to natural variation in environmental levels (Braune et al. 1991). For many years, researchers around the circumpolar north have monitored levels of contaminants in Arctic wildlife, and in the case of trace elements, particular focus has been on Hg (Rigét et al., 2011), while much less attention has been given to other elements (but see Rigét et al., 2004, Campbell et al., 2005, Øverjordet et al., 2015). In general, contamination of species that are harvested for food is of great concern to northern indigenous communities because many northern people still rely heavily on wild food to fulfill cultural and dietary needs (Kinloch et al., 1992, Priest and Usher, 2004, AMAP, 2009, Ford, 2009).

The common eider (Somateria mollissima) is a useful species to monitor trace elements in the north because they are harvested around most of the circumpolar Arctic for sport and subsistence, they accumulate trace elements, often in high concentrations (e.g., Norheim, 1987, Wenzel and Gabrielsen, 1995, Franson et al., 2000, Wayland et al., 2001, Wayland et al., 2002, Lovvorn et al., 2013, Mallory et al., 2014, Fenstad et al., 2017), and some literature reports concentrations that suggest there are local and broad regional patterns in trace elements concentrations within the species. In one review, Mallory et al. (2004) found evidence of significant regional differences in trace element concentrations in tissues, with Se and Hg higher in liver and muscle tissue of eiders breeding around Hudson Bay, Nunavut, Canada than elsewhere. More recently, Pratte et al. (2015) showed that eiders nesting farther north in Canada had higher Hg in their eggs, and for colonies located > 55°N, egg Se declined with increasing latitude. Marked differences in arsenic (As) and Cd in eggs among colonies were also detected (Pratte et al. 2015). Given these findings, the work presented here builds on existing data, and further explores how trace element concentrations in eiders may be related to latitude and other spatial patterns in the region.

In this study, we examined concentrations of essential and non-essential trace elements in livers of breeding female common eiders from three sites separated by approximately 20° in latitude across northeastern Canada. Previously we reported on increasing trends over time of hepatic Cd and zinc (Zn) in these samples (Mallory et al. 2014). Here, our objectives primarily focused on examining spatial patterns using a suite of nine elements. First, we assessed whether hepatic trace concentrations differed among eiders at these widely separated colonies, and particularly if they followed the pattern established by recent sampling of eggs (Pratte et al. 2015). We predicted that hepatic Hg would increase with increasing latitude, while Se and As would decrease. Second, we examined interactions between elements. In particular, studies have shown that high Se can prevent toxic effects of Hg (Ralston et al., 2007, Sørmo et al., 2011), but in marine birds this typically happens around molar Hg:Se ratios near 1 (Kim et al., 1996). Eiders rarely reach this ratio (Braune and Scheuhammer, 2008, Fenstad et al., 2017), so we did not expect high ratios for these sites. Importantly, although any single element may affect a species, increasingly there is evidence that many interactions may occur within the body between trace elements. Some elements have negative impacts on biota (e.g., Hg), but there are also combinations of elements that may reduce the toxicity of single elements (Shore et al., 2011). Additionally, some mixtures of elements can have a stronger negative effect than those that occur independently (Sarigiannis and Hansen, 2012), which can lead to cumulative effects in biota (Provencher et al. 2016). Lastly, we used multivariate analysis of hepatic trace element concentrations to explore whether the suite of trace elements varied in some related pattern across our sampling colonies, as a basis for future work using trace elements as geotracers of breeding origin.