Tracing the footprints of Arctic pollution: Spatial variations in toxic and essential elements in Svalbard reindeer (Rangifer tarandus platyrhynchus) faeces
Description
Using HR-ICP-MS, we obtained the concentration of 55 elements in Svalbard reindeer (Rangifer tarandus platyrhynchus) faeces (n=96) and soil (n=9) from two locations on Nordenskiöld land, Svalbard. The main aim was to compare the elemental composition and concentrations in faeces from the two reindeer populations to investigate whether Svalbard reindeer were exposed to toxic elements and to evaluate whether reindeer inhabiting pristine areas have a different faecal elemental composition as compared to reindeer living in areas more influenced by anthropogenic activities. Soil samples were analysed to study the geochemical background differences between the two sites. All faecal (freeze-dried) and soil (air-dried) samples were digested in nitric acid using a high-pressure microwave system prior to ICP-MS analysis. The reported data is provided in dry weight. Along with the faecal elemental composition data, we provide information on the sampling coordinates, the distance to the nearest shoreline, the year of sampling, the gender of the sampled individual and the estimated age of the sampled individual. Along with the soil elemental composition data, we provide the sampling coordinates, year of sampling and which soil horizon was sampled (in this case, all of the soil samples were topsoil samples (upper 10 cm layer). There were significant differences in several elemental concentrations between the two sites. Elements of geogenic origin (e.g., Al, Cu and Fe) were found at higher levels in faeces from Adventdalen. In comparison, levels of Ca, Se and the toxic elements Cd and Pb were higher in faecal samples from the Nordenskiöld coast. The significantly higher levels of faecal Cd and Pb at Nordenskiöld coast may be due to marine input, dietary differences between the populations, or possible anthropogenic influence from the nearby settlement of Barentsburg (located 15 km away). There was, however, a decoupling in elemental composition between faecal and soil samples, meaning that we did not find the same trends between the sites in the two matrices. This could derive from a selective plant uptake of elements from the surrounding soil.
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All faecal samples (n=94) were freeze-dried using an Alpha 1-2 LDplus for 24 hours before being homogenised using a TissueLyser II with Teflon® chambers (Qiagen, Hilden, Germany). The soil samples (n=9) were left to airdry until all the water had evaporated (which was determined when weight changes were within ± 5 % over a week). The edges of the dried samples were removed to avoid cross- or external contamination. The cores were homogenised using a cutting mill and stored in polyethylene bags. The dried, homogenised soil and faecal samples were digested in HNO3. Approximately 0.5g of faeces or 0.3g of soil was transferred to an 18mL polytetrafluoroethylene (PTFE) vial with 6.25 mL or 9 mL 50% (v/v) HNO3 acid, respectively. The samples were digested using a high-pressure microwave system (Milestone Ultraclave, EMLS, Leutkirch, Germany) for 150 minutes and thereafter diluted with ultrapure water up to 60g (faecal samples) or 110g (soil samples). Blank (ultrapure water and HNO3) samples were digested and analysed for quality assurance. High-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS, Thermo Finnigan model Element 2 instrument, Bremen, Germany) was used to identify and quantify the elemental composition of the samples. The final concentration of each element was obtained by subtracting the average of the method blank concentration of the respective element in all analysed samples. All data were analysed for normal distribution using a Shapiro-Wilk test and for equal variances using Levene's test. None of the faecal elemental data was normally distributed (a BoxCox transformation was applied to try and normalise the variables). All soil elemental data (except for Pb) and parameters (TOC and pH) fulfilled the assumptions of parametric tests. We used Mann-Whitney U and Spearman rank correlations to determine differences in elemental faecal concentrations between the two locations and to determine relationships among elements and between the elements and the distance to the ocean. A Student t-test was employed to evaluate significant differences in element concentration and soil parameters between the two locations (the Mann-Whitney U test was used for Pb). A principal component analysis (PCA) was conducted to explore the relationships among the elements and the spatial variation in the data set. The variable ocean distance was excluded from the PCA due to considerable differences between the sampling sites, which contributed significantly to the PCs and thus masked the contributions of the elements. All numerical data were normalised by centring and scaling it (using the mean and standard deviation) before performing the PCA. All statistical analysis was done using R Statistical Software (V4.2.2, R Core Team 2022).