Hair sampling location in harbor seals (Phoca vitulina) affects selenium and mercury concentrations: Implications for study design of trace element determination in pinnipeds

Hair is used to determine trace elements exposure and status of pinnipeds because it is an excretory route for many elements and can be collected non-lethally. Despite increased use, there have been few studies on how sampling designs and procedures (e.g., hair type, collection site) affect results. The objective of this study was to determine whether concentrations of an essential (selenium; Se) and non-essential element (mercury; Hg) differed between hair samples collected from two body locations on harbor seals (Phoca vitulina). Concentrations of Se and total Hg (THg) differed between mid-dorsal midline and neck samples, and although the absolute differences were relatively small (Δabsolute Se = 0.69 μg g−1, Δabsolute THg = 2.86 μg g−1), the relative differences were large (Δrelative Se = 49%, Δrelative THg = 17%). These differences highlight the need to standardize the collection site for trace element determination in pinnipeds.