Maternal transfer of trace elements to shark eggs and their dietary assimilation efficiencies

Dogfish (Scyliorhinus canicula) transferred trace elements (¹¹⁰Ag, ¹⁰⁹Cd, ⁵⁴Mn and ⁷⁵Se) from their diet to eggs, and their components (yolk and embryo, case and jelly) at greatly varying rates. Trace element levels in eggs showed positive linear relationships (p < 0.001; r²-0.83-0.91) with their cumulative rates of maternal ingestion over 61 days (maternal-to-egg transfer rates: mTFs). These mTFs varied by 2-3 orders of magnitude, with ⁵⁴Mn > ¹¹⁰Ag > ⁷⁵Se > ¹⁰⁹Cd, and their range encompassed those previously measured for ⁶⁰Co, ⁶⁵Zn, ²⁴¹Am and ¹³⁴Cs. For six of the eight trace elements, their mTFs were significantly influenced (p < 0.05; r² = 0.72) by both their dietary assimilation efficiency and their location within the egg (case). In contrast, both ¹¹⁰Ag and ⁵⁴Mn greatly exceeded the mTFs predicted by this multiple regression model by one and 2-3 orders of magnitude, respectively, and were predominantly transferred to the egg case. Among elements, contrasting rates of transfer and percentage distributions in egg components imply differing ecotoxicological and radiological detriments to the developing embryo.