Karen A. Kidd Robin Stewart Robert F Bertolo Nelson J. O’Driscoll Jennifer C Thera 2022 <div id="abs0010" class="abstract author" lang="en"><div id="abssec0010"><p id="abspara0010"><span>The&nbsp;biomagnification&nbsp;of toxic&nbsp;methylmercury&nbsp;(MeHg) and selenium (Se) through aquatic food webs using nitrogen&nbsp;stable isotopes&nbsp;(δ</span>¹⁵N) varies among ecosystems but underlying mechanisms are yet unexplained. Given the strong links between MeHg and thiol-containing amino acids and proteins containing selenocysteine, our hypothesis was that cysteine content is a better predictor of MeHg and Se transfer through lake food webs than δ¹⁵N. Food web samples were collected from six lakes in Kejimkujik National Park, Nova Scotia, Canada, and the regression slopes of log MeHg or Se versus protein-bound cysteine or bulk δ¹⁵N were compared. Across all six lakes, MeHg varied by a factor of 10 among taxa and was significantly and positively related to both cysteine (R²&nbsp;=&nbsp;0.65–0.80, p&nbsp;&lt;&nbsp;0.001) and δ¹⁵N (R²&nbsp;=&nbsp;0.88–0.94, p&nbsp;&lt;&nbsp;0.001), with no among-system differences in these slopes. In contrast, total Se concentrations varied by less than a factor of 2 among taxa in four lakes and were significantly related to cysteine in only two food webs (R²&nbsp;=&nbsp;0.20 &amp; 0.37, p&nbsp;=&nbsp;0.014 &amp;&nbsp;&lt;&nbsp;0.001); however, δ¹⁵<span>N was not a predictor of Se in any lake (p&nbsp;=&nbsp;0.052–0.777). Overall, these novel results indicate that cysteine content predicts MeHg, and sometimes Se, across&nbsp;trophic levels, providing a potential mechanism for among-system differences in their biomagnification.</span></p></div></div> application/pdf 10.1016/j.envpol.2022.119936 en Elsevier Using tissue cysteine to predict the trophic transfer of methylmercury and selenium in lake food webs article