Trophic transfer of Cd from natural periphyton to the grazing mayfly Centroptilum triangulifer in a life cycle test

In streams, periphyton biofilms are important sinks for trace metals such as cadmium and are primary food sources of many invertebrate consumers. To study Cd trophic transfer, we produced differentially contaminated diets by exposing natural periphyton to environmentally relevant dissolved Cd ranging from 0 to 10 μg L⁻¹ for 6-7 days using a radiotracer approach. On average, periphyton grown during three different seasons bioconcentrated Cd similarly - approximately 1315 (±442) -fold above dissolved concentrations. However, mayfly larvae (Centroptilum triangulifer) raised on these differentially contaminated diets (first instar through adulthood) had significantly higher trophic transfer factors from periphyton grown in Aug and Nov 2008 (4.30 ± 1.55) than from periphyton grown in Jan 2009 (0.85 ± 0.21). This Cd bioaccumulation difference is only partially explained by apparent food quality and subsequent growth differences. Taken together, these results suggest that primary producers at the base of food webs drive metal bioaccumulation by invertebrate grazers.