Selenium Bioaccumulation and Maternal Transfer in the Mayfly Centroptilum triangulifer in a Life-Cycle, Periphyton-Biofilm Trophic Assay JUSTIN M. CONLEY,* ,† DAVID H. FUNK, ‡ AND DAVID B. BUCHWALTER † Department of Environmental and Molecular Toxicology, North Carolina State University, Raleigh, North Carolina 27695, and Stroud Water Research Center, Avondale, Pennsylvania 19311 Received June 4, 2009. Revised manuscript received August 20, 2009. Accepted August 28, 2009. Selenium contamination in aquatic ecosystems provides management challenges because bioaccumulation in animals is largely a function of dietary exposure, whereas regulatory entities have traditionally focused on direct water to organism interactions. Selenium is known to be readily absorbed by primary producers and can potentially biomagnify in food webs and elicit adverse effects in higher trophic levels. However, selenium bioaccumulation in the invertebrate prey of many predatory animals is poorly understood. Here, we used 75 Se (as selenite) as a radiotracer to characterize Se bioaccumulation into natural periphyton bioﬁlms and subsequent dietary and maternal transfer in the mayﬂy, Centroptilum triangulifer, in a life-cycle assay. On average periphyton bioﬁlms bioconcentrated selenium 1113 ( (430)-fold following 7-9 days of exposure to a range of environmentally relevant dissolved concentrations (2.4-13.9 μgL -1 ). Mayﬂies grown to adulthood on these diets further biomagniﬁed Se with trophic transfer factors averaging 2.2 ( (0.4)-fold in postpartum maternal tissues. Adults then transferred 46.5 ( (8.8) % of their body burdens to eggs with an observed reduction in fecundity for mayﬂies fed on diets greater than ∼11 μgg -1 . These results suggest that at environmentally feasible dietary Se concentrations insects are potentially affected by Se exposure, and that the current presumption that insects are simply conduits of Se to higher trophic levels is inaccurate. Introduction Selenium is a nonmetal trace element that exhibits a narrow window between essential and toxic concentrations (1). Selenium can be an important contaminant in aquatic environments as a result of human activities, particularly those involving mining and burning of coal for power generation (2-9). Despite historic, high proﬁle examples of Se causing signiﬁcant ecological damage (e.g., Kesterson Reservoir, CA (10, 11), Belews Lake, NC 12, 13), surprisingly little data are available for Se dynamics in lotic ecosystems and the invertebrates therein. In lotic systems insects are typically the dominant invertebrate faunal group, contribute vastly to ecological function, and serve as a major food source for stream predators (14). Therefore to understand the potential impacts of Se contamination in lotic environments, it is essential to understand the dynamics of Se movement into primary producers and subsequent transfer to insects. Two paradigms dominate current understanding of potential Se impacts in aquatic ecosystems. The ﬁrst is that diet is the predominant route of exposure for organisms in aquatic food webs (5, 15-17), with dissolved Se concentra- tions being poor predictors of bioaccumulation and toxic effects (4, 18). This understanding has prompted the U.S. Environmental Protection Agency to move toward a tissue based standard for Se (19). A second dominant paradigm is that invertebrates act primarily as conduits of Se from primary producers to higher trophic level animals (e.g., ﬁsh and birds), but themselves are not adversely affected by Se exposure (6, 20). Here we used a laboratory test system to examine Se (as selenite, [SeO 3 2- ]) enrichment in natural periphyton bioﬁlms and the subsequent transfer to the mayﬂy Centroptilum triangulifer (Ephemeroptera: Baetidae) in a life cycle assay. The use of 75 Se as a radiotracer allowed us to quantify transfers of Se from water to periphyton, from periphyton to larval mayﬂies, and from adult mayﬂies to their eggs over a wide range of dietary Se exposure concentrations. We further report on the inﬂuence of Se bioaccumulation on mayﬂy fecundity. Materials and Methods Test Animals. The mayﬂy Centroptilum triangulifer (Ephemeroptera: Baetidae) was obtained from culture at the Stroud Water Research Center (Avondale, PA). Originally described as Cloeon triangulifer by McDunnough (21), this parthenogenetic species typically inhabits marginal areas of lotic systems. Negligible ﬂow requirements make this species particularly amenable to laboratory use as a test species. C. triangulifer has previously been used in studies of temper- ature and development (22), chlordane (23), and aluminum (24). More recently C. triangulifer has been used to examine the trophic transfer of cadmium from periphyton (25). Radioactivity Measurement. All measurements of ra- dioactivity in water, periphyton, C. triangulifer adults and eggs were performed using a Perkin-Elmer Wallac Wizard 1480 automatic gamma counter (Shelton, CT). Samples were counted for 3 min and all counting errors were generally <5%. Selenium concentrations are reported incorporating appropriate corrections for radioactive decay, counting efﬁciency, and ratio of 75 Se:stable Se. Labeling Periphyton with Se. To create differentially Se contaminated mayﬂy diets, acrylic plates (6.5 × 23 × 0.15 cm) were colonized by natural periphyton bioﬁlms by allowing fresh streamwater from White Clay Creek, PA (39°51′47”N, 75°47′07”W) to ﬂow continuously over the plates in a greenhouse as described previously (25, 26). Periphyton was grown in November 2008 and January 2009 for two distinct sets of experiments. Colonization was complete when the periphyton reached a thickness of approximately 1-2 mm. At this stage, periphyton consisted primarily of diatoms with some blue-green and green algae, along with some naturally colonizing consumers (predominantly micro- and meiofauna (26)). In each study, the colonized plates were placed in 2.0 L glass bottles holding 1.8 L of American Society for Testing and Materials (ASTM) artiﬁcial soft water (48 mg L -1 NaHCO 3 , 30 mg L -1 CaSO 4 · 2H 2 O, 30 mg L -1 MgSO 4 , and 2 mg L -1 KCl, pH 7.4). The initial pilot study plates (November 2008) were * Corresponding author phone: 919-513-0661; fax: 919-515-7169; e-mail: jmconley@ncsu.edu. † North Carolina State University. ‡ Stroud Water Research Center. Environ. Sci. Technol. 2009, 43, 7952–7957 7952 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 43, NO. 20, 2009 10.1021/es9016377 CCC: $40.75  2009 American Chemical Society Published on Web 09/15/2009 Downloaded by NORTH CAROLINA STATE UNIV on October 13, 2009 | http://pubs.acs.org Publication Date (Web): September 15, 2009 | doi: 10.1021/es9016377