Integrative assessment of selenium speciation, biogeochemistry, and distribution in a northern coldwater ecosystem
Authors: Janz David M , Liber Karsten , Pickering Ingrid J , Wiramanaden Cheryl IE , Weech Shari A , Gallego-Gallegos Maria , Driessnack Melissa K , Franz Eric D , Goertzen Meghan M , Phibbs James , Tse Justin J , Himbeault Kevin T , Robertson Erin L , Burnett-Seidel Charlene , England Kent , Gent Anne 
Published: July 2014

For the past decade, considerable research has been conducted at a series of small lakes receiving treated liquid effluent containing elevated selenium (Se) from the Key Lake uranium (U) milling operation in northern Saskatchewan, Canada. Several studies related to this site, including field collections of water, sediment, and biota (biofilm and/or periphyton, invertebrates, fish, and birds), semicontrolled mesocosm and in situ caging studies, and controlled laboratory experiments have recently been published. The aim of the present investigation was to compile the site-specific information obtained from this multidisciplinary research into an integrative perspective regarding the influence of Se speciation on biogeochemical cycling and food web transfer of Se in coldwater ecosystems. Within lakes, approximately 50% of sediment Se was in the form of elemental Se, although this ranged from 0% to 81% among samples. This spatial variation in elemental Se was positively correlated with finer particles (less sand) and percent total organic C content in sediments. Other Se species detected in sediments included selenosulfides, selenite, and inorganic metal selenides. In contrast, the major Se form in sediment-associated biofilm and/or periphyton was an organoselenium species modeled as selenomethionine (SeMet), illustrating the critical importance of this matrix in biotransformation of inorganic Se to organoselenium compounds and subsequent trophic transfer to benthic invertebrates at the base of the food web. Detritus displayed a Se speciation profile intermediate between sediment and biofilm, with both elemental Se and SeMet present. In benthic detritivore (chironomid) larvae and emergent adults, and in foraging and predatory fishes, SeMet was the dominant Se species. The proportion of total Se present as a SeMet-like species displayed a direct nonlinear relationship with increasing whole-body Se in invertebrates and fishes, plateauing at approximately 70% to 80% of total Se as a SeMet-like species. In fish collected from reference lakes, a selenocystine-like species was the major Se species detected. Similar Se speciation profiles were observed using 21-day mesocosm and in situ caging studies with native small-bodied fishes, illustrating the efficient bioaccumulation of Se and use of these semicontrolled approaches for future research. A simplified conceptual model illustrating changes in Se speciation through abiotic and biotic components of lakes was developed, which is likely applicable to a wide range of northern industrial sites receiving elevated Se loading into aquatic ecosystems. Integr Environ Assess Manag 2014;10:543–554. © 2014 SETAC

Key Points

Selenium speciation profiles were determined in biotic and abiotic compartments (whole sediments, detritus, periphyton and/or biofilm, benthic invertebrates, emergent insects, forage fish, and predatory fish) of a coldwater aquatic ecosystem using synchrotron-based X-ray absorption spectroscopy (XAS) Integrating the results of 10 previously published articles, this case study provides broader perspectives on the influence of Se speciation on biogeochemical cycling and food web transfer of Se in northern coldwater aquatic ecosystems Periphyton and/or biofilm at the sediment-water interface was the key driver of Se biotransformation to organoselenium species and subsequent trophic transfer to benthic invertebrates and fishes In benthic invertebrates and fishes, Se speciation profiles shifted from selenocystine-like species to selenomethionine-like species in a concentration-dependent manner, plateauing at approximately 70% to 80% of total Se as selenomethionine-like species