Integrative assessment of selenium speciation, biogeochemistry, and distribution in a northern coldwater ecosystem

Abstract

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.

Subcellular partitioning of metals and metalloids (As, Cd, Cu, Se and Zn) in liver and gonads of wild white suckers (Catostomus commersonii) collected downstream from a mining operation

“…As hepatic Se concentrations increased in white suckers, Se consistently increased in all subcellular fractions, the strongest increase being observed for the HDP fraction, followed by the debris+nuclei, HSP and mitochondria fractions (Figure 4). The presence of significant amounts of Se in almost every fraction, and particularly in the HDP pool, is consistent with the observation that, in vertebrates, Se is mainly found in organic forms, usually incorporated into proteins as selenoamino acids (selenocysteine, SeCys; selenomethionine, SeMet) (Janz et al, 2014(Janz et al, , 2010. Note that SeMet is not thought to confer heat-stability to proteins and thus proteins containing SeMet would be expected to report to the HDP fraction (Ponton et al, 2016).…”

Distribution of Experimentally Added Selenium in a Boreal Lake Ecosystem

“…Because Se in sediment did not appear to reach steady state after 77 d, removal of Se to sediment appears to be a slow process. However, detritivores have been shown to accumulate greater Se concentrations relative to other invertebrate types, suggesting that the sediment-detrital pathway can be an important source of Se accumulation in benthic aquatic food webs, particularly in boreal lake food webs with lower nutrients and lower lake productivity (Canton and Van Derveer 1997;Orr et al 2006;Muscatello et al 2008;Janz et al 2014). The K d values measured for sediment in the 0.12-, 1.0-, and 8.9-µg/L treatments were indeed within the range of values for lakes and reservoirs summarized by Presser and Luoma (2010) and were in general greater than those measured for rivers and creeks.…”

Selenium Interactions with Algae: Chemical Processes at Biological Uptake Sites, Bioaccumulation, and Intracellular Metabolism

“…Biogeochemical parameters, such as sediment reduction, oxidation (redox) conditions, and the presence of organic matter, can also explain some of the differences in Se accumulation among sites. Sediment total organic matter is positively correlated with surface sediment Se concentrations and the percent organic matter is positively correlated with the adsorption of weak acids (like Se(IV)) at low pH [10,37]. In fast-flowing waters, fine organic sediments that are high in organic matter and originate from dead and decaying plant or animal matter are typically removed from the system quickly.…”