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

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.

Swim performance and energy homeostasis in spottail shiner (Notropis hudsonius) collected downstream of a uranium mill.

The Key Lake uranium milling operation (Saskatchewan, Canada) releases complex effluent into the local watershed. The objective of the current study was to investigate whether fish from an effluent-receiving waterbody exhibited differences in swimming performance and energy homeostasis compared to fish from a local reference site. Juvenile spottail shiner (Notropis hudsonius) were collected from a lake downstream of the uranium mill, and compared to fish collected from a nearby reference lake. Critical swimming speed (U(crit); fatigue velocity), tail beat frequency, and tail amplitude did not differ significantly when comparing fish collected from the exposure lake and reference lake. Captured shiner used in swim tests were considered fatigued, and metabolic endpoints were compared between this group and non-fatigued fish, which were treated similarly but not subjected to swim tests. In both non-fatigued and fatigued shiner, liver glycogen was significantly greater in fish collected from the exposure lake compared to the reference lake. However, it is unclear if this effect, and others related to condition, were the result of contaminant exposure or other environmental factors. While there were no differences in plasma lactate, hematocrit or liver triglycerides in non-fatigued fish between sites, only fatigued reference fish had increased lactate and hematocrit and decreased triglycerides. In non-fatigued fish, plasma glucose did not significantly differ between sites, but significantly decreased after swimming only in fish from the exposure lake. In summary, shiner from the exposure site demonstrated similar swim endurance and possessed greater energy stores despite metabolic alterations compared to shiner from the reference site. Therefore, because fish collected downstream of the uranium mill operation had similar swimming ability as fish from the reference lake, U(crit) test results presented here may not reflect or be indicative of metabolic effects of complex effluent exposure.

Swimming performance and energy homeostasis in juvenile laboratory raised fathead minnow (Pimephales promelas) exposed to uranium mill effluent.

Research at the Key Lake uranium mill (Saskatchewan, Canada) suggests effluent discharged from the mill affects energy stores of resident fish, but the mechanisms by which energy homeostasis is affected and the subsequent effects on swimming performance are unknown. In the present study larvae were collected from laboratory raised adult fathead minnow (Pimephales promelas) exposed to 5% diluted uranium mill effluent or control (dechlorinated municipal) water, and reared in the same treatments to 60 days post hatch (dph). Critical swimming speed (U(crit)) was significantly lower in effluent exposed 60 dph fish compared to control fish. Fish used in tests were considered fatigued and compared to fish without swim testing (non-fatigued). There were no differences in whole body glycogen or triglyceride concentrations between effluent exposed versus control fish. However, fatigued fish from both treatments had significantly lower triglycerides, but not glycogen, compared to non-fatigued fish from the same treatment. Whole body ß-hydroxyacyl coenzymeA dehydrogenase activity was similar in fish from both treatments, but citrate synthase activity was significantly lower in effluent exposed fish. Our results suggest uranium mill effluent exposure in the laboratory affects aerobic energy metabolism and swimming performance in juvenile fathead minnow, which could affect wild fish survivability.

Expression, purification, crystallization and preliminary X-ray crystallographic studies of Deinococcus radiodurans thioredoxin reductase.

Deinococcus radiodurans, a Gram-positive bacterium capable of withstanding extreme ionizing radiation, contains two thioredoxins (Trx and Trx1) and a single thioredoxin reductase (TrxR) as part of its response to oxidative stress. Thioredoxin reductase is a member of the family of pyridine nucleotide-disulfide oxidoreductase flavoenzymes. Recombinant D. radiodurans TrxR with a His tag at the N-terminus was expressed in Escherichia coli and purified by metal-affinity chromatography. The protein was crystallized using the sitting-drop vapour-diffusion method in the presence of 35% PEG 4000, 0.2 M ammonium acetate and citric acid buffer pH 5.1 at 293 K. X-ray diffraction data were collected on a cryocooled crystal to a resolution of 1.9 angstroms using a synchrotron-radiation source. The space group was determined to be P3(2)21, with unit-cell parameters a = b = 84.33, c = 159.88 angstroms. The structure of the enzyme has been solved by molecular-replacement methods and structure refinement is in progress.