Laboratory and In situ Selenium Bioaccumulation Assessment in the Benthic Macroinvertebrates Hyalella azteca and Chironomus dilutus.

Selenium (Se) bioaccumulation and toxicity in aquatic vertebrates have been thoroughly investigated. Limited information is available on Se bioaccumulation at the base of aquatic food webs. In this study, we evaluated Se bioaccumulation in two benthic macroinvertebrates (BMI), Hyalella azteca and Chironomus dilutus raised in the laboratory and caged in-situ to a Canadian boreal lake e (i.e., McClean Lake) that receives continuous low-level inputs of Se (< 1 µg/L) from a uranium mill. Additional Se bioaccumulation assays were conducted in the laboratory with these BMI to (i) confirm field results, (ii) compare Se bioaccumulation in lab-read and native H. azteca populations and (iii) identify the major Se exposure pathway (surface water, top 1 cm and top 2-3 cm sediment layers) leading to Se bioaccumulation in H. azteca. Field and laboratory studies indicated overall comparable Se bioaccumulation and trophic transfer factors (TTFs) in co-exposed H. azteca (whole-body Se 0.9-3.1 µg/g d.w; TTFs 0.6-6.3) and C. dilutus (whole-body Se at 0.7-3.2 µg Se/g d.w.; TTFs 0.7-3.4). Native and lab-reared H. azteca populations exposed to sediment and periphyton from McClean Lake exhibited similar Se uptake and bioaccumulation (NLR, p = 0.003; 4.1 ± 0.8 µg Se/g d.w), demonstrating that lab-reared organisms are good surrogates to assess on-site Se bioaccumulation potential. The greater Se concentrations in H. azteca exposed to the top 1-3 cm sediment layer relative to waterborne exposure, corroborates the importance of the sediment-detrital pathway leading to greater Se bioaccumulation potential to higher trophic levels via BMI.

Risk assessment of glyphosate and malathion pollution and their potential impact on Oreochromis niloticus: role of organic selenium supplementation.

A field survey was conducted on five fish farms to trace glyphosate and malathion pollution with some physicochemical parameters. A precise half-life time, LC50-96h, of these agrochemicals on Oreochromis niloticus, as well as chronic exposure with organic selenium (OS) supplementation, were experimentally investigated. Oreochromis niloticus was subjected to the following: (negative control); (2 mg L-1 glyphosate); (0.5 mg L-1 malathion); (glyphosate 1.6 mg L-1 and 0.3 mg L-1 malathion); (glyphosate 2 mg L-1 and OS 0.8 g kg-1 diet); (malathion 0.5 mg L-1 and OS 0.8 g kg-1 diet) and (glyphosate 1.6 mg L-1; malathion 0.3 mg L-1 and OS 0.8 g kg-1 diet). Furthermore, data from the analyzed pond revealed a medium risk quotient (RQ) for both agrochemicals. The detected agrochemicals were related to their application, and vegetation type surrounding the farms, also their biodegradation was correlated to water pH, temperature, and salinity. Glyphosate and malathion had half-lives of 2.8 and 2.3 days and LC50-96h of 2.331 and 0.738 mg L-1, respectively. The severest nervous symptoms; increased oxidative stress markers, as well as high bacterial count in the livers and kidneys of fish challenged with Aeromonas hydrophila, were observed in the combined exposure, followed by a single exposure to malathion and then glyphosate. Organic selenium mitigated these impacts.

Comparative study of silicon and selenium to modulate chloroplast pigments levels, Hill activity, photosynthetic parameters and carbohydrate metabolism under arsenic stress in rice seedlings.

Arsenic (As) in groundwater severely harms global economic development by affecting growth and productivity of agricultural crops that causes human health risk. The comparative influence of silicon (Si) and selenium (Se) to modulate pigments levels, photosynthetic parameters using LI-6400XT Portable Photosynthesis System and carbohydrate metabolism under arsenate (As-V) stress in rice cv. MTU-1010 were evaluated. As(V) stress significantly decreased chlorophyll-a (32% on an average), chlorophyll-b (58% on an average), total chlorophyll (46% on an average), fluorescence intensity (31% on an average), carotene (39% on an average), xanthophyll (33% on an average), Hill activity (47% on an average) and the photosynthetic parameters, viz. intercellular CO2 concentration (52% on an average), net photosynthesis (54% on an average), transpiration rate (36% on an average) and stomatal conductance (38% on an average) in the test seedlings. As(V) + Si treatments enhanced the stated occurrences more than As(V) + Se treatments in rice seedlings. Sugar contents, viz. reducing (85% on an average) and non-reducing sugar (61% on an average), were increased, but starch content (57% on an average) was decreased in only As(V)-treated rice seedlings. The activities of carbohydrate metabolizing enzymes were increased, while sucrose synthase activity was decreased due to As(V) toxicity in the test seedlings. Co-application of Si and As(V) as well as Se and As(V) showed ameliorative effects on sugar and starch contents along with the activities of carbohydrate metabolizing enzymes, but more potential effect was observed under combined application of Si and As(V) in rice seedlings. Thus, it is an important purpose of this paper to compare the ability of Se and Si to alleviate As(V) toxicity in rice seedlings which will be an effective approach to develop possible strategies in As-contaminated agricultural soil to improve normal growth and productivity of rice plants.

Assessment of selenium spatial distribution using µ-XFR in cowpea (Vigna unguiculata (L.) Walp.) plants: Integration of physiological and biochemical responses.

Low concentrations of selenium (Se) are beneficial for plant growth. Foliar Se application at high concentrations is toxic to plants due to the formation of reactive oxygen species (ROS). This study characterized Se toxicity symptoms using X-ray fluorescence (XRF) technique in response to foliar Se application in cowpea plants. Five Se concentrations (0, 10, 25, 50, 100 e 150 g ha-1) were sprayed on leaves as sodium selenate. The visual symptoms of Se toxicity in cowpea leaves were separated into two stages: I) necrotic points with an irregular distribution and internerval chlorosis at the leaf limb border (50-100 g ha-1); II) total chlorosis with the formation of dark brown necrotic lesions (150 g ha-1). Foliar Se application at 50 g ha-1 increased photosynthetic pigments and yield. Ultrastructural analyses showed that Se foliar application above 50 g ha-1 disarranged the upper epidermis of cowpea leaves. Furthermore, Se application above 100 g ha-1 significantly increased the hydrogen peroxide concentration and lipid peroxidation inducing necrotic leaf lesions. Mapping of the elements in leaves using the XRF revealed high Se intensity, specifically in leaf necrotic lesions accompanied by calcium (Ca) as a possible attenuating mechanism of plant stress. The distribution of Se intensities in the seeds was homogeneous, without specific accumulation sites. Phosphorus (P) and sulfur (S) were found primarily located in the embryonic region. Understanding the factors involved in Se accumulation and its interaction with Ca support new preventive measurement technologies to prevent Se toxicity in plants.

Bioaccumulation of mercury and selenium in tissues of the mesopelagic fish Pacific hake (Merluccius productus) from the northern Gulf of California and the risk assessment on human health.

With the aim of evaluating health risk to hake consumers, mercury and selenium were measured in muscle, liver, gonads, kidney, and gills of 62 specimens of Merluccius productus from northern Gulf of California. Means ± confidence interval (95% confidence level) concentrations (mg kg-1 wet weight) of Hg in tissues were: gonads (1.01 ± 0.25) > muscle (0.44 ± 0.06) > gills (0.29 ± 0.04) > kidneys (0.20 ± 0.07) > liver (0.02 ± 0.004). No significant differences between sexes were found for Hg. The distribution of mean concentrations of Se (mg kg-1 wet weight) were: kidneys (4.61 ± 1.27) > liver (1.66 ± 0.22) > gonads (1.66 ± 0.75) > gills (0.86 ± 0.04) > muscle (0.40 ± 0.09). Se in gonads showed a significant difference between sex (females > males). Positive significant correlations with total length (p < 0.05) and total weight (p < 0.05) were found in the same tissue for both morphological variables: Hg in muscle, Se in muscle and Se in liver. An excess of Se over Hg (molar ratio Se:Hg > 1) was found in all tissues. The Hazard Quotient health risk index was evaluated for humans that consume muscle and gonads. The recommended Hg safe intake for adults and children were 110.0 and 33.0 g week-1, respectively for muscle; for gonads weekly consumption portions of 35.0 and 14.0 g for adults and children represent no Hg risk. There was no risk of exposure to Se.

Selenium and mercury in dolphinfish (Coryphaena hippurus) from the Gulf of California: inter-annual variations and selenium health benefit value.

With the aim of determining the benefit from consumption of dolphinfish Coryphaena hippurus from La Paz and Cabo San Lucas in the southern area of the Gulf of California, mercury (Hg) and selenium (Se) were measured in liver and muscle of specimens (n = 362) collected between 2006 and 2013. Mean levels of Hg in muscle (0.61 µg g-1) and liver (0.42 µg g-1) of all individuals from La Paz were significantly higher (p < 0.05) than in fish from Cabo San Lucas; in the case of Se, mean concentrations in liver (1.54 µg g-1) of all individuals from La Paz were significantly higher (p < 0.05) than in fish from Cabo San Lucas. Hg levels in muscle were positively and significantly (p < 0.05) correlated with fork length and weight of fish; in liver, Hg and Se were significantly (p < 0.05) correlated with fork length and weight of specimens. Levels of Hg and Se in muscle and liver among years varied significantly (p < 0.05); although there was not a defined pattern of temporal fluctuations for both elements, the lowest Hg levels occurred in 2009 when surface water temperatures were the highest for the sampled years. With respect to the Se health benefit value (HBVSe), results were positive and above the unit in all cases; it implies that consumption of dolphinfish in the southern Gulf of California is beneficial.

Bioavailability Assessment of Copper, Iron, Manganese, Molybdenum, Selenium, and Zinc from Selenium-Enriched Lettuce.

Cu, Fe, Mn, Mo, Selenium (Se), and Zn bioavailability from selenate- and selenite-enriched lettuce plants was studied by in vitro gastrointestinal digestion followed by an assay with Caco-2 cells. The plants were cultivated in the absence and presence of two concentrations (25 and 40 µmol/L of Se). After 28 days of cultivation, the plants were harvested, dried, and evaluated regarding the total concentration, bioaccessibility, and bioavailability of the analytes. The results showed that biofortification with selenate leads to higher Se absorption by the plant than biofortification with selenite. For the other nutrients, Mo showed high accumulation in the plants of selenate assays, and the presence of any Se species led to a reduction of the plant uptake of Cu and Fe. The accumulation of Zn and Mn was not strongly influenced by the presence of any Se species. The bioaccessibility values were approximately 71%, 10%, 52%, 84%, 71%, and 86% for Cu, Fe, Mn, Mo, Se, and Zn, respectively, and the contribution of the biofortified lettuce to the ingestion of these minerals is very small (except for Se and Mo). Due to the low concentrations of elements from digested plants, it was not possible to estimate the bioavailability for some elements, and for Mo and Zn, the values are below 6.9% and 3.4% of the total concentration, respectively. For Se, the bioavailability was greater for selenite-enriched than selenate-enriched plants (22% and 6.0%, respectively), because selenite is biotransformed by the plant to organic forms that are better assimilated by the cells.

Arsenic, selenium, and metals in a commercial and vulnerable fish from southwestern Atlantic estuaries: distribution in water and tissues and public health risk assessment.

The anadromous catfish Genidens barbus is a vulnerable and economically important species from the Southwestern Atlantic Ocean. Concentrations of As, Co, Fe, Se, and Zn were determined in water and muscle, gill, and liver of catfish from two southwestern Atlantic estuaries (Brazil and Argentina) and health risk via fish consumption was evaluated. High spatial variability was observed in the metals, As, and Se distribution for both estuaries. Considering all tissues, element concentrations (mg/kg, wet weight) were As = 0.41-23.50, Co = 0.01-2.9, Fe = 2.08-773, Se = 0.15-10.7, and Zn = 3.97-2808). Most of the trace elements tended to be higher in Brazil than in Argentina, except for Co, Fe, Se, and Zn in liver and Fe and Co in muscle and gill, respectively. Arsenic accumulation order was muscle > liver ≥ gill. Only As (muscle) was above the maximum recommended by international guidelines at both estuaries. The target hazard quotient ranged from 0.10 to 1.58, suggesting that people may experience significant health risks through catfish consumption. Supposing that the inorganic/toxic As ranged between 1 and 20% of the total, the recommended maximum intakes per capita bases were 6.1-95 and 8.4-138 kg/year (wet weight) for Brazil and Argentina, respectively. Carcinogenic risk for As intake was within the acceptable range but close to the recommended limit (> 10-4). These results highlights the importance of quantifying the As species in catfish muscle in order to generate more reliable risk estimates.

Assessment of selenium bioaccumulation in lactic acid bacteria.

Selenium is an essential micronutrient for living beings, as it helps to maintain the normal physiological functions of the organism. The numerous discoveries involving the importance of this element to the health of human beings have fostered interest in research to develop enriched and functional foods. The present study evaluated the potential for bacterial strains of Enterococcus faecalis (CH121 and CH124), Lactobacillus parabuchneri (ML4), Lactobacillus paracasei (ML13, ML33, CH135, and CH139), and Lactobacillus plantarum (CH131) to bioaccumulate Se in their biomass by adding different concentrations of sodium selenite (30 to 200 mg/L) to the culture medium. Quantification of Se with UV and visible molecular absorption spectroscopy showed that the investigated bacteria were able to bioaccumulate this micromineral into their biomass. Two of the L. paracasei strains (ML13 and CH135) bioaccumulated the highest Se concentrations (38.1 ± 1.7 mg/g and 40.7 ± 1.1 mg/g, respectively) after culture in the presence of 150 mg/L of Se. This bioaccumulation potential has applications in the development of dairy products and may be an alternative Se source in the diets of humans and other animals.

German Consumers' Attitude towards Selenium-Biofortified Apples and Acceptance of Related Nutrition and Health Claims.

The present study investigates consumers' acceptance of Se-biofortified apples, as well as Se health and nutrition claims that have been approved by the European Commission. Despite indications that such statements are more likely to be accepted if the carrier product itself has a healthy image, unprocessed fruits biofortified with Se have not been investigated in this context yet. Apples as the most frequently-consumed type of fresh fruit in Germany may offer the potential to improve the Se status of consumers when the produce is enriched with Se. Therefore, an online survey of 356 German adults was conducted to analyze different aspects that could affect the perception of and preference for the proposed product concept by consumers. The findings indicate a moderate acceptance of Se-biofortified apples, as well as of Se health and nutrition claims among the participants. Additional information about beneficial health effects of Se had a significant impact on consumer acceptance. People who regularly eat convenience food and prefer to buy apples at supermarkets were particularly attracted by the product idea. In conclusion, the results of the study indicate good prospects for a successful introduction of Se-rich apples in the German food market, if the produce is advertised with approved health and nutrition claims.

Assessment of antioxidative and selenium status by seleno-dependent glutathione peroxidase activity in different blood fractions using a pig model: issues for clinical nutrition and research.

Blood seleno-dependent glutathione peroxidase (SeGPX) activity is widely used as a metabolic indicator of systemic antioxidative status despite inconsistent responses in the literature. This study aimed to compare SeGPX activity profiles in different blood fractions, expressed with different reference units, and assess their impact on interpretation of results. Two studies on selenium (Se) metabolism in gilts, including long-term and peri-oestrus SeGPX activity profiles, were submitted to analysis of variance with double repeated measures, after data set standardization. Differences between studies were experimental period (three post-pubertal oestrus or five post-pubertal oestrus +30 days of gestation) and sample type (whole blood or blood plasma). No difference was observed between whole-blood long-term profiles (three oestrus) for SeGPX activity/mg haemoglobin (SeGPXhb) vs. SeGPX activity/ml whole blood (SeGPXwb; p = 0.29). No long-term difference was observed in whole blood between profiles according to dietary Se provision (basal and dietary Se-supplemented groups; p ≥ 0.12). Blood plasma long-term profiles (five oestrus + 30 days gestation) for SeGPX/mg blood plasma protein (SeGPXpro) were different from SeGPX/ml blood plasma (SeGPXpla) according or not to Se provision (p ≤ 0.007 and p < 0.001 respectively). However, regardless of Se provision (p ≥ 0.80), when excluding gestation from the model, blood plasma profiles were similar. During the peri-oestrus period (day -4 to +3), regardless of Se provision, SeGPX activity profiles differed according to reference units in both studies (p < 0.001). However, considering Se provision, similar profiles were observed in whole blood and blood plasma (p ≥ 0.27) for basal Se groups, whereas in Se-supplemented groups they differed for both sample types (p ≤ 0.02). In conclusion, reference units influence interpretation of SeGPX activity according to physiological state. During oxidative stress periods, this effect depends upon dietary Se provision.

Selenium uptake and assessment of the biochemical changes in Arthrospira (Spirulina) platensis biomass during the synthesis of selenium nanoparticles.

The process of selenium uptake by biomass of the cyanobacterium Arthrospira (Spirulina) platensis was investigated by neutron activation analysis at different selenium concentrations in solution and at different contact times. Experimental data showed good fit with the Freundlich adsorption isotherm model, with a regression coefficient value of 0.99. In terms of absorption dependence on time, the maximal selenium content was adsorbed in the first 5 min of interaction without significant further changes. It was also found that A. platensis biomass forms spherical selenium nanoparticles. Biochemical analysis was used to assess the changes in the main components of spirulina biomass (proteins, lipids, carbohydrates, and phycobilin) during nanoparticle formation.

An approach to assessment of Keshan disease elimination at the township level.

BACKGROUND: The aim of this study was to pilot a method of a small-scale survey for the assessment of Keshan disease (KD) elimination at township level. METHODS: The prevalence of chronic KD was obtained by case-searching the whole population. The endemic village with the highest prevalence of chronic KD was selected as the key village for the survey of latent KD prevalence rate among permanent residents. The selenium levels in the head hair of individuals in the key village was measured. The professionals of the department of endemic disease control, the township and village doctors were surveyed by pre-designed questionnaire survey for KD interventions. RESULTS: We conducted this study in 2013. Yuanbao township had a population of 16 487 people and 14 862 permanent residents. There were no acute or subacute KD cases in the previous 5 years. The prevalence rate of chronic KD and natural chronic KD were 6.7/10 000 and 3.4/10 000 respectively. The prevalence rate of latent KD was 250.6/10 000, higher than the elimination criterion. The head hair selenium levels were 0.23±0.18 mg/kg. CONCLUSIONS: The small-scale survey methodology for assessing KD elimination at township level was feasible. KD among the people living in Yuanbao township has not been eliminated.

Global assessment of cadmium concentrations in the skin of free-ranging sperm whales (Physeter macrocephalus).

Cadmium is a non-essential, toxic metal found accumulated in the organs of stranded cetaceans. Currently, there is no baseline cadmium concentration reported in a free-ranging, pelagic cetacean. The aim was to determine cadmium concentrations in the skin of free-ranging sperm whales (n=340) collected from 16 regions around the world during the voyage of the Odyssey (2000-2005) considering region, gender, and age in males. Cadmium was detected in 81% of skin biopsies with a mean of 0.3±0.04µg/g ww (0.02 to 12.4µg/g ww). These concentrations were higher than reported in literature in toothed whale skin (0.002-0.1µg/g ww). Concentrations by region were significantly different (p<0.0001) with the highest mean in Maldives and the Sea of Cortez (0.8 and 0.6µg/g ww, respectively). There was no significant difference in cadmium concentration by gender (p=0.42). Cadmium is known to have a long biological half-life, and cadmium concentrations in males were significantly higher in adults with a mean of 0.3µg/g ww compared to subadults with 0.2µg/g ww (p=0.03). Selenium, an element that binds to cadmium inhibiting its toxicity, had a moderately positive correlation with cadmium (r=0.41). Mercury, a toxic metal that positively correlates with cadmium in cetacean tissue, had a weakly positive relationship (r=0.20). The regional baselines reported in this study may be used to develop residue criteria for prediction of toxicological risk in sperm whale skin. Additionally, this study shows the extent of cadmium exposure in a pelagic cetacean that has global distribution.

Analysis of mercury and methylmercury concentrations, and selenium:mercury molar ratios for a toxicological assessment of sperm whales (Physeter macrocephalus) in the most recent stranding event along the Adriatic coast (Southern Italy, Mediterranean Sea).

Mass stranding of sperm whales (Physeter macrocephalus) is a rare event in the Mediterranean Sea. In September 2014, a pod of seven sperm whales became stranded along the Adriatic coast of Southern Italy. This is the seventh occurrence of this type since 1555 in this sea basin. Total concentrations of mercury (T-Hg), methylmercury (MeHg) and selenium (Se) were measured from brain, muscle, liver and kidney of three female sperm whales, which died in this event. Analyses showed considerable, age-dependent variations in Hg and Se concentrations in the different organs. The contamination levels of T-Hg in the liver (up to 200 mg kg(-1)) and brain (up to 21 mg kg(-1)) samples were markedly higher than those in the kidney and muscle samples. The liver and brain also showed the highest Se levels. Se:Hg molar ratios ⩾1 were observed in all the organs of the three sperm whales, suggesting that Se could protect the animals from Hg toxicity. The risk of Hg-associated neurotoxicity was assessed by comparing our values to thresholds set for neurotoxicity in mammals, and the role of Se in the detoxification process of T-Hg/MeHg is discussed herein.

Assessment of selenium and mercury in biological samples of normal and night blindness children of age groups (3-7) and (8-12) years.

The causes of night blindness in children are multifactorial and particular consideration has been given to childhood nutritional deficiency, which is the most common problem found in underdeveloped countries. Such deficiency can result in physiological and pathological processes that in turn influence biological sample composition. This study was designed to compare the levels of selenium (Se) and mercury (Hg) in scalp hair, blood, and urine of night blindness children age ranged (3-7) and (8-12) years of both genders, comparing them to sex- and age-matched controls. A microwave-assisted wet acid digestion procedure was developed as a sample pretreatment for the determination of Se and Hg in biological samples of night blindness children. The proposed method was validated by using conventional wet digestion and certified reference samples of hair, blood, and urine. The Se and Hg in biological samples were measured by electrothermal atomic absorption spectrometry and cold vapor atomic absorption spectrometry, prior to microwave acid digestion, respectively. The concentration of Se was decreased in scalp hair and blood samples of male and female night blindness children while Hg was higher in all biological samples as compared to referent subjects. The Se concentration was inversely associated with the risk of night blindness in both genders. These results add to an increasing body of evidence that Se is a protecting element for night blindness. These data present guidance to clinicians and other professional investigating deficiency of essential micronutrients in biological samples (scalp hair and blood) of night blindness children.

[Effects of sulfur on transformation of selenium in soil and uptake of selenium in rape].

The high-quality, high-yield rape (Brassica napus L. cv. Xiangnongyou 571) was chosen as the experimental material to undergo seedling stage soil cultivation and solution cultivation. This study was aimed to investigate the effects of sulfur (S) on the fraction and species of amend selenium (Se) in soil by applying S fertilizer, and to reveal the mechanism through which S controls the Se uptake of rape. The results showed that applications of both Se at 5 mg.kg-1 and S at 150 mg.kg-1 could provide some boost to rape growth, however such boost was unremarkable; S application could significantly reduce Se content in shoots and roots by as much as 64. 0% and 39. 1% , respectively; S application could significantly decrease the pH value and increase the organic matter content by as much as 0. 65 units and 1.76 g.kg-1 , respectively; S application could significantly decrease soluble Se and Fe/Mn oxide-bound Se, and significantly increase organic matter-bound Se, however, there was no remarkable effect on exchangeable and residual Se. S could significantly decrease the content of Se(IV) in the soluble Se and significantly increase the content of Se(IV) in the exchangeable Se, with remarkable decrease in Se(VI) content in both fractions, and no remarkable effect on Se(II). S had a profound effect on the uptake of Se by rape seedlings when Se( IV) and Se( VI) were applied. The Se contents in shoot and root of the Se( VI)-treated rape were 7.3 and 3.2 times respectively as high as that of the Se( IV)-treated rape, while with a S rate of 2 mmolL-1, their Se contents were lower than 32.6% and 8.7% of that of the Se(IV)-treated rape. In conclusion, in addition to improving crop growth, appropriate amount of S fertilizer could also reduce soil pH and increase organic content, causing available Se in soil to be Fe/Mn oxide-bound and organic matter-bound, and retarding its transformation to Se( VI), thus reducing Se uptake by rape. This has significant value for regulation of Se content in crops from Se-rich regions, ensuring food quality and safety, benefiting the long-term use of soil Se resources and regional economic development.

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.

Assessment of mercury and selenium tissular concentrations and total mercury body burden in 6 Steller sea lion pups from the Aleutian Islands.

Concentrations of total mercury ([THg]) and selenium ([TSe]) were measured in several tissue compartments in Steller sea lion (Eumetopias jubatus) pups; in addition we determined specific compartment and body burdens of THg. Compartmental and body burdens were calculated by multiplying specific compartment fresh weight by the [THg] (summing compartment burdens equals body burden). In all 6 pup tissue sets (1) highest [THg] was in hair, (2) lowest [THg] was in bone, and (3) pelt, muscle and liver burdens contributed the top three highest percentages of THg body burden. In 5 of 6 pups the Se:Hg molar ratios among compartments ranged from 0.9 to 43.0. The pup with the highest hair [THg] had Se:Hg molar ratios in 9 of 14 compartments that were ⩽ 0.7 potentially indicating an inadequate [TSe] relative to [THg].

An in situ assessment of selenium bioaccumulation from water-, sediment-, and dietary-exposure pathways using caged Chironomus dilutus larvae.

An in situ caging study was conducted downstream of a metal mine in northern Canada to determine the significance of surface water versus sediment exposure on selenium (Se) bioaccumulation in the benthic invertebrate Chironomus dilutus. Laboratory-reared C. dilutus larvae were exposed to either site-specific whole-sediment and surface water or surface water only for 10 d at sites with differing sediment and Se characteristics. Results showed elevated whole-body Se concentrations in C. dilutus larvae when exposed to sediment and water, compared with larvae exposed to Se in the surface water only at concentrations ranging from <1 µg Se/L to 12 µg Se/L. In response to these findings, a second in situ experiment was conducted to investigate the importance of dietary Se (biofilm and detritus) versus whole-sediment-exposure pathways. Larvae exposed to sediment detritus had the highest Se concentrations after 10 d of exposure (15.6 ± 1.9 µg/g dry wt) compared with larvae exposed to whole-sediment (12.9 ± 1.7 µg/g dry wt) or biofilm (9.9 ± 1.6 µg/g dry wt). Detritus and biofilm appear to be enriched sources of organic Se, which are more bioaccumulative than inorganic Se. Midge larvae from the reference treatment contained elevated concentrations of diselenides (i.e., selenocystine), while larvae from the biofilm treatment had the highest concentrations of selenomethionine-like compounds, which may be a biomarker of elevated Se exposures derived from anthropogenic sources. Whenever possible, Se concentrations in the organic fraction of sediment should be measured separately from whole-sediment Se and used for more accurate ecological risk assessments of potential Se impacts on aquatic ecosystems.