Detection of Selenocyanate in Biological Samples by HPLC with Fluorescence Detection Using König Reaction.

We developed a simple and sensitive HPLC method for the determination of selenocyanate (SeCN-). The König reaction, which is generally used for the determination of cyanide and thiocyanate, was applied for the post-column detection, and using barbituric acid as a fluorogenic reagent made it possible to detect SeCN- with high sensitivity. The limits of detection (LOD) and quantification (LOQ) were 73.5 fmol and 245.1 fmol, respectively. Subsequently, the amounts of SeCN- in human blood and in cultured cell samples were analyzed, and no SeCN- was detected in human whole blood. Interestingly, we have found that some of the spiked SeCN- decomposed to cyanide in human whole blood. Ascorbic acid suppressed the decomposition of SeCN- to cyanide by reducing the ferric ion, which is typically involved in SeCN- decomposition. Then, SeCN- was detected in cultured HEK293 cells exposed to selenite. The established HPLC method with fluorescence detection of SeCN- is useful for investigating small amounts of SeCN- in biological samples.

Identification of a novel selenium-containing compound, selenoneine, as the predominant chemical form of organic selenium in the blood of bluefin tuna.

A novel selenium-containing compound having a selenium atom in the imidazole ring, 2-selenyl-N(alpha),N(alpha),N(alpha)-trimethyl-L-histidine, 3-(2-hydroseleno-1H-imidazol-5-yl)-2-(trimethylammonio)propanoate, was identified from the blood and other tissues of the bluefin tuna, Thunnus orientalis. The selenium-containing compound was purified from the tuna blood in several chromatographic steps. High resolution mass spectrometry and nuclear magnetic resonance spectroscopy showed that the exact mass of the [M+H](+) ion of the compound was 533.0562 and the molecular formula was C(18)H(29)N(6)O(4)Se(2). Its gross structure was assigned as the oxidized dimeric form of an ergothioneine selenium analog in which the sulfur of ergothioneine is replaced by selenium. Therefore, we named this novel selenium-containing compound "selenoneine." By speciation analysis of organic selenium compounds using liquid chromatography inductively coupled plasma mass spectrometry, selenoneine was found widely distributed in various tissues of the tuna, with the highest concentration in blood; mackerel blood contained similar levels. Selenoneine was measurable at 2-4 orders of magnitude lower concentration in a limited set of tissues from squid, tilapia, pig, and chicken. Quantitatively, selenoneine is the predominant form of organic selenium in tuna tissues.

Simultaneous analysis of mercury and selenium species including chiral forms of selenomethionine in human urine and serum by HPLC column-switching coupled to ICP-MS.

The simultaneous speciation of elements is of great concern, especially in the study of the interactions of species in living organisms. Here we report a method based on the coupling of HPLC-ICP-MS that is capable of separating and analyzing different selenium and mercury species (Se-methylselenocysteine, selenite, selenate, L-selenomethionine, D-selenomethionine, methylmercury and inorganic mercury). The proposed method uses two different mobile phases that are suitable for selenium and mercury speciation and leads to a successful determination of all the species in less than 27 min with good efficiency and resolution. The method was efficiently applied for simultaneous speciation of mercury and selenium in urine and in serum, the latter from umbilical cord samples. Selenocystine has been successfully identified in the former sample. Detection limits obtained were between 0.30 and 2.46 ng. Recovery studies of samples spiked with all species were performed to check the reliability of the method, and satisfactory recoveries (93-110%) were obtained in all cases. The relative standard deviations (RSDs) for species with ten replicate determinations of 80 µg L(-1) were between 4.5 and 9.2%. The proposed method offers a deeper insight into selenium and mercury interactions in the human body.

Serum antioxidants and skin cancer risk: an 8-year community-based follow-up study.

BACKGROUND: Antioxidant nutrients can help prevent skin damage caused by ultraviolet radiation from sunlight, but it is not clear whether serum concentrations of such nutrients influence skin cancer risk. METHODS: We carried out a prospective study of the associations between serum concentrations of antioxidant nutrients and incidence (person-based and tumor-based) of basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) of the skin among a random subsample of 485 adults from an Australian community. Participants were divided into thirds, ranked according to their serum concentrations of carotenoids, alpha-tocopherol, and selenium measured in 1996 and were monitored for incident, histologically confirmed BCC and SCC tumors until 2004. RESULTS: Although there were no associations between baseline serum carotenoids or alpha-tocopherol concentrations and incidence of BCC or SCC, baseline serum selenium concentrations showed strong inverse associations with both BCC and SCC tumor incidence. Compared with participants with lowest selenium concentrations at baseline (0.4-1.0 micromol/L), those with the highest serum selenium concentrations (1.3-2.8 micromol/L) had a decreased incidence of BCC tumors (multivariate relative risk, 0.43; 95% confidence interval, 0.21-0.86; P(trend) = 0.02) and SCC tumors (multivariate relative risk, 0.36; 95% confidence interval, 0.15-0.82; P(trend) = 0.02). CONCLUSION: Relatively high serum selenium concentrations are associated with an approximately 60% decrease in subsequent tumor incidence of both BCC and SCC, whereas serum concentrations of carotenoids or alpha-tocopherol are not associated with later skin cancer incidence. A possible U-shaped association between serum selenium concentrations and SCC of the skin needs confirmation.

Aging decreases expression and activity of glutathione peroxidase-1 in human endothelial progenitor cells.

The mechanisms underlying effects of aging on functions of pro-angiogenic endothelial progenitor cells (EPCs) are poorly understood. Previous studies demonstrated that human EPCs express high levels of antioxidant enzymes as compared to mature endothelial cells. Here, we hypothesized that aging impairs antioxidant capacity of EPCs. So called "early EPCs" derived from cultured blood mononuclear cells were obtained from healthy young (average=24 years old) and old (average=72 years old) subjects. In EPCs of old subjects, the levels of glutathione peroxidase-1 (GPX1) protein and enzymatic activity were significantly reduced. The serum selenium levels in young and old subjects were not significantly different. Increasing selenium concentration in the cell culture also did not affect the protein levels of GPX1, suggesting the reduced GPX1 in old subject's EPCs is selenium independent. Expressions of catalase, Mn-superoxide dismutase (MnSOD), and CuZnSOD were not affected by aging. EPCs of old subjects were more sensitive to oxidative stress induced by H(2)O(2) as compared with EPCs of young subjects, suggesting that impairment of GPX1 during aging may contribute to low survival ability of EPCs in response to oxidative stress. The results indicate that GPX1 may represent a potential therapeutic target for enhancement of regenerative capacity of EPCs in old subjects.

Low internal exposure and absence of adverse effects in workers exposed to high air levels of inorganic selenium.

Selenium is an essential trace element for humans, but adverse health effects may occur after elevated intake. The margin between it is small. This study aimed to assess external and internal exposure in workers of a selenium-processing plant, in which elemental and inorganic selenium occurred. Selenium was analyzed in the form of the selenium concentration in plasma (Se-P), in erythrocytes (Se-RBC) and in personal air samples (Setotal-Air) of 17 exposed workers. Internal exposure was compared to 20 controls without occupational selenium exposure. For potential effects, glucose, HbA1c, proinsulin, prothrombin time and GPX were determined. Setotal-Air had a maximum of 2394 µg/m3 (median 319 µg/m3), containing a small water-soluble fraction (median 12.7 µg/m3, range 0.07-975 µg/m3). Se-P of the exposed ranged from 62 to 123 µg/L (median 105 µg/L), whereas the median of Se-RBC was 63.4 µg/L blood (range 51.9-92.7 µg/L). Both were significantly higher than the controls. No significant difference was found for the effect parameters. Biological effect monitoring of employees occupationally exposed to very high levels of selenium and inorganic selenium compounds did not show any indication of adverse health effects. The moderate increase of the internal selenium exposure compared to the high ambient exposure to selenium and its compounds suggests an efficient air protection or an extremely low resorption of elemental and inorganic species of selenium via inhalation.

Toenail selenium as an indicator of environmental exposure: A cross-sectional study.

The relation between toxicity and essentiality of selenium (Se) is of growing interest in human health, as the effects may widely differ depending of its different chemical species and the exposure levels. Toenail Se has been proposed as a reliable biomarker of long-term Se exposure, but few studies investigated the correlation between its toenail content and environmental determinants (i.e., dietary food intake). We aimed to determine the relation of toenail Se levels with serum Se species as well as food items. We recruited a random sample of Modena (Northern Italy) municipal residents, from whom we collected detailed personal information, dietary habits, toenail specimen for Se determination and a blood sample for serum Se speciation analysis. Toenail Se mean value was 0.96 µg/g (range, 0.47­1.60), with slightly higher levels in females, in non-obese subjects and in Se supplements users, while it was lower in current smokers. Toenail Se positively correlated with organic Se forms, mainly selenoprotein P and selenocysteine, and inversely with the inorganic forms (selenite and selenate). Toenail Se was not associated with meat, cereals and dairy products consumption, positively correlated with fruit and slightly with vegetable intake, and negatively with fish and seafood consumption. Finally, no clear association emerged with estimated air Se exposure.

Effect of organic and inorganic selenium supplementation on semen quality and blood enzymes in buffalo bulls.

The present study aimed to evaluate the effect of organic and inorganic selenium (Se) supplementation on semen quality and blood serum profiles of buffalo bulls. Nine mature buffalo bulls were divided into three groups: control (non-supplemented); organic Se (10 mg Sel-Plex®/head twice weekly) and inorganic Se (10 mg sodium selenite/head twice weekly). Semen was collected twice a week for 3 months during Se supplementation. Semen properties were evaluated from fresh ejaculate. Moreover, fructose concentration, aspartate and alanine transaminase (AST and ALT) activities, total protein and total cholesterol were assayed in seminal plasma. Additionally AST, ALT, testosterone and Se levels were determined in the blood serum. Results showed that Se supplementation significantly (P < 0.05) influences the semen parameters during 3 months of treatment. Organic Se significantly (P < 0.05) increased the percentage of viable sperms compared to inorganic Se and the control group. Fructose concentration was significantly higher (P < 0.05) in the seminal plasma of organic Se-treated bulls. Serum testosterone and Se concentrations were significantly (P < 0.05) increased in the Se supplemented groups than the control group. In conclusion, Se supplementation improved the parameters of buffalo bull semen and more precisely, organic Se was more effective for the improvement of semen quality and some blood components than inorganic Se.

The protective effects of selenoorganic compounds against peroxynitrite-induced changes in plasma proteins and lipids.

Many selenoorganic compounds play an important role in biochemical processes and act as antioxidants, enzyme inhibitors or drugs. The effects of a new selenocompound--bis(2-aminophenyl)-diselenide on oxidative/nitrative changes in human plasma proteins induced by peroxynitrite (ONOO(-)) were studied in vitro and compared with the those of ebselen, a well-known antioxidant. We also studied the role of the tested selenocompounds in peroxynitrite-induced plasma lipid peroxidation. Exposure of the plasma to peroxynitrite (0.1 mM) resulted in an increase in the level of carbonyl groups and nitrotyrosine residues in plasma proteins (estimated using the ELISA method and Western blot analysis). In the presence of different concentrations (0.025-0.1 mM) of the tested selenocompounds, 0.1 mM peroxynitrite caused a distinct decrease in the level of carbonyl group formation and tyrosine nitration in plasma proteins. Moreover, these selenocompounds also inhibited plasma lipid peroxidation induced by ONOO(-1) (0.1 mM). The obtained results indicate that in vitro bis(2-aminophenyl)-diselenide and ebselen have very similar protective effects against peroxynitrite-induced oxidative/nitrative damage to human plasma proteins and lipids.

Blood Clearance, Distribution, Transformation, Excretion, and Toxicity of Near-Infrared Quantum Dots Ag2Se in Mice.

As a novel fluorescent probe in the second near-infrared window, Ag2Se quantum dots (QDs) exhibit great prospect in in vivo imaging due to their maximal penetration depth and negligible background. However, the in vivo behavior and toxicity of Ag2Se QDs still largely remain unknown, which severely hinders their wide-ranging biomedical applications. Herein, we systematically studied the blood clearance, distribution, transformation, excretion, and toxicity of polyethylene glycol (PEG) coated Ag2Se QDs in mice after intravenous administration with a high dose of 8 µmol/kg body weight. QDs are quickly cleared from the blood with a circulation half-life of 0.4 h. QDs mainly accumulate in liver and spleen and are remarkably transformed into Ag and Se within 1 week. Ag is excreted from the body readily through both feces and urine, whereas Se is excreted hardly. The toxicological evaluations demonstrate that there is no overt acute toxicity of Ag2Se QDs to mice. Moreover, in regard to the in vivo stability problem of Ag2Se QDs, the biotransformation and its related metabolism are intensively discussed, and some promising coating means for Ag2Se QDs to avert transformation are proposed as well. Our work lays a solid foundation for safe applications of Ag2Se QDs in bioimaging in the future.

Biodistribution and Pharmacokinetic Study of 3,3' Diseleno Dipropionic Acid (DSePA), A Synthetic Radioprotector, in Mice.

BACKGROUND AND OBJECTIVES: 3,3' Diseleno dipropionic acid (DSePA), a synthetic compound has been shown to have radioprotective activity, especially as a lung radioprotector. In this study, the pharmacokinetics and biodistribution of DSePA in MX-1 tumour bearing SCID mice were evaluated. METHODS: Twenty SCID mice were administered DSePA (50 mg/kg bodyweight) by oral gavage following which four animals each were sacrificed at 15, 30 min, 1, 2 and 4 h. Blood and tissue samples were collected for determination of DSePA concentration by graphite furnace atomic absorption spectrometry (GFAAS) method. The control group (n = 4) was administered sterile water and sacrificed at 4 h. RESULTS: Peak plasma concentration (C max) of 2.7 µg/ml was observed at 15 min which returned to near baseline (baseline = 0.6 µg/ml) at 1 h following drug administration. Biphasic pharmacokinetics characterized by rapid distribution phase and a slower elimination phase were observed. Highest maximal concentration (C max) of the drug was observed in lung (19.2 µg/g at 30 min) followed by intestine (14.64 µg/g at 15 min) and kidney (12.96 µg/g at 15 min). There was negligible uptake in tumor tissue and no uptake in brain. CONCLUSIONS: DSePA has a favorable pharmacokinetic profile which makes it a potentially good candidate for further development as a radioprotective agent.

Selenium metabolism to the trimethylselenonium ion (TMSe) varies markedly because of polymorphisms in the indolethylamine N-methyltransferase gene.

BACKGROUND: Selenium is an essential element, but its metabolism in humans is not well characterized. A few small studies indicate that the trimethylselenonium ion (TMSe) is a common selenium metabolite in humans. OBJECTIVE: This study aimed to elucidate the human metabolism of selenium to TMSe. DESIGN: Study individuals constituted subsamples of 2 cohorts: 1) pregnant women (n = 228) and their 5-y-old children (n = 205) in rural Bangladesh with poor selenium status [median urinary selenium (U-Se): 6.4 µg/L in mothers, 14 µg/L in children] and 2) women in the Argentinian Andes (n = 83) with adequate selenium status (median U-Se: 24 µg/L). Total U-Se and blood selenium were measured by inductively coupled plasma mass spectrometry (ICPMS), and urinary concentrations of TMSe were measured by high-performance liquid chromatography/vapor generation/ICPMS. A genomewide association study (GWAS) was performed for 1,629,299 (after filtration) single nucleotide polymorphisms (SNPs) in the Bangladeshi women (n = 72) by using Illumina Omni5M, and results were validated by using real-time polymerase chain reaction. RESULTS: TMSe "producers" were prevalent (approximately one-third) among the Bangladeshi women and their children, in whom TMSe constituted ∼10-70% of U-Se, whereas "nonproducers" had, on average, 0.59% TMSe. The TMSe-producing women had, on average, 2-µg U-Se/L higher concentrations than did the nonproducers. In contrast, only 3 of the 83 Andean women were TMSe producers (6-15% TMSe in the urine); the average percentage among the nonproducers was 0.35%. Comparison of the percentage of urinary TMSe in mothers and children indicated a strong genetic influence. The GWAS identified 3 SNPs in the indolethylamine N-methyltransferase gene (INMT) that were strongly associated with percentage of TMSe (P < 0.001, false-discovery rate corrected) in both cohorts. CONCLUSIONS: There are remarkable population and individual variations in the formation of TMSe, which could largely be explained by SNPs in INMT. The TMSe-producing women had higher U-Se concentrations than did nonproducers, but further elucidation of the metabolic pathways of selenium is essential for the understanding of its role in human health. The MINIMat trial was registered at isrctn.org as ISRCTN16581394.

Effects of selenium dioxide on blood and femoral bone marrow of rats.

This study was undertaken to investigate the effects of selenium dioxide (SeO2) on rat blood and femoral bone-marrow oxidant mechanisms. Treatment with SeO2, 67 microg Se/kg i.p. daily for 14 d, significantly decreased lipid peroxidation and the concentrations of Fe in serum and bone marrow. The concentrations of Se in serum and bone-marrow cells were significantly increased after SeO2 treatment. The activities of glutathione peroxidase (GPx) in blood and bone-marrow cells were markedly increased. The levels of oxyhemoglobin in blood were significantly increased, while the concentrations of methemoglobin were decreased after SeO2 administration. The fragility of erythrocytes membranes was significantly decreased in SeO2-treated rats compared to controls. Data suggest that treatment with a low dose of SeO2 may provide antioxidant nutrients to blood and bone marrow.

Organic and inorganic selenium supplementation to lactating mothers increase the blood and milk Se concentrations and Se intake by breast-fed infants.

The aim of this study was to determine the effect of selenium (Se) supplementation to lactating women on Se concentrations and glutathione peroxidase (GSH-Px) activities in blood components of mothers and breast-fed infants and on milk Se levels and Se intake by breast-fed infants. Lactating mothers were supplied for 3 months with 200 micrograms Se/day in the form of yeast-Se (Y-Se) and sodium selenite. Initial blood and plasma Se levels of all women (n = 67) were 76.6 and 53.2 micrograms/L, respectively. After 3 months Se concentrations both in whole blood and in plasma from mothers and infants were significantly higher than the initial values. Y-Se exerts a stronger effects than selenite on blood and plasma Se levels. Initial milk Se concentration was 8.9 micrograms/L and after 1 month in both groups in reached a plateau at 14-16 micrograms/L. This resulted in an increase of Se intake in breast-fed infants from 6.1 to a plateau of 11-13 micrograms Se/day. GSH-Px activities in plasma and red cells of Y-Se group increased significantly and reached a plateau after 1 and 2 months, respectively, while in the selenite group the enzyme activities increased steadily throughout the entire period of the study. Selenite exerts a stronger effect on GSH-Px both in maternal and in infant blood components as compared with Y-Se. In milk the GSH-Px activity in the Y-Se group did not change during the study, while in the selenite group after 3 months it increased almost 2-fold compared to the initial value. In conclusion, this study shows that organic Se causes higher Se deposition than did the inorganic form.

Determination of selenium in serum by FI-HG-AAS and calculation of dietary intake.

A method was developed for the determination of selenium concentration in serum by flow injection-hydride generation-atomic absorption spectrometry (FI-HG-AAS) following microwave digestion of serum samples and reduction of selenate to selenite. The detection limit of the method was 0.3 microg Se/L and the characteristic concentration, corresponding to the 0.0044 absorbance signal, was 0.12 microg Se/L. The results from the analysis of two Seronorm standard reference materials showed good agreement with the certified values. The method was then used to analyze selenium in sera of Austrian and Slovenian people for the calculation of dietary intakes. The selenium concentrations in sera of mothers at delivery, their neonates, and the male and female adults were 71+/-14, 42+/-6, 75+/-21, and 65+/-16 microg/L for the Austrians and 62+/-15, 34+/-7, 70+/-12, and 66+/-15 microg/L for the Slovenians. The dietary intakes of selenium of the mothers and the male and the female adults were calculated as 52, 37, and 46 microg/d for the Austrians and 45, 38, and 32 microg/d for the Slovenians.

Sodium selenate partially corrects impaired functional responses in detrusor muscle in streptozotocin-induced diabetic rats.

Selenium selenate was administered to streptozotocin-induced diabetic rats to assess its effects on the detrusor muscle. Thirty-two rats were divided into four groups of eight subjects each. The study animals were made diabetic by means of a single intravenous injection of streptozotocin (STZ). The responsiveness of the detrusor was improved in the group injected with sodium selenate. Diabetes caused significant increases in carbachol and beta,gamma-MeATP-evoked contractions and significant decrease of contractions induced by electrical stimulation. Isoprenaline-induced relaxation of the detrusor muscle was diminished by diabetes, whereas ATP relaxation appeared to be increased. Although adenosine-induced relaxations in controls and in diabetic rats were accompanied by unchanged responses in normoxic conditions, a significant enhancement in the detrusor muscle was observed during hypoxia. This enhancement of adenosine responsiveness in hypoxic conditions is inhibited in diabetes. Treatment with sodium selenate prevented alterations of both carbachol-induced contractility and isoprenaline-evoked relaxation, whereas nerve-mediated contractions and purinergic responses were not improved in diabetic rats after treatment. Our data suggest that changes in cholinergic and adrenergic responses were the result of selenium deficiency in diabetic rats.

Evaluation of the efficacy of 2-hydroxy-4-methylselenobutanoic acid on growth performance and tissue selenium retention in growing pigs.

The aim of this study was to compare the efficacy of a new organic Se (2-hydroxy-4-methylselenobutanoic acid [HMSeBA]) source (SO) with sodium selenite (SS) and selenized yeast (SY) at various dietary levels for growth performance and tissue Se deposition in growing pigs. A total of 112 crossbred (Pietrain × [Large White × Landrace]) gilts were allotted at an average body weight of 26.73 kg to 7 dietary treatments with 8 replicate pens of 2 pigs per pen. Pigs were fed basal diets unsupplemented or supplemented either with SS, SY, or SO each at 0.1 or 0.3 mg Se/kg of diet for 32 d. Feed intake and BW were recorded during the experimental period. At the end of the experiment, blood, liver, and psoas major muscle of all gilts were collected for total Se and relative bioavailability determination. No differences were observed on final BW, ADG, ADFI, and G:F among dietary treatments. All Se-supplemented groups exhibited greater total Se contents in plasma (P < 0.01) and liver (P < 0.01) compared with unsupplemented control group. However, Se retention in psoas major muscle was improved only when organic Se source (SY or SO) was added to diets (P < 0.01). Regardless the Se level, the Se deposition in muscle was greater (P < 0.01) in pigs supplemented with SO than those supplemented with SY. Slope ratio assay confirmed the greater bioavailability of Se from organic compared with inorganic Se and also revealed that the relative bioavailability of Se from HMSeBA for plasma, liver, and muscle Se response was 170, 141, and 162%, respectively, for SY. This study shows a potential advantage of HMSeBA supplementation in the increase of Se contents in pig tissues, indicating that this new organic Se source could be an alternative source of Se in swine nutrition.

Distribution of mercury and selenium in blood compartments of bottlenose dolphins (Tursiops truncatus) from Sarasota Bay, Florida.

Total mercury and selenium concentrations ([THg], [Se]) in serum, plasma, whole blood, and packed cells were examined in a resident population of free-ranging bottlenose dolphins (Tursiops truncatus) from Sarasota Bay, Florida, USA. The authors determined how these elements partition in blood and assess compartment-specific associations. Determining the distribution of Se and THg can provide physiologic insight into potential association of Hg with selenol-containing biomolecules (e.g., antioxidants) in blood compartments. Concentrations of THg were ranked serum < plasma < whole blood < packed cells; whereas for Se concentrations, plasma < serum < whole blood < packed cells. The Se:THg molar ratio was greater than 1 in all compartments, with the higher ratios found in serum and plasma (plasma < serum) and the lower in whole blood and packed cells (packed cells < whole blood). Age was positively correlated with [THg] in all blood compartments and with [Se] in serum, plasma, and whole blood. Age was negatively correlated with Se:THg molar ratios in all blood compartments, driven by low [THg] in young animals. Although [THg] was highly correlated among all blood compartments, this was not the case for [Se]. The feasibility of calculating packed cell [THg], [Se], and Se:THg molar ratios using hematocrit measurements in combination with whole blood and plasma [THg] and [Se] was validated, allowing routine assessment of compartmentalization within erythrocytes using standard clinical measurements.

Riparian swallows as integrators of landscape change in a multiuse river system: implications for aquatic-to-terrestrial transfers of contaminants.

Recent research has highlighted the transfer of contaminants from aquatic to terrestrial ecosystems via predation of aquatic emergent insects by riparian consumers. The influence of adjacent land use and land cover (LULC) on aquatic-to-terrestrial contaminant transfer, however, has received limited attention. From 2010 to 2012, at 11 river reaches in the Scioto River basin (OH, USA), we investigated the relationships between LULC and selenium (Se) and mercury (Hg) concentrations in four species of riparian swallows. Hg concentrations in swallows were significantly higher at rural reaches than at urban reaches (t=-3.58, P<0.001, df=30), whereas Se concentrations were positively associated with adjacent land cover characterized by mature tree cover (R(2)=0.49, P=0.006). To an extent, these relationships appear to be mediated by swallow reliance on aquatic emergent insects. For example, tree swallows (Tachycineta bicolor) at urban reaches exhibited a higher proportion of aquatic prey in their diet, fed at a higher trophic level, and exhibited elevated Se levels. We also found that both Se and Hg concentrations in adult swallows were significantly higher than those observed in nestlings at both urban and rural reaches (Se: t=-2.83, P=0.033, df=3; Hg: t=-3.22, P=0.024, df=3). Collectively, our results indicate that riparian swallows integrate contaminant exposure in linked aquatic-terrestrial systems and that LULC may strongly regulate aquatic contaminant flux to terrestrial consumers.

Mercury and selenium concentrations in leatherback sea turtles (Dermochelys coriacea): population comparisons, implications for reproductive success, hazard quotients and directions for future research.

Leatherback sea turtles (Dermochelys coriacea) are long-distance migrants that travel thousands of km from foraging grounds to breeding and nesting grounds. These extensive journeys are fueled by ingestion of an estimated 300-400 kg of prey/d and likely result in exposure to high concentrations of environmental toxicants (e.g., mercury compounds). Increased bodily concentrations of mercury and its compounds in nesting female turtles may have detrimental effects on reproductive success. Leatherbacks have relatively low reproductive success compared with other sea turtles (global average hatching success ~50-60%). To assess toxicants and necessary nutrients as factors affecting leatherback turtle reproductive success at Sandy Point National Wildlife Refuge (SPNWR), St. Croix, U.S. Virgin Islands, we collected blood from nesting female leatherbacks and tissues from their hatchlings (blood from live turtles, liver and yolk sac from dead turtles). We compared the concentrations in those tissues to hatching and emergence success. We found that on SPNWR, hatching and emergence success were more closely related to seasonal factors than to total mercury and selenium concentrations in both nesting females and hatchlings. Selenium concentrations of nesting females were positively correlated with those of their hatchlings. Mercury and selenium in the liver of hatchlings were positively correlated with one another. Turtles with greater remigration intervals tended to have higher blood selenium concentrations, suggesting that selenium accumulates in leatherbacks through time. Through hazard quotients, we found evidence that selenium may be at or above concentrations that may cause physiologic harm to hatchlings. We also found evidence that population level differences exist for these trace elements. The concentrations of mercury and selenium established in this manuscript form a baseline for future toxicant studies.