Se Exposure Research Articles

Gestational methylmercury exposure selectively increases the sensitivity of operant behavior to cocaine.

Developmental methylmercury (MeHg) exposure alters dopamine neurotransmitter systems, but the selectivity of this and the effects of low, environmentally relevant MeHg exposure regimens are poorly understood. In previous reports, some including littermates of animals studied here, chronic, low-level exposures affected performance on reversal tasks and enhanced reinforcer efficacy. Using high- and low-rate operant behavior under a fixed interval (FI) schedule, sensitivity was examined to drugs that target noradrenergic and dopaminergic neurotransmitter systems. Female rats were exposed in utero to 0, 0.5, or 5 ppm of mercury, as MeHg, via maternal drinking water. Selenium (Se) is thought to attenuate MeHg's neurotoxicity, so animals consumed a diet containing 0.06 or 0.6 ppm of Se. At 11 months, they lever-pressed under a FI 120" schedule of sucrose reinforcement. Acute dose-effect curves were generated with cocaine, desipramine, SKF-38393, quinpirole, SCH-23390, and sulpiride. As compared with unexposed animals, those exposed to 5 ppm mercury, regardless of Se exposure, were 2 to 3 times more sensitive to the rate-reducing effects of high doses of cocaine and did not show increased responding earlier in the interval following moderate cocaine doses. Cocaine's effects in the 0.5 ppm Hg groups depended on dietary Se: low Se diet resulted in a rightward shift in the DEC compared to controls, whereas a high Se diet did not. No differential effects of MeHg were seen with the other drugs. Gestational MeHg exposure produces irreversible sensitivity to dopamine, but not norepinephrine, reuptake inhibitors and not to drugs that target D1 or D2 receptors.

Effects of Se on the uptake of essential elements in Pteris vittata L.

Selenium has been proven to be an antioxidant in plants at low dosages. To understand better the mechanisms of Se toxicity and benefit to plants, more investigations about effects of Se on the uptake of essential elements in plants would be desirable. In this study, hydroponic (nutrient solution culture) and pot (soil culture) experiments were simultaneously conducted to investigate the effects of Se on the uptake and distribution of essential elements in Pteris vittata. L (Chinese brake fern), an arsenic (As)-hyperaccumulator and a selenium (Se)-accumulator. Chinese brake fern took up much more Se in nutrient solution culture than in soil culture, with the highest Se content recorded as 1,573 mg kg(-1) in the roots, demonstrating remarkable tolerance to Se. In soil culture, Chinese brake fern also accumulated high content of Se, with the highest content measured as 81 mg kg(-1) and 233 mg kg(-1), in the fronds and roots, respectively. In soil culture, the addition of Se suppressed the uptake of most measured elements, including magnesium (Mg), potassium (K), phosphorus (P), iron (Fe), copper (Cu) and zinc (Zn). In nutrient solution culture, when the Se content in the tissues of Chinese brake fern was relatively low, the supplementation of Se suppressed the uptake of most essential elements; however, with the increase of Se content, stimulation effects of Se on the uptake of Ca, Mg, K were observed. An initial decrease followed by a rapid increase of Fe content in the fronds of Chinese brake fern was found with Se addition and tissue Se content increasing in nutrient solution culture, suggesting antagonistic and synergic roles of Se on these elements under low and high Se exposure, respectively. We suggest that Ca, Mg, K may be involved in the tolerance mechanism of Se, and that the regulation of Fe accumulation by Se in the fronds might be partially due to the dual effects of Se on Chinese brake fern.

Selenium assimilation and loss by an insect predator and its relationship to Se subcellular partitioning in two prey types

Subcellular selenium (Se) distributions in the oligochaete Tubifex tubifex and in the insect Chironomus riparius did not vary with Se exposure duration, which was consistent with the observations that the duration of prey Se exposure had little influence on either Se assimilation or loss by a predatory insect (the alderfly Sialis velata). However, these two prey types differed in how Se was distributed in their cells. Overall, the predator assimilated a mean of 66% of the Se present in its prey, which was similar to the mean percentage of Se in prey cells (62%) that was theoretically available for uptake (that is, Se in the protein and organelle fractions). Likewise, data for cadmium, nickel and thallium suggest that predictions of trace element transfer between prey and predator are facilitated by considering the subcellular partitioning of these contaminants in prey cells.

Physiological stress response in white suckers from agricultural drain waters containing pesticides and selenium

To assess the effect of agriculture drain water, a complex mixture containing pesticides and selenium (Se), on the physiological stress response, white suckers were collected from irrigation return flows in the summer and the fall and subjected to a stress challenge. Water (0.40–26.71 μg/L) and muscle Se (0.37–1.52 μg/g ww) levels were elevated at two sites and plasma acetylcholinesterase (AChE) activity (a marker of pesticide exposure) was lower in the fall (5.97±0.45 μmol/min/mL) than the summer (10.73±0.73 μmol/min/mL). Fish raised plasma cortisol levels in response to the stress challenge 11.8 times above basal levels (12.8±4.9 ng/mL). Multivariate statistics linked Se exposure to elevated plasma glucose levels, and pesticide exposure to elevated liver glycogen levels generating hypotheses for further testing. This study showed that white suckers accumulated Se from agricultural drain water and the complex mixtures present in the drain water influenced the physiological stress response.

What is an appropriate level of protection? An example considering selenium exposures by aquatic birds

Evaluating population-level risks to ecological receptors or developing toxicity thresholds intended to be protective of a population requires a population model to truly understand possible chemical-related impacts to the population of interest. For various reasons (e.g., lack of training in the application of population models to ecotoxicological questions), we often use laboratory-based (more common) or field-based (less common) toxicity data to develop a toxicity threshold that is assumed to be protective of population-level effects. Under this latter approach, an appropriate level of protection against exposure should focus on protecting the viability and productivity of populations of organisms, that is, maintaining approximately the same density of individuals over time. The EC values can be used to set technically defensible levels of protection, with the appropriate effect level being determined on the basis of data- and site-specific considerations and dose-response relationships that are amenable for use as inputs in population models. Even without the use of predictive population models, the ECO10 or EC20 are commonly used values in risk assessment or criteria development with the assumption of adequate protection of populations. In the Se example presented here, there is strong evidence that egg hatchability is the critical toxicity endpoint for birds based on dietary organic Se exposures and that mallards are a sensitive bird species. These factors support that the dietary Se EC10 derived by Ohlendorf (2003) is sufficiently low to not have any measurable effects on aquatic birds in the field. Further, effect levels below the EC10 are likely to be statistically indistinguishable from the controls in most situations (as it was for Se in this example), and, for Se and other naturally occurring elements, it is not unusual for lower EC values to approach or fall below background levels at a site. A determination as to whether higher EC values would also provide an adequate level of protection could be made by appropriate population modeling.

Influence of elevation and slope exposure upon productivity and must quality of "Touriga Nacional" (Sub-region of Douro Superior)

<p style="text-align: justify;"><strong>Aims</strong>: This work presents the results of a 3 year study on the influence of elevation and slope exposure upon the productivity and quality of the Touriga Nacional variety.</p><p style="text-align: justify;"><strong>Methods and results</strong>: Touriga Nacional variety standing on 18 plots dispersed along the sub-region of Douro Superior (laid out in a randomized complete block design). We determinate productivity, alcohol, volume, mass, total acidity, chromatic characteristics, anthocyanins, polyphenol index, maturation index, vegetative mass, vigour estimation and ravaz index.</p><p style="text-align: justify;"><strong>Conclusion</strong>: The results revealed a decrease in most parameters related to productivity and quality as the elevation increases and, simultaneously, the concentration of phenolic compounds increased proportionally in relation to elevation. In relation to the plots set either on northern or southern exposures, the SW and NW exposures surpass the N, S, NE, and SE exposures in terms of the concentrations phenolic compounds, but all other parameters, either productivity or quality related, had lower values.</p><p style="text-align: justify;"><strong>Significance and impact of study</strong>: The results confirm the importance of elevation and slope exposure of sub-region Douro Superior, in productivity and must quality of Touriga Nacional.</p>

Biomarkers of selenium status in the amazonian context: Blood, urine and sequential hair segments

Selenium (Se) is an essential element and deficit or excess of dietary Se is associated with health disorders. Relatively elevated Se levels have been reported in the Brazilian Amazon, where there are also important annual variations in the availability of different foods. The present study was conducted among six riparian communities of the Tapajós River to evaluate seasonal variations in blood and sequential hair cm Se concentrations, and to examine the relationships between Se in blood and hair, and blood and urine. Two cross-sectional studies were conducted, at the descending water (DWS, n=259) and the rising water (RWS, n=137) seasons, with repeated measures for a subgroup (n=112). Blood Se (B-Se), hair Se (H-Se) and urine Se (U-Se) were determined. Match-paired analyses were used for seasonal comparisons and the method of best fit was used to describe the relationships between biomarkers. B-Se levels presented a very large range (142-2447 microg/l) with no overall seasonal variation (median 284 and 292 microg/l, respectively). Sequential analysis of 13 cm hair strands showed significant variations over time: Se concentrations at the DWS were significantly lower compared with the rising water season (medians: 0.7 and 0.9 microg/g; ranges: 0.2-4.3 microg/g and 0.2-5.4 microg/g, respectively). At both seasons, the relationships between B-Se and H-Se were linear and highly significant (r(2)=67.9 and 63.6, respectively), while the relationship between B-Se and U-Se was best described by a sigmoid curve. Gender, age, education and smoking did not influence Se status or biomarker relationships. Variations in H-Se suggest that there may be seasonal availability of Se sources in local food. For populations presenting a large range and/or elevated Se exposure, sequential analyses of H-Se may provide a good reflection of variations in Se status.

Dietary exposure and trends of exposure to nutrient elements iodine, iron, selenium and sodium from the 2003–4 New Zealand Total Diet Survey

The mean dietary exposure to the nutrient elements iodine, Fe, Se and Na by eight age-sex groups of the New Zealand population was estimated from foods purchased and prepared as for consumption. A total of 968 samples comprising 121 foods were collected and analysed. Mean daily exposures were calculated from mean concentration levels of the selected nutrients in each food combined with simulated diets for a 25+-year-old male and female, a 19-24-year-old male, a 11-14-year-old boy and girl, a 5-6-year-old child, a 1-3-year-old toddler and a 6-12-month-old infant. Food concentrations and dietary exposures are reported and compared with nutrient reference values (for example, recommended daily intakes, adequate intakes or upper limits). Dietary iodine exposures for all age-sex groups were well below recommended levels and have steadily decreased since 1982, raising concern especially for the physical and mental development of infants and young children. Fe exposures meet the recommended daily intake for the average male and 11-14 year olds but are only about half that recommended for adult females. Se exposure is about 20 % less than optimal for females. Na exposures, excluding discretionary salt, are above the acceptable exposure level for all age-sex groups, and exceed the upper intake limits for 25+-year-old males, 19-24-year-old young males, and 11-14-year-old boys and girls by up to 125 % for an average consumer.

The effects of excessive selenium metabolism on protein expression of HepG2 cells

High selenium (Se) level in the culture medium was reported to delay cell growth and to cause morphological changes of HepG2 cells in our previous study. The purpose of this study was to use proteomic technique to explore the influence of excessive Se metabolism on the protein expression of HepG2 cells. After 24 hr of exposure in 20 μM of sodium selenite in medium, the expression of at least 30 proteins was significantly altered. Nine of the up‐regulated proteins included those participated in immune response (immunoglobulin heavy chain), collagen formation (proline 4‐hydroxylase), energy metabolism (mitochondrial ATP synthase), tumor suppressor protein (prohibitin), cell growth (FUBP1 protein, galectin‐3 carbohydrate recognition domain), and cell differentiation (human nucleoside diphosphate kinase, galectin‐3 carbohydrate recognition domain). The expression of 21 proteins was down regulated, which also included some proteins in the cellular activities such as energy metabolism, immune response, DNA replication (EF‐Tu) and cytoskeleton. Therefore alterations in protein expression occurred in the early phase of high Se exposure may be related to the later changes in the growth and morphology of HepG2 cells. Further analysis regarding the systemic relationship among the aforementioned proteins and many others is currently underway. (Sponsored by Office of Research and Development, Fu Jen Catholic University, Project 409531060439)

Selenium Speciation and Bioavailability in Biofortified Products Using Species-Unspecific Isotope Dilution and Reverse Phase Ion Pairing−Inductively Coupled Plasma−Mass Spectrometry

In some regions of the world, where the bioavailability of selenium (Se) in soil is low and/or declining (e.g., due to use of high-sulfur fertilizers), there is increased risk of adverse affects on animals and human health. In recent years, increased research attention has focused on understanding the relationships between Se contents in foods and supplements and their nutritional benefits for animal and humans. The objective of this study was to use a species-unspecific isotope dilution and reverse phase ion pairing-inductively coupled plasma-mass spectrometry techniques for the identification and quantification of Se species in biofortified grains (i.e., wheat and triticale), flour, and wheat biscuits. The information on Se species was used to gain an understanding of the bioavailability of Se in biofortified and process-fortified wheat biscuits used in a clinical trail. The major Se species identified in biofortified and process-fortified samples were selenomethionine (76-85%) and selenomethionine selenoxide (51-60%), respectively. Total plasma Se concentrations in the biofortified Se exposure group were found to increase throughout the 6 month trial period (mean=122 microg L(-1) at 0 months to 194 microg L(-1) at 6 months). In contrast, the trial group exposed to process-fortified Se biscuits showed little increase in mean total Se plasma concentrations until 4 months of exposure (mean=122 microg L(-1) at 0 months to 140 microg L(-1) at 4 months) that remained constant until the end of the trial period (mean=140 microg L(-1) at 4 months to 138 microg L(-1) at 6 months). The difference in total Se plasma concentrations may be due to the presence and bioavailability of different Se species in biofortified and process-fortified biscuits. An understanding of Se speciation in foods enables better understanding of pathways and their potential benefits for animals and humans.

Characterizing the toxicity of pulsed selenium exposure to Daphnia magna

The acute toxicity of selenium (Se) to aquatic biota has been studied extensively for decades. However, most studies have used a constant concentration aqueous exposure of Se to an invertebrate species. Since constant concentration exposure of toxicants to invertebrates is unusual in the environment, episodic exposure or pulsed exposures may represent true risk to aquatic biota more accurately. This research was designed to characterize the toxicity effects of pulsed Se exposure to Daphnia magna. Selenium exposure was varied during a 21-d chronic toxicity test to examine the effects of exposure concentration, duration, and recovery on survival, growth, and reproduction of D. magna. While D. magna did not die during exposures, latent mortality was observed. Latent mortality increased with exposure concentration and duration. Hence, standard toxicity test using continuous exposures would underestimate Se toxicity. Risk assessment method using results of continuous exposure would underestimate risk of Se to biota. For double-pulse exposures, cumulative mortality on day 21 was higher when time interval between pulses was shorter. With the same total exposure time, continuous exposure caused higher toxicity than did pulsed exposures due to recovery and tolerance development in D. magna after earlier pulses. Growth and reproduction of surviving D. magna were not affected by pulsed Se exposure due to recovery of D. magna after removal of the pulses. Based on these results, risk assessment for Se should take latent effects and the effect of recovery in to account.

Metabolic responses of weeping willows to selenate and selenite

Selenium (Se) is one of the most widely distributed elements of the earth's crust at low concentrations. The extensive use of Se-containing chemicals due to anthropogenic activities has increased the ecological risk to environmental compartments. Plants, under unfavorable environmental conditions, often increase the formation of reactive oxygen species (ROS), and consequently plant antioxidant enzymatic systems have been proposed to be important in plant stress tolerance. The goal of this study was to find out the metabolic responses of plants to Se, to provide quantitative information whether exogenous Se has a beneficial role in plants, and to investigate the potential of vegetation management of Se for potential phytoremediation. Pre-rooted plants of weeping willows (Salix babylonica L.) were grown hydroponically in growth chambers and treated with Na2SeO4 or Na2SeO3 at 24.0 +/- 1 degrees C for 168 h. Five different treatment concentrations were used, ranging from 0.44 to 8.72 mg Se/L for the treatments exposed to SeO4(2-) and from 0.50 to 10.0 mg Se/L for the treatments exposed to SeO3(2-), respectively. Transpiration rates, soluble protein contents and antioxidative enzyme activities of the plants were monitored to evaluate toxicity from exogenous Se exposure. At the end of the study, total Se in the hydroponic solution was analyzed by hydride generation-atomic fluorescence spectrometry (HG-AFS). Both chemical forms of Se at low concentrations showed growth-promoting effects on plants. A significant decrease of transpiration rates and of soluble protein contents of plants was observed at higher Se concentrations after 168 h of exposure. Measurable change of superoxide dismutases (SOD) activity in leaves was only detected under high Se treatments. Catalase (CAT) activity was significantly affected by the Se application. Slight change of peroxidase (POD) activity was measured in all treatments, whereas significant inhibition of POD activity was detected for the plants exposed to SeO3(2-) of 10.0 mg Se/L. Se-induced stress appeared in all treatments, thus resulting in measurable increase of glutathione peroxidase (GSH-Px) activity of the plants. Although both chemical forms of Se were taken up by weeping willows efficiently, their uptake rates were different. Of all measured parameters, POD and CAT activities in leaves were noted the most sensitive indicator for the plants exposed to SeO4(2-) and SeO3(2-), respectively. Deleterious effects on plant physiological functions due to Se application were not observed over 168 h of exposure. This is largely due to the fact that well-established antioxidant enzymatic systems in plants and higher activities of GSH-Px largely reduced the negative effects on plants; SeO3(2-) caused much more severe stress to plants than SeO4(2-) at higher Se application rates. The uptake mechanisms between the two chemical species were quite different. Neither visible toxic symptoms nor metabolic lesions were observed at low concentrations of Se, probably due to the effective established enzymatic systems in weeping willows. All selected parameters for toxicity determination were significantly correlated to Se application, but metabolic responses of plants to SeO4(2-) and SeO3(2-) were quite different. GSH-Px in leaves was probably the principle enzyme responsible for stress reduction from Se exposure. Due to their different chemical properties, weeping willows showed a faster uptake rate for SeO4(2-) than for SeO3(2-). Exogenous Se has a beneficial role in plants and vegetation management of Se is a potential remediation strategy in cleaning up Se-contaminated sites. Further investigation on the biochemical mechanism of Se metabolism will provide insight to the specific interactions between Se and plants on the molecular level. Weeping willow has a sound potential for phytoremediation of Se-contaminated sediment and groundwater because the tree is not only tolerant to Se but also uptakes chemical species from the environment.

The Effect of Cadmium and Selenium on The Testicular Function and Tissue Injury in Male Rats

The effect of the sub lethal dose of cadmium chloride CdCh 7mglkgl body I weight ) was investigated on the testis and some sperm parameters in rats .. To evaluate the effect of cadmium exposure as CdCh, was orally administered to mature male rats( 250-300g I body weight) for 28 days and the effects on the sperm count , sperm motility , sperm abnormality , sperm death percentages and testes weight, as well as testicular histology were observed. To evaluate the beneficial action of Selenium against Cadmium chloride-induced reduced sperm count and sperm abnormalities and testes injury in albino rats , an additional two groups of rats were treated for same period with SeCiz 8m/kgl body weight ) and Cd - Se combination · respectively to determine the reversibility of Cd-induced changes The sperm counts, sperm motility, sperm abnormality and sperm ) death percentages were significantly decreased following 28th day of CdCh treatment, but were unaffected by Se and Cd- Se exposures. The testicular, epididymis, prostate and seminal vesicle weight were noticeably reduced with Cd-treatment as compared to control. The changes caused by cadmium are mostly recovered by Se administration. Cadmiu·m chloride exposure injures the fertility parameters of male rats and the effects are reversible due to Se supplementation. On the other hand, co-administration of Se at the above mentioned dose to Cadmium treated rats led to the most significant decline in testes tissue damage alorig with elevated ·sperm count and . reduction in the percentage of abnormal spenn population. The protective action of Se and the antagonistic effect of both Se and Cadmium induced testes tissue damage are discussed.

Functional relationships among selenium concentrations in the diet, target tissues, and nondestructive tissue samples of two species of snakes

Nondestructive sampling methods, such as removal of feathers for contaminant analysis, are desirable in ecological monitoring programs that seek to minimize the impacts of harvesting organisms. Although many reptiles are declining worldwide, nondestructive sampling techniques seldom have been employed for assessing contaminant exposure in these organisms. In this study, we examined the utility of nondestructive tissue sampling for assessing Se exposure in reptiles. We describe the functional relationships among dietary Se concentrations, target tissue Se concentrations, and Se concentrations in nondestructive tissue samples (blood and tail tissue biopsy) in two species of snakes that had been exposed to Se under very different experimental protocols. Using nonlinear regression, we found strong positive correlations (r2 > 0.92) in all comparisons among Se concentrations in nondestructive tissues, diet, and target tissues. Moreover, equations describing these relationships can be used to estimate concentrations of Se in diet and target organs, from known concentrations of Se in nondestructive tissue samples. Although the current paucity of toxicity data on reptiles precludes tests of our models, we demonstrate how the equations describing these relationships might be used to make predictions about Se accumulation in target organs for risk assessment. Future studies on reptiles that examine these relationships under different Se exposure conditions, and those that document physiological responses of reptiles to various concentrations of Se, will help to refine our models and test their efficacy for predicting health risk.

Chronic Effects of Dietary Selenium on Juvenile Sacramento Splittail (Pogonichthys macrolepidotus)

The chronic effects of dietary selenium (Se) exposure in juvenile Sacramento splittail (Pogonichthys macrolepidotus) were investigated in the laboratory. A total of 960 (40 fish per tank, 3 tanks per diet) 7-month-old juvenile splittail were fed one of eight Purified-Casein diets supplemented with selenized yeast for 9 months in a flow-through system. These diets contained the following: 0.4 (control), 0.7, 1.4, 2.7, 6.6, 12.6, 26.0, and 57.6 mg of Se kg(-1) dry weight. Survival, Se tissue concentration, growth, gross morphology, and liver histopathology were assessed at 5- and 9-month of exposure. Mortalities occurred only in the two highest Se treatments and were accounted for 8.3 and 18.3% at 5-month and 10.0 and 34.3% at 9-month, respectively. Liver and muscle Se concentration were significantly correlated with dietary Se concentration. Fish exposed to 0.4-12.6 mg of Se kg(-1) diets had reached equilibrium in liver Se concentration by 5 month. Splittail fed diets at concentrations > or =26.0 mg of Se kg(-1) had not reached equilibrium in liver, and muscle Se concentrations and grew significantly slower (p < 0.05) at 5- and 9-month exposure. Se-induced deformities were observed in fish fed > or =2.7 mg of Se kg(-1) diets at 5-month and in fish fed > or =0.7 mg of Se kg(-1) diets at 9-month. Fish fed 26.0 and 57.6 mg of Se kg(-1) diets had higher liver lesion scores at 5-month while fish fed 6.6 and 57.6 mg of Se kg(-1) diet had higher liver lesion scores at 9-month. Results indicate that survivals, growth, changes of tissue Se concentrations, and histopathology of juvenile splittail were dose-dependent, but their response thresholds to dietary Se concentrations differed and depended on treatment concentrations and duration of exposure. Chronic exposure to 6.6 mg of Se kg(-1) diet induced deleterious health effects that can potentially impact survival of juvenile splittail.

Maternal transfer of selenium in Alligator mississippiensis nesting downstream from a coal-burning power plant.

Selenium (Se) is embryotoxic in many oviparous vertebrates, but little is known about maternal transfer of Se and its impact in reptiles. Over a four-year period, we collected three clutches of eggs of the American alligator (Alligator mississippiensis) from a single nest at a site contaminated with Se and compared egg and hatchling Se concentrations and clutch viability from this nest to nests downstream from the contaminated site (two clutches from two nests) and at a reference site (two clutches from two nests). Eggs and hatchlings from the nest at the Se-contaminated site and downstream nests had elevated Se concentrations (2.1-7.8 ppm) and lower viability (30-54%) compared to reference nests (1.4-2.3 ppm and 67-74% viability), but Se concentrations did not exceed reproductive toxicity thresholds established for other oviparous vertebrates. Selenium concentrations were higher in chorioallantoic membranes of eggs from Se-contaminated sites, suggesting that this tissue may be useful as a nondestructive index of Se exposure for embryos of A. mississippiensis. Examination of these data suggests that further studies on uptake, accumulation, and reproductive success of crocodilian embryos exposed to excessive Se are warranted.

Strain relaxation during the layer by layer growth of cubic CdSe onto ZnSe

A detailed reflection high-energy electron diffraction analysis shows relevant features of the lattice parameter relaxation of CdSe thin films grown in a layer-by-layer mode onto ZnSe. In situ investigations of different azimuths show a clear lattice parameter oscillation in the [110] azimuth. The lattice parameter has a minimum value (similar to that of ZnSe) during Se exposure steps, and a higher and increasing lattice parameter during Cd exposure steps. The behavior is ascribed to the formation of CdSe islands during Cd exposure steps. The cumulative effect in CdSe exposure steps is considered to be a consequence of a decrease in the island size with the number of cycles. Actual plastic deformation does occur after 5 ML.

Exposure and potential food chain transfer factor of Cd, Se and Zn in marine fish Lutjanus argentimaculatus

Radiotracer techniques were employed to quantify the rates of uptake from aqueous and dietary sources, and rates of elimination of Cd, Se and Zn by a marine predatory fish, the mangrove snapper Lutjanus argentimaculatus. The relative significance of bioaccumulation of metals by fish from water and food and the food chain transfer factor were then assessed using a kinetic modeling approach. Cd and Zn in the aqueous phase exhibited an approximately linear uptake pattern over a 1 to 2 d exposure, whereas Se exhibited a 2-compartmental uptake at a low ambient concentration, with a slow initial uptake followed by a rapid increase in Se influx. Most of the accumulated aqueous Se and Zn were incorporated into the muscles, whereas Cd was evenly distributed in the viscera and the remaining tissue, with a lower proportion in the gills. The influx rates were dependent on the ambient metal concentration and were tissue-specific for each metal. The assimilation efficiency of trace metals in fish ingesting different prey (copepods, Artemia sp. and clam tissue) ranged from 6 to 24% for Cd, 32 to 68% for Se and 15 to 46% for Zn, and decreased with an increase in ingestion rate. The efflux rate constant of Cd in fish following uptake from the dietary phase (0.047 d -1 ) was higher than that following aqueous uptake (0.025 d -1 ), whereas the efflux rate constants of Se and Zn were comparable between these 2 exposure pathways. Our modeling calculations indicate that dietary uptake of Cd and Zn dominates their accumulation in fish when zooplankton are the main prey, whereas aqueous uptake may be the dominant pathway when planktivorous fish are the dominant prey for the predatory fish. Dietary uptake always dominates Se accumulation in these fish. The modeling results also indicated that the food chain transfer factor of Cd was <0.5 in the fish regard- less of the ingestion rate and the assimilation efficiency, consistent with the results of field studies. However, Se and Zn may potentially be biomagnified when the ingestion rate and assimilation effi- ciency are at the high end of the range possibly encountered by the predatory fish.

Role of selenium toxicity and oxidative stress in aquatic birds

Adverse effects of selenium (Se) in wild aquatic birds have been documented as a consequence of pollution of the aquatic environment by subsurface agricultural drainwater and other sources. These effects include mortality, impaired reproduction with teratogenesis, reduced growth, histopathological lesions and alterations in hepatic glutathione metabolism. A review is provided, relating adverse biological effects of Se in aquatic birds to altered glutathione metabolism and oxidative stress. Laboratory studies, mainly with an organic form of Se, selenomethionine, have revealed oxidative stress in different stages of the mallard ( Anas platyrhynchos) life cycle. As dietary and tissue concentrations of Se increase, increases in plasma and hepatic GSH peroxidase activities occur, followed by dose-dependent increases in the ratio of hepatic oxidized to reduced glutathione (GSSG:GSH) and ultimately hepatic lipid peroxidation measured as an increase in thiobarbituric acid reactive substances (TBARS). One or more of these oxidative effects were associated with teratogenesis (4.6 ppm wet weight Se in eggs), reduced growth in ducklings (15 ppm Se in liver), diminished immune function (5 ppm Se in liver) and histopathological lesions (29 ppm Se in liver) in adults. Manifestations of Se-related effects on glutathione metabolism were also apparent in field studies in seven species of aquatic birds. Reduced growth and possibly immune function but increased liver:body weight and hepatic GSSG:GSH ratios were apparent in american avocet ( Recurvirostra americana) hatchlings from eggs containing 9 ppm Se. In black-necked stilts ( Himantopus mexicanus), which contained somewhat lower Se concentrations, a decrease in hepatic GSH was apparent with few other effects. In adult American coots ( Fulica americana), signs of Se toxicosis included emaciation, abnormal feather loss and histopathological lesions. Mean liver concentrations of 28 ppm Se (ww) in the coots were associated with elevated hepatic GSH peroxidase, depletion of hepatic protein bound thiols and total thiols, but a small increase in GSH. Diving ducks in the San Francisco Bay area exhibited a positive correlation between hepatic Se concentration and GSH peroxidase activity ( r=0.63, P<0.05), but a negative correlation between hepatic Se and GSH concentration ( r=−0.740, P<0.05). In willets ( Catoptrophorus semipalmatus) from the San Diego area, positive correlations occurred between hepatic Se concentration and GSSG ( r=0.70, P<0.001), GSSG:GSH ratio, and TBARS. In emperor geese ( Chen canagica) from western Alaska, blood levels of up to 9.4 ppm occurred and were associated with increased plasma GSH peroxidase activity ( r=0.62, P<0.001), but with decreased plasma GSSG reductase activity. When evaluating Se toxicity, interactive nutritional factors, including other elements and dietary protein, should also be taken into consideration. Further studies are needed to examine the relationship between different forms of environmentally occurring selenium, arsenic and mercury on reproduction, hepatotoxicity and immune function of aquatic birds. Further selenium nutritional interaction studies may also help to illucidate the mechanism of selenium induced teratogenesis, by optimizing GSH and other antioxidant defense mechanisms in a manner that would stabilize or raise the cell's threshold for susceptibility to toxic attack from excess selenium. It is concluded that Se-related manifestations of oxidative stress may serve as useful bioindicators of Se exposure and toxicity in wild aquatic birds.

Daily intake of Se by adult population of Mumbai, India

The atmospheric Se levels in Mumbai varied between 0.02 and 1.92 ng m −3 with a mean concentration of 0.21 ng m −3. The daily intake of Se by the adult population of Mumbai is 61.9 μg day −1. Differential pulse cathodic stripping voltammetry (DP-CSV) has been used for the determination of Se in air particulate and food samples. The detection limit of Se using DPCSV was found to be 0.05 ng ml −1. The reliability of estimation was further assessed through the analysis of standard reference materials (SRMs), tuna fish, animal blood, milk powder and fish tissue obtained from IAEA. The frequency distribution of dietary intake levels of selenium for Mumbai adults showed that approximately 61% of the studied population have a dietary intake of 30–90 μg day −1. Ingestion was found to be the main route of Se exposure for Mumbai adults. The turn over time of Se through blood is 17 days.