The bioavailability of various selenium compounds to a marine wading bird

The uptake of dietary selenium (about 3.5 mg/kg AF dry wt) as selenomethionine, selenocystine, selenite, selenate, and fish selenium in the plasma and red blood cells (RBC) of the oystercatcher has been investigated. The birds received the various selenium compounds subsequently, for at least 9 wk. After dietary supplementation of selenocystine, selenite, and selenate, plasma selenium was about 350 μg/L and RBC selenium 2.1 mg/kg dry wt. After supplementation of selenomethionine, the plasma concentration increased to 630 μg/L, and the RBC concentration to 4.1 mg/kg dry wt. When the fodder contained 3.1 mg/kg fish Se, an average plasma and RBC concentration of 415 μg/L and 14.4 mg/kg dry wt, respectively, was measured. The maximal increase of the selenium concentration in the plasma was attained at first sampling, 14 d after a change in dietary selenium (selenomethione or fish Se); the uptake seemed to be a concentration-regulated process. RBC concentrations (γ in mg/kg dry wt) increased with time (X in d) according toY=a?be^?cX . Fifty percent of the total increase was attained within 17d, suggesting that diffusion into the RBC played a role. The selenium concentration in the plasma was positively correlated with the (fish) Se concentration in the fodder; the RBC concentration (60 d after the change in diet) was positively correlated with the plasma concentration. When the diet contained fish Se, the blood selenium concentrations of the captive birds were similar to the concentrations measured in field birds. Fish Se is a yet undetermined selenium compound. The present experiment showed that fish Se differed from selenomethionine, selenocystine, selenite, or selenate in uptake from the food and uptake in the RBC.     

Biological monitoring of exposure to ambient lead and cadmium using avian feathers: A study from Northern India

Biological monitoring of exposure to ambient environmental lead and cadmium was performed using feathers of 26 species of birds native to Western Uttar Pradesh in Northern India. The rationale of this study was to address three questions. First, is there any avian species that can be treated as a suitable bioindicator of lead or cadmium present in the environment? Second, do the birds selectively accumulate lead and cadmium in their feathers and exhibit interspecies variation? Third, is there any threat to endangered species of this region from metal pollution? Average concentration of lead in the feathers of selected birds ranged from 3.40 µg/g in parrot to 301.6 µg/g in golden pheasant, whereas cadmium concentration was higher ranging from 40.20 µg/g in red crow to 450 µg/g in blue macaw. A comparison of results made through ANOVA revealed a significant difference in the concentration of lead (df = 25; F = 3965.54) and cadmium (df = 25; F = 8537.27) in their feathers. We hypothesize that feathers of synanthropic birds may be treated as suitable noninvasive tool to monitor the ambient environmental contamination by lead and cadmium. Their accumulation in endangered birds may lead to population decline causing serious ecological disturbances in the region.     

Critical Review of Proposed Residue-Based Selenium Toxicity Thresholds for Freshwater Fish

Proposed fish toxicity thresholds for interpreting the biological significance of selenium concentrations measured in environmental media include 2 to 5?µg/L in water, 4?mg/kg dw in fish whole body tissue, 10?mg/kg dw in fish ovaries, and 3?mg/kg dw in fish diets. Use of these thresholds would likely identify fish populations as being at risk at numerous sites across the U.S. However, selenium effects on fish populations in the field have only been conclusively demonstrated at a few locations. Based on our critical review, these threshold values are not consistent with USEPA methodology for deriving criteria, in many cases are not supported by the scientific literature, and, as a result, are generally overly conservative. Based on currently available information, we believe the scientific literature is not supportive of generic sediment or water thresholds, but is supportive of alternative separate whole body thresholds of 9?mg/kg dw for warmwater fish and 6?mg/kg dw for larval coldwater anadromous fish, an ovary threshold of 17?mg/kg dw for warmwater fish, and fish dietary thresholds of 10 and 11?mg/kg dw for warmwater fish and larval coldwater anadromous fish, respectively.     

A Dietary Assessment of Selenium Risk to Aquatic Birds on a Coal Mine Affected Stream in Alberta,Canada

Selenium is a trace element of concern in the McLeod River basin downstream from two recently-closed coal mines in west-central Alberta, Canada. Aquatic birds breed on streams in the area and may be exposed to excessive amounts of selenium through their diets. In this article, we present the results of a dietary-based assessment of the risk that selenium may pose to two aquatic bird species, the American Dipper (Cinclus mexicanus) and the Harlequin Duck (Histrionicus histrionicus), on one of the coal mine–affected streams, the Gregg River. The study consisted of (1) a literature-based toxicity assessment, (2) simulation of selenium exposure in the diets and eggs of the two species, and (3) a risk assessment that coupled information on toxicity and exposure. Diet and egg selenium concentrations associated with a 20% hatch failure rate were 6.4 and 17 μ g · g^?1 dry wt, respectively. Simulated dietary selenium concentrations were about 2.0–2.5 μ g · g^?1 higher on the Gregg River than on reference streams for both species. Simulated predicted egg concentrations averaged 2.0 and 1.4 μ g · g^?1 higher on the Gregg River than on reference streams for American Dippers and Harlequin Ducks, respectively. When simulated dietary concentrations were considered, hatch failure rates on the Gregg River were predicted to average 12% higher in American Dippers and 8% higher in Harlequin Ducks than at reference streams. Corresponding values were only 3% for both species when predicted egg concentrations were used. Elevated levels of selenium in insects in some of the reference streams were unexpected and raised a question as to whether aquatic birds have evolved a higher tolerance level for dietary selenium in these areas.     

Hypothesis of Historical Effects From Selenium on Endangered Fish in the Colorado River Basin

Anthropogenic selenium contamination of aquatic ecosystems was first associated with cooling reservoirs of coal-fired power plants in the late 1970s, and later with drainage water from agricultural irrigation activities in the 1980s. In the 1990s, selenium contamination has been raised as a concern in the recovery of currently endangered fish in the Colorado River system. Widespread contamination from seleniferous drain waters from agriculture has been documented in the upper and lower Colorado River basins. Historically, irrigation started in the upper Colorado River basin in the late 1880s. In the 1930s, selenium concentrations in various drains, tributaries, and major rivers in the upper and lower Colorado River basins were in the 100?s and 1000?s of µg/L. Native fish inhabiting large rivers such as the Colorado pikeminnow and razorback sucker were abundant before 1890, but became rare after 1910 to 1920, before the influence of mainstem reservoirs in the upper and lower Colorado River. A hypothesis is presented that selenium contamination of the tributaries and major rivers of the Colorado River basin in the 1890 to 1910 period caused the decline of the endangered fish and continues to inhibit their recovery.     

The fate of selenium in the Imperial and Brawley constructed wetlands in the Imperial Valley (California)

The New River Wetlands Project is comprised of two constructed treatment wetland sites supplied with water from the New River and agricultural drainage water from the Imperial Valley in California. Bioaccumulation of selenium has created toxic conditions for wildlife in similar wetlands in other areas. Selenium levels in water (at wetland inflow and outflow), sediments, plants, invertebrates, and fish were analyzed for both wetland sites from 2006 to 2007. An average of 56% of the total mass of selenium in the inflow was removed at the Imperial site, and 70% was removed at the Brawley site. Most of the retained selenium (8 kg at the Imperial site and 2 kg at the Brawley site) was in the sediments. Less than 1% of the selenium accumulated in plant tissues. Mass balance calculations estimated that 17–61% of the selenium was lost through volatilization. After 6 years of operation of these wetlands, concentrations of selenium in fish and invertebrates were at or above threshold ranges for reproductive effects in birds and fish. Constructed wetlands are an efficient method for removing selenium from agricultural drainwater, although they need to be monitored over the long-term for potential risks posed by bioaccumulation of selenium.     

Mercury Toxicity and the Mitigating Role of Selenium

Mercury is a well-known environmental toxicant, particularly in its most common organic form, methylmercury. Consumption of fish and shellfish that contain methylmercury is a dominant source of mercury exposure in humans and piscivorous wildlife. Considerable efforts have focused on assessment of mercury and its attendant risks in the environment and food sources, including the studies reported in this issue. However, studies of mercury intoxication have frequently failed to consider the protective effects of the essential trace element, selenium. Mercury binds to selenium with extraordinarily high affinity, and high maternal exposures inhibit selenium-dependent enzyme activities in fetal brains. However, increased maternal dietary selenium intakes preserve these enzyme activities, thereby preventing the pathological effects that would otherwise arise in their absence. Recent evidence indicates that assessments of mercury exposure and tissue levels need to consider selenium intakes and tissue distributions in order to provide meaningful risk evaluations.     

Egg Selenium Concentrations as Predictors of Avian Toxicity

Aquatic birds are exposed to selenium through their diet by ingesting aquatic invertebrates that have accumulated selenium from water and the food chain. However, dietary composition is highly variable among species, over time, and across sites, making it difficult to provide accurate estimations of dietary exposure for particular species at specific locations. Selenium accumulates in the egg, resulting in embryo malformation, embryonic death, and decreased survival of juveniles. If the relationship between egg concentration and these reproductive parameters can be defined with sufficient certainty, then risk assessments can be performed through analysis of egg selenium concentrations. Other researchers have proposed egg toxicity thresholds that lead to conclusions of widespread selenium toxicoses in waterbirds. However, we believe these values are overly conservative and that it is unlikely that selenium is posing a significant risk to wild birds in areas where the current water quality criterion is being met. Through the use of simple statistical models (logit, probit, and Weibull functions) we are able to express mortality and teratogenicity relationships for mallards (Anas platyrhynchos) in such a manner that the risk manager can be presented with information about the probability of reduced duckling survival if mean egg selenium (MES) concentrations are known. Data analysis indicates that the two endpoints (mortality and teratogenesis) cannot be distinguished statistically. Commonly used effects thresholds (the EC₁₀ and EC₂₀) correspond to 16 and 21?mg/kg dw MES using the most sensitive endpoint, chick mortality. Both of these values are higher than the 6?mg/kg dw level proposed by Skorupa (1998) who based his estimate on field-observational data potentially confounded by other environmental stress factors. The mortality and teratogenicity endpoints presented here relate selenium exposure to risk to individuals within a population and do not provide information about the probability of selenium causing changes in population growth rates, either at the local or regional levels.     

Toxicity Reference Values for the Toxic Effects of Polychlorinated Biphenyls to Aquatic Mammals

Threshold tissue residue concentrations of polychlorinated biphenyls (PCBs) and 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQs) were derived from the published results of semi-field (i.e., field collected food items were used as a medium of exposure to PCBs in laboratory reared animals) or field toxicity studies conducted with seals, European otters and mink. Based on biomagnification factors (BMFs) and concentrations of PCBs or TEQs measured in fish fed in the diet of experimental aquatic mammals, dietary threshold concentrations were estimated. Hepatic vitamin A, thyroid hormone concentration, suppression of natural killer (NK) cell activity and proliferative response of lymphocytes to mitogens were the toxicity endpoints measured in aquatic mammals. Threshold concentrations for PCBs or TEQs in livers of aquatic mammals to elicit the physiological effects ranged from 6.6 to 11?µg PCBs/g (geometric mean: 8.7?µ/g) and 160 to 1400?pg TEQs/g (geometric mean: 520?pg/g), lipid weight, respectively. The BMFs for PCBs and TEQs varied depending on the marine mammal species, and therefore the dietary threshold concentrations could be referred only by a range of values (rather than a mean value), which were 10 to 150?ng PCBs/g and 1.4 to 1.9?pg TEQs/g, wet weight, for PCBs and TEQs, respectively.     

Human serum albumin-bound selenium (Se-HSA) in serum and its correlation with other selenium species

IntroductionSelenium (Se) is a trace element with different toxicological and nutritional properties according to its chemical forms. Among the wide range of selenium species, human serum albumin-bound selenium (Se-HSA) has still uncertain composition in terms of organic or inorganic selenium species. This study aimed at investigating the relation between Se-HSA levels with total selenium and the specific organic and inorganic selenium species.MethodsWe determined levels of total selenium and selenium species in serum of participants enrolled in two populations of the Emilia-Romagna region, in Northern Italy. Anion exchange chromatography coupled with inductively coupled plasma dynamic reaction cell mass spectrometry was used as quantification method. Correlations between Se-HSA and the other selenium compounds were analyzed using linear regression and restricted cubic spline regression models, adjusted for potential confounders.ResultsThe first cohort comprised 50 participants (men/women: 26/24) with median (interquartile range, IQR) age 50 (55−62) years, while the second was composed of 104 participants (M/W: 50/54), median (IQR) age 48 (44−53) years. Median (IQR) levels of total selenium were 118.5 (109−136) µg/L and 116.5 (106−128) µg/L, respectively, while Se-HSA was 25.5 µg/L (16.2–51.5) and 1.1 (0.03–3.1) µg/L, respectively. In both populations, Se-HSA was positively associated with inorganic selenium species. Conversely, Se-HSA was inversely associated with organic selenium, especially with selenoprotein P-bound-Se (Se-SELENOP) and less strongly with selenomethionine-bound-Se (Se-Met), while the relation was null or even positive with other organic species. Evaluation of non-linear trends showed a substantially positive association with inorganic selenium, particularly selenite, until a concentration of 30 µg/L, above which a plateau was reached. The association with Se-SELENOP was inverse and strong until 100 µg/L, while it was almost null at higher levels.ConclusionsOur findings seem to indicate that Se-HSA incorporates more selenium when circulating levels of inorganic compounds are higher, thus supporting its mainly inorganic nature, particularly at high circulating levels of selenite.     

Using tree leaves and barks collected from contaminated and uncontaminated areas as indicators of air metallic pollution

Abstract

The aim of this study was to show the usefulness of woody species in assessing air pollution by cadmium, copper, lead, and zinc. For this, washed leaves, unwashed leaves, and barks of a coniferous species (Cupressus sempervirens var. fastigiata) and a broadleaved one (Eucalyptus cladocalyx F. Muell) were analyzed for cadmium, copper, lead and zinc contents. A transect sampling approach was carried out during spring 2016. Fifty stations were selected along an intensive traffic road, and three in a control area. The results showed that the highest concentrations were recorded in barks for copper (21.86?µg/g, 23.33?µg/g) and lead (14.53?µg/g, 63.33?µg/g), and in unwashed leaves for cadmium (0.57?µg/g, 1.19?µg/g) and zinc (48.94?µg/g, 47.6?µg/g) for E. cladocalyx F. Muell, and C. sempervirens var. fastigiata, respectively. Lead and zinc are the most accumulated metals compared to cadmium and copper in all samples. The studied metal contents in urban area were significantly higher than that of the control one. This represents that traffic road has influenced the metals contamination of the surrounding area. Results of the bioconcentration factor (BCF) for both species indicate that the studied species could be used as biomonitors to identify ecological problems and to predict effect on wildlife habitats. The highest values of metal accumulation index (MAI) indicate the effectiveness of these trees for controlling the air metals in the polluted areas. Result shows too that the studied species could be used for phytoextraction of heavy metals from the polluted soils and/or air.     

Tissue-specific accumulation and speciation of selenium in rainbow trout (Oncorhynchus mykiss) exposed to elevated dietary selenomethionine

The toxicity of selenium in fish is influenced by its chemical speciation and the exposure route. In the natural environment, selenium exposure to fish occurs primarily in the form of selenomethionine in diet. Thus, the main objective of this study was to examine the tissue-specific selenium burden and speciation in fish exposed to elevated dietary selenomethionine. Rainbow trout (Oncorhynchus mykiss) were treated with dietary selenomethionine (40 μg g(-1) dry mass) for 2 weeks, and at the end of the exposure different tissue samples were collected to assess the tissue-specific distribution and speciation of selenium. We used synchrotron-based X-ray absorption near edge spectroscopy (XANES) to determine the selenium speciation profile. Selenomethionine, selenocysteine and selenocystine were found to be the predominant form of selenium in all of the tissues; however their relative proportion varied across different tissues. In general, the organs primarily involved in selenium handling in fish (e.g., liver, kidney) accumulated a higher percentage of selenocystine. We also found that dietary selenomethionine exposure resulted into a marked increase in selenium burden of all major tissues in fish including the brain. Collectively, our findings provide new insights into the tissue-specific distribution and speciation of selenium in fish exposed to selenomethionine via diet.     

Stream ecosystem response to, and recovery from, experimental exposure to selenium

The effects of selenium on streamecosystems were studied in outdoor,experimental stream mesocosms during a dosingperiod in which sodium selenite was added atnominal concentrations of 30 µg/L,10 µg/L, and 2.5 µg/L. The durationof the high, medium, and low treatments were573 d, 972 d, and 311 d, respectively. Apost-dosing period of three years (hightreatment) and two years (medium, lowtreatments) also was studied. Seleniumconcentrations in water, sediment, plants, andmacroinvertebrates were measured throughoutthe dosing and recovery periods. Fatheadminnows and bluegill sunfish were periodicallyheld in the streams to measure seleniumaccumulation and its effects on fish survivaland reproduction. Quantitative samples ofmacroinvertebrates were collected to assessselenium effects on macroinvertebratecommunities.Mean selenium concentration inwater was quite close to the nominalconcentration. Selenium accumulated in thesediment in all three treated streams, but notin the control streams. Sediment seleniumdecreased slowly after dosing ceased, but wasstill significantly higher than in controlstreams three years (high treatment) and twoyears (medium treatment) later.Macrophytetissue selenium concentrations weresignificantly greater in all three treatmentsthan those in the control streams duringdosing. Macrophyte selenium bioaccumulationfactors (BAFs) ranged from about 300 to 1900. Tissue selenium decreased rapidly in all threetreatments after dosing ended.During dosing,selenium concentrations in animals from allthree treatments were significantly higherthan in those from control streams. The BAFsfor macroinvertebrates ranged from 1100 to2000. Isopods accumulated more, and amphipodsless, selenium than other invertebrates. Therewere no significant effects of selenium onmacroinvertebrate abundance, richness ordiversity. Several macroinvertebrates werenot affected by exposure to selenium, butisopod and Tubifex populations weredramatically reduced in the high and mediumtreatments. After dosing, mean seleniumconcentration in macroinvertebrates decreasedslowly.Bluegill sunfish accumulated seleniumduring dosing and after selenium additionsceased. Tissue selenium was highest in theliver, followed by the gonads, skeletalmuscle, and whole body. Tissue seleniumconcentrations one (high, medium) and two(high) years after dosing were lower thanduring dosing, but whole body, skeletal muscleand liver concentrations were high enough tobe considered potentially toxic.Recovery ofselenium contaminated streams includes bothreduction of tissue selenium concentration tonon-toxic levels in fish and their foodorganisms and recovery of populations of taxadeleteriously affected by selenium exposure. Our results suggest that when selenium iseliminated from the water in streams, seleniumconcentrations in sediment, plants,macroinvertebrates, and fishes will decreaseto levels that approach concentrationsconsidered to be non-toxic to fish andwildlife and that affected populations willrecover within several years. Based onselenium accumulation in the food chain andthe presence of real, but not statisticallysignificant, effects on fish mortality andreproduction in the low treatment streams, wesupport a selenium water quality criterion forthe protection of fishes and sensitiveinvertebrates of 2 µg/L or less.     

Relationships among nutrition and reproduction and relevance for wild animals

This review discusses aspects of feeding ecology, nutrition, and dietary husbandry that are particularly relevant to reproductive success in wild animals. Emphasis has been placed on recently published literature. Special attention has been given to requirements for energy and protein and the unique roles of essential amino acids, essential fatty acids, calcium, phosphorus, zinc, copper, selenium, and vitamins A, C, D, and E. Information has been drawn from research with mammals, birds, reptiles, amphibians, and fish, including the domestic and laboratory species that play such a large role in elucidating mechanisms connecting nutrition and reproduction. Zoo Biol 23:475–487, 2004. © 2004 Wiley-Liss, Inc.     

A Prospective Study of Selenium Concentration and Risk of Preeclampsia in Pregnant Iranian Women: a Nested Case–Control Study

Preeclampsia remains a leading cause of maternal and perinatal mortality and morbidity worldwide; however, its specific etiology still remains obscure. Some studies implicate poor maternal selenium status predisposing the mother to preeclampsia. This study was designed to determine changes in plasma selenium levels in women having preeclampsia as compared with those with normal pregnancy. In a nested case–control study, 650 normal primigravida in their first 24–28 weeks participated in the study. After 3 months of follow-up of all subjects, blood selenium levels were measured in 38 women presenting consecutively with preeclampsia and in 38 women having a normal pregnancy by atomic absorption spectrophotometry. Birth outcomes were recorded, such as gestational age at delivery, height, weight, birth head circumflex and 1-min Apgar score. Preeclampsia affects about 5.84 % of pregnancies, and in our study, there were no significant differences in age, anthropometric indices, and family history of preeclampsia between the preeclamptic and control groups. The selenium concentrations in plasma in women with preeclampsia were significantly lower as compared with those in women with normal pregnancy (70.63?±?21.41 versus 82.03?±?15.54 μg/L, p?<?0.05). Being in the bottom tertile of selenium concentration (less than 62.2 μg/L) was associated with greater risk of preeclampsia in pregnant women. The reduced selenium in the maternal circulations observed in the preeclamptic mothers support the hypothesis that insufficient selenium concentration may be a contributing factor to the pathophysiological mechanisms associated with preeclampsia, and optimizing the dietary selenium intake through supplementation could produce demonstrable clinical benefits.     

Influence of Dietary Sodium Selenite on Tissue Selenium Levels of Growing Pigs

Twenty Norwegian Landrace pigs were divided into 5 groups and fed a basal diet consisting of a mixture of dried skim milk and whey powder together with ground barley. The diet was supplemented with 0, 0.2, 0.8, 1.2 and 2.2 μg selenium as sodium selenite and was fed for 12 weeks. The muscle selenium level was increased by a factor of about 4 and the liver selenium by a factor of about 12 when the dietary selenium supplement was increased from zero to 2.2 μg/g. There was a significant linear correlation between dietary selenium and selenium concentrations in tissues. Possible benefit for humans consuming meat from animals having received the selenium doses used in this experiment are discussed. dietary selenium; tissue levels; pigs.     

Dietary selenium for the mitigation of radiation injury: effects of selenium dose escalation and timing of supplementation

We recently reported that daily dietary supplementation with 100?μg selenium (a dose exceeding a rat's nutritional requirement by about 33-fold) initiated immediately after total-body irradiation (TBI) and maintained for 21?weeks mitigates radiation nephropathy in a rat model as indicated by blood urea nitrogen (BUN) levels and histopathological criteria (Radiat Res. 2009; 17:368-73). In this follow-up study, we explored the risks and benefits of delaying the onset of supplementation, shortening periods of supplementation, and escalating selenium supplementation beyond 100?μg/day. Supplementation with 200?μg selenium/day (as selenite or seleno-l-methionine) substantially improved the mitigation of radiation nephropathy by lowering BUN levels at 4?months after TBI from 115 to as low as 34?mg/dl and by proportionally lowering the incidence of histopathological abnormalities. Shortening the period of supplementation to 3 or 2?months did not compromise efficacy. Delaying the onset of supplementation for 1?week reduced but did not abrogate the mitigation of radiation nephropathy. Supplementation with 300?μg/day mitigated radiation nephropathy less effectively than 200?μg and was poorly tolerated. Rats that had been given 10?Gy of TBI were less tolerant of high-dose selenium than nonirradiated rats. This reduced tolerance of high-dose selenium would need to be taken into consideration when selenium is used for the mitigation of radiation injury in victims of nuclear accidents or acts of radiological terrorism. The high dose requirements, the pronounced threshold effect, and the superior performance of selenite suggest that the mitigation of radiation nephropathy involves mechanisms that go beyond the induction of selenoproteins.     

Identification and Determination of Selenoneine, 2-Selenyl-N α , N α , N α -Trimethyl-l-Histidine, as the Major Organic Selenium in Blood Cells in a Fish-Eating Population on Remote Japanese Islands

Selenoneine is the major selenium compound in fish muscles, and fish appears to be an important source of selenium in the fish-eating population. Selenoneine has strong antioxidant activity and a detoxifying function against methylmercury (MeHg) toxicity. Dietary intake, bioaccumulation, and metabolism of selenoneine have not been characterized in humans. A nutritional survey was conducted in remote islands of the Kagoshima Prefecture in Japan. To evaluate the potential risks and benefits of fish consumption for health, we measured concentrations of selenoneine, total selenium, MeHg, inorganic mercury, and polyunsaturated fatty acid (LC-PUFA) in the blood of a fish-eating human population. The erythrocyte, leukocyte, and platelet residues following removal of serum (cellular fraction) contained 0.510 μg Se/g, 0.212 μg selenoneine Se/g, and 0.262 μg Se-containing proteins Se/g, whereas the serum contained 0.174 μg total Se/g. Selenoneine was highly concentrated in the cellular fraction in a manner that was dependent on subjects' frequency of fish consumption. Concentrations of selenoneine were closely correlated with concentrations of MeHg in the cellular fraction. Selenoneine is the major chemical form of selenium in the blood cells of this fish-eating human population and may be an important biomarker for selenium redox status.     

Digestive physiology: a view from molecules to ecosystem

Digestive physiology links physiology to applications valued by society, such as understanding ecology and ecological toxicology and managing and conserving species. Here I illustrate this applied and integrative perspective with several avian case studies. The match between digestive features and diet provides evidence of tradeoffs that preclude doing well on all possible substrates with a single digestive design, and this influences ecological niche partitioning. But some birds, such as wild house sparrow (Passer domesticus) nestlings, are digestively very flexible. Their intestinal maltase activity and mRNA for intestinal maltase glucoamylase specifically and reversibly change when they switch among foods with different starch content. Houses sparrows and many other birds absorb hydrolyzed water-soluble monomers, such as glucose, mainly passively via tight junctions between enterocytes (i.e., paracellular absorption). Such species might be good models for studying this process, which is important biomedically for absorption of drugs. High paracellular absorption may enhance absorption of low molecular weight, natural water-soluble toxins. Also, reliance of American robins (Turdus migratorius) on passive absorption makes them less sensitive to types of plant toxins that inhibit mediated glucose absorption, such as phlorizin or the flavanoid isoquercetrin. Determining absorption of environmental contaminants is another important ecological application. Common loon (Gavia immer) chicks absorbed 83% of methyl mercury in fish meals, eliminate the mercury slowly, and consequently are predicted in the wild to bioaccumulate mercury to higher concentrations than in their foods. The quantitative details can be used to set regulatory levels for mercury that will protect wildlife.