Selenium Concentrations In Eggs Research Articles

Bioaccumulation and effects of selenium from surface coal mining in an aquatic songbird

Open-pit mining operations are hailed for safe working conditions for miners as well as economically and logistically favourable outcomes for mining companies. However, ecological impacts of these operations may persist for decades. Expansions of open-pit coal mining in British Columbia of Western Canada are planned. Governmental regulation of background contaminants leached from these mines into nearby water systems were established to mitigate environmental impacts associated with these operations. We analyzed water, periphyton, invertebrate, and American dipper (Cinclus mexicanus) blood, egg, and feather samples for selenium and mercury exposure related to mining operations in the Elk Valley. We also quantified effects associated with exposure on clutch size and hatching success. Selenium concentrations in water, periphyton, and invertebrates were significantly higher downstream of mines compared to reference sites within and outside of the Elk River watershed. Selenium concentrations in water from exposed sites exceeded current regulatory levels established to protect wildlife by up to 20 times. Mercury concentrations were below toxic levels for birds in all media and did not factor into determination of selenium exposure or effects. Egg selenium concentrations were on average 0.9 times the regulatory threshold. Our stable isotope analyses showed that diets of nesting females included a negligible proportion of higher order consumers. We did not detect a significant effect of selenium on the rate of hatching success or clutch size of dippers nesting in exposed sites. We conclude that at the time of the investigation, selenium exposure was not impairing hatching of American dippers at the sampled locations.

Maternal transfer of contaminants in birds: Mercury and selenium concentrations in parents and their eggs

We conducted a detailed assessment of the maternal transfer of mercury and selenium to eggs in three bird species (n = 107 parents and n = 339 eggs), and developed predictive equations linking contaminant concentrations in eggs to those in six tissues of the mother (blood, muscle, liver, kidney, breast feathers, and head feathers). Mercury concentrations in eggs were positively correlated with mercury concentrations in each of the mother's internal tissues (R2 ≥ 0.95), but generally not with feathers. For each species, the proportion of mercury transferred to eggs decreased as mercury concentrations in the mother increased. At the same maternal mercury concentration, the proportion of mercury transferred to eggs differed among species, such that Forster's tern (Sterna forsteri) and black-necked stilt (Himantopus mexicanus) females transferred more methylmercury to their eggs than American avocet (Recurvirostra americana) females. Selenium concentrations in eggs also were correlated with selenium concentrations in the mother's liver (R2 = 0.87). Furthermore, mercury and selenium concentrations in tern eggs were positively correlated with those in the father (R2 = 0.84). Incubating male terns had 21% higher mercury concentrations in blood compared to incubating females at the same egg mercury concentration. We provide equations to predict contaminant concentrations in eggs from each of the commonly sampled bird tissues.

Assessment of larval deformities and selenium accumulation in northern pike (Esox lucius) and white sucker (Catostomus commersoni) exposed to metal mining effluent

Uranium mining and milling operations in northern Saskatchewan (Canada) release effluents with elevated levels of certain trace metals and metalloids, including selenium. The goal of the present study was to evaluate the presence of selenium-induced deformities in northern pike (Esox lucius) and white sucker (Catostomus commersoni) larvae originating from adults collected downstream of a uranium mine. Eggs were fertilized in the field and incubated in the laboratory following a two-way (crossover) analysis-of-variance experimental design to discriminate effects from maternal transfer versus those from exposure to site water in the developing embryos. Selenium concentrations in northern pike and white sucker eggs (8.02 and 4.89 microg/g dry wt, respectively; mean +/- standard error throughout) from the exposure site were approximately two- to threefold higher than reference (2.35 +/- 0.20 and 1.94 +/- 0.25 microg/g dry wt, respectively). Among all evaluated deformities (skeletal curvatures, craniofacial deformities, fin deformities, and edema), only edema in white sucker fry from the exposure site was slightly elevated ( approximately 3%) compared to reference. The occurrence of edema, however, can be associated with factors other than selenium (e.g., other metals and organic compounds). Both fish species displayed strong linear relationships between the selenium concentrations in eggs and other tissues (muscle, liver, kidney, and bone), suggesting that selenium concentrations in eggs could be predicted from selenium concentrations in adult tissues. The lack of a clear, toxic response in the present study is in agreement with selenium thresholds for early life-stage deformities reported in other studies, with egg selenium concentrations in northern pike and white sucker collected at the exposure site being less than the 10 microg/g (dry wt) threshold associated with the presence of deformities.

Effect of Sodium Selenite and Zinc-L-selenomethionine on Performance and Selenium Concentrations in Eggs of Laying Hens

The objective of this study was to determine the effect of sodium selenite and zinc-L-selenomethionine on performance and egg Se concentration in laying hens. Two hundred and twenty-four CP Browns aged 71 weeks were divided according to a 2x3 factorial in a completely randomized design. One more group without additional Se supplementation was used as a negative control. Each treatment consisted of four replicates and each replicate contained eight laying hens. The dietary treatments were Tl: basal diet; T2, T3 and T4: basal diets plus 0.3, 1.0 and 3.0 mg Se from sodium selenite/kg, respectively; T5, T6 and T7: basal diets plus 0.3, 1.0 and 3.0 mg Se from zinc-L-selenomethionine/kg, respectively. The findings revealed that feed conversion rate/kg eggs, egg production, egg weight, Haugh units and eggshell thickness were not affected by source and level of Se (p>0.05). Increasing level of dietary Se significantly increased (p<0.05 the Se content of eggs. Zinc-L-selenomethionine markedly increased p<0.05 egg Se concentration as compared with sodium selenite. The results indicated that Se source did not influence performance of laying hens. However, zinc-L-selenomethionine increased p<0.05 egg Se concentration more than sodium selenite.

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

ABSTRACT 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.

Effect of Selenium Source and Level in Hen's Diet on Tissue Selenium Deposition and Egg Selenium Concentrations

The present study was conducted in a 2 x 4 factorial arrangement in a randomized complete block (RCB) design to compare the effects of a commercial inorganic Se source (sodium selenite, SS) with a commercial organic Se source (Se-enriched yeast, SY) on tissue Se distribution and blood and whole-egg Se concentrations in laying hens. Both Se sources were added into the basal diet at 0, 0.2, 0.5, and 1.0 mg/kg of Se. Seven hundred 68 week old Rohman laying hens were fed with a basal diet containing 0.15 mg/kg DM (dry matter) of Se for 2 weeks, and then, they were allocated randomly into seven groups and were investigated for 28 days. Each group was replicated five times with five cages of four hens per cage in each replicate. During the experiment, two eggs per replicate from each treatment were collected every 7 days and blood was sampled on days 0, 14, and 28 for whole-egg and whole-blood Se analyses. At the end of the experiment, two hens per replicate from each treatment were slaughtered, and muscle (cardiac and breast muscles), liver, spleen, and kidney were sampled for the determination of Se concentrations. The results showed that the addition of Se from either source caused a significant increase in whole-egg and whole-blood Se concentrations (p < 0.01) and Se concentrations in liver, kidney, spleen, and cardiac and breast muscles (p < 0.05) of hens in comparison to the control. Both Se sources and Se levels significantly influenced (p < 0.01) Se concentrations in egg, blood, and the above-mentioned tissues. There was a more significant increase in the Se concentrations in egg (p < 0.01), spleen (p < 0.05), and breast muscle (p < 0.01) and a decrease (p < 0.01) in whole-blood and kidney from hens fed SY than those from hens fed SS. The order of Se distribution was liver > kidney > spleen > cardiac muscle > egg > blood > breast muscle, irrespective of the addition level or source. It was concluded that meat and eggs from hens fed commercial SY are a potential source of Se for humans.

Mercury and Selenium in American White Pelicans Breeding at Pyramid Lake, Nevada

Abstract American White Pelicans (Pelecanus erythrorhynchos) that breed on Anaho Island, Pyramid Lake, Nevada, are potentially exposed to a variety of contaminants. Therefore, the reproductive success of this colony was monitored in 1996 and eggs, blood and feathers from nestlings, livers from adults and nestlings, regurgitated fish from nestlings, and fish from representative feeding areas were collected and analyzed for mercury and selenium to determine exposure to the pelicans and sources of contamination. Additional samples were collected and analyzed in 1988, 1992, and 2004. Reproductive success at the Anaho Island colony was normal in 1996 based on hatching rates of eggs (≥75% in undisturbed areas) and survival of nestlings. Mercury and selenium concentrations in eggs were generally below known effect levels and did not appear to have an adverse impact on hatching success. Mercury and selenium concentrations in fish ranged widely, with mercury of greatest concern. Microscopic lesions characteristic ...

The American Dipper as a Bioindicator of Selenium Contamination in a Coal Mine-Affected Stream in West-Central Alberta, Canada

Elevated levels of selenium have been found in water and aquatic biota downstream from two open-pit coal mines in the Rocky Mountain foothills of Alberta. Birds are particularly sensitive to excessive dietary selenium. However, there is relatively little information on selenium accumulation in birds' eggs on fast-flowing mountain streams. We determined levels of selenium in water samples, caddisfly larvae and eggs of American dippers (Cinclus mexicanus) nesting on the Gregg River, downstream from the mines, and on reference streams in the same general vicinity. Selenium levels (mean, 95% confidence limits) in water samples and caddisflies collected from sites near dipper nests on the Gregg River (water: 4.26, 1.90-9.56 microg L(-1); caddisflies: 8.43, 7.51-9.46 microg g dry wt(-1)) were greater than those collected from sites near nests on reference rivers (water: 0.38, 0.21-0.71 microg L(-1); caddisflies: 4.65, 4.35-4.97 microg g dry wt(-1)). The mean (+/- 1SE) selenium level in dipper eggs from the Gregg River (6.3 +/- 0.2 microg g(-1) dry wt) was significantly higher than it was in eggs from reference streams (4.9 +/- 0.2 microg g(-1) dry wt). Concentrations of selenium in eggs were significantly correlated with those in water samples (r = 0.45). The maximum selenium level in eggs from the Gregg River (9.0 microg g(-1)) may have been high enough to warrant concern from an ecotoxicological perspective. The American dipper can serve as a useful bioindicator of selenium contamination in mountainous, lotic ecosystems.

Accumulation of Selenium and Lack of Severe Effects on Productivity of American Dippers (Cinclus mexicanus) and Spotted Sandpipers (Actitis macularia)

Selenium has been found at elevated concentrations in water, sediments, and aquatic biota in the Elk River (British Columbia, Canada) and some of its tributaries downstream of several coal mines. Selenium water concentrations in those areas exceed Canadian and British Columbia guidelines and are above levels at which adverse effects to fish and waterfowl could occur. We compared selenium concentrations in the eggs of two riverine waterbirds, American dippers and spotted sandpipers, with measures of productivity: the number of eggs laid, egg hatchability, and nestling survival. In American dippers, the mean egg selenium concentration from the exposed areas, 1.10 +/- SE 0.059 microg/g wet weight, was indistinguishable from the reference areas, 0.96 +/- SE 0.059 microg/g wet weight. For spotted sandpipers, the mean egg selenium concentration in the exposed areas, 2.2 +/- 0.5 microg/g wet weight, was significantly higher than in the reference areas, 1.2 +/- 0.14 microg/g wet weight, but less than reported thresholds for waterfowl and other shorebirds. There were no significant differences in egg hatchability between dippers in reference and exposed areas, but reduced hatchability was apparent for sandpipers in exposed locations. Despite the slightly reduced hatchability in sandpipers, overall productivity was higher than regional norms for both species; thus, selenium did not affect the number of young recruited to local populations. We did not observe teratogenic effects in either species, although none was expected at these concentrations. Despite moderately high selenium concentrations in the water, mean egg selenium concentrations were less than predicted from uptake models. We hypothesise that the relatively low uptake of selenium into the eggs of the two waterbirds in this study is likely due to their lotic environment's low biological transformation and uptake rates.

Selenium impacts on razorback sucker, Colorado River, Colorado: II. Eggs

Effects on hatching and development of fertilized eggs in adult razorback sucker (Xyrauchen texanus) exposed to selenium in flooded bottomland sites near Grand Junction, Colorado, were determined. After 9 months exposure, fish were collected and induced to spawn and eggs collected for inorganic element analyses. A 9-day egg study was conducted with five spawns from Horsethief ponds, six spawns from Adobe Creek channel, and four spawns from North Pond using a reference water and site waters. Selenium concentrations in eggs were 6.5μg/g from Horsethief, 46μg/g from Adobe Creek, 38μg/g from North Pond, and 6.0μg/g from brood stock. Eggs from young adults had a smaller diameter and higher moisture content than brood stock. There were no differences among the four sources in viability, survival, hatch, hatchability, or mortality of deformed embryos or larvae. Adobe Creek larvae had more deformed embryos in eggs held in site water than held in reference water. There were significant negative correlations between selenium concentrations in adult muscle plugs and percent hatch, egg diameter, and deformities in embryos. Results from this study suggest that selenium contamination in parts of the upper basin of the Colorado River should be a major concern to recovery efforts for endangered fish.

Maternal Transfer of Contaminants to Eggs in Common Grackles (Quiscalus quiscala) Nesting on Coal Fly Ash Basins

Coal combustion is a major source of trace elements to the environment. Aquatic disposal of wastes from this process can result in reproductive failure in many wildlife species, but little is known regarding impacts on avian fauna. Individual eggs were collected from common grackles (Quiscalus quiscala) nesting in association with coal fly ash settling basins and a reference site to determine if females from the contaminated site transfered trace elements to their eggs. Whole clutches were also collected from both sites to examine inter- and intra-clutch variability of maternally transferred contaminants. Selenium was the only trace element found in significantly higher concentrations in ash basin eggs (x = 5.88 +/- 0.44 microg/g DW) than in reference eggs (x = 2.69 +/- 0.13 microg/g DW). Selenium concentrations in eggs from the ash basins were above background levels, but did not exceed higher proposed Se toxicity thresholds. Inter- and intra-clutch variation was higher for ash basin clutches than reference clutches. The relationship between selenium concentrations and laying order (estimated by egg mass) was not statistically significant, but increased Se concentration in the second egg of most ash basin clutches followed by declining concentrations in subsequent eggs suggested that further examination of this pattern might be warranted.

Mercury, methylmercury, and selenium concentrations in eggs of common loons (Gavia immer) from Canada.

Concentrations of Hg and Se were determined for a total of 125 Common Loon (Gavia immer) eggs collected from lakes in Alberta, Saskatchewan, Ontario, Quebec, New Brunswick and Nova Scotia, Canada between 1972 and 1997. Resulting data were compared to Hg and/or Se concentrations known or suspected to cause reproductive impairment in birds. Organic (methyl) Hg analyses were also performed on a subset of 24 loon eggs. Thirty-nine of 125 eggs had total Hg levels exceeding those (0.6 microg g(-1) ww, or approximately 2.5 microg g(-1) dw) previously reported to be associated with reproductive impairment in common loons (Barr, 1986), and 9 of 125 eggs had Hg concentrations higher than the level associated with reproductive impairment in birds generally 1 microg g(-1) ww; (Thompson, 1996). Selenium concentrations in loon egg samples were less than levels known to cause reproductive impairment in birds. A weak but significant positive correlation was observed between egg-Hg and -Se concentrations (r = 0.511, p < 0.05). On average, methylmercury accounted for about 87% of total Hg in 24 eggs analysed for both total and organic Hg. In this subset of eggs, the relationship between organic (methyl) Hg and Se was significant (r = 0.538, p = 0.007) while that found between inorganic Hg and Se in the same eggs was not significant (r = 0.353, p = 0.091). This relationship was unexpected and was contrary to relationships established for organic and inorganic Hg vs. Se in adult loon liver and kidney tissue (Scheuhammer et al., 1998b).

Selenium in Blood of Predatory Birds from Kesterson Reservoir and Other Areas in California

Kesterson Reservoir (Merced County, California) is a selenium-contaminated grassland (previously a wetland) that supports a variety of upland birds and other wildlife. Although aquatic birds that occupied a wet Kesterson Reservoir in the early to mid-1980s suffered high mortality and reproductive failure due to selenium exposure, similar effects have not been identified in terrestrial birds. To better characterize selenium exposure and potential effects in terrestrial species, we analyzed blood for selenium concentrations (blood-Se) from predatory bird species at Kesterson and reference areas in California from 1994 to 1998. Except for loggerhead shrikes (Lanius ludovicianus), blood-Se was significantly higher in birds from Kesterson than in birds from other areas. Among species at Kesterson, blood-Se was higher in loggerhead shrikes and northern harriers (Circus cyaneus) than in other species sampled, possibly due to shrikes spending a relatively large proportion of time foraging at Kesterson. In general, data corroborated earlier modeled predictions of selenium accumulation in Kesterson raptors. Calculated (based on blood-Se) but not observed selenium concentrations in eggs of predatory birds from Kesterson exceed a previously established avian toxicity threshold of 10 ppm.

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.

Selenium Concentrations in Eggs of American Avocets and Black-Necked Stilts at an Evaporation Basin and Freshwater Wetland in California

Avian reproductive impairment has been observed at tile-drainage agricultural evaporation basins in the San Joaquin Valley, California, where evaporation basin operators are required to mitigate for reproductive effects to wildlife that feed and nest at these sites. We compared recurvirostrid eggs collected at a 296-ha selenium-contaminated agricultural evaporation basin from 1987 to 1996 and at a 58-ha freshwater mitigation wetland from 1994 to 1996. The eggs were analyzed to determine if selenium exposure changed at the evaporation basin after the freshwater mitigation wetland was established. Mean concentrations of selenium in American avocet (Recurvirostra americana) eggs were significantly lower (P 0.05) between the 2 sites during the postmitigation period. In contrast, selenium concentrations in black-necked stilt (Himantopus mexicanus) eggs at the evaporation basin did not differ (P > 0.05) between the pre- and postmitigation periods (4.5 mg/kg vs. 5.4 mg/kg), Selenium concentrations in stilt eggs were lower (P < 0.05) at the mitigation wetland (3.5 mg/kg) compared to the evaporation basin (5.4 mg/kg) during the postmitigation period. These results indicate that while creation of the freshwater mitigation wetland provided new breeding and a clean foraging habitat for stilts, these mitigation efforts did not succeed in reducing selenium intake by stilts that continned to nest at the evaporation basin. However, the freshwater wetland provided a clean' foraging area for stilts, which tend to select for freshwater babitats, and successfully attracted stilts away from the evaporation basin.

A Teratogenic Deformity Index for Evaluating Impacts of Selenium on Fish Populations

This paper describes a method for using teratogenic deformities in fish as the basis for evaluating impacts of selenium contamination. Teratogenic deformities are reliable bioindicators of selenium toxicosis in fish. They are produced in response to dietary exposure of parent fish and subsequent deposition of selenium in eggs. There is a close parallel between selenium concentrations in eggs, incidence of teratogenic deformities in larvae, and magnitude of reproductive failure. Using these relationships, an index was developed for teratogenic-based assessment of impacts to fish populations. The index is composed of three ratings that signify increasing levels of terata-induced population mortality: 1, negligible impact (<5% population mortality); 2, slight to moderate impact (5–20% population mortality); 3, major impact (>20% population mortality). Each rating is based on the anticipated population-level impact of the corresponding degree of mortality. Teratogenic-based impact assessment provides a conclusive cause–effect linkage between the contaminant and the fish. It is particularly useful for verifying selenium-induced impacts on reproductive success because poor reproduction can be caused by many things—i.e., fluctuating water levels, nest predation, food shortages, poor recruitment, etc. The index given here should be a useful tool for evaluating the effect of selenium on fish populations. Moreover, application of this technique may save considerable time and money by identifying the most efficient use of manpower and funds early in the assessment process.

Selenium concentrations in the razorback sucker (Xyrauchen texanus): Substitution of non-lethal muscle plugs for muscle tissue in contaminant assessment

A single muscle plug was collected from each of 25 live razorback suckers inhabiting the Colorado River basin and analyzed for selenium by instrumental neutron activation. Eight fish from Ashley Creek and three from Razorback Bar exhibited selenium concentrations exceeding 8 μg/g, a level associated with reproductive failure in fish. Concentrations of selenium in eggs and milt were significantly correlated with selenium concentrations in muscle plugs and together indicate a possible explanation for the decline of this species in the Colorado River basin. Muscle plugs (<50mg) and muscle tissue (20 g) were collected from dorsal, anterior, and posterior areas of common carp, flannelmouth sucker, and an archived razorback sucker and analyzed for selenium. Concentrations of selenium in muscle plugs were significantly correlated with selenium concentrations in muscle tissue from the same location and fish (r=0.97). Coefficients of variation for selenium concentrations in each fish were <6.5% for muscle tissue, but ranged from 1.5 to 32.4% for muscle plugs. Increased variation in muscle plugs was attributed to lower selenium concentrations found in the anterior muscle plugs of flannelmouth suckers. Mean selenium concentrations in muscle plugs and tissue from dorsal and posterior areas and muscle tissue from the anterior area were not significantly different. The non-lethal collection of a muscle plug from dorsal and posterior areas of the razorback sucker and other fish species may provide an accurate assessment of selenium concentrations that exist in adjacent muscle tissue.

Selenium in eggs and milt of razorback sucker (Xyrauchen texanus) in the middle Green River, Utah

Eggs from three female and milt from five male endangered razorback suckers (Xyrauchen texanus) were collected from the Razorback Bar (about 20 km upstream of Ashley Creek) in the Green River of northeastern Utah. Eggs, but not milt, had concentrations of selenium that were above the range of selenium concentrations in control fish from laboratory studies or reference fish from field studies. The concentrations, however, were below those reported in selenium-exposed fish that had reproductive problems in laboratory studies or field investigations. Tests with three streamside spawned pairs of razorback suckers, which were sampled for eggs and milt in this study, resulted in no hatching of fertilized eggs. Concentrations of selenium in eggs and milt were significantly correlated with selenium concentrations in muscle plugs taken from the same fish, but egg and milt concentrations were not significantly different from muscle plugs. Selenium concentrations in eggs of razorback suckers in the Green River may be sufficiently elevated to cause reproductive problems that are contributing to the decline of this species in the upper Colorado River Basin.

Reproduction of mallards following overwinter exposure to selenium

Forty pairs of mallards ( Anas platyrhynchos) were fed 15 ppm selenium as selenomethionine for about 21 weeks during winter. Twenty pairs served as controls. At the end of 21 weeks, which coincided with the onset of the reproductive season, selenium treatment was ended. Four birds died while on selenium treatment. Treated females lost weight, and their egg-laying was delayed. Hatching success of some of the first eggs laid by selenium-treated females was lower than that of controls, and a few of these early eggs contained deformed embryos, but, after a period of about two weeks off the selenium-treated diet, reproductive success returned to a level comparable with that of controls. The return to normal reproductive success was the result of a corresponding decrease in selenium concentrations in eggs once selenium treatment ended.

Impaired Reproduction of Mallards Fed an Organic Form of Selenium

We fed mallards (Anas platyrhynchos) diets supplemented with 0-, 1-, 2-, 4-, 8-, or 16-ppm selenium in the form of selenomethionine. We fed another group of mallards a diet containing 16-ppm selenium as selenocystine. Females fed the control diet produced a mean of 8.1 ducklings that survived to 6 days of age, which was significantly greater than the 4.6 young produced by females fed 8-ppm selenium as selenomethionine and the zero surviving young of females fed 16-ppm selenium as selenomethionine. Selenocystine did not impair reproduction. Diets containing 8and 16-ppm selenium as selenomethionine caused malformations in 6.8 and 67.9%, respectively, of unhatched eggs compared with 0.6% for controls. The most common malformations were of eyes, bill, legs, and feet. Selenium did not affect the onset or frequency of egg laying, egg size, shell thickness, fertility of eggs, or sex ratio of ducklings. Reduced survival and growth occurred in ducklings hatched from groups whose parents had received 8or 16-ppm selenium as selenomethionine, even though all ducklings were fed a control diet. Concentrations of selenium in eggs and liver of adults could be predicted from dietary concentrations. We conclude that the dietary threshold of selenium as selenomethionine necessary to impair reproduction is between 4 and 8 ppm. It is difficult to identify 1 level of selenium in eggs that will be diagnostic of reproductive impairment in the field because different chemical forms of selenium appear to have different toxicities in eggs. However, when eggs from a wild population contain > 1-ppm selenium on a wet-weight basis, reproductive impairment may be possible and should be evaluated in that population. At 5-ppm selenium in eggs, reproductive impairment is much more likely to occur. J. WILDL. MANAGE. 53(2):418-428 Selenium is a trace element in the earth's crust and, in small amounts, is essential to good health in animals. Too much selenium, however, is toxic to animals. Reproductive failure of chickens caused by selenium poisoning was noted in South Dakota as early as the 1930's (Poley and Moxon 1938). Grains grown on seleniferous soils proved to be the source of the toxic concentrations of