Comparative acute toxicity and bioconcentration of selenium by the midge Chironomus decorus exposed to selenate,selenite, and seleno-DL-methionine

The increased flux of selenium into aquatic ecosystems due to anthropogenic activities has resulted in the degradation of several systems. Initial experiments examined the comparative acute toxicity of waterborne selenate, selenite, and seleno-DL-methionine to fourth instar Chironomus decorus larvae resulting in 48-h LC₅₀ concentrations of 23.7, 48.2, and 194 mg Se/L, respectively. The relative toxicities of the selenium forms are reversed compared to previous studies on other species and demonstrate that relative waterborne selenium toxicity is species specific. Studies examining the kinetics of selenate and selenite (the dominant waterborne forms) accumulation by C. decorus larvae exposed to the 48-h LC₅₀ selenium concentrations showed initial rapid uptake and subsequent plateauing with maximum concentrations attained by 16 h. The final whole body selenium levels were approximately 63 mg Se/kg for selenate and 85 mg Se/kg for selenite. Comparative bioconcentration experiments demonstrated that after 48 h selenium accumulation was greater in larval C. decorus exposed to 25 mg Se/L as seleno-DL-methionine than in those exposed to 25 mg Se/L as selenate and selenite.     

Effects of elevated foodborne selenium on growth and reproduction of the fathead minnow (Pimephales promelas)

Several field studies of selenium-contaminated lakes and reservoirs have indicated the possibility of selenium-induced reproductive failure in important populations of fish. These investigators have hypothesized that bioaccumulation of selenium through the food chain led to fish selenium levels high enough to elicit toxic responses. The present investigation was designed to determine the effects of elevated foodborne selenium on the fathead minnow (Pimephales promelas). Fish were fed a diet spiked with a mixture of inorganic (selenite and selenate) and organic (seleno-L-methionine) selenium and effects on growth and reproduction were determined. Growth was significantly inhibited at the highest selenium treatment levels evaluated (20 and 30 ppm Se). There were no significant treatment effects on any of the reproductive parameters measured. Reasons for the disparity between selenium-induced reproductive impairment observed in other species and apparent lack of impairment in fathead minnows may involve reduced bioaccumulation of selenium by minnows due to differences in gut morphology and physiology.     

Comparative toxicity of selenite and selenate to the amphipodHyalella azteca

Selenium contamination of aquatic ecosystems is rapidly becoming a concern throughout the United States, leading to a lowering of the freshwater selenium criteria by the U.S. Environmental Protection Agency from 35 g/L to 5 g/L measured as total selenium. However, considerable information indicates important differences in bioaccumulation and toxicity between the various selenium forms. We conducted a series of experiments to determine the comparative toxicity of selenite and selenate to the amphipodHyallela azteca. In 48 h, 96 h, and 240 h (10 d) LC50 tests, selenite was 2 to 4 times more toxic than selenate, the difference decreasing as exposure time increased. This difference in toxicity was even more pronounced in the 24 d reproductive bioassay, where selenite caused a significant decrease in number of young per female at 200 g/L while selenate had no effect up through 700 g/L (the highest concentration tested).     

Toxicity of selenomethionine- and seleno-contaminated sediment to the amphipod Corophium sp

The acute toxicity of four chemical species of selenium to juvenile amphipods (Corophium sp.) was assessed in water-only tests. The seleno-amino acid compounds seleno-L-methionine and seleno-DL-cystine were found to be more toxic (96-h LC(50) values of 1.5 and 12.7 microg Se/L) than the inorganic selenite and selenate (96-h NOEC values of 58 and 116 microg Se/L). New marine sediment testing procedures were developed using juvenile and adult Corophium sp. Both life stages were highly sensitive to seleno-L-methionine-spiked sediment. The juveniles were approximately five times more sensitive, with a 10-day LC(50) of 1.6 microg Se/g (dry weight) compared to 7.6 microg Se/g (dry weight) for the adults. Sediment collected from three sites in Lake Macquarie, a marine barrier lagoon with elevated concentrations of total selenium, had no effect on the survival of adult Corophium over 10 days. The toxicity of seleno-L-methionine to other amphipod species occurring in Lake Macquarie was assessed in water-only tests, with Paracalliope australis being highly sensitive (96-h LC(50) 2.58 microg Se/L).     

Toxicity and accumulation of selenite and selenate in the unicellular marine alga Cricosphaera elongata

The toxicity and bioaccumulation of selenium in the 4⁺ and 6⁺ oxidation states were investigated in a marine unicellular alga Cricosphaera elongata in culture. Selenite was more toxic than selenate. Exponentially growing cells and cells in the stationary phase of C. elongata rapidly accumulated selenite (0.1 and 1.0 mg/L Na₂SeO₃) and selenate (0.1 and 1.0 mg/L Na₂SeO₄). Within the first two hours of contact, the amount of selenium taken up decreased sharply in exponentially growing cells, while cells in the stationary phase continued accumulating selenium until a plateau was reached. The presence of metabolic inhibitors such as KCN (potassium cyanide) or DCMU (3-(3,4-dichloro-phenyl)-1,1 dimethylurea) or glutaraldehyde did not modify the first phase of accumulation of selenite by C. elongata in the stationary phase, whereas further accumulation was inhibited. Possible mechanims of accumulation of selenium are discussed. In a series of long term experiments (14 or 31 d), intracellular partitioning of Se in C. elongata cells, exposed to selenite, was analysed; total, protein-bound and free cytosolic selenium concentrations increased with selenium concentration added to the culture medium (0.1 or 1 mg/L Na₂SeO₃) and with exposure time (at 0.1 mg/L Na₂SeO₃) from 14 d or 31 d. Most of the selenium was associated with proteins; these proteins may represent a form of storage or detoxication of selenium.     

The antagonism between selenium and cadmium in a freshwater mollusc

The protective effect of selenium against cadmium toxicity in rats is well documented. Data concerning such protection are lacking in invertebrates. The object of this study was to check whether such an antagonism between Se and Cd can be found in the freshwater molluscLymnaea stagnalis L. In the presence of sublethal amounts of selenium, sensitivity with respect to cadmium is nearly halved. Sublethal amounts of cadmium give additional protection against the toxic effects of selenium, since this concentration completely prevented mortality due to high doses of selenite (3 mg/L Se) and selenate (15 mg/L Se).     

Bioaccumulation of selenate,selenite, and seleno-DL-methionine by the brine fly larvae Ephydra cinerea Jones

High concentrations of selenium threaten waterfowl at California San Joaquin Valley agricultural wastewater evaporation ponds. This study evaluates and compares two routes of Se exposure and uptake by third instar Ephydra cinerea (brine fly) larvae. A 48-h static bioconcentration bioassay provided information on the larval uptake of selenate, selenite, and seleno-DL-methionine (SeMet) at Se waterborne concentrations ranging from 10.0–20,000 ug/L. At equivalent concentration levels, SeMet was bioconcentrated to a greater extent than selenite, which was bioconcentrated more than selenate. Forty-eight-hour static bioconcentration vs. biomagnification bioassays allowed for comparisons of the two routes of exposure of selenate, selenite, and SeMet. Biomagnification was determined to be the primary Se uptake pathway, exemplified most notably in the selenite treatment. Measured agar-based food unit Se levels presented evidence that the uptake of selenite, and especially SeMet, by microbial populations was transferred to E. cinerea larvae as they scavenged for bacteria and yeast, etc. in the diet matrix. As a primary dietary item of waterfowl at evaporation ponds, E. cinerea in seleniferous waters presents a potentially high hazard.     

Acute toxicity of boron,molybdenum, and selenium to fry of chinook salmon and coho salmon

The acute toxicities of boron, molybdenum, and various forms of selenium, individually and in environmentally relevant mixtures, to swim-up and advanced fry of chinook salmon (Oncorhynchus tshawytscha) and coho salmon (O. kisutch) were determined in site-specific fresh and brackish waters. Boron and molybdenum were relatively non-toxic (96-hr LC50s > 100 mg/L) to both life stages of both species. Selenite was significantly more toxic than selenate to both species. Swim-up fry tested in fresh water were significantly more sensitive than advanced fry in brackish water to selenate and selenite. No mortalities occurred in any concentrations tested of seleno-DL-methionine; however, in the highest concentration (21.6 mg Se/L), at least 50% of the fish showed pronounced surfacing behavior. Coho salmon were more sensitive than chinook salmon to both selenate and selenite at either life stage; only the swim-up fry of coho salmon were more sensitive than chinook salmon to boron. In additional tests with swim-up chinook salmon, differences in the characteristics of the dilution water did not significantly modify the relative toxicities of boron, selenate, and selenite. In binary mixture studies, the joint acute toxic action of selenate and selenite, combined in various ratios, was additive to both species. Based on a comparison of the individual acute values for chinook salmon to the expected environmental concentrations, the margin of safety for boron was only 56 in fresh and 46 in brackish water. The margins of safety for selenate and selenite exceeded 275 in both fresh and brackish waters. However, the margin of safety for both selenate and selenite in the mixture test was 145 in fresh water and 220 in brackish water.     

The effect of sulfate on the bioconcentration of selenate by Chironomus decorus and Daphnia magna

Agricultural drainage containing high concentrations of selenium (Se) poses a continuing threat to wildlife in California's San Joaquin Valley. Drainage water from this area frequently contains high concentrations of sulfate, which are known to have mediating effects on the bioaccumulation and toxicity of Se in some organisms. It has been proposed that sulfate concentration should be a consideration in determining water quality criteria for Se. As a step toward analyzing the viability of such a plan, this study evaluated the effect of varying sulfate concentration on Se bioconcentration by two aquatic invertebrates. Fourth instar Chironomus decorus and neonate Daphnia magna were exposed, for a 48 h period, to 5.92 and 0.71 mg Se/L, as selenate, respectively. The selenium:sulfur (Se:S) ratio in the dilution waters ranged from 1:0 to 1:480 for C. decorus and 1:3 to 1:240 for D. magna. Increasing sulfate concentrations significantly reduced the accumulation of Se by both organisms. However, D. magna and C. decorus bioconcentrate Se differently at low sulfate concentrations. This difference can be explained by a two permease model for selenate/sulfate absorption. Although this experiment showed that sulfate may reduce selenate bioavailability to aquatic invertebrates, there is no indication that sulfate may completely eliminate selenate absorption. Thus, further research should be performed before sulfate concentration becomes a factor in the determination of water quality standards for selenium.     

Bioavailability of selenium from raw and cooked ground beef assessed in selenium-deficient Fischer rats.

The literature on the bioavailability of selenium (Se) from meats, especially beef, is meager, and that which existed when this research began suggested that Se was not highly bioavailable. In addition, much of the analytical values for Se in beef predated the Food and Drug Administration's 1973 approval of Se as an additive to feeds and mineral premixes of livestock.

One hundred and thirty-six weanling female Fischer 344 rats were divided into two dietary groups: the selenium deficient group in which animals were fed a torula yeast (TY) basal diet which contained 0.008 mg/kg Se and the control group in which animals were fed the TY diet to which was added 0.10 mg/kg Se as sodium selenite.

After 6 weeks of dietary treatment liver glutathione peroxidase (GSHPx) activity had fallen in the Se-deficient rats to 2.4% of that of control rats. At this time (week 6) rats from the Se-deficient TY diet were refed diets containing 0.10 mg/kg Se as selenite, selenate, raw or cooked ground beef that had been freeze-dried. During the Se-repletion period rats were sacrificed at weeks 1, 3, 5 and 8. Liver GSHPx activity and total Se levels in liver and muscle tissue were the criteria of Se bioavailability. After 8 weeks of Se resupplementation the recovery of liver GSHPx activity compared to the control animals (set at 100%) were selenite (98%, p > 0.05), selenate (117%, p < 0.05), raw beef (127%, p < 0.05) and cooked ground beef (139%, p < 0.05). Total Se in both liver and muscle tissue reflected the liver GSHPx activity with the total Se concentration in tissues being highest for cooked beef.

The data suggest that bioavailability of Se from ground beef is greater than that from either selenite or selenate.     

The retention and distribution by healthy young men of stable isotopes of selenium consumed as selenite, selenate or hydroponically-grown broccoli are dependent on the isotopic form

Twenty-seven healthy young men were randomly assigned to diets that supplied low (32.6 microg/d) or high (226.5 microg/d) levels of selenium for a 105-d study. After consuming the diets for 85 d, subjects were fed a test meal that contained 74Se in the form of selenite or selenate and 82Se incorporated into hydroponically-raised broccoli. Urine, fecal and blood samples were collected daily. Isotope absorption was not different (P > 0.05) for selenate and Se in broccoli; Se absorption from selenite was highly variable and was not included in statistical analyses. Significantly more isotope was absorbed by subjects fed the high Se diet (P = 0. 015). Urinary isotope excretion was greater when selenate was fed than when broccoli was fed (P = 0.0001), and consequently more Se from broccoli (as compared to selenate) was retained (59.2 +/- 2.4 and 36.4 +/- 4.6% for Se in broccoli and selenate, respectively; P = 0.0001). Despite the higher retention, less isotope from broccoli than from selenate was present in the plasma. Plasma proteins separated by gel permeation chromatography showed that most of the isotopes were distributed between two medium molecular weight peaks. Less isotope was found in plasma proteins of subjects fed the high Se diet, but the form of Se had no effect on isotope distribution. These results show that dietary Se intake alters the retention of stable isotopes of Se and that humans retain and distribute Se from broccoli in a different manner than Se from inorganic salts.     

Selenium uptake by larval Chironomus decorus from a Ruppia maritima-based benthic/detrital substrate

Elevated levels of selenium have led to the contamination of several aquatic ecosystems. Much of the selenium contamination has resulted from agricultural irrigation and drainage of seleniferous soils. Disposal of selenium contaminated drainwater in evaporation ponds has led to selenium bioaccumulation and toxicity in waterfowl and shorebirds using these ponds. Studies have demonstrated that it is a seleno-amino acid that causes the observed toxicity. However, selenate is the dominant form of selenium in agricultural drainwater, and the biotransformation of selenate into seleno-amino acids has been shown to be greatly limited relative to the more reduced selenium species. We hypothesize that it is in the benthic zone, where the reducing environment facilitates conversion of selenate to selenium forms more conducive to biotransformation, that most biotransformation and subsequent bioaccumulation of seleno-amino acids takes place, and that movement of selenium into the benthic-detrital food chain is a key pathway leading to selenium bioaccumulation. This hypothesis was investigated by conducting laboratory benthic-detrital food chain experiments using the common evaporation pond macrophyte Ruppia maritima as the benthic-detrital substrate. Larval Chironomus decorus were reared on the contaminated Ruppia substrate, and the resulting bioaccumulation and toxicity in the larvae were determined.     

Biofortification with selenium and implications in the absorption of macronutrients in Raphanus sativus L.

It is well known that selenium (Se) is an essential element for humans, presenting antioxidant functions. This study aimed to evaluate the efficiency of Raphanus sativus L. as an agricultural crop indicated for selenium biofortification and to investigate the influence of different sources and forms of application on Se accumulation and macronutrient absorption. The experiment followed a randomized complete design with five replicates, arranged in a 2 × 2 + 1 factorial scheme, consisting of two sources of Se (sodium selenate and sodium selenite) and two forms of application (application in the soil at the dose of 1.2 mg kg⁻¹ of Se and foliar application at the dose of 50 μmol L⁻¹ of Se), with a control treatment without the addition of selenium. The accumulations of Se in the leaf, root, and whole plants were higher with the selenate source applied via soil when compared with the foliar application. For the selenite source applied via soil, Se root contents were higher when compared with the fertilization via leaf. The Se content in the root was lower for the selenate applied via soil when compared with the other treatments and the control. Raphanus sativus L is an agricultural crop suitable for the agronomic biofortification of selenium, since it concentrates the appropriate levels of Se in the roots and leaves, not harming the crop yield. The application of Se in the form of selenate and via soil was the best technique to increase the contents of Se in the plant, without causing damages in the accumulation of biomass, despite having led to a reduction in the accumulation of S.     

Toxicity of organic and inorganic selenium to mallard ducklings

The toxicity of selenomethionine and sodium selenite to mallard ducklings (Anas platyrhynchos) was measured by feeding each form from hatching to six weeks of age at dietary concentrations of 0, 10, 20, 40, and 80 ppm selenium. At 80 ppm selenium, sodium selenite caused 97.5% mortality by six weeks and selenomethionine caused 100% mortality. At 40 ppm, these two forms of selenium caused 25 and 12.5% mortality. No mortality occurred at 10 or 20 ppm. Diets containing 20, 40, or 80 ppm selenium in both forms caused decreases in food consumption and growth. The only statistically significant effect of 10 ppm selenium was with sodium selenite, which resulted in larger livers than controls. Selenomethionine was more readily stored in the liver than sodium selenite at levels above 10 ppm selenium in the diet. Based on comparisons of residues of selenium in livers of surviving and dead ducklings, concentrations in the liver were not diagnostic of death due to selenium poisoning. Because both forms of selenium resulted in severe reductions in food consumption, selenium-induced starvation may have been related to duckling mortality. It was not clear whether either form of selenium at 10 ppm in the diet resulted in a leveling off of selenium concentrations in the liver within six weeks.     

Toxicity and oxidative stress of different forms of organic selenium and dietary protein in mallard ducklings

Concentrations of over 100 ppm (mg/kg) selenium (Se) have been found in aquatic plants and insects associated with irrigation drainwater and toxicity to fish and wildlife. Composition of diet for wild ducklings can vary in selenium-contaminated environments. Earlier studies have compared toxicities and oxidative stress of Se as selenite to those of seleno-DL-methionine (DL) in mallards (Anas platyrhynchos). This study compares DL, seleno-L-methionine (L), selenized yeast (Y) and selenized wheat (W). Day-old mallard ducklings received an untreated diet (controls) containing 75% wheat (22% protein) or the same diet containing 15 or 30 ppm Se in the above forms except for 30 ppm Se as W. After 2 weeks, blood and liver samples were collected for biochemical assays and Se analysis. All forms of selenium caused significant increases in plasma and hepatic glutathione peroxidase activities. Se as L at 30 ppm in the diet was the most toxic form, resulting in high mortality (64%) and impaired growth (>50%) in survivors and the greatest increase in ratio of oxidized to reduced hepatic glutathione (GSH). Se as both L and DL decreased the concentrations of hepatic GSH and total thiols. Se as Y accumulated the least in liver (approximately 50% of other forms) and had less effect on GSH and total thiols. In a second experiment, in which the basal diet was a commercial duck feed (22% protein), survival was not affected by 30 ppm Se as DL, L, or Y and oxidative effects on GSH metabolism were less pronounced than with the wheat diet.     

硒多糖、亚硒酸钠对大鼠血硒浓度和肝细胞色素P_(450)单加氧酶系的影响

研究了一次和连续７天腹腔注射硒多糖、亚硒酸钠对大鼠血硒浓度及肝细胞色素Ｐ４５０、ｂ５、ＮＡＤ（Ｐ）Ｈ－细胞色素Ｃ还原酶、谷胱甘肽硫转移酶（ＧＳＴ）和谷胱甘肽过氧化物酶（ＧＳＨ－Ｐｘ）的影响；并比较了硒多糖与亚硒酸钠的作用。结果表明：一次腹腔注射Ｓｅ０．６ｍｇ／ｋｇ体重的硒多糖和亚硒酸钠后，血硒浓度迅速增加，在注射后２小时血硒浓度达到高峰，随后血硒浓度逐渐下降。亚硒酸钠在大鼠体内的吸收和排出均较硒多糖快。连续７天腹腔注射０．２ｍｇ／ｋｇ体重剂量硒多糖和亚硒酸钠后，硒多糖和亚硒酸钠组大鼠血硒浓度分别为对照组的２．６倍和２．１倍，其中硒多糖组的血硒含量显著高于亚硒酸钠组（Ｐ＜０．０５）；硒多糖和亚硒酸钠在体内、外均降低肝细胞色素Ｐ４５０、ｂ５的含量，抑制ＧＳＴ的活性，硒多糖的作用尤为显著，分别为对照组的５７％、７０％和６２％（Ｐ＜０．０５）。两种硒化合物对ＮＡＤ（Ｐ）Ｈ－细胞色素Ｃ还原酶无明显影响。硒多糖和亚硒酸钠均能显著增强ＧＳＨ－Ｐｘ的活性（Ｐ＜０．０５）。     

Toxicity of inorganic contaminants, individually and in environmental mixtures, to three endangered fishes (Colorado squawfish, bonytail, and razorback sucker)

Two life stages of three federally-listed endangered fishes, Colorado squawfish (Ptychocheilus lucius), bonytail (Gila elegans), and razorback sucker (Xyrauchen texanus) were exposed to copper, selenate, selenite, and zinc individually, and to mixtures of nine inorganics in a reconstituted water that simulated the water quality of the middle Green River, Utah. The mixtures simulated environmental ratios of arsenate, boron, copper, molybdenum, selenate, selenite, uranium, vanadium, and zinc in two tributaries, Ashley Creek and Stewart Lake outlet, of the middle Green River. The rank order of toxicity of the individual inorganics, from most to least toxic, was: copper > zinc > selenite > selenate. Colorado squawfish larvae were more sensitive to all four inorganics and the two mixtures than the juveniles, whereas there was no consistent response between the two life stages for the other two species. There was no consistent difference in sensitivity to the inorganics among the three endangered fishes. Both mixtures exhibited either additive or greater than additive toxicity to these fishes. The primary toxic components in the mixtures, based on toxic units, were copper and zinc. Acute toxicity values were compared to measured environmental concentrations in the two tributaries to derive margins of uncertainty. Margins of uncertainty were low for both mixtures (9–22 for the Stewart Lake outlet mixture, and 12–32 for the Ashley Creek mixture), indicating that mixtures of inorganics derived from irrigation activities may pose a hazard to endangered fishes in the Green River.     

Comparison of Selenium Toxicity in Sunflower and Maize Seedlings Grown in Hydroponic Cultures

Several studies have demonstrated that selenium (Se) at low concentrations is beneficial, whereas high Se concentrations can induce toxicity. Controlling Se uptake, metabolism, translocation and accumulation in plants is important to decrease potential health risks and helping to select proper biofortification methods to improve the nutritional content of plant-based foods. The uptake and distribution of Se, changes in Se content, and effects of various concentrations of Se in two forms (sodium selenite and sodium selenate) on sunflower and maize plants were measured in nutrient solution experiments. Results revealed the Se content in shoots and roots of both sunflower and maize plants significantly increased as the Se level increased. In this study, the highest exposure concentrations (30 and 90 mg/L, respectively) caused toxicity in both sunflower and maize. While both Se forms damaged and inhibited plant growth, each behaved differently, as toxicity due to selenite was observed more than in the selenate treatments. Sunflower demonstrated a high Se accumulation capacity, with higher translocation of selenate from roots to shoots compared with selenite. Since in seleniferous soils, a high change in plants’ capability exists to uptake Se from these soils and also most of the cultivated crop plants have a bit tolerance to high Se levels, distinction of plants with different Se tolerance is important. This study has tried to discuss about it.     

Active absorption of selenate by rat ileum

Intestinal absorption of selenate and selenite in rats was investigated in vitro by using everted sacs of the duodenum, jejunum and ileum. Only the ileal sacs incubated with selenate accumulated selenium in the serosal fluid during the incubation. Selenium transport across the ileum did not occur against a concentration gradient when selenite instead of selenate was present in the incubation medium. Sulfate and thiosulfate significantly inhibited ileal selenate transport. Decreasing the activity of the Na+,K+-ATPase, by the addition of ouabain, resulted in a significant reduction of concentrative selenate transport by the ileum. Furthermore L-leucine, but not D-glucose and D-galactose, significantly reduced selenium absorption by ileal sacs incubated with selenate. It is concluded from these results that selenate is transported actively by the ileal mucosa and that a common transport mechanism for selenate and sulfate exists. The Na+-gradient across the intestinal brush border membrane seems to be capable of energizing active ileal selenate transport.     

Active oxygen species generation and cellular damage by additives of parenteral preparations: selenium and sulfhydryl compounds.

We investigated the relationship between active oxygen species (AOS) generation and cultured vascular endothelial cellular damage caused by simultaneous exposure to selenium compounds and sulfhydryl compounds such as cysteine (Cys) or reduced glutathione (GSH). Selenium compounds, selenite, selenate or selenomethionine (SeMet), are added to total parenteral nutrition (TPN) and intravenously administered. We confirmed by luminol dependent chemiluminescence, an indicator of AOS generation, that selenite generates AOS in the presence of clinical concentrations of sulfhydryl compounds, 0.5 mM Cys or 0.5 mM GSH, and that the amount of AOS generated reaches the maximum when their mole ratio is 1:50. However, AOS generation was not observed after simultaneous administration of various concentrations of selenate or SeMet with sulfhydryl compounds. Moreover, simultaneous exposure to 10 microM selenite and sulfhydryl compounds was found to result in significant increases in the [3H]-adenine and lactate dehydrogenase (LDH) release rates from cells, a significant decrease in the amount of cellular protein, and enhancement of cellular damage as compared with after exposure to selenite alone. However, simultaneous exposure to 10 microM selenate or 10 microM SeMet together with sulfhydryl compounds did not induce cellular damage. These findings revealed that selenite generates AOS and causes cellular damage in the presence of sulfhydryl compounds. Accordingly, it seems better to choose selenate or SeMet instead of selenite when a selenium compound is to be added to TPN.