<p>The present research was designed to investigate the mechanisms of cellular transport, metabolism and toxicity of selenium [inorganic (selenite) and organic (selenomethionine)] in a model teleost, rainbow trout (<i>Oncorhynchus mykiss</i>), using both <i>in vitro</i> and <i>in vivo</i> experimental approaches. The transport properties of selenite and its thiol (glutathione and cysteine) reduced forms were examined in isolated enterocytes and hepatocytes. The kinetics of selenite uptake revealed a linear profile in both cell types, suggesting a low affinity transport process. However, the uptake kinetics was different between the two cell types in the presence of extracellular glutathione, since a concentration-dependent Hill uptake kinetics was recorded in enterocytes, while a linear kinetics persisted in hepatocytes. Both cysteine and glutathione augmented cellular selenium accumulation in these cells. The selenium transport was found to be energy independent, but sensitive to the extracellular pH and inorganic mercury. The pharmacological examination suggested that the cellular transport of selenite is primarily mediated by anion transport systems (e.g., sulphite transporters and/or bicarbonate transporters), although cell-specific differences in transport efficiency was apparent. The metabolism of selenite, selenate and selenomethionine in hepatocytes was examined using X-ray absorption near edge structure spectroscopy (XANES). Inorganic and organic forms of selenium appeared to be metabolized <i>via</i> different cellular pathways, as both selenite and selenate were found to be metabolized into elemental selenium, whereas selenocystine constituted the primary metabolite of selenomethionine. My findings also suggested direct enzymatic transformation of selenomethionine into methylselenol at high exposure level, a process that leads to enhanced intracellular reactive oxygen species generation because of the redox-reactive properties of methylselenol. To validate the metabolite profile of selenium observed in <i>in vitro</i> studies, the tissue-specific differences in selenium metabolism <i>in vivo</i> was analyzed in fish exposed to elevated dietary selenomethionine for two weeks. Similar to the observation in hepatocytes, selenocystine and selenomethionine were found to be the major selenium species across tissues, although there were differences in their relative proportion in different tissues. In addition, a good correlation between the total selenium burden and selenocystine fraction was recorded among all the major tissues except gonads. To understand the role of oxidative stress in cellular toxicity of selenium, isolated trout hepatocytes were exposed to increasing dosage of selenite and selenomethionine over a period of 24h. Selenite was found to be 10 times more toxic than selenomethionine to the hepatocytes. Both selenite and selenomethionine induced rapid generation of reactive oxygen species, which subsequently triggered an upregulation of enzymatic antioxidants. Interestingly, a sharp dose-dependent decrease in intracellular thiol redox (reduced to oxidized glutathione ratio) was recorded with exposure to both selenite and selenomethionine, indicating that glutathione plays an important role in mediating selenium toxicity. At the high exposure dosage, both selenium compounds compromised membrane and DNA integrity, disrupted intracellular calcium homeostasis, and induced enzymatic apoptosis pathway, ultimately leading to cell death <i>via</i> aponecrosis. These findings suggested that high selenium exposure causes cellular toxicity by inducing a rapid loss of the intracellular reducing milieu. Overall, the findings from the present study provided novel information on the transport, metabolism and toxicity of selenium in fish. This fundamental information will be useful in understanding the chemical species-specific toxicity of selenium in fish, and may help in identifying cellular biomarkers for assessing the health of selenium-impacted natural fish populations.

El Decabromodifenil èter (BDE-209) és un retardant de la flama àmpliament utilitzat i font de preocupació a causa de la toxicitat mostrada per altres Difenil Èters Polibromats (PBDEs). La presència de PBDEs en la llet materna fa preocupant la seva exposició durant el desenvolupament. Pensem que l’exposició primerenca a BDE-209 pot produir efectes a llarg termini i interactuar amb factors genètics, com el genotip de l’ApolipoproteinaE. Ratolins portadors de les diferents isoformeshumanes de l’ApoE foren tractats amb una dosi oral aguda de 0, 10 o 30 mg / kg de BDE-209 en el dia postnatal 10 i van ser avaluats per neurocomportament durant el desenvolupament, a l'edat adulta i la vellesa. L’exposició a BDE-209 indueix un retard en el desenvolupament físic i neuromotor i en la compactació de la mielina en els ratolins ApoE2, disminueix els nivells de tiroxina lliure en les femelles adultes i disminueix l'activitat en ratolins ApoE4. Els efectes més consistents durant tota la vida s'observen en ratolins ApoE3 i consisteixen en problemes d'aprenentatge als 4 mesos, i problemes d'aprenentatge i memòria i un augment de l'ansietat als 12 mesos. / Decabromodiphenyl Ether (BDE-209) is a flame retardant widely used and source of concern because ofthe toxicity showed by other Polibrominateddiphenyl ethers (PBDEs). The presenceof PBDEs in human’s breast milkmakes worrying its exposure during development. We hypothesised that an early exposure to BDE-209 can induce long-term impairments and interact with genetic factors, such as ApolipoproteinE genotype. Mice carrying the different Human ApoE isoforms treated with an acute oral dose of 0, 10 or 30 mg/kg of BDE-209 on postnatal day 10 were assessed for neurobehaviourduring development, in young adulthood and old age. BDE-209 exposure inducesadelay in physic and neuromotordevelopment and in myelin compaction in ApoE2 mice, decreases the levels of free thyroxin in adult femalesand decreases activity in ApoE4 mice. The most consistent effects across the lifespan are observed in ApoE3 mice and consist of impaired learning at 4 months, and impaired learning and memory and increased anxiety at 12 months.

<p>The present research was designed to investigate the mechanisms of cellular transport, metabolism and toxicity of selenium [inorganic (selenite) and organic (selenomethionine)] in a model teleost, rainbow trout (<i>Oncorhynchus mykiss</i>), using both <i>in vitro</i> and <i>in vivo</i> experimental approaches. The transport properties of selenite and its thiol (glutathione and cysteine) reduced forms were examined in isolated enterocytes and hepatocytes. The kinetics of selenite uptake revealed a linear profile in both cell types, suggesting a low affinity transport process. However, the uptake kinetics was different between the two cell types in the presence of extracellular glutathione, since a concentration-dependent Hill uptake kinetics was recorded in enterocytes, while a linear kinetics persisted in hepatocytes. Both cysteine and glutathione augmented cellular selenium accumulation in these cells. The selenium transport was found to be energy independent, but sensitive to the extracellular pH and inorganic mercury. The pharmacological examination suggested that the cellular transport of selenite is primarily mediated by anion transport systems (e.g., sulphite transporters and/or bicarbonate transporters), although cell-specific differences in transport efficiency was apparent. The metabolism of selenite, selenate and selenomethionine in hepatocytes was examined using X-ray absorption near edge structure spectroscopy (XANES). Inorganic and organic forms of selenium appeared to be metabolized <i>via</i> different cellular pathways, as both selenite and selenate were found to be metabolized into elemental selenium, whereas selenocystine constituted the primary metabolite of selenomethionine. My findings also suggested direct enzymatic transformation of selenomethionine into methylselenol at high exposure level, a process that leads to enhanced intracellular reactive oxygen species generation because of the redox-reactive properties of methylselenol. To validate the metabolite profile of selenium observed in <i>in vitro</i> studies, the tissue-specific differences in selenium metabolism <i>in vivo</i> was analyzed in fish exposed to elevated dietary selenomethionine for two weeks. Similar to the observation in hepatocytes, selenocystine and selenomethionine were found to be the major selenium species across tissues, although there were differences in their relative proportion in different tissues. In addition, a good correlation between the total selenium burden and selenocystine fraction was recorded among all the major tissues except gonads. To understand the role of oxidative stress in cellular toxicity of selenium, isolated trout hepatocytes were exposed to increasing dosage of selenite and selenomethionine over a period of 24h. Selenite was found to be 10 times more toxic than selenomethionine to the hepatocytes. Both selenite and selenomethionine induced rapid generation of reactive oxygen species, which subsequently triggered an upregulation of enzymatic antioxidants. Interestingly, a sharp dose-dependent decrease in intracellular thiol redox (reduced to oxidized glutathione ratio) was recorded with exposure to both selenite and selenomethionine, indicating that glutathione plays an important role in mediating selenium toxicity. At the high exposure dosage, both selenium compounds compromised membrane and DNA integrity, disrupted intracellular calcium homeostasis, and induced enzymatic apoptosis pathway, ultimately leading to cell death <i>via</i> aponecrosis. These findings suggested that high selenium exposure causes cellular toxicity by inducing a rapid loss of the intracellular reducing milieu. Overall, the findings from the present study provided novel information on the transport, metabolism and toxicity of selenium in fish. This fundamental information will be useful in understanding the chemical species-specific toxicity of selenium in fish, and may help in identifying cellular biomarkers for assessing the health of selenium-impacted natural fish populations.

Previous studies exposing fish to xenoestrogens have demonstrated vitellogenin (VTG) induction, delayed gametogenesis, altered sex distribution, and decreased reproductive performance, with a majority of those studies focusing on exposure to single chemicals. The objective of this study was to determine the effects of binary mixtures of a weak estrogen receptor agonist, nonylphenol (NP) and a potent estrogen receptor agonist, 17α-ethinylestradiol (EE) on sex distribution, gametogenesis, VTG induction, heat shock protein 70 (HSP70) expression and reproductive capacity in zebrafish (Danio rerio). Fish were exposed from 2 to 60 days post-hatch (dph) to nominal concentrations of 10 or 100 µg/l NP (NP10 or NP100, respectively), 1 or 10 ng/l EE (EE1 or EE10, respectively), 1 ng/l EE + 10 or 100 µg/l NP (EE1+NP10 or EE1+NP100, respectively), 10 ng/l EE + 10 or 100 µg/l NP (EE10+NP10 or EE10+NP100, respectively) or solvent control (0.01% acetone v/v) in a static-renewal system with replacement every 48h. At 60 dph, fish from each treatment were euthanized for histological examination of gonads, and whole body VTG and HSP70 levels. Remaining fish were reared in clean water until adulthood (240 dph) for breeding studies. In all EE10 exposure groups (EE10, EE10+NP10 and EE10+NP100), increasing NP concentration acted less than additively to the action of EE in terms of VTG induction at 60 dph. Similarly, a less than additivity of effect was observed with egg production, where EE1+NP100 exposure resulted in significantly more eggs produced per breeding trial than EE1 alone. Histological staging of oogenesis revealed suppressed gametogenesis in females at 60 dph. There were no differences among treatment groups in whole body HSP70 expression in 60 dph fish or in gonadal HSP70 expression in adult fish. Although there was no statistical evidence of non-additivity, breeding trials in adults revealed significant reductions in egg viability, egg hatchability and/or F1 swim-up success, suggesting that developmental exposures to xenoestrogens may cause irreversible effects on egg quality and progeny even after depuration. In conclusion, these results suggest that environmentally relevant mixtures of NP and EE can produce additive or non-additive effects depending on the particular response being determined and the respective exposure concentrations of each chemical. Thus, it is recommended that caution be exercised in ecological risk assessments when assuming additivity in piscine responses to xenoestrogen mixtures.

Kaohsiung harbor is the biggest one in Taiwan. Many previous researches revealed that the pollution of organotin was usually serious in harbors. TBT contained in the antifouling paint of vessels would release into the seawater and contaminate the harbor area. In this study, shrimps (Acetes intermedius) and water samples were collected from Xinbin wharf and the second port entrance in Kaohsiung harbor. After pretreatment, ethylated with sodium tetraethylborate and extracted by hexanes, contents of organotin compounds were analyzed by GC-FPD. The results showed that TBT and DBT were the predominant organotin species in Kaohsiung harbor. In seawater, the concentration of DBT ( 98-257 ng/L ) was higher than TBT ( 17-133 ng/L). In shrimps, the concentration of TBT ( 228-480 ng/g ) was higher than DBT ( 98-257 ng/g). The concentration of TBT in shrimps decreased with the increased wet weight. There was no significant variation for the organotin concentrations in the shrimp samples collected from the second port entrance during the period from September 2002 to May 2003. The bioconcentration factor (BCF) of TBT ranged between 6700-17900. The organotin concentrations in shrimps collected from Xinbin wharf also showed no significant variation from August 2002 to May 2003. The BCF values of TBT were between 2200-8300. The ability of shrimps to concentrate organotin compounds was between that of fishes and neogastropods. There were significant differences for the organotin concentrations in shrimps sampled from different sampling area. The shrimps sampled from Kaohsiung harbor were significantly higher in organotin concentration than Tungkang. According to the risk assessment, shrimps from Tungkang were much lower than the tolerable daily intake, however, the shrimps from Kaohsiung harbor were well beyond the dangerous level . In order to understand the toxicity of organotin compounds to the shrimps, experiments on acute toxicity test were conducted. The 72-h LC50 of TBT was 47£gg/L. After toxicity test, live shrimps which were exposed to organotin for 72 hours were assayed. The concentration of TBT in shrimps increased with the exposure concentrations. DBT which was the degradation product of TBT also showed the same trend. The 72-h LC50 of DBT was 225£gg/L. After toxicity test period, the concentration of DBT and its metabolite MBT in shrimps also increased with the increased exposure concentrations. The accumulation rate of the shrimps at 30£gg/L TBT was 17ng/g-h and the elimination rate was 8.8 ng/g-h. The accumulation rate of the shrimps at 100£gg/L DBT was 12 ng/g-h and the elimination rate was 4.2 ng/g-h.

No description available.

Acid soils limit the growth of aluminum-(Al) sensitive crops such as alfalfa (Medicago sativa L.). Management of acid subsoils can be difficult due to physical and economic constraints. Field experiments were conducted at two locations to evaluate the effectiveness of surface-applied gypsum and a flue gas desulfurization by-product for reducing the toxic effects of acid subsoils on alfalfa. The materials were applied at rates of 0, 5, 10, and 15 Mg ha-1. In addition, a glasshouse experiment was conducted that used 0, 5, and 10 Mg ha-1 of gypsum only. Field studies were concluded 41 and 45 months after treatment application at the two locations. No effect of material on alfalfa yield or tissue mineral concentration was observed. Also, rate did not affect yield. However, there were differences in plant tissue mineral concentration in several harvests that were related to rate. Soil was sampled periodically to 120 cm and indicated movement of Ca and S into the soil profile to depths of 60 and 120 cm, respectively. Subsoil pHH2O and pHCaCl2 were not affected by treatment. Extractable and exchangeable Al were not reduced by movement of Ca and S into the soil. In the glasshouse study, alfalfa yields and root growth were not affected by gypsum rate. As gypsum rate increased, plant tissue S increased, but K and Mg decreased. Alfalfa roots did not grow below 60 cm, even though there was indication of material movement to 90 cm in the soil. Although sulfur moved to 75 cm, no effect on soil Al was observed. Leachate collected from the bottoms of columns indicated that soil cations were leached as a result of gypsum application. Gypsum and the flue gas desulfurization by-product did not significantly affect the acid soils used in these studies or improve alfalfa growth.

Thesis (Ph.D.)--University of Delaware, 2009. / Principal faculty advisor: Chin-Pao Huang, Dept. of Civil & Environmental Engineering. Includes bibliographical references.

Ph.d.

No description available.