Inhibition of cadmium-induced hypertension in rats

In a low cadmium environment, adding 10 parts per million (ppm) of cadmium to the drinking water of rats for 3 to 18 months induced increases in systolic pressure averaging 12 to 18 mm Hg. The pressor effect of the cadmium was inhibited by adding 3.6 ppm of selenium or 200 ppm of zinc to the drinking water or by dissolving the cadmium in hard water rather than deionized water. A second experiment with 2.5 ppm of cadmium and smaller amounts of selenium and zinc was confirmatory.Exposure to 10 ppm of cadmium increased renal, hepatic, and cardiac cadmium many fold from barely detectable control levels; however, the increases were much less when the cadmium was dissolved in hard water. Cadmium exposure also increased tissue zinc by 30 to 60%. The addition of selenium to cadmium further increased cardiac cadmium, but the addition of zinc to cadmium had no further effect on tissue cadmium. Tissue selenium concentrations were suggestively bot not significantly higher following selenium exposure. Cadmium alone, or combined with selenium or zinc, increased renal copper; while the combination of cadmium and selenium increased hepatic copper.     

Selenium in the belgian soils and its uptake by rye-grass

Data obtained by atomic absorption spectroscopy showed a selenium concentration of only 0.11 ppm as an average value for the most representative agricultural soils in Belgium. The selenium content in rye-grass grown on different soil types was between 0.05 and 0.11 ppm, and positively correlated with the soil selenium level.Addition of selenium in the form of selenite to the different soil types resulted in an increased selenium uptake by the plant. The ultimate concentration in the plant depended on the structural and chemical composition of the soil. Twelve other elements were determined in the soils by energy-dispersive X-ray fluorescence; none showed a strong correlation with the soil selenium content or with the selenium uptake by ryegrass.     

The effects of humic acid on the chemical and biological properties of selenium in the environment

To shed light on the causes of Kaschin-Beck disease, which can be prevented by supplementation of the diet with sodium selenite, the interactions between inorganic selenium compounds (selenite and selenate) and humic/fulvic acid were investigated. Selenate was found to be slowly reduced to selenite by humic acid in acidic solution. Selenite was adsorbed on manganese dioxide and iron(III) oxide from solution to a much greater degree than on kaolin, humic acid, Yongshu soil, or silicon dioxide. Feeding mice a diet supplemented with sodium selenite increased the selenium concentration in the kidney, liver, spleen, lung, heart and blood. A diet containing sodium selenite and fulvic acid caused the selenium concentrations in the organs, with the exception of the spleen, to be lower than observed with the selenite-only diet. Selenium and fulvic acid increase the activity of glutathione peroxidase. Sodium selenite and fulvic acid injected in combination into the abdominal cavity of mice and rats were less toxic than either substance alone. Selenite and fulvic acid applied separately enhanced the luminosity of photobacterium phosphoreum T-3 at low concentrations but depressed the luminosity at higher concentrations. Selenite and fulvic acid in combination caused a larger enhancement and a smaller depression of the luminosity than observed with either substance alone. The hypothesis is formulated that Kaschin-Beck disease is caused by selenium levels insufficient to prevent the toxic effects of the organic compounds present in the drinking water of the regions in which the disease is endemic.     

Review of toxicity test results submitted in support of pesticide tolerance petitions.

A long term-low level exposure (LLE) experiment was conducted on rats to determine the metabolic patterns for realistic environmental dietary levels of cadmium. Male rats fed with 61 ppb of cadmium ad libitum, 50 labelled with ¹⁰⁹Cd radiotracer as cadmium chloride via drinking mineral water and 11 unlabelled via food for 2 years. The diet was characterized in its metal content by neutron activation analysis to obtain the total dietary intake of different elements.The kidney was found to be the tissue with the major concentration of cadmium which accumulated continuously during the experiment.The variation of the accumulation pattern of Cd concentration in the liver and intestine indicated an initial rapid increase of Cd during the first 100 days. After this period an apparent equilibrium was attained in both these tissues until the end of the study.The intracellular distribution of cadmium in kidneys, liver, intestine and pancreas were similar, the cytosol fractions containing about 80% of the cellular cadmium. Dialysis experiments indicated that significant amounts of cadmium were able to be associated with cellular organelles, the mitochondria representing the most important organelle capable of binding cadmium.The cytoplasmatic Cd-profiles obtained at various stages of the experiment showed that the metal was only bound to a low-molecular-weight component, cadmium-binding protein (CdBP), which represents the specific cellular-binding component for cadmium under the long term-low level exposure (LLE) conditions.No significant variations in the concentrations of the elements in different organs were observed in animals supplemented with ¹⁰⁹Cd in respect to ¹⁰⁹Cd untreated controls.     

Selenium in the environment

Selenium is one of the most widely distributed elements of the earth's crust. Much of the selenium in the earth's crust occurs associated with sulfide minerals. The presence or absence of selenium in any soil is dependent upon the composition of the parent material, and is also dependent upon leaching or processes subsequent to soil formation, that may have added selenium. Selenium can be easily oxidized from Se⁰ to Se⁺⁴ or Se⁺⁶. Selenium is usually recovered as a by-product of the refining of the sulfide ores of other metals such as copper. The greatest amounts of selenium are used for the manufacture of the photoelectric cell.Selenium is taken up by plants as selenate, selenite or organic selenium. Se⁷⁵ selenite in 30 minutes was translocated primarily to selenomethionine. In sheep or pigs the duodenum is the main site of Se⁷⁵ absorption. Selenium is excreted in the feces, the urine, and the expired air, the amounts and proportions depending upon the level and form of the intake, the nature of the rest of the diet, and the species. A dietary intake of 0.1 μg/g Se provides a satisfactory margin of safety for grazing sheep and cattle. In humans, the recommended daily allowance for selenium is between 100 to 200 μg/day. The toxicity of selenium to animals varies with the amounts of chemical forms of selenium ingested, with the duration and continuity of intake, and with the type and nature of the diet, especially its protein and sulfate content.Deficiency of selenium results in selenium responsive diseases in various animal species, such as muscular dystrophy, exudative diathesis and hepatosis dietetica. Selenium also prevents several type of chemically induced cancer in animals, and, where more selenium occurs in the environment, human cancer death rates are lower. Selenium deficient rats and lambs develop abnormal electrocardiograms accompanied by blood pressure changes. Human heart disease mortality is also lower in the high selenium areas. In China, a large clinical trial is underway showing that selenium prevents a congestive heart failure in children from severely selenium deficient areas.     

Natural variation of copper,zinc, cadmium and selenium concentrations in Bembicium nanum and their potential use as a biomonitor of trace metals

Copper, zinc, cadmium and selenium were measured in the gastropod mollusc Bembicium nanum at two uncontaminated locations, Jervis Bay and Rosedale, NSW, to determine natural variability of metals associated with gender, mass, shore position and temporal variability. Trace metals were also measured in B. nanum at three industrialised locations to determine the accumulation of trace metals in contaminated environments.Copper, zinc, cadmium and selenium concentrations were not significantly different between male and female B. nanum. No significant relationships were found between zinc, cadmium and selenium concentrations and mass. There was a significant relationship between copper concentration and mass but only 19% of the variation was explained by mass. Generally inherent variability within samples had a greater influence than gender or variations in mass on trace metal concentrations.No trend was found in cadmium and selenium concentrations with variation in shoreline position. Copper and zinc concentrations increased further away from the low tide mark, with a decrease in metal concentrations at the furthest site from the water. Variability in metal concentrations is attributable to variations in food source, food availability and different immersion times.Copper, zinc, cadmium and selenium concentrations varied over a 12-month period. Copper, cadmium and selenium were taken up and lost over time, as metal body burden followed the same trend as metal concentrations. Zinc concentrations were influenced by mass. Copper and cadmium concentrations fluctuated throughout the 12-month period but with no clear seasonal trends. Selenium concentrations peaked in spring (October), with concentrations remaining uniform over the other months. These differences in mean concentrations between months were most likely due to inherent trace metal variability associated with differences in food availability and changes in metabolic rates associated with changes in temperature during the study period.Measurement of trace metals in B. nanum at contaminated sites showed that B. nanum accumulates metals in response to contamination.B. nanum meets most of the requirements to be a biomonitor of trace metal contamination as they are abundant, sedentary, easy to identify, provide sufficient tissue for analysis, tolerate high concentrations of pollutants and they accumulate trace metals in response to contamination. However, as trace metal concentration can vary with mass, shoreline position and temporally, care must be taken to collect individual organisms with similar mass from similar shoreline positions and times.     

Adsorptive selenite removal from water using iron-coated GAC adsorbents

Removal of selenite from aqueous phase using iron-coated granular activated carbons (GAC) was investigated in this study. Five different types of GAC were used for iron coating by oxidizing ferrous chloride with sodium hypochlorite and the iron-coated GAC (Fe-GAC) were tested for selenite removal. Nitrogen adsorption-desorption analyses indicated that Brunauer-Emmett-Teller (BET) specific surface area, pore size, and pore volume decreased with the iron coating. The Darco 12x20 GAC was shown to be the most effective adsorbent among the five tested GACs after iron coating. Among the different concentrations used for iron coating, the Darco 12x20 GAC coated with 0.1M ferrous chloride achieved the highest selenite removal (97.3%). High removal efficiency of selenite occurred in a wide range of pH (i.e., 2-8), but the efficiency decreased when pH was higher than 8. Adsorption kinetics showed that selenite removal efficiency reached more than 90% after 6-h adsorption for initial selenium concentration of 2mg/L and equilibrium was obtained after 48h. A pseudo-second-order kinetic model was found to characterize the adsorption kinetics well for all the initial selenium concentrations and temperatures tested (R(2)>/=0.9969). Three temperatures (25, 35, 45 degrees C) were used to examine temperature effect on the adsorption behavior of the Fe-GAC with initial selenium concentration of 1mg/L. Activation energy was calculated to be 30.42kJ/mol. Adsorption isotherms for initial selenium concentration of 2mg/L at various temperatures and ionic strengths were developed and the data generally fit the Langmuir model well (R(2)>/=0.994). The adsorption capacity reached as high as 2.50mg-Se/g-adsorbent at equilibrium for initial concentration of 2mg/L at 25 degrees C. The Gibbs free energy was determined to be negative, indicating the spontaneous nature of the adsorption reaction. Oxyanion competitive adsorption showed that sulfate (0.1-5mM) barely affected selenite adsorption. Other anions (phosphate, silicate and carbonate) impact selenite adsorption to various degrees with phosphate completely excluded selenite adsorption at 5mM. The possible adsorption mechanisms were discussed.     

Non-linear uptake and hormesis effects of selenium in red-winged blackbirds (Agelaius phoeniceus)

Effects of selenium on reproductive success were assessed in red-winged blackbirds (Agelaius phoeniceus). Mean egg selenium (MES) ranged from 2.96 to 21.7 mg/kg dry weight with individual eggs up to 40 mg/kg. Uptake was non-linear: increments in MES declined as aqueous selenium increased; the asymptote was approximately 23 mg/kg. Eggs were heavier and more were laid in 2004 compared to 2005, a year of record rainfall and below-normal temperatures. Mortality of embryos that were incubated to full term was low (2.6% in 2004 and 3.2% in 2005), as was the prevalence of embryonic defects (2.7% in 2004 and 5.1% in 2005). Abnormalities in nestlings were also rare. Egg mortality was caused by predation, weather, and parental abandonment. Nestlings died from predation, starvation, and hypothermia associated with rain and cold, drowning, and bacterial infections. Nestling liver concentrations reached 81 mg/kg dry wt. selenium and were highest at the most highly selenium-exposed sites. Blood glutathione peroxidase (a selenium-dependent enzyme indicative of selenium exposure) was unrelated to liver selenium concentrations, egg selenium, or ambient selenium exposure. The selenium concentration in prey that parents fed to nestlings was higher at the selenium-exposed sites (up to 37 mg/kg dry wt. Se) compared to reference sites. Aqueous selenate:selenite ratios were related to redox differences and were much higher at the site with the highest MES, liver selenium, and prey item selenium concentrations. Hatchability showed U-shaped, or hormesis, relationships with MES: productivity increased with selenium concentrations at low exposures and decreased at high exposures. The effects threshold was approximately 22 mg/kg dry wt. MES.     

Absence of cadmium in the blood of horses fed oats grown on municipal sludge-amended soil

Effluents from a number of industries which are typically treated in municipal sewage plants result in cadmium-containing sludge. Disposal of such sewage sludge by application to agricultural land can result in uptake of cadmium by crops. In this study, oats were grown on soils which had been amended with sewage sludge from Syracuse, New York. The cadmium concentration in the sludge-grown oats was 1.79 ppm dry weight. Horses were fed the sludge-grown oats for 6 weeks during which time blood samples were taken for the determination of cadmium. No significant differences (p greater than 0.05) were found in the concentration of cadmium in the blood of the horses consuming the oats compared with that in the blood before feeding began (control). The well-known efficient accumulation of renal cadmium by horses may account for a lack of significantly increased cadmium in blood during the feeding period.     

Detoxification of selenite and mercury by reduction and mutual protection in the assimilation of both elements by Pseudomonas fluorescens

A study on the assimilation and detoxification of selenium and mercury and on the interaction between these two elements was conducted on Pseudomonas fluorescens. P. fluorescens was able to convert separately both elements to their elemental forms, which are less toxic and biologically less available. To study the converting mechanism of selenite to elemental Se, cells were grown in the presence of various selenite concentrations and several parameters such as extracellular protein concentrations, pH, carbohydrate concentrations, isocitrate dehydrogenase (ICDH) and malic enzyme were monitored. Transmission electron microscopy (TEM) and various analytical methods were applied to confirm the interaction between selenium and cell. The former appeared as a red precipitate localized predominantly in the consumed culture medium. P. fluorescens also resisted to the toxic effect of mercury by converting Hg2+ to the volatile and less toxic form Hg0. Mercury reductase was likely responsible for the conversion of Hg2+ to Hg0. More importantly, the interaction between mercury and selenium was also studied. The presence of selenite significantly reduced the accumulation of mercury in P. fluorescens. It was also interesting to note that mercury appeared to behave as a protecting agent against selenium intoxication as the bioaccumulation of Se was also inhibited by this metal. The formation of Se-Hg complexes could explain this mutual protective effect. No precipitate of elemental Se could be detected when Hg was present in the cultures.     

Adsorption mechanism of selenate and selenite on the binary oxide systems

Removal of selenium oxyanions by the binary oxide systems, Al- or Fe-oxides mixed with X-ray noncrystalline SiO₂, was previously not well understood. This study evaluates the adsorption capacity and kinetics of selenium oxyanions by different metal hydroxides onto SiO₂, and uses X-ray absorption spectroscopy (XAS) to assess the interaction between selenium oxyanions and the sorbents at pH 5.0. The binary oxide systems of Al(III)- or Fe(III)-oxides mixed with SiO₂ were prepared, and were characterized for their surface area, point of zero charge (PZC), pH envelopes, X-ray diffraction analysis (XRD), and then macro-scale adsorption isotherm and kinetics of selenite and selenate, micro-scale adsorption XAS. The adsorption capacity of selenite and selenate on Al(III)/SiO₂ is greater than on Fe(III)/SiO₂. Adsorption isothermal and kinetic data of selenium can be well fitted to the Langmuir isotherm and pseudo-second-order kinetic models. Based on simple geometrical constraints, selenite on both the binary oxide systems forms bidentate inner-sphere surface complexes, and selenate on Fe(III)/SiO₂ forms stronger complexes than on Al(III)/SiO₂.     

Whole blood selenium content in healthy adults in the Czech Republic

Over a 5-year period, from 1996 to 2001, blood selenium levels were recorded in a set of 2414 healthy blood donors (1781 men and 633 women; 880 smokers and 1534 nonsmokers) living in four selected areas of the Czech Republic. About 100 blood samples per year and region were analyzed using the HGA method. The internal and external quality controls of this method were performed throughout the duration of the study. In general, blood selenium concentrations (81.9 and 106.7 microg/l for median and 90th percentile, respectively) did not reach optimum values; in approximately 10% of the population sample, values lower than 60 microg/l were detected. Nonetheless, the values obtained increased significantly, with median concentrations of 73.2 microg/l in 1996 and 91.5 microg/l in 2001. The percentage of subjects with a whole blood selenium level of less than 60 microg/l also decreased from nearly 20% in 1996 to 0.2% in 2001. No substantial regional or gender-related differences were observed, but significantly lower blood selenium levels were found in smokers as opposed to nonsmokers. Although mild selenium deficiency continues to be observed, the data presented do not indicate extremely low selenium levels in the population sample.     

Temporal trends of cadmium and mercury in Greenland marine biota

Data for cadmium and mercury in Greenland marine biota (blue mussels, polar cod, shorthorn sculpin, glaucous gull and ringed seals) over a period of 20 years has been analysed in order to assess temporal changes. Most of the comparisons were conducted between tissue samples collected in the mid-1980s and mid-1990s. Cadmium data from a few time series obtained at reference sites during monitoring of mining activities were also included. No overall temporal trends in cadmium or mercury concentrations were found within the 20-year period assessed. However, cadmium concentrations in ringed seals tended to increase in the period from late-1970s to the mid-1980s. From the mid-1980s to the mid-1990s cadmium concentrations in ringed seals decreased again, whilst mercury concentrations showed a tendency to increase in the same period. The observed changes may reflect natural fluctuations caused by factors such as a shift in feeding behaviour, rather than changes in anthropogenic exposure.     

Distribution of 23 elements in the kidney,liver and lungs of workers from a smeltery and refinery in north Sweden exposed to a number of elements and of a control group

The levels of antimony, arsenic, cadmium, caesium, chromium, cobalt, copper, gold, iron, lanthanum, lead, manganese, mercury, molybdenum, phosphorus, rubidium, scandium, selenium, silver, tellurium, tin, tungsten and zinc in the kidney, liver and lungs of autopsy specimens from exposed workers in North Sweden, as well as from a control group, have been assayed quantitatively. The workers had been exposed to several elements and their compounds, e.g. lead, mercury, arsenic and cadmium, for long periods in arsenic, lead or selenium plants and in a lead or copper smelter.The chemical analysis was by neutron activation analysis and atomic absorption spectrophotometry.Median levels of antimony, arsenic, cadmium, chromium, cobalt, lanthanum, lead or selenium in kidney, liver or lungs in the exposed worker group were found to be about 2 to 16 times as great as the corresponding levels for the control group. Long biological half-life values were observed for these elements, especially in lung tissue.     

A morphometric study of effects of nickel, chromium and cadmium on the secondary lamellae of rainbow trout gills

Rainbow trout were exposed in a constantly-flowing hard water for 3.5 days to concentrations of nickel and chromium at about 0.05 and 0.2 respectively, of the 48-h LC50 for this species, and for 234 days to cadmium at about 0.001 of its 48-h LC50.Morphometric measurements were made of structural components of the gill secondary lamellae from fish, both immediately following their removal from the test solution and at various intervals (up to 21 days) during which they were kept in “clean” water.Diffusing capacities were calculated and indicated changes in the ability of fish to transfer oxygen from the water to the blood. Only nickel appeared to have a marked harmful effect, and recovery to normal diffusing capacity occurred within 21 days.Following the chromium and cadmium treatments, statistically significant changes were not detectable but possible trends were indicated. In the case of cadmium, some suggestion of an increase in diffusing capacity at the lowest concentration (0.002 mg l⁻¹) was observed.     

Acidic deposition and human exposure to toxic metals

Acid precipitation affects the solubility of several metals in aquatic systems and in soil. Cadmium levels in tap water samples from geological areas having low resistance to acidic pollution were significantly higher than those in samples from a neighbouring reference area where there was a different geological structure. The median cadmium levels and pH values were 0.14 microgram l-1 and 5.6 respectively, for the acidic areas compared with 0.07 microgram l-1 and 6.4 respectively for the reference area. Further, there was a significant inverse relationship between both cadmium and lead contents and the pH values of the samples. The mobility of the metals was thus dependent on the acidity. The blood lead levels in 195 subjects from the acidic areas were lower than those in 91 subjects from the reference area (medians 60 vs. 70 micrograms l-1); no significant differences were found in blood cadmium or blood mercury levels. Subjects in the acidic areas had lower plasma selenium levels than those from the reference area (medians 85 vs. 90 micrograms l-1); the difference was mainly attributed to subjects with private wells. The data may indicate a negative effect of the acidic pollution on selenium intake via water and/or foods. There was also a positive relationship between intake of fish on the one hand and blood mercury and plasma selenium on the other, which is in accordance with the role of fish as a source of these metals.     

Cadmium and zinc accumulation in soybean: A threat to food safety?

A greenhouse study was conducted to quantify cadmium and zinc accumulated by soybean (Glycine max (L.) Merr.) when the metals were supplied separately and together. The highest dose of cadmium (100 mg/kg) reduced plant height and dry weight (down to 40% and 34% of control, respectively); the highest dose of zinc (2000 mg/kg) reduced plant height to 55% of control and dry weight to 70% of control. With both metals present, the plants were approximately the same size as those treated with cadmium only. The concentration of cadmium in the roots was unaffected by zinc. In other tissues, the effect of zinc on the accumulation of cadmium depended on the doses provided. At low doses, the addition of zinc reduced the concentration of cadmium in aboveground tissues to 40-50% of that found in plants exposed to cadmium only. However, when applied in high doses, the presence of zinc in cadmium-contaminated soils increased the uptake and accumulation of cadmium in aboveground tissues by up to 42%. In contrast, at high doses, the presence of cadmium in zinc-contaminated soil resulted in approximately 35% lower concentrations of zinc in all tissues. At a lower dose, cadmium had no effect on concentration of zinc in the plant tissues. The effects of high doses of one metal on the uptake of the other metal can be partially explained by the effects of one metal on the bioavailability of the other metal. In soils to which only one metal was added, bioavailable cadmium was 70-80% of the total cadmium, and bioavailable zinc was 50-70% of the total zinc. When both metals were added to the soil, 80-100% of the cadmium and 46-60% of the zinc were bioavailable. Concentrations of both metals were highest in root tissues (10-fold higher for cadmium, and up to 2-fold higher for zinc). Although relatively little cadmium was translocated to pods and seeds, the seeds of all plants (including those from control and zinc-treated plants) had concentrations of cadmium 3-4 times above the limit of 0.2 mg/kg set by the Codex Alimentarius Commission. This was surprising given that cadmium in the soil was only 1 mg/kg well below the maximum allowable amount for agricultural soil. While it is possible that more cadmium was accumulated by plants in this study than that which might occur under agricultural field conditions, these results reinforce the need to monitor concentrations of toxic metals in food crops.     

Interaction of gaseous pollutants with aerosols in Asia during March 2002

The Asian Dust Aerosol Model (ADAM) and the aerosol dynamic model with the output of the fifth generation of mesoscale model (MM5) in a grid of 60x60 km2 over the Asian domain have been performed with and without the heterogeneous reaction (gas-aerosol interaction) to estimate the effect of the gas-aerosol interaction on the formation of aerosol for the period of 1-31 March 2002 when a severe Asian dust event has been observed during this period. The simulated gas-phase pollutants concentrations and aerosols are compared with those observed in South Korea and the East Asia Network (EANET). The results indicate that the present modeling system including ADAM, aerosol dynamic model and MM5 model simulates quite well and the gas-phase pollutants concentrations observed in South Korea and the simulated aerosol concentrations with the gas-aerosol interaction yield much better results in concentrations than those without the gas-aerosol interaction. It is found that the favorable regions for the gas-aerosol interaction in Asia are eastern China (high pollutants emissions), Korea, Japan and the East China Sea that are downstream regions of the Asian dust sources and relatively high relative humidity. In these regions the concentrations of SO2 and O3 decrease whereas the concentrations of sulfate and nitrate increase significantly due to the gas-aerosol interaction. In particular, the increase of sulfate concentration due to the interaction is more than 30% of the corresponding concentration without the gas-aerosol interaction. It is also found that the time-area mean column concentrations of PM10, sulfate, nitrate in the model domain are respectively to be 154.9, 3.2, 3.6 mg m(-2) without the gas-aerosol interaction. However, with the gas-aerosol interaction these values have been increased to 0.6% (155.8 mg m(-2)), 16% (3.7 mg m(-2)), and 14% (4.1 mg m(-2)) of the corresponding concentration without the gas-aerosol interaction. On the other hand, the time-area mean concentration of ammonium is found to decrease about 13% (1.8 mg m(-2) to 1.6 mg m(-2)) due to the gas-aerosol interaction. The result clearly indicates the importance of the gas-aerosol interaction on the tropospheric chemistry during the long-range transport period.     

Ascorbic acid, garlic extract and taurine alleviate cadmium-induced oxidative stress in freshwater catfish (Clarias batrachus)

An experiment was conducted to investigate bioaccumulation potential of cadmium (Cd) and changes in oxidative stress indices in liver and kidney tissues from Cd-exposed catfish (Clarias batrachus) with or without simultaneous treatment of water with ascorbic acid, garlic extract or taurine. C. batrachus (n = 324) with average length of 20 ± 4 cm and weight of 86 ± 5 g were used for the present investigation. Fishes were divided into nine groups (I to IX) each comprising 36 fishes. The fishes of groups II, III, IV and V were challenged with 5 ppm of cadmium chloride monohydrate (CdCl₂.H₂O), whereas groups VI, VII, VIII and IX were exposed to 10 ppm CdCl₂.H₂O solution for a period of 45 days. Group I was kept as negative control and the fishes of this group were maintained in water containing no added Cadmium. Group II and VI were maintained as Cd exposed non treated control to serve as positive controls. Fishes of III and VII, IV and VIII, V and IX received ascorbic acid (5 ppm), extract of dried garlic (5 ppm) or taurine (5 ppm), respectively during the entire experiment period. The concentrations of Cd in liver and kidney increased significantly following exposure to Cd and the level continued to rise with the increase in exposure duration. Treatment of tank water with ascorbic acid, garlic or taurine significantly reduced the Cd concentrations in tissues compared to the positive control group, but the level in Cd exposed groups was greater than the negative control group. Fishes exposed to Cd and treated with ascorbic acid, garlic or taurine had reduced oxidative stress as evidenced from lower concentration of lipid peroxides and higher activities of superoxide dismutase and catalase in liver, kidney and erythrocytes compared to fishes exposed to Cd. The reduction in Cd induced oxidative stress was highest in ascorbic acid treated group followed by garlic and taurine treatment. The results suggest that ascorbic acid, garlic and taurine have potential to reduce tissue accumulation of Cd and associated oxidative stress in freshwater catfish.     

Speciation of selenium in plant water extracts by ion exchange chromatography-hydride generation atomic absorption spectrometry

Determination of selenium (Se) speciation in plants is important in studying the bioavailability and toxicity of Se in Se-contaminated soil/sediment. In this study, we used an anion exchange resin (Dowex 1-10X) to separate Se into non-amino acid organic Se, Se-amino acids, selenite (Se [IV]) and selenate (Se [VI]) in a plant (Stanleya pinnata) extract. The hydride generation atomic absorption spectrometry (HGAAS) was used to determine concentrations of these Se compounds in plant extracts. Results showed that Se compounds can be quantitatively separated by the resin column. Recovery of five spiked standard Se compounds (trimethylselenonium ion (TMSe+), dimethylselenoxide (DMSeO), selenomethionine (Semet), Se [IV] and Se [VII]) in the plant extract ranged from 92.9 to 103%. Water extractable Se accounted for 60.4-72.6% of the total Se in the plant. Among the soluble Se compounds in the plant extract, Se-amino acids were 73-85.5%, Se [VI] ranged from 7.5 to 19.5% and non-amino acid organic Se was less than 7%. Se [IV] in most samples was below the detection limit (1 microg/g). This study showed that considerable amounts of the accumulated Se [VI] in the plant was metabolized to Se-amino acids during growth of the plant.