The Experts below are selected from a list of 288 Experts worldwide ranked by ideXlab platform
A. W. Knight - One of the best experts on this subject based on the ideXlab platform.
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Bioaccumulation of Selenate, selenite, and seleno-DL-methionine by the brine fly larvae Ephydra cinerea Jones
Archives of Environmental Contamination and Toxicology, 1995Co-Authors: T. N. Rosetta, A. W. KnightAbstract: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.
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Effect of sulfate level on selenium uptake by Ruppia maritima
Chemosphere, 1995Co-Authors: F.c. Bailey, A. W. Knight, R.s. Ogle, S.j. KlaineAbstract:Abstract Ruppia maritima (wigeongrass), the dominant aquatic macrophyte in the agricultural drainage evaporation ponds of the Central Valley of California, is a food source for various waterfowl and shorebirds. Whole-plant uptake and accumulation of Selenate (SeO4−2 or Se+6), selenite (SeO3−2 or Se+4), and seleno-methionine (Se−2) by R. maritima from artificial evaporation pond water was compared over a 21 day period, and the effect of sulfate, a known Selenate antagonist, on Se uptake was investigated. Plants were treated with 10, 100, or 1000 ug/l as selenium. Under both high and low sulfate conditions, R. maritima was found to accumulate seleno-methionine to a much higher level than either selenite or Selenate. However, under low sulfate conditions, Selenate uptake was two orders of magnitude greater than under high sulfate conditions, indicating a sulfate/Selenate antagonism. Bioconcentration factors for seleno-methionine under high and low sulfate conditions and for Selenate under low sulfate conditions were very high (up to 21,800 for seleno-methionine and 1080 for Selenate).
Allen W. Knight - One of the best experts on this subject based on the ideXlab platform.
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Comparative acute toxicity and bioconcentration of selenium by the midge Chironomus decorus exposed to Selenate, selenite, and seleno-DL-methionine
Archives of Environmental Contamination and Toxicology, 1993Co-Authors: Kurt J. Maier, Allen W. KnightAbstract: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 LC_50 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 LC_50 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.
Norman Terry - One of the best experts on this subject based on the ideXlab platform.
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Selenium volatilization and accumulation by twenty aquatic plant species
Journal of Environmental Quality, 1999Co-Authors: Elizabeth A. H. Pilon-smits, M. P. De Souza, G. Hong, Ata Amini, R. C. Bravo, S. T. Payabyab, Norman TerryAbstract:Aquatic plants can remove selenium (Se) from agricultural or industrial wastewater through Se accumulation and volatilization, that is, the conversion of Selenate or selenite to volatile forms of Se. To identify aquatic plant species that will be good at removing Se from contaminated water, 20 plant species were screened for their ability to accumulate and volatilize Se when supplied with 20 μM Selenate or selenite under controlled conditions. There was at least a 50-fold variation in Se accumulation and volatilization capacity among the plant species tested, regardless of the form of Se supplied. The best plant species for Se volatilization from Selenate were also the best species for selenite volatilization. Selenium volatilization rates were twofold higher from selenite than from Selenate but more Selenate-Se was translocated into harvestable plant tissues than selenite-Se. Several aquatic plant species showed Se volatilization and accumulation rates (per unit surface area) that were comparable with Indian mustard [Brassica juncea (L.)], the best-known terrestrial plant species for Se phytoremediation. Therefore, many wetland species identified in this study, for example, parrot's feather (Myriophyllum brasiliense Camb.), iris-leaved rush (Juncus xiphioides), cattail (Typha latifolia L.), saltmarsh bulrush (Scirpus robustus), etc., have a great potential for Se phytoremediation in wetlands.
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rate limiting steps in selenium assimilation and volatilization by indian mustard
Plant Physiology, 1998Co-Authors: Mark P De Souza, Elizabeth A H Pilonsmits, Mel C Lytle, Seongbin Hwang, Todd S U Honma, Norman TerryAbstract:Se can be accumulated by plants and volatilized to dimethylselenide, providing an attractive technology for Se phytoremediation. To determine the rate-limiting steps in Se volatilization from Selenate and selenite, time- and concentration-dependent kinetics of Se accumulation and volatilization were studied in Indian mustard (Brassica juncea). Time-dependent kinetic studies showed that Selenate was taken up 2-fold faster than selenite. Selenate was rapidly translocated to the shoot, away from the root, the site of volatilization, whereas only approximately 10% of the selenite was translocated. For both Selenate- and selenite-supplied plants, Se accumulation and volatilization increased linearly with external Se concentration up to 20 mM; volatilization rates were also linearly correlated with root Se concentrations. Se-volatilization rates were 2- to 3-fold higher from plants supplied with selenite compared with Selenate. Se speciation by x-ray absorption spectroscopy revealed that selenite-supplied plants accumulated organic Se, most likely selenomethionine, whereas Selenate-supplied plants accumulated Selenate. Our data suggest that Se volatilization from Selenate is limited by the rate of Selenate reduction, as well as by the availability of Se in roots, as influenced by uptake and translocation. Se volatilization from selenite may be limited by selenite uptake and by the conversion of selenomethionine to dimethylselenide.
Dongli Liang - One of the best experts on this subject based on the ideXlab platform.
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effects of selenite and Selenate application on distribution and transformation of selenium fractions in soil and its bioavailability for wheat triticum aestivum l
Environmental Science and Pollution Research, 2017Co-Authors: Fayaz Ali, Qin Peng, Dan Wang, Zewei Cui, Jie Huang, Dongli LiangAbstract:This study investigated the effect of Selenate and selenite application on the distribution, transformation of selenium (Se) fractions in soil, as well as the accumulation and availability of Se in each part of wheat plants. A pot experiment was conducted using different concentrations of exogenous selenite or Selenate (0.5, 1, 2.5, 5, and 10 mg Se kg−1 soil). Sequential extraction was used to determine the Se fractions in soil, and different models were used to study the behavior of Se in soil and its availability to wheat. Results showed that the distribution and availability of Se in soil and its accumulation in wheat affected both by Se concentrations and forms of exogenous Se. In selenite-treated soil, the proportion of exchangeable and carbonate-bound Se (EXC–Se) (21–42%) fraction increased compared to that in control (12%), while organic matter-bound Se (OM–Se) (23–33%) and Fe–Mn oxide-bound Se (FMO–Se) (11–15%) fractions decreased compare with those in control (37 and 32%, respectively). In Selenate-treated soil, soluble-Se (SOL–Se) fraction (30–54%) increased and the OM–Se (9.8–20%) and FMO–Se (4.7–14.2%) fractions decreased compared with those in control. Residual Se (RES–Se) fraction was increased for selenite (7.4–13.4%) and Selenate (12–20%) treatments compared with that in control (6.5%). In comparison with control, the available Se (SOL−Se + EXC−Se) fraction increased for both selenite (32–47%) or Selenate (54–72%) treatments. Moreover, at the same rate of Se application, Se availability was higher in wheat grown in Selenate-treated soils than that in selenite-treated soils. The redistribution index (Uts) of Se increased from 1 (in control) to 1.2–1.9 and 1.5–2 for selenite and Selenate treatments, respectively; additionally, the mobility factor (MF) in Selenate-treated soil was 40–90% higher than that in selenite-treated soil. Furthermore, relative bonding intensity (IR) for both selenite (0.38–0.45) and Selenate treatment (0.33–0.41) decreased compared with that in control (0.55). These differences indicated that selenite and Selenate varied in terms of fixation capacities in soil, in transformation and distribution of Se in soil fractions, and in their availability to plants. The results of Michaelis–Menten equation demonstrated the high affinity of leaf to Selenate, and the high affinity of roots and grains to selenite. Selenate was dominant in nearly all parts of wheat plants and in each application level. However, the affinity of selenite to wheat grains suggests that selenite is a useful Se fertilizer that must be considered in biofortification programs. In-depth studies at the pot and field scales by using different wheat varieties and application methods of Se in different ecological zones must be conducted to elucidate the mechanism and biochemical properties of Se in soil-plant system and ultimately produce Se-rich staple foods.
Fangjie Zhao - One of the best experts on this subject based on the ideXlab platform.
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selenium uptake translocation and speciation in wheat supplied with Selenate or selenite
New Phytologist, 2008Co-Authors: S P Mcgrath, Fangjie ZhaoAbstract:Selenite can be a dominant form of selenium (Se) in aerobic soils; however, unlike Selenate, the mechanism of selenite uptake by plants remains unclear. Uptake, translocation and Se speciation in wheat (Triticum aestivum) supplied with Selenate or selenite, or both, were investigated in hydroponic experiments. The kinetics of selenite influx was determined in short-term (30 min) experiments. Selenium speciation in the water-extractable fraction of roots and shoots was determined by HPLC-ICPMS. Plants absorbed similar amounts of Se within 1 d when supplied with selenite or Selenate. Selenate and selenite uptake were enhanced in sulphur-starved and phosphorus-starved plants, respectively. Phosphate markedly increased K(m) of the selenite influx. Selenate and selenite uptake were both metabolically dependent. Selenite was rapidly converted to organic forms in roots, with limited translocation to shoots. Selenomethionine, selenomethionine Se-oxide, Se-methyl-selenocysteine and several other unidentified Se species were detected in the root extracts and xylem sap from selenite-treated plants. Selenate was highly mobile in xylem transport, but little was assimilated to organic forms in 1 d. The presence of selenite decreased Selenate uptake and xylem transport. Selenite uptake is an active process likely mediated, at least partly, by phosphate transporters. Selenite and Selenate differ greatly in the ease of assimilation and xylem transport.
