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A major goal of phytoremediation is to transform fast-growing plants with genes from plant species that hyperaccumulate toxic trace elements. We overexpressed the gene encoding selenocysteine methyltransferase (SMT) from the selenium (Se) hyperaccumulator Astragalus bisulcatus in Arabidopsis and Indian mustard (Brassica juncea). SMT detoxifies selenocysteine by methylating it to methylselenocysteine, a nonprotein amino acid, thereby diminishing the toxic misincorporation of Se into protein. Our Indian mustard transgenic plants accumulated more Se in the form of methylselenocysteine than the wild type. SMT transgenic seedlings tolerated Se, particularly selenite, significantly better than the wild type, producing 3-to 7-fold greater biomass and 3-fold longer root lengths. Moreover, SMT plants had significantly increased Se accumulation and volatilization. This is the first study, to our knowledge, in which a fast-growing plant was genetically engineered to overexpress a gene from a hyperaccumulator in order to increase phytoremediation potential.Although selenium (Se) is a necessary micronutrient for humans and animals at very low doses, it is extremely toxic at higher doses (Wilber, 1983). Excess Se has been implicated in birth defects, sterility, and disease in animals, fish, and wildlife and loss of hair, teeth, and nails, fatigue, and even death in humans (Moxon, 1937;Eisler, 1985;Lemly and Smith, 1987;Sorenson, 1991). Environmental Se pollution is a worldwide problem. Anthropogenic Se pollution arises from many sources, such as aqueous discharges from electric power plants, coal ash leachates, refinery effluents, and industrial wastewater (American Medical Association, 1989). Selenium also occurs naturally in soils formed from Se-bearing shales. This leads to Se-contaminated irrigation drainage water, one of the most serious agricultural problems in the western United States and other areas with similar environments and geological conditions (Presser and Ohlendorf, 1987).Cleaning up Se-contaminated soil and water is a major concern. Phytoremediation, using plants to remove, stabilize, or detoxify pollutants, is a promising technology for remediating Se-contaminated soil and water (Terry et al., 2000). In a process called phytoextraction, plants extract Se from soils and water into their tissues, which can be harvested and removed. Selenium is unusual among trace elements because it can also be removed from the ground ecosystem by phytovolatilization, i.e. plants metabolize inorganic Se to relatively nontoxic, volatile forms (dimethyl selenide [DMSe] and dimethyl diselenide [DMDSe]), which escape to the atmosphere (Lewis et al., 1966;Terry et al., 2000). Selenium phytoremediation has been achieved under field conditions using fast-growing plant species, such as Indian mustard (Brassica juncea; Bañ uelos et al., 1997), which accumulates Se to hundreds of parts per million (Bañ uelos and Schrale, 1989). Hyperaccumulating plant species, such as Astragalus bisulcatus, have adapted to seleniferous soils and accum...

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The tremendous increase in the use of engineered nanoparticles in daily life has raised concerns about their impact on the environment and in biological systems. Among them, silver-containing material is of high industrial interest and of manifold use in consumer products, mainly because of their antimicrobial activity. Therefore, analytical methods are urgently needed for the reliable determination of Ag nanoparticles and their corresponding Ag(I) species. In this study, we present the development of coupling reversed-phase high-performance liquid chromatography (HPLC) to inductively coupled plasma-mass spectrometry (ICPMS) for the speciation of engineered Ag-containing nanoparticles and Ag(I) species. The method has been designed for the separation/detection of all investigated silver species in a single chromatographic run. For this purpose, the addition of thiosulfate to the mobile phase has been used to elute Ag(I) species from the column without degradation of the other species. The analytical figures of merit show repeatable results for the recoveries (>80%) of both, the Ag nanoparticles and Ag(I) species. The obtained detection limits are in the medium ng·L(-1) range and therefore allow the trace analysis of the sought analytes in real samples. However, the matrix (e.g., fetal bovine serum) showed an impact on the retention behavior of the Ag nanoparticles, so that for size determinations the use of gold nanoparticles as internal size standard is suggested. Finally, the analysis of textile products exemplarily demonstrates the applicability to the analysis of real samples. Besides silver-containing nanoparticles, Ag(I) species can be identified as one of the major species in the extraction solution from sports socks. However, extraction conditions will be the subject of further investigations in the future in order to obtain reliable quantitative data.