Investigation of distribution and oxidation state of copper in soil-inhabiting nematodes by means of synchrotron radiation

摘要

Free-living nematodes provide a good tool for environmental monitoring, because the nematode community structure is an appropriate bio-indicator. Soil-inhabiting species can be used for the characterization of soil functioning and heavy-metal pollution. To investigate the uptake and distribution of copper in the soil-inhabiting nematodes Xiphinema vuittenezi, starved animals were kept in CuSO_4 and Cu(NO_3)_2 solutions with a concentration of 1mmol/dm~3 for 24h. The treatment with CuSO_4 was also carried out at higher concentration (0.5mol/dm~3) for 1h. The nematodes were mounted onto polyimide tape, and after a 2-min-long freezing in liquid nitrogen, they were lyophilized for 72h. The suitability of the sample preparation method was studied by the scanning electron microscopy and focused ion beam techniques. Elemental maps were recorded with two different lateral resolutions (8μm*8μm and 2μm*2μm). Elevated copper and sulfur content was found along the stylet. The oxidation state of copper was studied by X-ray absorption near edge structure spectroscopy. The spectra of solid standards and copper-amino acid complexes in aqueous solution were obtained as well. The oxidation state of copper within the nematodes was found to be +2 in all cases. The X-ray absorption near edge structure spectra of nematodes treated with different copper compounds showed high similarity, however, the spectrum of untreated animals indicated a different chemical environment of copper.