Interactive Effects Of Earthworm Eisenia Fetida And Bean Plant Phaseolus Vulgaris L On The Fate Of Soil Selenium

Selenium（Se）is an essential micronutrient for animals with a narrow margin between nutritional essentiality and potential toxicity.Se toxicity is largely related to inorganic forms of Se in soil,i.e.selenite and selenate that enter food chains through plant uptake,posing risks to higher trophic levels organisms.This experiment investigated the effect of earthworm activity on Se bioavailability in the soil and the subsequent uptake by plants,using earthworm Eisenia fetida and bean plant Phaseolus vulgaris L,both of which were exposed to either selenite or selenate at 1 or 4 mg Se kg^-1for 16 weeks.For all the Se treatments,plants took up Se for selenate（up to 221-fold）faster than selenite,with up to 84%of the Se rapidly transported to shoots.In the presence of earthworms,Se accumulation obviously increased for selenate-supplied plants,while the Se translocation factor increased by 0.85-4.08%for all but the 1 mg kg^-1 selenite treatment.As to earthworms,faster Se accumulation in tissues(up to 274.38 mg.kg^-1 DW)was observed at exposure to Se as selenate.To assess potential Se toxicity to humans and other animals,we further conducted Se speciation analysis on the Se-exposed plants and earthworms using X-ray absorption spectroscopy.Compared to worm-free treatments,the percentage of organo-Se,i.e.,Se Met and Cys Se Se Cys,increased in beans（about 8.7-34%）in the presence of earthworms for selenate,while the elemental Se portion was significantly reduced in the 1mg.kg^-1treatment or even missing from the 4mg.kg^-1 treatment,which is opposite to the results for selenite.Surprisingly,elemental Se（41.7-65%）was found dominant in earthworms,regardless of the form of Se supplied.In conclusion,earthworms clearly enhanced Se uptake and translocation in plants,leading to elevated Se levels in the shoots.To prevent resulting hazards to the health of humans and other animals,caution should be taken while consuming beans or other shoot parts harvested from the soil where earthworm activity is high.Meanwhile,the significant reduction in soil Se suggests phytoextraction treatment of Se polluted soils can be improved using earthworms as an aid to bean plants.However,further research is still needed to evaluate potential risks of Se-laden earthworms to its predators in the soil ecosystem,although they may only contain relatively stable Se species.