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Selected metals in earthworms, lettuce and soil amended with sewage sludge

University of British Columbia

Earthworms (Lumbricus rubellus, Aporrectodea spp. and Octolasion cyaneum) were kept in soil treated with six application rates of milorganite. After ten days, the earthworms, their faeces and the soil were analyzed for cadmium, copper, lead and zinc. Cadmium and Zn were concentrated in the worm tissue of all three taxa, over soil levels, whereas Cu and Pb were not. Cadmium concentrations in the body tissue increased with increasing soil Cd, until soil concentrations reached 7 ug/gm, after which the body tissue concentrations levelled out. The body tissue Cd and Zn concentrations exceeded the concentration of these metals in the faeces. The faeces had higher Cu and Pb concentrations than the body tissue. The earthworms appear to be capable of accumulating Cd and regulating body tissue concentrations of Cu, Pb and Zn. There were differences among earthworm taxa in the metal concentrations in both body tissues and faeces. Aporrectodea spp. had the lowest body tissue Cd concentrations, as well as, had lower faecal Cd concentrations than L. rubellus. Body tissue Cd concentrations for L. rubellus and O. cyaneum were not different. Copper and Pb concentrations in the body tissue of O. cyaneum were greater than those for the other two taxa, which did not differ significantly in their Cu and Pb concentrations. Lumbricus rubellus had higher Cu levels in its faeces than did Aporrectodea spp., whereas there were no differences in the faecal Pb concentrations for the three taxa. Zinc concentrations were different in the body tissues of all three taxa and was highest in the Aporrectodea spp. The latter taxon also had the lowest faecal Zn concentrations. Earthworms might be useful biological monitors of Cd pollution, but not for Cu, Pb and Zn, in soils receiving sewage sludge. In the experiment on the possible effects of milorganite and earthworms on growth and on mtal uptake by lettuce, the addition of the sewage sludge resulted in a significant increase in plant yield. The cadmium and zinc concentrations in leaf and root tissue were significantly increased by milorganite additions and nickel concentrations were decreased. Copper concentrations were unaffected by the sludge. Mean lead concentrations were higher in the milorganite treatments. However, the variability was great and there was not significant differences. The addition of milorganite to the soil resulted in increased concentrations of diethylene triamine penta acetic acid (DTPA) extractable metals. At an application rate of 20 gm milorganite/kg soil, DTPA extractable Cu, Ni and Zn were significantly correlated with lettuce leaf concentrations for these 3 metals. However, at the higher milorganite application rate of 50 gm/kg, only DTPA extractable Zn was significantly correlated with plant tissue concentrations. The addition of earthworms to the soil did not affect lettuce yields or the concentrations of DTPA extractable metals. Lead concentrations in the roots were significantly lower when earthworms were present in the soil. Earthworms did not affect the concentrations of Cd, Cu, Ni and Zn in lettuce tissues.

Text

2010-04-20

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http://hdl.handle.net/2429/23956

Soil Science

University of British Columbia

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