Toxic Effects Of Cadmium On Maize Seedlings And Earthworm In Fluvo-aquic Soils Of Beijing

Soil pollution with cadmium （Cd） is a serious problem worldwide, and it has arousedintensive concerns recently among scientists, regulators, and public. Cd is difficult to removefrom soil, and may be accumulated by plants and transferred to higher organisms throughfood chain. Therefore, Cd pollution in soil can do harm to both ecosystems and human health.Terrestrial ecotoxicological data are essential for the development of risk-based ecologicalsoil screening levels. Presently, few studies have been involved in the ecotoxicity assessmentof Cd in Chinese soils, which is incompatible with the increasing requirement of ecologicalrisk assessment at contaminated sites in China. In the present study, toxicities of Cd to themaize （Zea mays L.） and earthworm Eisenia fetida were investigated in fluvo-aquic soil fromBeijing with pot trials and PCR-DGGE analysis methods etc.1. The results showed that Cd could stunt growth and development of maize seedlings atconcentrations higher than100mg·kg^-1. The effective concentration (EC₅₀) causing50%reduction of plant height was654.6mg·kg^-1, and the EC₅₀s for root and shoot biomass （dryweight） were323.6and110.2mg·kg^-1, respectively. The shoot biomass could serve as asuitable endpoint for assessing metal ecotoxicity to plant seedlings. Cadmium could be takenup and accumulated in both root and above-ground tissues of maize seedlings. Generally, theconcentration of Cd decreased in the order: root> stem> leaves, and in particular abioaccumulation of Cd was observed in maize root with bioaccumulation factor （BAF） largerthan1. Cadmium could exert great impacts on the composition of maize rhizosphere microbecommunity. The population of certain rhizosphere microbes declined under the stress of Cd,and some species might be subject to extinction at concentration of1000mg·kg^-1, indicating asever interference and threat of high-level Cd contamination on plant seedling, rhizospheremicrobes, and the interaction between plant and microbes.2. The results showed that Earthworm Eisenia growth stunt and its reproduction capacitydeclined by the middle and higher Cd concentrations treats in the soil. The effectiveconcentration (EC₅₀) causing50%reduction of cocoon production was83.2mg·kg^-1. Itdemonstrated that earthworms were able to uptake soil cadmium and retained it in theirtissues （BAF>1）. 3. The results of combination culture of earthworms and maize showed that earthwormscould strengthen the toxicity of Cd to plant height and shoot, but reduce the toxicity of Cd toroot. On the other hand, planting maize in soil increased the cocoon production ofearthworms. The effective concentration (EC₅₀) causing50%reduction of cocoon productionwas135.2mg·kg^-1then. Meanwhile, the concentration of Cd in earthworms and the BAFwere reduced compared to the treatments without maize.