title: Calcite encrustation in macro-algae Chara and its implication to the formation of carbonate-bound cadmium.
abstract: We studied the relationship between macro-algae Chara (Stoneworts) calcite (CaCO(3)) encrustation and the speciation of cadmium (Cd) accumulated by the plant. Results showed that 17% of the total Cd (0.3mgkg(-1)) accumulated by Chara fibrosa exposed to 1 microg Cd L(-1) was carbonate-bound. The percentage of carbonate-bound Cd in the plant exposed to 10 microg Cd L(-1) increased from 48% in young thalli (total Ca<50 mg g(-1), total Cd: 125 mg kg(-1)) to 63% in calcified mature thalli (total Ca: 190 mg g(-1); total Cd: 134 mg kg(-1)). Based on mineral saturation calculation and reliability analysis of the sequential fractionation procedure, precipitation of otavite (CdCO(3)) and co-precipitation of Cd with calcite, occurring in the alkaline regions of Chara cell wall, are probably the mechanisms of carbonate-bound Cd formation. Thick marl sediment frequently found beneath charophyte meadows suggests a long-term storage of Ca as well as the precipitated or co-precipitated Cd in the sediment after the plant senescence and decomposition.
authors.affiliation: Department of Environmental Science, Saitama University, 255 Shimo-okubo, Sakura-Ku, Saitama, Japan. siong@mail.saitama-u.ac.jp
authors.forename: Kian
authors.initials: K
authors.lastname: Siong
authors.forename: Takashi
authors.initials: T
authors.lastname: Asaeda
mesh_terms: D002104:Cadmium / Q000378:metabolism*; D002119:Calcium Carbonate / Q000378:metabolism*; D002254:Carbonates / Q000378:metabolism; D044522:Characeae / Q000378:metabolism*; D011232:Chemical Precipitation; D056890:Eukaryota / Q000378:metabolism; D012987:Soil
chemical_list: D002254:Carbonates; D012987:Soil; D002104:Cadmium; C038075:cadmium carbonate; D002119:Calcium Carbonate