两种典型土壤胶体对镉的生物有效性的影响

采用黑麦草盆栽试验,研究了人工Cd污染(10.91mg·kg-1)黄棕壤和红壤(简称原土)及其胶体组分(简称胶体)和去胶后组分(简称去胶)Cd的生物有效性,并研究了EDTA对Cd解吸和生物有效性的影响.结果表明:(1)各处理黑麦草株高、地上部干重、根干重、总生物量都表现为胶体＞原土＞去胶,胶体上总生物量分别是原土和去胶处理的(1.31±0.02)倍和(1.82±0 21)倍.(2)黑麦草体内Cd浓度、及其对Cd的富集系数都表现为胶体＜原土＜去胶,表明胶体中Cd的生物有效性＜原土＜去胶.(3)黄棕壤各组分Cd的解吸率分别表现为胶体和原土约为0,去胶组分为(10.5±3.5)%,红壤各组分平均为(20.8±1 9)%,但加入EDTA则明显增加了Cd的解吸,导致黑麦草体内Cd浓度显著增加,黑麦草地上部干重、根干重、总生物量降低.EDTA对Cd的活化作用表现为去胶＞原土＞胶体,黄棕壤＞红壤,EDTA对各处理植株Cd总量的影响与此吻合.这说明,土壤镉的生物有效性受土壤胶体及其pH等的强烈影响.

Effect of two typical soil colloids on the bioavailability of cadmium to ryegrass

A greenhouse pot experiment with ryegrass was conducted to investigate the bioavailability of Cd in two simulated Cd-contaminated soils (yellow brown soil and red soil) and their components (colloids and de-colloid soils). EDTA effect on mobilization and bioavailability of Cd in the above growth substrates was also explored in this study. The results showed that: (1) the mean shoot height, shoot and root weight of ryegrass grown in different Cd-contaminated soils or their components were in the following decreasing order with colloid treatment> original soil treatment> de-colloid soil treatment. The total biomass of ryegrass grown in the Cd-contaminated colloid was 1.31±0.02 and 1.82±0.21 times higher than those in original soil and de-colloid soil, respectively. (2) Cd concentration and bioaccumulation factor in shoot and root were followed by colloid < raw soil < de-colloid soil, indicating the bioavailability of Cd in different soil components was colloid < raw soil < de-colloid soil. (3) the addition of EDTA into the original soils or their components led to significant increase of Cd concentration in shoot and root and the decrease of ryegrass biomass due to Cd phytotoxicity; and (4) Cd mobilization facilitated by EDTA was obvious especially in the yellow brown soil and two de-colloid soil components. It was concluded that Cd bioavailability was, to a great extent, affected by soil colloid quality and soil pH.