典型污灌区土壤中Cd的形态、有效性及其影响因子

The forms, bioavailability of Cd in soils of typical sewage irrigation fields in northern China and its control factors

采集了北京、山东、天津、河北及辽宁5个典型污灌区土壤,外源添加1.20mg/kg的Cd,经过30d老化后,研究了不同污灌区土壤中小麦Cd的吸收、转运系数,同时利用离子色谱及WHAM6.0模型对污灌区土壤溶液性质及自由Cd^(2+)形态等进行了测定.结果表明,不同污灌区土壤中,小麦根、茎叶对Cd的富集系数(BCF)与植株体内Cd的根-茎叶转运系数(TF)有显著差异;二种不同Cd敏感性小麦茎叶对土壤Cd的富集系数为0.064~0.465,最大相差626.5%,不同污灌区土壤Cd的富集系数大小表现为辽宁棕壤最大,山东棕壤最小;植株根-茎叶Cd转运系数(TF)表现为河北褐土>辽宁棕壤~北京潮土>天津潮土>山东棕壤.不同污灌区土壤中,自由Cd^(2+)形态含量与Cd植物有效性呈显著正相关;植株根、茎叶中Cd含量与土壤中自由Cd离子含量的负对数[p(Cd^(2+))]呈显著(P<0.001)的负相关关系,方程分别为:y=-3.3106x+17.681(R^2=0.929);y=-0.3389x+1.7743(R^2=0.916).外源添加1.20mg/kg Cd土壤中,溶液自由Cd^(2+)形态的变化值[△p(Cd^(2+))]与pH值、EC含量呈正相关,而与溶液中Cl^-、Na^+、Ca^(2+)含量呈负相关.由此可以推断,由污灌引起的土壤中Cl^-、Na^+、Ca^(2+)等离子含量的增加将导致土壤中Cd环境风险增大.

Five typical sewage irrigated soils（i.e. from the sewage irrigated soil sites of Beijing, Shandong, Tianjin, Hebei and Liaoning） were collected. The soils were added with 1.20mg/kg Cd with CdCl_2 solution and incubated for 30 d aging period. A pot experiment was conducted to study the bioconcentration factors（BCF）, root to shoot translocation coefficient（TF） of Cd by wheat in different sewage irrigation field soils. The soil solution properties of sewage irrigation soil and the forms of Cd in solution（free Cd-（2＋）） were determined using ion chromatography and WHAM6.0 model. The results showed that significant differences（P〈0.05） were observed for the bioconcentration factors（BCF） and root to shoot translocation coefficient（TF） of Cd by wheat in different sewage irrigation soils, the BCFs of Cd in plant shoots ranged from 0.064-0.465, with a maximum variation of 626.5%. Among the tested sewage irrigation soils, the largest BCF of Cd was observed with the brown soil from Liaoning site and the smallest with the brown soil from Shandong site; the variation of root to shoot transfer coefficient（TF） of Cd followed the order of cinnamon soil from Hebei brown soil from Liaoning alluvial soil from Beijing alluvial soil from Tianjin brown soil from Shandong. Significant（P〈0.05） positive correlation were observed between the free Cd-（2＋） in soil solutions and the phyto-availability of Cd in different sewage irrigation soils, a significant negative correlation（P〈0.001） was observed between the Cd concentrations of plant roots/shoots and the negative logarithm of free Cd-（2＋）[p（Cd-（2＋））] in soil solutions, with the equations of y =-3.3106x＋ 17.681（R-2=0.929） and y =-0.3389x＋1.7743（R-2=0.916） for roots and shoots respectively. The changes of free Cd-（2＋） in soil solutions [△p（Cd-（2＋））] varied significantly among the soils and were affected by soil properties greatly, in general, positive correlations were observed between the △p（Cd-（2＋）） and pH and EC of the soils, while negative correlation were found between the △p（Cd-（2＋）） and Cl-, Na-＋, Ca-（2＋） concentration in soil solutions, it can be inferred that the increment of Cl-, Na-＋, Ca-（2＋） content in field soils induced by sewage irrigation will lead to increased environmental risk of Cd in the field soils.