Study On The Toxic Effects Of Cadmium To Vegetables In Different Soils

A series of pot experiments with12soils of various properties and2Cd-sensitive crops, Chinese cabbage and tomato, were carried out to study the effects of soil properties on the toxicity of soil Cd to plants and to compare the difference between different endpoints and the different ways of expressing the toxicity threshold of Cd. This study was aimed to provide scientific basis for selecting the best measurement endpoint, the best way to express the toxicity threshold of Cd and establishing the regional benchmark of Cd for soil environment. The main results were as follows:1. The EC10values were calculated based on the10%reduction of plant growth indices based on the pot experimental results. The EC10values (expressed as the CaCl2-extractable Cd) for the shoot biomass (fresh weight), shoot height, root biomass (fresh weight) and root length of Chinese cabbage ranged from0.01～0.24mg·kg-1,0.04～18.50mg·kg-1,0.02-1.76mg·kg-1and0.11～9.18mg·kg-1, respectively, representing24,462.5,88and8.5-fold variations among the soils. The EC10values (expressed as the total Cd) for the shoot biomass (fresh weight), shoot height, root biomass (fresh weight) and root length of Chinese cabbage were between0.04～1.32mg·kg-1、0.11～4.19mg·kg-1、0.01～0.77mg·kg-1,0.05～46.71mg·kg-1, respectively, representing33,38.1,77and934-fold variations among the soils. The EC10values of the same soil varied with the different growth indicies. The EC10values of the fresh weight of shoot biomass of Chinese cabbage and the fresh weight of tomato root were better to indicate the toxic effects of Cd to the corresponding plant than the other growth indices.2. The EC10values based on total soil Cd,0.1mol·L-1CaCl2-extractable Cd, DTPA-extractable Cd and water-soluble Cd differed greatly. The EC10values of the same growth indicies from most soils decreased in the order of total Cd based> DTPA-extractable based> CaCl2-based> water-soluble based. The variation of the EC10values based on available soil Cd (CaCl2-extractable Cd, DTPA-extractable Cd) was smaller than that based on total soil Cd and water-soluble Cd.3. Regression analysis between the EC10values and5soil parameters showed that there was no significant correlations between the soil properties and the EC10values of Chinese cabbage whereas the free iron was significantly correlated with the EC10(based on water-soluble Cd) of the fresh weight of tomato shoot. And organic matter content was the most important factor influencing the EC10of the root length of tomato.