Accumulation Characteristics Of Cadmium By Cabbage Cultivars In Yellow Soil And Its Safety Thresholds

In recent years,the serious heavy metal pollution of soil and agricultural products in China has became a threat for human health.Vegetables are an indispensable part of the daily diet.At present the sown area of vegetables accounts for more than 10% of the total sown area in China.The planted vegetables in different regions are polluted with Cd.The pollution level of different vegetable species is different,and leaf vegetables were worse than others.A pot experiment was conducted using 20 different Chinese cabbage cultivars(Brassica rapa pekinensis)in Guizhou,and the soil was polluted by Cd with different Cd addition levels of 0,0.3,0.6,1.2,2.4 and 4.8 mg/kg in yellow soil.This paper gave a study on properties of Cd-accumulation and physiology of different Chinese cabbage cultivars,and discussed their safety thresholds of available Cd and total Cd.The aim was to provide an economic and effective way for the safe production of cabbage in polluted yellow soil by Cd,and to provide a theoretical basis for guiding the production of non-polluted vegetables.The results were as follows:(1)The soil pH of this pot experiment was 5.07.The effects of Cd on agronomic traits reflected in plant heights,biomass of shoots and roots of cabbage,and it had greater effect on biomass of shoots than plant heights and biomass of shoots.The plant heights of 65%(13)cultivars,biomass of shoots of 90%(18)cultivars and biomass of roots of 75%(15)cultivars were significantly affected by Cd.With the increase of Cd concentration,the effects of Cd addition on the growth of Chinese cabbage varied with varieties.The results showed that in the range of Cd concentrations promoted the growth of cabbage,whereas inhibited its growth when the concentrations of Cd was larger than the moderate value.(2)The activities of SOD,POD and CAT of different cabbage cultivars varied with the increase of soil Cd concentration.The activities of SOD in most cultivars were lower than the CK when added at a concentration of 4.8 mg/kg in yellow soil.The POD activities of 15 cultivars such as Huayuwutacai,Maye huoguocai,Shandong No.19,Gaokang 100,Lubai No.3,Jiwopadibai,Jincai No.3,Kangbingdamaye,Xiaoza 56,Huayujingpinhuangxincai,Lubai No.6,Jiwopadibai,Houyezaoshu No.5,Zhongqingmaye and Sijichunqiuwang were lower than the control values.this suggested that the rate of reactive oxygen species produced by the stress concentration exceeded the eliminated efficiency of antioxidant enzyme.The activities of SOD and POD decreased because the enzyme system may be damaged.The activities of SOD and POD in cultivars which bioaccumulation factor of shoots was higher than 1 were generally higher than those in other cultivars.(3)13 cultivars,including Huayuwutacai,Xintaiyuanerqing,Gaokang 100,Padihuoguocai,Jincai No.3,K,Xiaozao 56,Huayujingpinhuangxincai,Koukouxiangtian,Houyezaoshu No.5,Zhongqingmaye,Xinshandong No.4 and Sijichunqiuwang,showed strong bioaccumulation factor of Cd,because the bioaccumulation factor of shoots was higher than 1.The bioaccumulation factor of shoots of 7 cultivars was less than 1.The bioaccumulation factor in shoots and translocation factor in roots of Jincai No.3 were the maximum,which were 1.71 and 1.38,respectively.The bioaccumulation factor in shoots and translocation factor in roots of Shandong NO.19 were the minimum,which were 0.44 and 0.33,respectively.This experiment concluded that Jincai No.3,Kangbingdamaye,Xiaoza No.56,Koukouxiangtian and Zhongqingmaye were high Cd-accumulation cultivars,Shandong No.19,Jiwopadibai,and Youzaohuang were low Cd-accumulation cultivars.(4)The order of the safety thresholds of available Cd based on pot experiment is: Shandong No.19 > Jiwopadibai > Lubai No.6 > Youzaohuang > Lubai No.3 > Gaokang 100 > Fengyanxiaojiang > Koukouxiangtian > Xinshandong No.4 > Xiaoza No.56 > Mayehuoguocai > Huayujingpinhuangxincai > Sijichunqiuwang > Kangbingdamaye > Padihuoguocai > Houyezaoshu No.5 > Xintaiyuanerqing > Zhongqingmaye > Jincai No.3.The safety thresholds of available Cd in Jincai No.3,Kangbingdamaye,Xiaoza No.56,Koukouxiangtian and Zhongqingmaye were 0.04,0.05,0.06,0.06 and 0.04 mg/kg,respectively.The safety thresholds of total Cd were 0.22,0.24,0.27,0.27 and 0.22 mg/kg,respectively.The safety thresholds of available Cd in Shandong No.19,Jiwopadibai,and Youzaohuang were 0.16,0.11 and 0.11 mg/kg,respectively.The safety thresholds of total Cd were 0.48,0.37,and 0.37 mg/kg,respectively.The thresholds of available cadmium in soils of cabbage cultivars varied greatly.The maximum value was 0.16 mg/kg,the minimum value was 0.04 mg/kg,and the maximum value was 4 times of the minimum value.