| With the rapid development of economy, agriculture and industry, the problem of environment quality in our country is becoming worse and worse, especially the soil pollution of cadmium. The standard of cadmium in current national soil environmental quality standard (GB15648-1995) is too broad, it does not concern the influences of different soil characteristics, exposure ways to human beings etc., the formulation of a new standard of cadmium is urgent. Therefore, before the new standard of cadmium is formulated, studying the migration and transformation of cadmium on soils and getting cadmium ecological threshold of different soils through biological toxicity experiments are significant.In this study,18 different field soils from 14 provinces in China were collected, and 21 field soils were collected from Jiangsu province, we studied the adsorption of cadmium on these 39 field soils. In addition, Langmuir equation was used to fit the results, the range of maximum adsorption of cadmium on different soils was from 655.5 to 4145 mg/kg. Results showed that the adsorption of cadmium on 39 soils were very different from each other, characteristics of soils were main factors which affect the migration and transformation of cadmium in soils. The adsorption of cadmium in different soils are relate to soil pH, organic matter content, and clay content. The higher soil pH, the more content of OM and clay, the more cadmium will be adsorbed by soil.In this study, the effects of 2,3-Pyridinedicarboxylic acid and 4,5-Imidazoledicarboxylic acid on Cd2+ adsorption on four soils with different characteristics was investigated. The results showed that the adsorption of Cd2+ on soils depended on the characteristics of soils. The presence of ionic liquids significantly affected the adsorption of Cd2+ on soils. Compared with the control, the presence of 1 mmol/L 2,3-Pyridinedicarboxylic acid reduced the maximum adsorption of Cd2+ on Wujin, Wuxian, Nanjing and Yixing soils by 209,834,667 and 509 mg/kg, respectively, whereas adding 1 mmol/L 4,5-Imidazoledicarboxylic acid decreased the maximum adsorption of Cd2+ by 226,54,124 and 81 mg/kg on Wujin, Wuxian, Nanjing and Yixing soils, respectively. Therefore, the effect of 2,3-Pyridinedicarboxylic acid on the adsorption of Cd2+ on test soils was greater than 4,5-Imidazoledicarboxylic acid did. The free Cd2+ ion in the equilibrium solution measured by Cd ion selected electrode showed that both two ionic liquids were able to complex with Cd2+, leading to decreased Cd2+ ion concentration in soil solution, and consequently, reduced the adsorption of Cd2+ on soils. The complexing capability of 2,3-Pyridinedicarboxylic was stronger than that of 4,5-Imidazoledicarboxylic acid, which resulted in great inhibition of Cd2+adsorption on soils. Our results indicate that ionic liquids could decrease the adsorption of Cd2+ on soils, but increase the mobilization and environmental risk of Cd2+.Folsomia candida is wildly used in springtail toxicity experiments, in this study we investigated the acute and chronic toxicity of cadmium to Folsomia candida on 18 different field soils. In acute toxicity test, the LC50 of Cd to folsomia candida was 881.85 mg/kg on Hefei paddy soil. The LC50 of Cd were all over 1000 mg/kg on the other 17 test soils, this was due to the avoidance behavior of folsomia candida. The results of acute toxicity showed that the toxicity of cadmium to Folsomia candida was probably influenced by characteristics of soils, and the results provide experiment basis for chronic toxicity.In chronic toxicity, cadmium on different soils showed different toxicities to Folsomia candida, and the differences were obvious. The toxicity threshold of Cd for 50% of maximal inhibition effect (EC50) of Folsomia candida ranged from 50.12 to 271.73 mg/kg, cadmium on the soil from Xiangxiang showed the strongest toxicity, and cadmium on the soil from Ningbo showed the weakest toxicity. The correlation between EC50 of Folsomia candida and characteristics of different soils were analyzed, but the correlation was not significant, this was the same with other foreign studies. However, when the concentration of cadmium was 500 mg/kg on test soils, the correlation between adult relative mortality, larvae relative inhibition rate and characteristics of soils, including pH, the content of organic matter and clay, was significant, larvae relative inhibition rate= 144.644-8.161pH-0.276OM+0.219Clay (P=0.009<0.005,R2=0.549), adult relative mortality=159.82-11.007pH-0.377OM+0.118Clay (P=0.002< 0.05,R2=0.643)(OM means the organic matter content of test soils, Clay means the clay content of test soils). The higher soil pH, the more content of organic matter, the less toxicity of cadmium to Folsomia candida. |
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