Study On The Security Thresholds Of Soil Cadmium For Different Kinds Of Crops In Fujian Province

An investigation was carried out in order to realize the accumulation characteristics of cadmium from soil by12crop varieties in the agricultural fields near some major cities in Fujian Province. The total and available contents of Cd in the soils, and the Cd concentrations of the edible parts of the crops were determined. The security thresholds and the thresholds for banning cultivation were developed based on the above results. The main results were as follows:(1) The average Cd concentrations of the12kinds of crops ranged between0.006and0.156mg/kg (FW) in the order of:chili<cabbage<tomato<cowpea<lotus<sweet potatoes<radish<lettuce<mustard<rape<celery<spinach.(2) Among the12kinds of crops, the Cd concentrations of9crops showed significant correlations with the available soil Cd, and those of only5kinds of crops had significant correlations with the total soil Cd, suggesting that it is better for the available soil Cd in indicating the Cd availability of the soils than the total soil Cd. Stepwise multiple regression analysis between the Cd concentrations of the crops and pH, CEC, and the contents of available Cd, organic matter, clay, silt and sand of the soils indicated that the available soil Cd is the best indicator in predicting the Cd concentration of the crops without significant influences from the other soil parameters.(3) The accumulation coefficients of Cd (based on available soil Cd) differed greatly among the various varieties of crops. Celery showed the strongest accumulation capacity of Soil Cd among all the varieties of crops while lotus the weakest. The accumulation coefficient of celery was4.7650, which was112.38times than that of lotus (0.0424). As for the crop groups, leafy vegetable showed the strongest accumulation capacity whereas beans vegetables the weakest. The accumulation coefficient of Cd (based on available soil Cd) generally decreased with the increase of available soil Cd.(4) The security thresholds and the thresholds for banning cultivation (expressed as available soil Cd) were calculated based on the regression equations between the contents of available soil Cd and the Cd in the crops. The security thresholds of each crop were3.31mg/kg(cabbage),0.25mg/kg (spinach),0.52mg/kg (mustard),0.22mg/kg (celery),0.48mg/kg (rape),3.20mg/kg (radish),0.57mg/kg (lettuce),23.26mg/kg (cowpea), and0.50mg/kg (sweet potato), respectively. The thresholds for banning cultivation for each crop were4.97mg/kg (cabbage),0.38mg/kg (spinach),0.78mg/kg (mustard),0.33mg/kg (celery),0.71mg/kg (rape),4.80mg/kg (radish),0.86mg/kg (lettuce),34.89mg/kg (cowpea), and0.75mg/kg (sweet potato), respectively.(5) The security thresholds and the thresholds for banning cultivation expressed as total soil Cd were calculated based on the regression equations between the contents of total soil Cd and the Cd in the crops, and from those expressed as available soil Cd. The security thresholds of each crop were106.43mg/kg (cabbage),1.88mg/kg (mustard),5.58mg/kg (rape),0.99mg/kg (lettuce),2.43mg/kg (sweet potato),9.78mg/kg (radish), and96.32mg/kg (cowpea), respectively. The thresholds for banning cultivation for each crop were159.65mg/kg (cabbage),2.82mg/kg (mustard),8.37mg/kg (rape),1.49mg/kg (lettuce),3.65mg/kg (sweet potato),14.67mg/kg (radish), and144.50mg/kg (cowpea), respectively.