Study On The Safety Threshold Values Of Soil Zn Of Different Categories Of Vegetables

An investigation involving 23 vegetable varieties in 5 groups in 11 counties or districts of Fujian Province was conducted.The Zn concentrations in the edible parts of the vegetable and the soils,the Zn availability of the soils and the influencing factors,and the accumulation characteristics of the vegetables to accumulate Zn from the soils were studied.The security thresholds of Zn in the soil for vegetable cultivation were then calculated for the sake of supporting the soil planning for vegetable cultivation.The main results were as follows:1.The pH of the soil samples ranged from 3.30 to 7.54 with an average of 5.70.The average content of<0.002mm clay,organic matter and CEC were 19.31%,30.22g/kg and 9.34 Cmol(＋)/kg,respectively.2.The total soil Zn was between 35.83 and 3778.04 mg/kg.It was shown by stepwise regression analysis that pH and CEC of the soils had greater contribution to the total soil Zn than the other soil properties(contents of organic matter and clay).The total soil Zn increased with increasing pH and CEC.3.The available soil Zn varied from 0.14 to 108.44 mg/kg.The average contents of available soil Zn of every sampling area did not exceed the secondary standard value(available soil Zn<35 mg/kg)of<Standard for heavy-metal pollution classification for agricultural soils in Fujian Province>.The stepwise regression analysis showed that the contents of organic matter,total soil Zn and clay were more important for available soil Zn than soil pH and CEC.4.The Zn concentrations(FW)of the vegetable samples ranged from 0.13 to 54.20 mg/kg with only 0.9%of the samples contained higher Zn concentration than the food hygiene standard of China.The mean Zn concentrations of various vegetable groups were in the order of tuber vegetables>leafy vegetables>fruit vegetables>flower vegetables>root vegetables.5.The accumulation coefficients based on total soil Zn were from 0.0007 to 0.4057 with the average being 0.0279,and decreased with increasing total soil Zn.The accumulation coefficients based on available soil Zn were from 0.0277 to 47.7037 with a mean of 0.9745,and tended to decreased as total soil Zn increased.6.The security thresholds of soil Zn for vegetable cultivation were calculated according to the regression equations between the Zn concentrations in vegetables and the available or total soil Zn contents in the soils.The thresholds of soil Zn for banning vegetable cultivation were also calculated by multiplying the security thresholds with 1.5.Agricultural soils were classified into three classes,that is,security area,limitation area and banning cultivation area.