Study On Zinc And Its Transfer Characteristics In Soil-vegetable System

The contents and availability of soil Zn and its influencing factors, and the transfer characteristics of Zn from the soils to the edible parts of 20 vegetable species were studied based on an investigation carried out over the suburb areas of 8 cities in Fujian Province. The main results were as follows:1. The contents of the total Zn in the surface soils ranged between 36.31 and 410.97 mg/kg with an average of 146.64 mg/kg, which was higher than the soil background value of Fujian Province. 19.2% of the soils contained more Zn than the second level limits of China soil environmental quality (GB15618-1995) and 67.7% of soils contained more Zn than the first level limits of the China soil environmental quality standard(GB15618-1995). The total soil Zn had significant and positive correlations with soil pH, CEC, and the contents of free iron, organic matter and clay (<0.002mm).2. The available Zn extracted by DTPA varied from 0.83 to 54.2 mg/kg with an average being 21.99 mg/kg. The availability degree of soil Zn (ratio of the available Zn concentration to the total Zn concentration) was in the range between 0.36% and 21.99% with a mean of 12.12%. The availability degree of soil Zn decreased with the increase of the soil pH, total Zn, available Zn and soil organic matter, showing significant and negative correlation with soil silt particle (0.02～0.002 mm) .3. The Zn contents (fresh weight) of the edible parts of the vegetables were in the range between 0.65 mg/kg and 54.2 mg/kg (FW).Only three vegetable samples contained higher Zn than the limit of the China food hygiene standard (20 mg/kg, GB13106-91) .4. The Zn contents of towel gourd, lotus had significant and positive correlations with the total soil Zn. The Zn concentrations of kidney bean, lotus and eggplant significantly correlated with the DTPA-extractable Zn. The Zn concentration of all the other vegetables did not significantly correlated with the total or DTPA-extractable Zn. Soil-to-plant transfer factors of Zn(total Zn based or available Zn based)decreased with the increase of soil total Zn or available Zn, respectively, most of which can be best described by exponential equation.5. A single-factor pollution index has been adopted to evaluate the Zn pollution degree of the soils and the vegetables. The evaluation based on the second limit of China soil environment quality standard (pH<6.5, Zn<200 mg/kg) showed that 19% of the soils have been slightly polluted. The evaluation based on the national food andhygiene standard showed that 98% of the vegetable samples were not polluted.