The Research On Heavy Metal Migration In Soil-vegetable System

Absorbed by soil crop, heavy metal endangers human body health ultimately through the food chain transmission and enrichment. In research area which is in the north suburb production soil of vegetables of Xi'an, we set isolation body in typical samples and planted Tonghao and cabbage. In different stages of vegetables growing period , we collected soil and vegetable samples, measured the content of heavy metal including Pb,Cd,Cr, analyzed transform rule in migration of heavy metals in soil vegetables system.The results showed that content of soil heavy metal Cd is in average for 3.2 mg/kg, more than the state soil environment quality secondary standard, content of heavy metal Pb and Cr for average 46.8 mg/kg,50.9 mg/kg respectively, failed to exceed standard; In Chinese cabbage, the maximum content of heavy metals Pb is 0.82 mg/kg which is beyond the standard value of non pollution vegetables about 3.1 times, meantime, content of heavy metal Cd and Cr did not exceed standard; In Tonghao, the content of heavy metals Pb is 0.51 mg/kg, more than non pollution vegetables standard value about 1.6 times, the content of heavy metal Cd is 0.08 mg/kg, more than pollution free vegetables standard value 0.6 times, only the content of heavy metal Cr did not exceed standard value.In soil Chinese Cabbage system, the average error percentage of the heavy metal Pb, Cd and Cr is: 1.47%, 3.93% and 3.34% respectively, so three kinds of heavy metals in system is balanceable totally. The most powerful absorption for heavy metals Pb of Chinese cabbage is after 14 days of its planted, heavy metal Pb in cabbage is major from 20~30cm depth of soil; The absorption of Chinese cabbage for heavy metal Cd in its growth stage is unchanged on the whole; Chinese cabbage, absorptive capacity for heavy metal Cr is strongest in the seven days before the harvest, mainly in 20~30cm, 40~50cm deep of soil.In soil Tonghao system, the average error percentage of the heavy metal Pb, Cd and Cr is 3.19%, 3.55% and 2.80% respectively, so three kinds of heavy metals in system is balanceable totally. The strongest absorbing ability of Tonghao for heavy metal Pb is in its 28 days after planting and before its harvest. The heavy metal Pb in Tonghao is mainly from 0~10cm, 20~30cm, 40~50cm deep of soil; The strongest absorbing ability of Tonghao for heavy metal Cd is in 28 days after its growing to the harvest, mainly in 0~30cm depth of soil; The strongest absorbing ability of Tonghao for heavy metal Cr is after 23~28 days of its planting, mainly concentrated in the 30~50cm deep of soil.