| With the fast development of our country’s industry, an increasing number of people and the quick development of the process of urbanization, the content of harmful heavy metals (such as Pb, Cd, Hg, As and Cr, etc.) which enter into soil through various ways are constantly increasing. Heavy metals posed a serious threat to the safety of China’s agro-ecological environment. These days, food contamination problems often occur and become increasingly prominent, which causes the general concern of the government and consumers. The environmental quality of orchard soil directly affects the growth of fruit trees, producing fruit, life, and fruit quality. The content of heavy metals in soil have become an important indicator for the environmental quality producing pollution-free fruit. The pollution and treatment of the soil heavy metal has become a hot research in the field of environmental science.The soil acidification was very serious in Golden Orchard of Chongqing, mainly fertilized organic manure, also fertilized a certain amount of chemical fertilizer according to the fruit trees growing and the surrounding environment changes. Heavy metals brought by fertilizing and atmospheric deposition could accumulate in orchard soil, the fixed heavy metals (such as Pb, Cd) in orchard soil were in acid environment over a long period of time. In addition, heavy metals were activated and then released slowly in eluviation of the acid rain, increasing the content of the available heavy metals in soil, then increasing the risk into the body of fruit tree, thus affecting the growth of the fruit tree and fruit quality. According to another report, acidified water was found in Jinyun Mountain. Irrigation water was another resource of heavy metal for the orchard soil.In this paper, the contents of heavy metals and pH in soil section of Golden Orchard in Chongqing were monitored, including pear garden, mandarin orange garden, jujube garden, cherry garden, blood orange garden, loquat garden, peach garden, grape garden and navel orange garden, pollution assessment was performed by using pollution indices based on the environmental quality standard for the producing area of the nuisance free fruits and the producing area of the green food; In situ immobilization of Pb, Cd in orchard soil was studied by using soil ameliorants in the loquat garden and peach garden according to the result of pollution assessment, comparing the passivation effect of different ameliorants; investigating the effect about In Situ Immobilization of Pb, Cd in Orchard Soil through measuring the contents of Pb, Cd in fruit tree leaves and fruits, so as to improve the orchard ecological environment, ensure fruit production safety and promote the sustainable development of the local fruit industry, the main conclusions were listed as follows.(1) The range of the surface soil (0-20 cm) pH in the gardens in Golden Orchard was 3.31～4.02, the acidity order from high to low was mandarin orange garden, jujube garden, navel orange garden, loquat garden, pear garden, grape garden, blood orange garden, cherry garden, peach garden, the range of the lower layer soil (20～40 cm) pH was 3.36-4.52, the acidity order from high to low was mandarin orange garden, loquat garden, jujube garden, pear garden, navel orange garden, blood orange garden, peach garden, grape garden, cherry garden. In the 0-40 cm soil layer, the pH of the upper layer was higher than that in the lower layer in each garden. According to grading standards of the soil acidity, the soil under pH＜5.0 was strongly acid soil, it appeared that the Golden Orchard soil had been seriously acidification.The contents of five heavy metals (As, Cd, Cr, Hg, Pb) were different in 0-20, 20～40 cm soil layers in the same park, Cd contents in 0-20,20～40 cm soil layers in blood orange garden were 0.28 and 0.21 mg-kg-1, respectively, the change was not obvious; Hg contents in 0～20,20～40 cm soil layers were 0.21 and 0.06 mg-kg-1, respectively, the change was very obvious. The contents of the five heavy metals in the upper layer were higher than those in the lower layer in the same park, the contents of the same heavy metal varied in the different parks, within these heavy metals, the contents of Cd, Cr, Hg had bigger differences. Cd contents in 0-20 cm soil layer in the mandarin orange and loquat garden were 0.17 and 0.34 mg-kg-1, respectively. Cr contents in 0-20 cm soil layer in pear garden and mandarin orange were 61.42 and 23.05 mg-kg-1, respectively. Hg contents in 0-20 cm soil layer in jujube garden and blood orange garden were 0.09 and 0.21 mg-kg-1, respectively, but the contents of As, Pb had relatively smaller differences. As contents in 0-20 cm soil layer in pear garden and loquat garden were 3.74 and 6.99 mg-kg-1, respectively. Pb contents in 0～20 cm soil layer in mandarin orange garden and peach garden were 21.11 and 37.73 mg-kg-1, respectively. Hg content in blood orange garden was maximum (0.21 mg/kg), and Cr contents in pear garden was maximum (61.42 mg-kg-1), the contents of As, Cd in loquat garden were maximum (6.99 and 0.34 mg-kg-1), and Pb contents in peach garden was maximum (37.73 mg-kg-1). From the total amount of heavy metals, because the soil in each garden was acidity, according to the limit standards of heavy metal contents in soil under pH< 6.5 with the measured value, such as Cd was 0.3 mg-kg-1, Cd contents in loquat garden, peach garden and grape garden were higher than the limit standard value.(2) Taking the environmental quality standard for the producing area of the nuisance free fruits as a standard, the single factor pollution indices of As, Cr, Pb, Hg were all no more than 0.7 in each park soil of Golden Orchard, soil environment was in a clean state; the single factor pollution indices of Cd in 0-20 and 20～40 cm soil layers in loquat garden and grape garden,0-20 cm soil layer in peach garden was higher than 1, reaching the level of light pollution. Nemerow pollution indices of the five heavy metals in the soils in pear garden, mandarin orange garden, jujube garden, cherry garden, blood orange garden, navel orange garden, peach garden and grape garden were all less than 0.7, not enough to cause pollution for fruit production, soil environmental quality was judged to be clean. Nemerow pollution index of 0-20 cm soil layers in loquat garden was 0.75, and soil environmental quality was judged as nearly clean.Taking the environmental quality standard for the producing area of the green food as a standard, the single factor pollution indices of Cd in each park were higher than other heavy metals,0-20 and 20～40 cm soil layers in loquat garden and grape garden, 0-20 cm soil layer in peach garden reached lightly polluted. The content of Cd in 20～40 cm soil layer in pear garden and blood orange garden,0-20 cm soil layer in navel orange garden and cherry garden reached alert level. In addition, the contents of Pb in 0-20 cm soil layer in loquat garden and peach garden were also in alert level. Nemerow pollution indices of the soil in pear garden, mandarin orange garden, jujube garden, cherry garden, blood orange garden and navel orange garden were all less than 0.7, and soil environmental quality was judged as clean; Nemerow pollution indices of 0-20 cm soil layer in loquat garden, peach garden, and grape garden were 0.82,0.78, and 0.74, and soil environmental quality was judged as nearly clean.(3) On the basis of heavy metals pollution assessment in Golden Orchard Soil, In situ immobilization of Pb, Cd in orchard soil was studied by using soil ameliorants in the loquat garden and peach garden. The study showed that all ameliorant treatments could decrease soil acidity in loquat garden and peach garden except the treatment of superphosphate, ameliorant treatments decreased the bioavailability of Pb, Cd in soil, and reduced the contents of Pb, Cd in fruits. Compared with the contrast, soil pH in loquat garden and peach garden increased 0.93 and 0.79 with the treatment of quicklime for 120 d, respectively. In loquat garden and peach garden, the effect of decreasing the content of the available Pb in soil with the treatment of quicklime and superphosphate for 150 d was the best, decreasing by 3.46% and 3.56%, respectively; In loquat garden, the effect of decreasing the content of the available Cd in soil with the treatment of quicklime for 150 d was the best decreasing by 10.95%; In peach garden, the effect of decreasing the content of the available Cd in soil with the treatment of quicklime, superphosphate and organic manure for 150 d was the best, decreasing by 7.09%. According to the heavy metal limit standard in the food (fruit) (Pb≤0.1 mg·kg-1, Cd≤0.05 mg·kg-1), finding that the content of the Pb in loquat exceeded the standard 14.7%, the content of the Pb, Cd in peach exceeded the standard 6.4%,4.8% without the treatment of the ameliorant. The effect of decreasing the content of the Pb in loquat and peach with the treatment of quicklime and superphosphate was the best, decreasing by 18.3% and 14.44%, respectively; The treatment of ameliorants could decrease the content of Cd in loquat further, the effect of decreasing the content of the Cd in loquat and peach with the treatment of quicklime was the best, decreasing by 30.91% and 24.62%, respectively. |
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