三峡库区紫色土不同成土母质Cu,Zn污染评价

On Contents of Cu and Zn in Different Parent Materials of Purple Soil and Pollution Assessment in the Three Gorges Reservoir Area

以三峡库区核心区重庆市不同区县紫色土3种发育母质的为研究对象，研究了表层土壤重金属Cu、Zn的含量，并对土壤重金属含量随时间变化趋势进行分析。结果表明，供试的三峡库区核心区暗紫泥、灰棕紫泥和红棕紫泥3种成土母质紫色土全Cu含量为25.0～36.9 mg／kg ，平均含量为30.5 mg／kg ，其中暗紫泥和红棕紫泥土属的全Cu含量则超过紫色土全Cu含量背景值；3种成土母质紫色土的全Zn含量为73.9～75.9 mg／kg ，平均含量为75.1 mg／kg ，低于全国紫色土全Zn平均值。暗紫泥、灰棕紫泥和红棕紫泥3种土属的土壤全Cu含量高低次序与其全Zn含量的大小顺序相同，这表明紫色土的成土母质仍是土壤全Cu、全Zn含量的主要因素。土壤有效Cu含量顺序依次为暗紫泥，红棕紫泥和灰棕紫泥；有效Zn含量大小次序为暗紫泥，灰棕紫泥和红棕紫泥；3种紫色土的有效态Cu、Zn含量都比重庆市紫色土重金属背景值要高，这说明在近30年的人类活动影响下，3种母质发育紫色土表层有效态Cu、Zn都有累积现象。以重庆市紫色土重金属背景值作为评价标准，暗紫泥、灰棕紫泥和红棕紫泥的内梅罗综合指数分别为0.85，1.74和1.86，表明灰棕紫泥和红棕紫泥土属的紫色土Cu、Zn含量达到了轻度污染，暗紫泥土属紫色土Cu、Zn含量已经达到污染警戒线，但未达到土壤发生Cu、Zn重金属污染程度。

The composition of soils is strongly affected by the geochemical character of the parent rock . Pedogenesis appears to be responsible for the accumulation of Zn ,Cu in the upper soil .The objects of this paper are to evaluate the changing tendencies of Cu ,Zn concentration with time for the surface level of three kinds of purple soils （unibiacteata soil ,red brow n purple soil and grey brow n purple soil ） w hich are developed from three main soil parent materials .The total Cu contents of three purple soils are 36 .9 ,25 . 0 ,and 29 .6 mg.kg -1 respectively ,and the total Zn contents are 75 .9 ,73 .9 ,and 75 .6 mg.kg -1 .The results show that the Zn contents of three purple soils are lower than the background value of purple soil（82 .8 mg·kg ^-1 ） ,but the Cu contents in unibiacteata soil and red brow n purple soil are higher than the background value of purple soil （26 .3 mg·kg^ -1 ） .The orders of total Cu and total Zn contents are con-sistent with the orders of heavy metal background values of three purple soils ,which indicates that the soil parent materials are still the main influencing factors on total Cu ,Zn contents in purple soils .The reasons can be attributed to the fact that the physical weathering of purple soil parent material is strong ,the char-acter differences of purple rock are clearly preserved to the purple soils w hich are formed by purple parent material .The order of effective Cu contents is ：unibiacteata soil〉red brown purple soil〉grey brown pur-ple soil ,and the same order can also found be in total Cu and total Zn .The order of bioavailable Zn con-tents is ：unibiacteata soil〉 grey brown purple soil〉red brown purple soil .The available Cu ,Zn contents and the total Cu ,Zn contents have approximately the same level of order .Compared with the values of heavy metal contents from the second national soil survey in 1984 ,the total Zn contents of three purple soils decrease ,w hich account for 93 .4% ,98 .1% ,96 .8% of the content of the second soil survey .How-ever ,the contents of effective Cu ,Zn and total Cu increase .The upward trends of effective Cu ,Zn are greater than total Cu ,w hich means that soil bioavailable Cu ,Zn and total Cu can accumulate in the surface level of three soils because of the nearly 30 years human activities ,and human activities have greater im-pact on the effective metal contents .The contaminate valuation standard of Nemerow index method is the heavy metal background values of three purple soils in Chongqing .The background values of countrywide purple soil haven＇t been selected .T he Nemerow indexes of unibiacteata soil ,grey brow n purple soil ,red brown purple soil are 0 .85 ,1 .74 ,and 1 .86 ,respectively .The grey brown purple soil and red brown pur-ple soil are under slight Cu ,Zn pollution ,w hile Cu ,Zn pollution hasn＆#39;t been found in the unibiacteata soil .However ,the contents of Cu ,Zn of unibiacteata soil reach the pollution warning level .Because of the difference of heavy metal contents in purple soil with different original rock development ,the heavy metal background values of three purple soils are better valuation standards than the background values of countrywide purple soil .More accurate evaluations of the status of heavy metal contaminates in purple soil could be obtained .