Migration Characteristics And Bioavailability Of Cd In Soils Ameded With Sewage Sludge In Potato System

With the development of socio-economy in China,the amount of sewage sludge increased dramatically as the sewage increased.The composition of sewage sludge is complex,and it is containing not only a large amount of organic matter,nitrogen,phosphorus and other nutrients needed for plants,but it also contains heavy metals and other hazardous materials.Discharging of sewage sludge results in a waste of resources and causes environmental pollution.And the loess has characteristics of poor permeability,low organic matter content and easy to compaction,thus,sewage sludge can be used as soil conditioner.In this study,sewage sludge and Malan loess mixed according to a certain proportion(0%,1%,2%,4%,8%).Using as test soil.In order to simulate the different pollution levels,different concentration of gradients of Cd stress added to the test soil.Tessier sequential extraction procedure was used to analyze the chemical form of the Cd in soil amended by different proportion of sewage sludge and the change characteristics of activities in Urease,invertase and alkaline phosphatase in the tested soil.The pot experiment was conducted to study the transformation and bioavailability of the Cd in soil –potato system.The research results summarized as follows:With the increase of Cd stress,the content of Cd in soils amended by a different proportion of sewage sludge was increasing and the CAB showed the highest value.Which revealed that the potential risk of Cd increased in tested soils as the Cd pollution level increasing.Under the same Cd stress level,the content of EXC and CAB decreased and FMO and OM increased as the sludge proportion elevated.This means that application of sludge can reduce the amount of movable Cd and then minimizes the risk of secondary pollution caused by Cd.We studied the activities of Urease,invertase and alkaline phosphatase in soils amended by a different proportion sludge,and the results showed that at first,the activity in all of the above increased and then decreased as the Cd stress increased.It suggested that a certain degree of Cd could promote the enzyme activity in a tested soils,while the effect was changed to depress when Cd stress was further increased,under the same Cd stress level,enzyme activity increased with rising of sludge proportion.In loess,pH,organic matter,and EC was low,The amount of pH was decreased while the contents of organic matter,EC were increased in soil amended with different proportion of sludge,and soil fertility has improved.At the same time,the contents of Cu,Zn,Ni and Cd in the tested soils increased as the sludge ratio raised.However.The contents of heavy metals in soil amended with sludge were not exceeding the ? standard of soil quality.Therefore,although the application of sewage sludge to loess helps to improve the soil fertility but also increases the risk of heavy metals pollution.Firstly,with the increase of Cd stress,the dry weight of all part of potato increased and then decreased.When the Cd level reached 1.6mg /kg,the dry weight of potato reached its maximum level.Thus,applying a certain proportion of sludge to the loess can effectively promote the growth of potatoes and the growth of potato is better in soil amended with 2% sludge.Cd uptake by different parts of potato increased in soil amended with different proportion sludge with the increase of Cd stress.Thus the Cd stress can promoted Cd uptake in potato organs,and the contents of Cd in a different part were :stems >>skin >tubers.Under the same Cd stress level,the Cd uptake in various organs of potato increased with the rising of sludge proportion.There was a significant positive correlation between the contents of Cd in the organs and the total amount of Cd in the tested soils,which indicated that the bioavailability of Cd was higher when Cd pollution in tested soils was serious.The result showed that the main contributions of Cd in potato were FMO and OM.In the scale of this study,the content of Cd in all part of potatoes which are growing in soil amended by sewage sludge exceed the heavy metal standard in food products,which might not be edible.When Cd pollution level is less than 0.5mg/kg,the Cd content in tubers of potato is lower than the heavy metal standard in feed,thus this may use as feed.