Remediation Of Agricultural Soils Polluted By Cadmium And Arsenic Using Different Amendments Under Rice-wheat Rotation System

The heavy metal contamination in agricultural soil has become serious increasingly with the process of urban industrialization and rural intensification in the Yantze Delta area.The absorption and accumulation of cadmium(Cd)and arsenic(As)in food crops,especially in wheat and rice,has become one of the main concerns in our country and even the world.Currently,chemical passivation in situ has been considered as an efficient and feasible method for decreasing the availability of heavy metals in polluted farmland.Taking the typical pollution soil of Cd-As in Zhejiang province as the studying target.A two-year's test of immobilization in situ in a wheat-rice rotation was conducted to determine the effects of soil conditioner,iron-based biochar,swine manure-derived biochar,organic fertilizer and hydrated lime on the bioavailability of Cd and As in soil and the accumulation in crops.Furthermore,the health risk assessment via dietary intake associated with local eating habits has been implemented.The main results were summarized as follows:(1)Soil pH increased in a short time with the application of the five kinds of amendments.And hydrated lime(L),soil conditioner(T)and iron-based biochar showed better effect in increasing soil pH.The combined treatment of swine manure-derived biochar and hydrated lime(MB+)showed better performance than the single application of swine manure-derived biochar in increasing soil pH,and the similar results has been found in organic fertilizer + hydrated lime(F+)treatment.Both mixed treatment(MB+ and F+)could increase soil pH by 1.47?2.36 units.(2)The effect of five amendments on decreasing the bioavailability of Cd and As in soil are quite different.At the maturation stage of the second year,the result showed that the effect in decreasing available Cd rank from high to low as follows:L>T2>IB2>T 1>IB 1>MB+>MB2>F+>F>MB 1>CK;For available As,the sequence is:IB1>MB2>IB2>MB1>T1>MB+>CK>L>T2>F>F+.In summary,the iron-based biochar revealed the best performance in reducing the availability of Cd and As.(3)The contribution of five amendments to build wheat yield was greater than rice.The highest yield for wheat and rice in the second year were both observed in the treatment of high-dose of soil conditioner(T2).Compare to control,T2 treatment could increase wheat and rice grain yield by 24.46%and 11.24%,respectively.It has been also found that the grain yield was not cogredient with the dosage's increasing.For example,the high-dose iron-based biochar(IB2)showed lower yield than its low-dose(IB1)treatment in two years of wheat production.(4)Through contrasting the absorption and accumulation of Cd and As in different parts of wheat and rice,we found that the treatment of hydrated lime(L),high-dose soil conditioner(T2)and high-dose iron-based biochar were significantly decreased the Cd and As concentration in wheat and rice grain,compared to control.However,there was no significantly difference in the transfer coefficient from root to shoot(TFRS)and transfer coefficient from shoot to grain(TFSS).(5)According to health risk assessment via the exposure route of dietary intake,we found that the hazard quotient(HQ)value of Cd and As associated with rice consumption was higher than wheat consumption.In wheat and rice,the HQ value of As was 3.09?6.09 times higher than Cd.Compare to control,all amendments showed significantly effect on reducing accumulative risk(AR).