Effects Of Eombined Amendment And Exogenous Iron On Transport And Accumulation Of Cd And In Soil-Rice System

In this study,an in-situ paddy experiment was conducted to study the remedying effects of a combined amendment(calcium carbonate + diatomite + ferric sulfate)stabilizing Cd in a certain Cd contaminated paddy soil for spring and autumn rice planting.Another pot experiment was conducted to study the remedying effects of exogenous iron on the transport and accumulation of Cd in soil-rice system.The main results are as follows:(1)An in-situ paddy experiment was conducted to study the remedying effects of a combined amendment(calcium carbonate + diatomite + ferric sulfate)on Cd bioavailability in soil and Cd accumulation in rice for spring and autumn rice planted in a certain Cd contaminated paddy soil in Beishan Town,Changsha,Hunan Province.The results showed that:Application of the combined amendment significantly increased soil pH and CEC values in two cultivated seasons,but decreased soil OM contents for the spring rice.During the experiment,the contents of TCLP-extractable Cd and CaCl2-extractable Cd in soil reduced by 18.0%-33.0%and 5.4%-57.9%,respectively.The Cd contents in brown rice,husk,leave and root for the spring rice decreased by 29.6%-56.1%,52.1%-54.0%,18.1%-80.7%and 24.4%-41.6%,respectively,due to applying the combined amendment.(2)There were significant differences in Cd transport capacity between spring rice and autumn rice,and the transportation of soil Cd in autumn rice was smoother than that in spring rice.For the autumn rice,the effects of the combined amendment were not significant(P>0.05),except for the Cd content in husk increasing a little for applying 2 g·kg-1 of the combined amendment.Significantly positive correlations were found between the Cd contents in brown rice and the contents of TCLP-extractable Cd or CaCl2-extractable Cd in soil.Application of the combined amendment inhibited Cd uptake by rice root and reduced Cd contents in brown rice for the spring rice effectively.The values of the target hazard THQ for Cd were less than 1 in the studied area,indicating that intake of Cd through consuming rice would not pose potential health risks to the local individuals.However,these remedying effects were significantly weakened for the autumn rice due to loss of the combined amendment with the movement of irrigation water in the spring season.We suggested that supplement of the combined amendment was necessary between two rice cultivated seasons.(3)A pot experiment was conducted to study the effects of exogenous iron on translocation and accmulation of Cd for two rices "XiangWanxian 12“and "Weiyou 46" planted in two different levels of Cd contamination soil.The results showed that:Application of the exogenous iron significantly reduced soil pH,which reduced by 0.24?0.67 units for XiangWanxiang 12 and 0.07?0.60 units for Weiyou 46 in the low Cd contaminated soil,respectively.In the moderate Cd contaminated soil,soil pH values reduced by 0.17?0.70 units for XiangWanxiang 12 and 0.19?0.46 units Weiyou 46,respectively.The contents of CaCl2-extractable Cd showed a trend of initial decrease and then increase.The contents of TCLP-extractable Cd increased with increasing the amount of exogenous iron.(4)Exogenous iron significantly promoted the iron plaque formation.The amounts of iron plaque on the root surface of "Xiang-Wanxian 12" and "Weiyou 46"were increased by 49.1%-79.9%and 55.6%-95.6%in the low Cd contaminated soil,respectively.The amounts of iron plaque on the root surface of "Xiang-Wanxian 12"and "Weiyou 46" were increased by 44.3%?78.0%and 22.9%?52.4%in the moderate Cd contaminated soil,respectively.After application of exogenous iron,the amounts of iron plaque in the two rice varieties were between 42171?77353 Fe mg·kg-1RDW-1,which could inhibited Cd uptake by rice root and reduced Cd contents in brown rice effectively.(5)Cd contents in brown rice of "Xiang-Wanxian 12" and "Weiyou 46"decreased by 33.2%?41.7%,33.87%?74.4%in the low Cd contaminated soil,respectively,due to applying the exogenous iron.In the moderate Cd contaminated soil,Cd contents in brown rice of "Xiang-Wanxian 12" reduced by 42.5%maximumly.Most Cd was accumulated in rice leaves,and then followed by brown rice,the least in the husks in the aboveground parts,and the sequence was leave>husk>brown rice.Fe contents in brown rice,leave,husk in two rice varieties increased,and showed a relatively stable in brown rice.In the moderate Cd contaminated soil,significantly negative correlations were found between Fe contents in brown rice and Cd contents in brown rice,and the correlation coefficent R was-0.630(n = 15,R0.05= 0.514),which concluded that increased Fe contents inhibited Cd contents in brown rice.