Inhibition Effect Of Hydroxyapatite On Absorbing And Gathering Cadmium,lead And Zinc Of Different Indicas

A pot experiment was carried out in order to study the effects of hydroxyapatite(HAP)on the absorption and accumulation of Cd,Pb and Zn by three indica rice(Donglian 5,Teyou 009 and Yiyou 673).The relevant mechanisms were also discussed.The main results were as follows:(1)The availability of Cd?Pb and Zn in the soils was decreased by HAP.The more HAP added,the lower available Cd,Pb and Zn in the soils.With the same dosage of HAP,the available Cd and Pb were reduced more significantly than available Zn.The available amounts of the metals in the soils cultivated with different rice varieties responded differently when HAP was added.In tillering stage,the available Cd,Pb and Zn in the soil of Donglian 5 were lower than those of Teyou 009 and Yiyou 673.In mature stage,he available Cd,Pb and Zn in the soil of Donglian 5 were higher than those of,Teyou 009 and Yiyou 673.(2)Weak acid extractable Cd was the predominant fraction in the control soil.When HAP was added,weak acid extractable Cd gradually transformed into reducible Cd.The percentage of weak acid extractable Cd,Pb znd Zn over total soil Cd,Pb and Zn in mature stage was higher than that in tillering stage while the percentage of reducible Cd,Pb and Zn was lower than that in tillering stage.HAP promoted the transformation of weak acid extractable Pb into reducible Pb whereas it did not significantly influence the percentage of oxidizable and residual fractions.The effects of HAP on Zn fractions in the soils were negligible.(3)XANES results showed that in both the soil and the root of rice(Donglian 5),free Pb2+ was greatly reduced while chloropyromorphite in the soil was significantly increased.(4)In tillering stage,HAP suppressed the uptake Cd by the rice.However,this inhibitory effects weakened with time.HAP decreased the Cd concentration in the plants of Donglian 5 and Teyou 009 more significantly than that of Yiyou 673.The Zn concentration in all parts of Donglian 5 and Teyou 009 was reduced by HAP application while that in the root of Yiyou 673 was increased by low dosage of HAP.(5)The Cd transfer in the plant of Teyou 009 and Yiyou 673 was facilitied obviously by HAP application while that within Donglian 5 was either facilitied or inhibited.The transfer of Pb was generally inhibited by HAP,especially the transfer between stem or leaf to brown rice.HAP primarily promoted the Zn transfer within the plant of Donglian 5.However,both promotion and inhibition were observed for Zn transfer within the plants of Teyou 009 and Yiyou 673.(6)The application of HAP decreased the Pb contents in the brown rice of Donglian 5,Teyou 009 and Yiyou 673 by 45.4%?92.0%?73.2%?92.7%and 17.4%?88.9%respectively.The Cd contents in the brown rice of Teyou 009 and Yiyou 673 were increased while that of Donglian 5 was decreased by HAP application.The effect of HAP on Zn concentration in the brown rice was generally weaker than that on Cd or Pb concentrations in the brown rice.The Zn concentration in the brown rice of Donglian 5 and Yiyou 673 was slightly increased while that of Teyou 009 was slightly reduced by HAP application.(7)The available soil Pb in the soil was significantly correlated with the content of Pb in the brown rice.However,there was no significant correlation between the available Cd and Zn in the soil and the Cd and Zn content in the brown rice,indicating that the effect of the transfer of Cd and Zn within the rice plant on the accumulation of Cd and Zn in the brown rice was more important than that of Pb.