| Since the fast developing transgenic Bt plants can impact ecosystem operation and biodiversity by retaining and accumulating the released toxins, broad concerns about environmental security arose among peoples. Taking the latosol of Chengmai County, Hainan province, latosolic red soil of Nanning City, Guangxi province, red soil of Xianning City, Hubei province, yellow soil of Huaxitongmuling in Guiyang City, Guizhou province and paddy soil of Nanchang city, Jiangxi province as research targets,the effect on Bt toxin adsorption by different forms of iron and aluminium oxides, such as organic complex state, free state, amouphous state, interlayer state, adsorption state and exchangeable state, was studied and the comparison of isothermal adsorption characteristics of Bt toxins in all the selected soils whose iron and aluminium oxides of different forms being removed and unremoved previously was focused on in particular. Besides, the research covers isothermal adsorption characteristics of Bt toxins in goethite, hematite and gibbsite. The whole study will provide reference for defining the effect of different forms of iron and aluminium oxides on Bt toxins adsorption, facilitate exploration of characteristics of migration and accumulation for the toxins in soil released by transgenic Bt plants, and is of far reaching importance on in-depth study of effect on ecological environment brought by original Bt toxins. The main results are showed below.1) The adsorption amount of Bt toxin in the selected 5 kinds of soils increased after the Fep-Alp being removed. Comparing with Fep-Alp-unremoved soil, the toxin adsorption amount increse of 18.5%,3.5%,12.4%,15.5%,52.9% goes for latosol, latosolic red soil, red soil, yellow soil and paddy soil respectively. The increasing toxin adsorption amount was in positive correlation with the content of removed Fep, and in negative correlation with that of removed Alp. Besides, it is related with the decreased organic matters.2) The adsorption amount of the Bt toxins on the surface of Fed-Ald-removed soils-latosol, latosolic red soil, red soil, yellow soil and paddy soil declined significantly up to 55.6%,37.0%,70.5%,21.8% and 45.8% respectively. Moreover, being attributable to the Fed-Ald-removing treatment, the number of negative charges on the soil surface was raised while the superficial area was diminished, and their ratio grew up, promoting the Bt toxin adsorption capacity falled off. 3) The Bt toxins adsorption amount for Feo-Alo-removed soils-latosol, latosolic red soil and paddy soil significantly decreased comparing with that for unremoved soils, up to 27.7%,34.6% and 14.4%, in contrast to slight reduction of 6.3% and 12.4% for Feo-Alo-removed yellow soil and red soil. Besides, responding to the Feo-Alo-removing treatment, the soil point of zero change(PZC)was lowered, the amount of permanent negative charges grew up, and Bt toxins adsorption content diminished.4) The adsorption amount of Bt toxin in all the selected 5 kinds of soils declined sharply after the InFe-InAl being removed, up to 37.5%,39.3%,38.2%,14.0%,18.8% comparing with that in untreated soils. What's more, this treatment led to the increase of negative charges between two layers, reinforcement of the electrostatic repulsion among Bt toxins attached with negative charges, and reduction of Bt toxins adsorption capacity. Besides, the dropping amount of hydroxyls which can ligand-exchange with carboxyls and hydroxyls of toxins also contributed to the adsorption amount of Bt toxins decline.5) The Bt toxins adsorption amount for HyFe-HyAl-removed soils-latosol, latosolic red soil and paddy soil significantly dropped off from 182.1,210.1 and 157.8mg g-1 to124.3,156.7 and 116.7mg g-1 respectively comparing with that for unremoved soils, up to 31.7%,25.4% and 26.1%. However, the significant reduction did not apply to the treatments with HyFe-HyAl-removed red and yellow soils, instead with 3.1% and 6.3%'s cutback. On the basis of low content of HyFe for all the 5 soils, the effect of Fed on Bt toxins adsorption could be ignored. Hence, the dropping of toxin adsorption content was primarily caused by removing of HyAl.6) The Bt toxins adsorption content declined markably in all the 5 tested soils after ExFe-ExAl being removed. The close reductions for atosol, latosolic red soil, red soil, yellow soil and paddy soil reached up to 22.4%,23.1%,24.5%,23.3% and 21.3% respectively, due to the removal of Ale mainly. The removal of ExFe-ExAl led to the rise of some ions'hydration radius and cutback of adsorption energy supply, resulting in Bt toxins adsorption content decrease because of the difficulty enhancement for adsorption.7) For all the 5 tested soils, the 6 kinds of Fe-Al oxides of different forms exerted distinctive degree of effect on Bt toxins adsorption. For latosol, the order of effect degree brought by different forms of Fe-Al was free state> interlayer state> amouphous state, adsorption state, organic complex state> exchangeable state; for latosolic, it was free state, interlayer state> organic complex state, amouphous state, adsorption state> exchangeable state; for red soil, it was free state, interlayer state> organic complex state, amouphous state> exchangeable state, adsorption state; for yellow soil, it was free state, exchangeable state> organic complex state> amouphous state, interlayer state, adsorption state; for paddy soil, it was free state> amouphous state, interlayer state, organic complex state> exchangeable state,adsorption state.8) The adsorption isotherms of Bt toxin were L-type either on the surface of soil or mineral, both of them being prone to adsorb Bt toxins. The Freundlich and Langmuir equation fitting results showed that the maximal adsorption affinity applied to the Fep-Alp-removed soil, comparing with the minimal one for the Fed-Ald-removed soil. As Bt toxin concentration increased, the adsorption amounts of Bt toxin appeared to increase rapidly. Besides, the drastic disparity of adsorption isotherms of Bt toxin, which decreased in the order Geothite>Hematite>Gibbsite, were observed among different mineral surfaces. KeyWords:Bacillus thuringiensis; Bt toxin; adsorption; iron and aluminium oxides...
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