| In resent years,agricultural soil contamination by heavy metals is an increasingly severe issue.Rice as one of the staple food crops has been polluted to varying degrees in some southern provinces of China.Cadmium(Cd),lead(Pb),and arsenic(As)threat human health seriously,so it has been a hot spot to reduce metal(loid)s uptake by rice.Titanium gypsum(TG)is an industrial by-product mainly containing calcium sulfate and iron(?)oxide.However,the consumption rate of titanium gypsum is still considerably low and it is mainly used as a substitute for natural gypsum.An amendment(simulated titanium gypsum,STG)was newly developed to evaluate whether STG or TG can passivate the multicontaminated paddy soil by heavy metals.A soil incubation experiment and two consecutive pot trials were conducted to study the effect of STG on metal(loid)s immobilization in soil solution and metal(loid)s uptake by rice,respectively.Then the feasibility of TG on simultaneous stabilization in contaminated soil was verified by rice pot trial and the mechanism was preliminarily discussed.Primary results were summarized as follows:(1)The soil incubation experiment was conduced to evalute the effect of STG and TG on Cd,Pb,and As in flooded paddy soil.Compared to the control,we found that the addition of STG and TG significantly decreased soil pH and DOC concentration but not DON before 28 d;while on 28 d,the soil pH values and DOC/DON concentrations of each treatment were similar.The addition of 0.3%STG and 0.3%TG significantly decreased 75.5%and 70.2%Cd,86.7%and 79.0%Pb,69.3%and 72.5%As in soil solutions,respectively.However,the addition of STG and TG had little effect on the fraction of metal(loid)s in air-dried soil,and the key factor influenced the phytoavailability of metal(loid)s might be flooded condition.(2)For evaluating the stabilization and persistence of STG on reducing Cd,Pb,and As accumulation in rice plant,a one-off application of STG was conducted to soil and rice was subsequently cultivated on it for two consecutive seasons.It showed that the treatments of STG maintained better plant growth in the first season.Meanwhile,the addition of STG could induce the decrease of soil pH.In the second season,the rice plant of all treatments grown better because of more chemical fertilizer.In addition,the amendment significantly decreased the concentration of DOC but not DON,and obviously decreased Cd,Pb,and As uptake by two seasons rice.The mechanism of STG reducing Cd,Pb,and As uptake by rice might be the formation of Fe/Mn plaque in the rhizosphere.(3)Then the effect of titanium gypsum(TG)on metal(loid)s uptake by rice was investigated.Pot trial was conducted and found that TG treatments obviously promoted the growth of rice and to some extent reduced the accumulation of Cd,Pb,and As in rice tissues.The addition of TG led to the decrease of soil pH,but had different effects on DOC/DON concentrations of rhizosphere/bulk soils.The immobilization effect of TG on Cd and As in soil was not as good as that of STG because Cd and As concentration of TG was much higher than STG.Thus direct addition of TG to soil posed certain environmental risks.TG of two additive ratios significantly increased Mn plaque on root surface,but almost had no effect on the formation of Fe plaque.The addition of TG decreasced the DCB-Cd,DCB-Pb,and DCB-As concentrations of root surface,similar to those concentrations of rice root,which indicated that one of the mechanisms of TG preventing Cd,Pb,and As from entering rice might be the formation of Fe/Mn plaque on root surface. |
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