The Effects Of Co Or Ni On The Accumulation And Transformation Of Mercury In Rice Plants

Mercury(Hg)is a global pollutant with high toxicity.Rice consumption is a main source of methylmercury(MeHg)exposure for residents living in Hg mine area in china.The uptake and accumulation of trace elements in rice could be affected by the mercury exposure.Therefore,it is beneficial to explore the effect of trace elements,especially beneficial elements,on the uptake and accumulation of mercury in rice.In this paper,the effect of cobalt(Co)and nickel(Ni)addition on the absorption and translocation of IHg and MeHg in rice plants were investigated.The results are listed as follows:1.The transportation and transformation of IHg and MeHg in rice tissues exposed to different forms of Hg with the addition of Co were investigated using ICP-MS,HPLC-ICP-MS and SR-XANES.The distribution of mercury in rice tissues exposed to Co-MeHg was studied using SRXRF.The addition of Co promoted the content of mercury in the roots,but inhibited the absorption and accumulation of mercury in the shoot with the exposure to IHg.The absorption and transportation of Hg in rice seedlings was promoted with the Co-MeHg co-exposure.The speciation of Hg in rice tissues was not changed when exposed to IHg with the addition of Co.However,the addition of Co could promote the demethylation of MeHg in rice roots on MeHg exposure early(before 8 days)and then inhibited after 16 days.SR-XANES results indicated that methylated and demethylated mercury in rice roots or shoots prefered to be bound to biomolecules containing thiols,for example CH3-Hg-SR and RS-Hg-SR.The results of SRXRF further showed that Co could promote the accumulation of mercury in the pericycle of rice roots,but had little change on the distribution of mercury in shoots.2.The effect of Ni on the transportation and transformation of IHg and MeHg in rice tissues were investigated using ICP-MS and HPLC-ICP-MS.It was shown that Ni could promote the total mercury content in the roots and shoots,and the total mercury content in rice tissues increased with the increasing of the concentration of Ni.The speciation of Hg in rice tissues did not change exposed to IHg with the addition of Ni.When exposed to MeHg and Ni,the percent of IHg in growing rice roots increased while MeHg decreased significantly.The percent of IHg and MeHg in rice shoots increased with the increasing of culture time.This suggested prominent demethylation of methylmercury occurred.And the addition of Ni promoted the demethylation of methylmercury in rice roots.3.The effect of different forms of Hg on the absorption and transportation of Co and Ni in rice tissues were also investigated.The Co contents in rice roots were increased first and then decreased with the exposure of IHg,however,inhibited the uptake of Ni by rice roots.When exposed to MeHg,the absorption of Co and Ni in rice roots was inhibited by Hg.Except the 0.5MeHg+10Co group,the contents of Co and Ni in the rice shoots of each exposure group were increased under Hg addition.Both IHg and MeHg could promote the transportation of Co and Ni from the rice roots to the aboveground part,and the promotion of MeHg was stronger than that of IHg.