| Cd accumulation in grains of staple crops may have important impact on human health through dietary intake.Growing of hybrid rice cultivars are increasingly extended in South China for high rice production.However,much attention has been to the higher Cd uptake and grain accumulation by the hybrid rice than the conventional rice for the last 5 years.In this thesis,a comparative study of grain concentration of heavy metals Cd,Zn and Se between rice grains and non-rice grains and of Cd accumulation in plants between cultivars of hybrid rices was conducted.Grain samples of some rice and other cereals were collected from agro-markets of Nanjing and their contents of Cd,Se and Zn were determined with atomic adsorption spectroscopy(AAS),atomic fluoresce spectroscopy(AFS) and AAS respectively.The results showed that:(1) The grain Se contents of the studied cereals fall below the guideline value by WHO of 0.1mg·kg-1,while over 50%of foodstaff grain samples had a grain Cd concentration over the China Food Security Guideline of 0.05mg·kg-1,indicating potential Se deficiency and over-loading of Cd from food exposure for dietary intake;(2) There was much difference in the metal contents between the cereals grains,being more significant with Cd and Se than with Zn;Soybean grains contained high contents of Cd and Zd but not Se than corn grains;(3) Most of the foodstaff grains contained Cd over 0.05mg·kg-1,a limit value of China Food Security Guideline without a Cd/Zn ratio over 0.015,a threshold value for potential Cd toxicity to human.Taking in account of the small consumption relative to rice,a guideline value of 0.2mg·kg-1,same for rice grains is suggested.To understanding the possible mechanism for the enhanced Cd uptake by hybrid rice cultivars,a Pot experiments were conducted with two rice cultivars(a super hybrid rice and a common hybrid rice) on two different soils with and without Cd spiking(2.5mgCd/kg soil) to soils.The uptake and partitioning of Cd by rice was determined with atomic adsorption spectroscopy(AAS) at different growth stages.The results showed that on the basis of total biomass construction,the most intense active Cd uptake for both hybrid rice cultivars happened at the heading stage.Compared to common hybrid rice cultivars,Cd uptake by super rice ones was much enhanced under Cd spiking.While super rice cultivars had a higher capacity to translocate and partition Cd to grains than the common rice under no Cd spiking.That is,under no Cd pollution,the Cd translocation and partitioning drive the grain Cd level by the rice cultivars.However,with spiked Cd,soil factor may become significant in controlling the Cd availability as super rice had Cd uptake in grains as several folds as common rice cultivars when grown in an acidic soil.This explained intense enhanced Cd uptake and accumulation in rice grains by hybrid rice cultivars grown in red soil region from South China as reported in previous studies.
|
PDF Full Text Request