| Selenium（Se）is an essential micronutrient for human,which has essential biological functions,such as improving human immunity and act as an anti-cancer agent.Rice（Oryza sativa L.）is an important food crop in China.Eating Se enriched rice grains is one of the main ways for human body to supplement Se.Cadmium（Cd）is one of the most harmful elements to human body.Rice tends to easily accumulate Cd,and Cd-contaminated rice poses major food safety concerns.Guangxi has the largest area of Se rich soil in China,but it is also a typical geological background area with high Cd content in soil,and there is Cd associated phenomenon in Se rich soil.Current studies are mostly based on the antagonistic mechanism of exogenous Se on Cd accumulation in rice,but less attention is paid to the enrichment characteristics of Se and Cd in rice in natural high-Cd and Se-rich areas,and there is little research on the bioavailability of Cd in rice under the coexistence of Se.In this study,196 soil samples（0-20 cm）and corresponding rice grains samples were collected from a typical high Se and Cd background area in three counties of Guangxi.The contents of Se and Cd in soil and rice grains as well as the main physical and chemical properties of soil were analyzed,and the relationship and influencing factors of Se and Cd in soil and rice grains were identified.And through the experiment with rats,analysis of different proportion of Se-Cd relative bioavailability of Se,Cd in rice grains,study the influence of the relative bioavailability of Se-Cd on rice grains mechanism,evaluation of high Se and Cd background area residents long-term eating local rice intake of Se and Cd health risks,in order to understand the relationship between Se and Cd in soil-rice-animal,provide scientific basis for food safety,and provide reference for health risk research of population in high Se and Cd background area.The main results are as follows:1.Soil total Se content in the study area ranged from 0.26 to 2.73 mg·kg-1,and 93.37%of the sample sites had soil Se content exceeding 0.4 mg·kg-1 and soil total Cd content between 0.30 to 3.09 mg·kg-1.The average contents of soil total Se and soil total Cd were 0.82±0.39 mg·kg-1 and 0.78±0.57 mg·kg-1,respectively.The contents of Se and Cd in rice grains ranged from 0.001-0.21 mg·kg-1 and0.02-1.06 mg·kg-1,respectively,and the average contents were 0.05±0.03 mg·kg-1and 0.26±0.22 mg·kg-1,respectively.Se content of rice grains was extremely significant（p<0.01）positively correlated with soil total Se（r=0.287）and available Se（r=0.300）content,significant（p<0.05）positively correlated with the ratio availability of soil Se（r=0.148）,and extremely significant negatively correlated with the ratio availability of soil Cd（r=-0.217）;The Cd content of rice grains was extremely significant positively correlated with soil total Cd（r=0.230）and available Cd（r=0.250）content,but significant or extremely significant negatively correlated with soil available Se（r=-0.152）content and the ratio availability of soil Se（r=-0.253）.In addition,the ratio availability of soil Se and Se content of rice grains decreased with the increase of soil available Cd/Se molar ratio.The higher the soil available Se/Cd molar ratio was,the lower the ratio availability of soil Cd and Cd content of rice grains were.Therefore,the contents of Se and Cd in rice grains were controlled by their total and effective contents in soil,and the interaction of Se and Cd in soil reduced the accumulation of Se and Cd in rice grains.2.The correlation between the contents of Se and Cd in rice grains and the main physical and chemical properties of soil was analyzed.The results showed that Se content of rice grains was extremely significant negatively correlated with soil organic matter（r=-0.220）content,but not significant（p>0.05）with other physical and chemical properties.Cd content of rice grains was extremely significant negatively correlated with soil p H（r=-0.286）,soil exchangeable Ca（r=-0.200）and soil exchangeable Mg（r=-0.253）content,but not significant with other physical and chemical properties.The results showed that Se content of rice grains was mainly affected by soil organic matter;Cd content of rice grains was mainly affected by soil p H,exchangeable calcium and exchangeable magnesium.3.The rats were fed rice with different proportions of Se and Cd,and the biochemical indexes of serum and liver were analyzed.The results showed that compared with the control group,the activities of glutamic oxaloacetic transaminase（GOT）in serum and malondialdehyde（MDA）in liver of Cd rice group were significantly increased,while the activities of Superoxide dismutase（SOD）and Glutathione peroxidase（GSH-Px）in liver were significantly decreased.Compared with Cd rice group（Cd group）,GOT activity in serum and MDA content in liver of rats in low Se-Cd rice group（LSe-Cd group）,middle Se-Cd rice group（MSe-Cd group）and high Se-Cd rice group（HSe-Cd group）were significantly decreased,while SOD activity and GSH-Px activity were significantly increased.The results showed that Se intake in rice could significantly improve the activities of antioxidant enzymes in rat liver,thus alleviating Cd induced liver oxidative damage and protecting rat liver.4.The relative bioavailability of Se and Cd in rice with different Se and Cd ratio was evaluated by using rat liver as the biological target organ.The results showed that there was no significant difference in the relative bioavailability of Se between LSe-Cd group（62.90±5.42%）and MSe-Cd group（58.66±4.93%）,but it was significantly higher than that of HSe-Cd（38.31±5.67%）.Compared with the relative bioavailability of Cd in rice of Cd group（83.36±7.13%）,the relative bioavailability of Cd in rice of LSe-Cd group,MSe-Cd group and HSe-Cd group decreased significantly to 66.41±8.53%,53.00±4.99%and 58.81±4.42%,respectively。The results showed that the demand for Se in rats was limited,the bioavailability of Se in rice was not dose-dependent,but the bioavailability of Cd in rice was inhibited by Se content in rice.5.Based on the relative bioavailability method,the target hazard quotient was used to assess the health risk of long-term consumption of local rice grains in the study area,and the maximum permissible dietary Se or Cd content in rice was predicted.The results showed that the bioavailability of Se in rice grains was used to assess the health risk of long-term intake of Se from local rice grains in the study area,and it was found that there was no health risk of long-term intake of Se from local rice in the study area,and Se content of rice grains in the study area did not exceed the predicted value;The relative bioavailability of Cd in Se-free and Se-fortified rice was used to assess the health risks of long-term Cd intake by residents in the study area who ate local rice,and it was found that the assessment result of the Se-free group was that there was a health risk of long-term Cd intake by residents in the study area who ate local rice,while the assessment result of the Se-fortified group was that there was no health risk.The proportion of Cd content exceeding the predicted value in rice in the study area decreased from 44.39%to31.63%.These results indicated that increased dietary Se intake could reduce the relative bioavailability of Cd in rice grains,thus reducing the potential health hazards caused by Cd contamination in rice. |
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