海南稻田土壤硒与重金属的含量、分布及其安全性

Abstract

Selenium(Se) is an essential nutrient element for human beings,with many diseases potentially arising from a deficiency or excess of Se.It is recommended that Se should be consumed through foods as part of normal diet and much research has focused on the development of Se-enriched foods.Se concentrations in food depend on the amount of Se in the soil where the crops or forages are grown.However Se deficiency in soil is widespread throughout the world.In China,the soils of approximately 72% of counties have been found to be severely or slightly lacking in Se.However,a wide distribution of Se-enriched soils was found in the geological survey of Hainan Province in 2006,accounting for about 27% of the land area of Hainan Province.As rice is a staple human food,the growing of Se-enriched rice is an obvious first application of Se-enriched soils in Hainan.The development of Se-enriched rice requires investigation of the concentration and distribution of Se in the paddy soils of Hainan Province.It has also been reported that Se in soils is often accompanied by heavy metals.Therefore,it is important to investigate correlations between Se and heavy metals and their ecological security,which will contribute to the regional identification of clean and Se-enriched paddy soils.Two hundred and eighty typical plough layer(0—20cm) paddy soils were sampled from 18 counties of Hainan Province to measure the concentrations of Se and the heavy metals,i.e.Hg,Cd,Cr,Pb and As,study their distribution,and establish correlations between them.Assessment of the ecological security of Se and the heavy metals was then conducted.Mean concetrations of heavy metals were lower than the 1st grade of the soil quality standard and background soil values in China.Compared with soil quality requirements for green food production,the results were assessed as clean by the pollution index method of individual and comprehensive factors(Nemerow).When compared with background soil values of Hainan,the Hakanson potential ecological risk index of the paddy soils was 211.54 and the potential ecological hazard coefficients of Hg and Cd were 102.61and 98.89,respectively,which represent a strong ecological risk level.Compared with the background soil value of Hainan,Hg and Cd concentrations were elevated 1.56 times and 2.3 times,respectively,indicating that pollution sources of Hg and Cd should be controlled.Se concentrations in the paddy soils ranged from trace to 1.532mg/kg and the mean value was 0.211mg/kg.47.5% of the paddy soils had Se concentrations which were equal to or greater than the medium level(0.175mg/kg).High Se concentrations in the paddy soils were focused in Haikou and its surrounding area in the northeast of Hainan,i.e.Chengmai,Dingan,and Wenchang,as well as Qionghai,Wanning,and Baoting in the southeast of Hainan Province.As the mean concentrations of heavy metals were low,heavy metals pollution can be ignored.Therefore,Se-enriched rice could be planted in the above areas of paddy soils with high Se concentrations.Significant(P0.05 or P0.01) positive correlations between concentrations of Se and Hg,Cd or As were observed.Therefore in order to produce green and Se-enriched rice,more attention should be paid to the availability and interaction of these elements.