海南稻田土壤硒与重金属的含量、分布及其安全性

采集了海南省18个市(县)代表性的稻田土壤耕作层(0—20cm)样品280个,研究了硒(Se)和5种有毒重金属元素(Hg、Cd、Cr、Pb和As)的含量、分布及其相关关系,并对Se和重金属的安全性进行评价,可为合理区划清洁且富Se稻田提供理论依据。结果表明:海南稻田土壤中Hg、Cd、Cr、Pb和As平均含量均低于国家土壤环境质量一级标准值和全国土壤背景值,以绿色食品产地环境技术条件限量标准为标准,用单项污染指数法和内梅罗综合污染指数法评价海南稻田土壤重金属的污染状况,结果都是清洁的。但以海南省土壤背景值做参比值,Hakanson潜在生态危害指数达到211.54,属于强生态危害,从潜在生态危害系数来看,Hg(102.61)和Cd(98.89)达到强生态危害,分别比海南省土壤背景值增加1.56和2.3倍,今后应注意控制Hg和Cd污染源。稻田土壤Se含量从痕量到1.532mg/kg之间,平均值为0.211mg/kg,占47.5%的稻田土壤Se含量处于中等及以上水平(>0.175mg/kg)。Se含量高的稻田土壤主要集中在东北部的海口及其周边的澄迈、定安、文昌和琼海,还有东南部的万宁和保亭。由于重金属平均含量还比较低,可暂时忽略重金属污染,故可在上述Se含量高的稻田土壤上种植富Se水稻。稻田土壤Se含量与Hg、Cd和As含量呈极显著或显著正相关,因此今后应加强研究稻田土壤Se与Hg、Cd和As的有效性及其相互作用,以便生产出绿色的富Se优质大米。

Concentrations and distributions of selenium and heavy metals in Hainan paddy soil and assessment of ecological security

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 the use 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 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 grades of the soil quality standard and background 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 co-respective factors. 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 1.532 mg.kg-1and the mean value was 0.211 mg.kg-1.47.5% of the paddy soils had Se concentrations which were equal to or greater than the medium level (>0.175 mg/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 (P<0.05 or P<0.01) 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.