施用污泥对小青菜产量及重金属镉、铬积累的影响

Influences of Application of Sludge on Yield of Brassica chinensis and Accumulation of Heavy Metal Cadmium and Chromium

采用盆栽方式,以河南省具有代表性的新乡、开封、许昌、郑州四地污水处理厂的干化污泥作为有机肥种植小青菜,研究在连续4季分别施入不同来源和数量的污泥后小青菜的产量变化及重金属Cd、Cr在小青菜中的积累情况,并对采收的小青菜进行农产品安全评价。结果表明：施用污泥能提高小青菜产量,但长期大量施用污泥增加小青菜硝酸盐和Cd、Cr的含量,威胁食品安全。因此,研究制定科学的污泥施用限量,严格控制污泥土地利用的年限,十分必要。

This paper tries to integrate income distribution into the framework of neoclassical growth theory through the analysis of effects of human capital on income distribution. Labor market is divided into markets for the skilled and the unskilled workers. To become skilled one involves the investment of human capital and the decision of the worker. Based on the assumptions of the depreciation rates of human and physical capital to be 1 and 0, respectively, the way for social welfare maximization is proposed. But there will still exist distributive inequality, and the inequality index may even be a constant. The rates of returns to both human and physical capital should be the same when the economy equilibrates. For individuals who are able to invest in human capital, there is no difference in investing both kinds of capital. These workers can migrate between the two labor markets according to fluctuations in relative wages of both workers and in relative rates of returns of both capitals. Their migration may lead the economy to go away from equilibrium on the one hand and bring it back to new equilibrium on the other hand, meanwhile, the inequality remains within a certain range.