Studies showed that DDT levels were still high in Tianjin, China, even though its use was banned in 1983. To estimate current risk of DDT to human health in Tianjin area, a non-steady-state (Level IV) multimedia fugacity model was used to simulate the fate and transfer of pp'-DDT before and after the ban. The ordinary linear equations of Level IV model were solved with a matrix approach. The calculated pp'-DDT concentration in air, water, soil, and sediment reached a maximum in the 1980s and then decreased, and agree well with those measured. The biggest bulk sinks of pp'-DDT were soil and sediment, which accounted for 90% of total amount of pp'-DDT in the environment. Air deposition and diffusions through the interfaces of water-air and water sediment were the major intermedia transfer processes, while the degradation in soil and sediment were the key eliminating routes for pp'-DDT in the environment. (c) 2005 Elsevier Inc. All rights reserved.
This paper examines the efficiency in resource allocation in China. We estimate production functions at the provincial level and use these functions to compute time series for marginal products of capital and labor. We found that dispersion in the marginal product of capital declined from 1970 to 1984 and then became stable afterward, whereas the dispersion in the marginal product of labor declined initially but the trend has been reversed since 1993. We argue that this reversal may indicate any of the following: (1) policy-driven labor migration adding to labor market inefficiency; (2) the presence of increasing returns in labor; and (3) both capital and labor having become mobile since 1993.