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Based on the irrigation norm of typical district and county, and revised by the isoline map of Chinese crops water demand, the change of crops program was analyzed as well as the agricultural water use and its GDP benefits. Then the virtual water was calculated for years. At last, the input-output method was used to calculate the trade of virtual water in Beijing. As the results, the virtual water for cereal crops has been decreasing in Beijing, from 1.832 x 10(9) m3 in 1990 to 4.283 x 10(8) m3 in 2004. Otherwise the virtual water for technical crops has been increasing, which is from 9.06 x 10(8) m3 in 1990 to 1.492 x 10(9) m3 in 2004. On the whole, the virtual water for crops has been decreasing in Beijing. From the angle of primary products Beijing is a virtual water importing area. Virtual water importing of annual average is 2.37 x 10(8) m3, which is about 5.93% of the total water of Beijing. Virtual water has been an important supplement of local real water of Beijing.

Virtual water content of grains and vegetables in Beijing's districts is calculated and analyzed for many years by irrigating water quota method, which is compared with the distribution and exploitation of groundwater in Beijing. The results indicate the virtual water content of grains shows a downward trend in all the districts, but the grain production in Yanqing district brings great pressure to the local groundwater. Secondly, the virtual water content of vegetables shows an upward trend in Shunyi District, Daxing district and Pinggu District and is accounting for more and more gradually. Thirdly, the total virtual water volume of grains is decreasing, and the total virtual water volume of vegetables is increasing and the total virtual water volume of crops in Beijing is reducing in recent years, which corresponds with the structural adjustment of policies.

The toxicity to Photobacterium phosphoreum of different mixture systems of sodium dodecyl sulfate (SDS) and three substituted aromatic compounds according to equiconcentration ratio of 1 : 1, as well as individual toxicity, were determined respectively. The joint toxicity was evaluated by toxicity unit (TU), additive index (AI), similarity parameter (lambda), and mixtures toxicity index (MTI). Four evaluating methods were compared and the modes of joint action of different systems were analyzed primarily. The coherent results were obtained from four different evaluating methods. Conclusions can be drawn that the binary joint effects of phenol and toluene mixed with SDS showed weak synergistic, while the other joint effects of SDS and substituted aromatic compounds were antagonistic. Of the evaluating methods, Toxic Unit is most sensitive with higher value of its parameter. Mechanisms of joint toxicity action could be discussed according to luminescence principle of Photobacterium phosphoreum and molecule structures of the mixture components.