Abstract: With the increasing area of transgenic Bt and Bt+CpTI cottons planting, it's of significance to assess the environmental risk of their toxins release. In this paper, a pot experiment with transgenic Bt cotton"Zhong 30" and Bt+CpTI cottons “Zhong 41" and “Shuangkang 321" was conducted to study the persistence characteristics of their toxins in soil and the effects of these toxins on soil hydrolase activity. The results showed that Bt toxin was introduced into soil after 30 days of seedlings growth, and the introduced amount of CpTI toxin was differed with the cultivars. Compared with the relevant non-transgenic cottons, the planting of“Zhong 30" and “Zhong 41" had nosignificant effects on the activities of soil urease, proteinase and phosphomonoesterase, while that of “Shuangkang 321" decreased soil phosphomonoesterse activity significantly. From the viewpoints of toxin release and its effects on soil hydrolase activity, the planting of "Zhong 41"caused fewer disturbances on soil biological activities.

Key words: Chlorophyll a, Phaeopigments, Sediment