Abstract: By the methods of pollen grain dyeing and PCR analysis, this paper measured the distance and intensity of pollen dispersal, and determined the frequency of gene flow (FGF) of transgenic Bt cotton. The results showed that the frequency of pollen dispersal (FPD) among flowers was significantly higher on the same cotton plant than on different ones (P<0.01). The average FPD at a distance of 1 m from the dyed Bt cotton plot to its east, south, west and north was estimated to be 44.8%， 48.9%， 57.1% and 21.5%,respectively, and declined with increasing distance in the four directions. Within the range of 25 m, the distance and direction of pollen dispersal could affect FGF significantly (P<0.01), and FGF generally tended to decrease with increasing distance from the Bt cotton plot, with a frequency of 2.0% at the farthest distance of 25m.

Key words: Veterinary medicines, Ecotoxicology, Environmental impact