Bt Research 2025, Vol.16, No.5, 214-223 http://microbescipublisher.com/index.php/bt 220 Larger particles will settle to the surface faster, while finer particles may float longer distances. But no matter which one, the Bt toxin usually does not stay in the atmosphere for too long. The researchers simulated the spray drift of pesticides and found that the aerosol formed by spraying the Bt formulation mostly settled within a range of tens of meters (Zhou et al., 2015), and only extremely small amounts can float further away with the PM2.5 particles. Therefore, atmospheric particulate matter plays more role as a local transport carrier and does not lead to the long-term accumulation of Bt toxins in the atmospheric environment. Atmospheric particulate matter also has a certain adsorption and protection effect on Bt toxins. When Bt protein adheres to the surface of particulate matter, it may be protected from direct UV irradiation and ozone oxidation to a certain extent, thereby slightly delaying its inactivated degradation (Figure 2) (Liu et al., 2021). Figure 2 The multi-interfacial transport behaviors of Bt toxins in the environment (Adopted from Liu et al., 2021) 7 Case Analysis: Research and Practice of Degradation of Bt Toxins under Different Environmental Conditions 7.1 Research cases of degradation of long-term planting of Bt crops in farmland soil Farmlands that have long-term continuous cultivation of Bt genetically modified crops are an important place to evaluate the environmental retention and degradation of Bt toxins. Nine-year continuous cropping test of Bt rice – The 9-year insect-resistant Bt rice strain (Huahui No. 1, etc.) was continuously planted in a test field in Hubei. The rice rhizosphere soil was collected regularly every year to detect the Cry1Ab/1Ac protein content in the tillering stage, heading stage, maturation stage and post-harvest stage. The results show that a small amount of Bt protein can be detected in the rhizosphere soil of Bt rice during each fertility period (up to the order of about 2 ng·g⁻¹), but the Bt protein in the soil has basically been completely degraded 60 days after harvest (Gruber et al., 2011). More importantly, compared with the data from year 1 and year 9, there is no cumulative increase in the concentration of Bt protein in soil, and the detection value of the growth season in year 9 is comparable to that in year 1. This shows that although Bt proteins are input to the soil every year, the degradation and loss process is sufficient to clear it and will not be enriched year after year in the soil (Wang et al., 2022). This result greatly alleviates people's concerns about the "accumulation of Bt proteins into disasters" and is also an important evidence for the environmental safety of Bt crops. 7.2 Examples of monitoring and degradation of Bt toxins in lakes and rivers The ways Bt toxins enter water bodies include farmland runoff carrying, Bt biological pesticides are directly used for aquatic pest control, etc. In natural water bodies such as lakes and rivers, field monitoring and degradation of
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