Which of the following methods is considered safest for deep-water injection?

Deep-water injection is a method used to manage aquatic pests by delivering treatment materials below the surface of the water, minimizing exposure to non-target organisms and reducing the risk of surface contamination. Among the options provided, bottom placement is considered the safest method for deep-water injection.

Using bottom placement means that the treatment is applied directly to the substrate at the bottom of the water body. This approach can ensure that the active ingredients are effectively concentrated in the area where pest organisms reside and reduces the likelihood of dispersal to other areas of the water body, protecting both the surface water environment and non-target species. It also minimizes the potential for wind and water currents to carry the treatment away from the intended application site.

In contrast, surface spraying, aerial applications, and subsurface injections carry greater risks of unintended exposure. Surface applications can lead to the material drifting on currents or affecting non-target organisms at the water's surface. Aerial applications may pose similar risks of drift and contamination of adjacent areas. Subsurface injections, while generally safer than surface methods, can still create disturbances that may affect water quality and inadvertently expose non-target organisms. Therefore, bottom placement is the most controlled method and is specifically designed to mitigate risks associated with aquatic pest management in deeper water environments.