It's all information on ingesting it. There's nothing about submersing it underwater. The only information is some vague warning that it MAY release fungicide over time.

"Ecotoxicity : The product is not expected to leach harmful amounts of preservative into the environment; however, some preservative may migrate into soil and water. The wood preservatives in this product contain insecticides and fungicides, whic h when released into the environment at high enough concentrations, are expected to adversely affect or destroy contaminated plants. They may be harmful or fatal to wildlife. Toxicological and ecotoxicity testing have not been performed on this produc t.
Environmental fate information is not available. "