Final answer:
The toxic substance formed by nitrogenous waste is ammonia. Nitrogenous wastes tend to form toxic ammonia, which raises the pH of body fluids.
Step-by-step explanation:
The toxic substance that is formed by nitrogenous waste is ammonia.
During the breakdown of nitrogen-containing macromolecules, excess nitrogen is excreted from the body. Nitrogenous wastes tend to form toxic ammonia, which raises the pH of body fluids. Animals that live in aquatic environments release ammonia into the water, while terrestrial organisms convert ammonia into a relatively nontoxic form such as urea or uric acid.