Pothos Root Rot. The white stuff is perlite lol. During this time you may want to prune your plant regularly to keep it from becoming too heavy.
Root rot can have two sources one is a prolonged exposure to overwatered conditions that can cause some of the roots to die back due to a lack of oxygen. As they die they can start to decay or rot away. Poor drainage and plant crowding favor their development.
Continually watering with too cold of water can also result in root rot.
Some of the small fine roots were blackish brown and pulled apart. If the root rot is extreme you can propagate the plant to start growing a new one. To treat remove the plant from the soil and wash the roots clean under running water. During this time you may want to prune your plant regularly to keep it from becoming too heavy.