  Entanglement degradation in open quantum systems is reviewed in the
Choi-Jamio{\l}kowski representation of linear maps. In addition to physical
processes of entanglement dissociation and entanglement annihilation, we
consider quantum dynamics transforming arbitrary input states into those that
remain positive under partial transpose (PPT-inducing channels). Such
evolutions form a convex subset of distillation-prohibiting channels. A
relation between the above channels and entanglement-binding ones is clarified.
An example of the distillation-prohibiting map $\Phi\otimes\Phi$ is given,
where $\Phi$ is not entanglement binding.
