Question

phytoremediation is when plants are used to clean soil of toxic waste. what is a problem with phytoremediation?
the plants that now have the pollutant in them must still be disposed of somewhere.
the waste can leak out of the plants if they eat too much of it.
this process happens too fast to be effective, at all.
it requires a thick, plastic liner and liners are very expensive.

Explanation:

Phytoremediation involves plants taking up pollutants. Once they do, those plants still need proper disposal as the pollutants are now in them. The other options have inaccuracies - waste doesn't "leak" out as plants don't "eat" pollutants in that sense, the process is often slow rather than too fast, and it doesn't typically require a thick plastic liner like some other remediation methods.

Answer:

The plants that now have the pollutant in them must still be disposed of somewhere.