Depends on the toxin. I can't think of any example off of the top of my head, and it's a bit hard.

Toxins that bioaccumulate either are produced outside and don't work well inside a biological system (heavy metals, etc) or are fat-soluble

Easiest for plants to do is make neurotoxins as they don't have a nervous system to get bothered by it. But those are usually water-soluble.