There are readily available glues for many plastics but most specifically mention that are not suitable for polyethylene or polypropylene. There are commercially available adhesives for these polys , body shops use them a lot. The bigger issue here is that often the ends of the toe rail break off where the screw attaches it. That is a stress point and i am not sure even if glued, that the fix will hold under stress. There are two methods I have seen to repair. The first is to replace the entire toe rail usually with a piece of starboard or poly if you can find it. The second is to 'sister' a new end to the existing rail. This can be done with a scarf joint, glued and bolted or a but joint bolted with a backer plate. Depending on your skills, the backer plate can be inset in the back (routed pocket) so that very little shows. Sometimes the inset backer plate approach can be used to reattach the broken off piece.
By the way, I have two broken off ends on my toe rails but there is enough end left to keep the screw seated. I try to not notice the tips
FYI: I don't think that the pressure of yout feet breaks the rails. It seems to be the expansion and contraction from temperature changes that puts pressure on the screws. If you want to reduce the possibility of these breaks, elongate the holes a bit.