Maybe I am completely off, but I would suggest not to use any of those materials. If it has to be done to respect some law, then so be it, but otherwise, I'd rather not.
I'd suggest to have the playground be in very simple (and not completely well curated, for reasons mentioned in point 2) grass. Some trees as well.
The reasons are many, but I'll mention a couple:
a physical reason: falling on the soil can be harder that on plastic/rubber, and this teaches kids a wonderful lesson, that is "falling hurts". While it may sounds like a Spartan advice, the whole idea of becoming conscious of your body limits and of your surrondings passes via the fact that sometimes you bump into things. Also, it's quite difficult, at least for my daughters, to get serously injured at the playground/park as long as there's one of us keeping an eye on them all the time. Usually, from our experience, kids get injured on the toy where they climb/play on, not by falling on the ground. So, they learn the lesson, but not necessarily hurting much, which is, I'd say, good.
an educative reason: grass gives you a chance to watch nature with your kids, watch flowers, sit in the grass, look at insects and their behaviour and so on. It's a great chance to spend time with the kids and look at how things grow. If the grass/trees are too much curated (as in the English grass) you won't see much nature there, that's why I mentioned not to curate it too much.
there's also a creative reason: nature seldom repeats itself. Looking at how nature has evolved plants or insects or birds, and how each individual is different from the others, proves to be a wonderful occasion for kids to be creative in doing things. Not to mention the fact that you can do many, many things with natural material (my oldest daughter started with daisy chains and ended up creating rings and other geometrical figures: she didn't know the names, she is 4 and this episode happened way back, but she mentioned seeing those shapes in the park. Of course I took the chance to do a bit of geometry there :) )
Sources: 2 daughters, 1 zillion parks/playgrounds, living on the border of countryside in Europe and not having too much rubber in playgrounds. Also, another source that I found amusing: the teachers at our kindergarten, and then school, always had/have a project of "outdoor" teaching for kids ages 2-5 (like going out looking at trees, bark, and so on). I was absolutely happy seeing pictures of them out in the rain or the snow, playing/tasting/getting dirty/ecc.
Other parents, of course, less.
Another source I can't find now, is a park in UK (I am not in the UK) where there are several materials, nothing is curated, and kids have a chance to try anything and everything (say: light a fire). I find the concept amusing, even if I would suggest quite some supervision there. :) If I find the link I'll add it, the main point being that the kids in the park where actively engaged in using their creativity to come up with something and almost never bored.