[fho]

I was obviously very young so I might have misunderstood my parents, but from what I remember, asbestos was mixed in with the gravel that was used to pave paths and/or playgrounds. I remember the "red way" and another playground that at some points switched from red gravel to gray gravel.

[hansword]

Thanks for answering!

I still can't find anything, but, well...

[fho]

No idea, asbestos was used a lot back then. I guess it is entirely possible that some random playgrounds in Bielefeld did not make big headlines. That was pre-internet also, no ideas if local newspapers from back then would be digitised and/or easily searchable.