The important thing for your course work is that they are non-toxic and fully biodegradable. Most commonly having a gelatine shell with a vegetable or fish oil based fill with a non-toxic dye, they used to be made by the same people as make human medicines in capsule form (and some still are I think). They have to be made non-toxic, as you're likely to get a mouthful if they hit the face mask
! The only possibly dodgy constituent is the Titanium Dioxide, which can occasionally leave white stains for quite a while.
However I do know of at least one site which is in protected woodland and the relevant authorities have no problems with letting the owner run games there, as he has done for well over 16-18 years now.