It's really hard to know what the long-term safety of something is. You need a
long-term study to know, and if it's something like a
drug or
genetically modified food or
drain cleaner or whatnot, the
economic interests of the creators of such things are not maintained by having them spend
20-50 years finding out what really happens with their products.
So, most long-term testing is done in the wild. You release a product and then try and figure out if anything happened a few generations down the road. Actually, you don't try and figure out, you just hope for the best that nothing bad will happen, or if it does, that no one will be able to trace it back to what you did. Yes, we're all guinea pigs, whether we volunteered or not.