Scientists show the safety by searching diligently for unsafety and not finding it.
That's not proof. A ten year drug trial may fail to show problems that take 20 years to surface, but that doesn't mean the drug is safe.
I suspect a lot of these chemicals fall into that hard-to-find-problems category. Only when they are an overwhelming part of our environment for decades or even generations will we start to understand the effects.
So this is not just a matter of money. It's a hard problem.