If you can prove that a company intentionally polluted knowing that the pollutants were harmful then by all means, have the EPA bring a lawsuit against them. But I don't believe in punishing everyone because of the possibility of misdeeds by some. I especially don't believe in it if no one realized the pollution was dangerous when the pollution was occurring, unless you could somehow prove that they intentionally didn't look into it or blocked that research.
Uh, this shit is PRECISELY what went on throughout the last century (and still continues to this day).
It has been proven countless times that companies will do blatantly illegal and harmful things, knowing full well how harmful they are as long as they believe their risk:benefit ratio is good enough. (See: Flint, Bhopal, Love Canal, Hinkley CA, etc. etc. etc.)
Oh, and as for the "if they knowingly use harmful pollutants use a lawsuit" is bullshit. The legal system is set up so that all they need to do is say they didn't know and they'll get off with a warning, or force the public into a long drawn-out civil legal battle that can take decades to decide. The point of all the EPA regulations is so that these companies can't claim that they "didn't know". These regulations are there so this shit doesn't have to turn into a decades long civil battle, with lots of "did they or didn't they know" going on.
Your argument is like saying that food safety regulations aren't needed, because restaurants will figure out if they make people sick on their own, and we can TOTALLY trust them to stop doing something that does, even if it costs them extra money, right?