I'd challenge anyone who thinks we know all of them in the USA.
It doesn't even take the corruption that a big employer in a small town automatically creates to have a 'hidden' superfund site.
It only takes the lack of dedicated professionals testing everything all the time. Tracking sources and types of pollution is _not only_ difficult, highly technical work that requires a lot of infrastructure- but it also _requires its own R&D to keep up with new industrial chemicals_. This means it's fiercely expensive, manpower-limited, and that it takes a long, long time.
What country is going to dedicate that amount of resources to find problems that'll cost even more money to clean up (or possibly can't be cleaned up at all)? Maybe Norway. Maybe.
Except now we know the consequences and have the experience and moreover have alternatives (even in simple management, mitigation terms) which might not existed five decades ago.
