If we're purely focused on economics, without any moral judegements or other human values inserted, then the answer is the typical answer for negative externalities. The companies that are exerting economic losses on others via pollution and loss of use of land and loss of health, etc. must pay for those losses in order for a free market to properly price the economic benefit of producing those chemicals. When local politicians say that they're not going to do that in order to attract these businesses, they are explicitly optimizing for worse economic outcomes.

Of course, taking a purely economic view is fairly cold and uncaring. The other issues should also be at play. But I don't think they offer anything more generous to these companies