When it comes to acid rain or oil spills or depleted fisheries or tainted groundwater or fluorocarbon propellants or radiation leaks or sexually transmitted diseases, national frontiers are simple irrelevant. Toxins don't stop for customs inspections and microbes don't carry passports. North America became a water and free-trade zone long before NAFTA loosened up the market in goods.
Doing is the great thing, for if people resolutely do what is right, they come in time to like doing it.