Those environments of course also don't last very long as decay will cause those isotopes to disappear after short period (days to decades).This is plainly visible in the area around Chernobyl today where background radiation (except in some hotspots) has fallen to a level where it's been safe for people to work right next to reactor 4 without special protective clothing for decades, where now the Ukraine is actively promoting tourism into the area which is a haven for wildlife.
Also, plutonium happens to be particularly toxic due to its chemistry, which aggravates the damage it can do.The biggest danger from radioisotopes with mid-to-long half lives is that they can keep an entire region of earth nastily radioactive for a very long time, e.g.hundreds or thousands or even tens of thousand of years.That's the main reason why disposing of reactor wastes, which often contain just such isotopes, is such a contentious issue.Bismuth (as in the main ingredient in a popular pink stomach relief aid) is ironically in this category, with a half-life so long it's hard even to tell that it is radioactive. And according to at least some reports (eg articles.mercola.com/sites/articles/archive/2014/02/10/…) polonium-210 is the main cause of tobacco-related cancers, via multiple unfortunate accidental concentration steps that begin with traces of uranium-238 found in phosphate fertilizers.
Because the press have heard of Plutonium and Pu=atomic bombs=bad Plutonium's danger is over stated, it's insoluble so hard to get into the food chain and even if ingested is going to go straight through you.
If I start with the same amount of nuclei, the short half-lived nuclei undergo more disintegrations per second.
Scientists consider radionuclides with short half lives to be a lot more dangerous because they are.
In terms of contamination, contamination by short lived stuff, can probably be waited out.
For instance if milk has too much I-131 (halflife 8days), and it were made into powdered milk or cheese, and left on the shelf for a few months it would then be harmless, whereas if a foodstuff were contaminated with Cesium-137 halflife 30years, it is impractical to wait for it to decay. the shorter half-lived substance will always have fewer distintegrations per second."?
Arguments for having U-238 laying around actually make some sense; plutonium in any form whatsoever... BTW, the most unregulated fissionable material is thorium. It's like saying that Di Hydrogen-Monoxide is dangerous because of what it did to the Titanic.