[7thOF7th]

Uranium and associated decay products thorium-230 and radium-226 will remain hazardous for thousands of years.

U235 enriched to a 20%-50% mix with U238 will render the surface area it settles on inhabitable for centuries

[GSlob]

All these products would come to equilibrium concentration quite a few years [geological time scale] down the road. Freshly concentrated U-235 does not have them.