The two iridium isotopes found in nature are both stable, not radioactive. It is, however, highly corrosion resistent, high density, and very high melting point. The original kilogram prototype was made with 10% iridium in the alloy, which would be a stupid thing to do if it was highly radioactive and thus losing mass.well, if you think about it, actual iridium is highly radioactive, so the farmer is also getting radiation poisoning and not batting an eye!
You forgot the multiple days, especially early on where the farmer eats nothing...seriously how many calories does this guy burn per day