That seems more like an oversight of Wikipedia. If Plutonium isn't chemically toxic, that would make it pretty much the only heavy metal (besides gold) that isn't.
Recent research with one of the least radioactive isotopes
of plutonium (plutonium-242, which has a half-life of
376,000 years) indicates that plutonium in the body may
contribute to the development of tumors. In general,
however, plutonium isotopic mixtures that are commonly
encountered in the nuclear fuel cycle, nuclear weapons
programs, or thermoelectric generator applications exhibit
much higher radiological toxicity than chemical toxicity.
(albeit a bit hard to read if you don't parse TeX) seems to say that of 144 beagle dogs who inhaled plutonium oxide, 93 died of bone tumors, 46 of lung tumors and 2 of liver tumors. Although I can't figure out from the abstract what the dose was.
They say it's 0.6-60 Gy. If my calculation is correct, to get a 10Gy dose over ~2.5 years due to the 5.15Mev alphas from Pu239, that would mean they contained 6.7e-8 kg Pu239 / kg body mass, i.e. .06mg/kg body mass. So it's fair to say that it's pretty bad. Unless I dropped a factor N_A or something... ;-)
.06mg/kg is a pretty small lethal dose. That's probably entirely due to the radioactivity. Tetraethyl lead has a lethal dose of something like 1.2mg/kg http://www.inchem.org/documents/pims/chemical/organlea.htm which is 20 times higher. But that's organic lead, which is rapidly absorbed; lead oxide is something like 600 mg/kg, ten thousand times higher than the dose you calculated for plutonium. But, in that case we're comparing the ingested dose to the dose absorbed; you'd have to ingest about 150mg/kg of PuO₂ to absorb 0.06mg/kg of it.
Also, though, the fatal dose of another heavy metal like lead might be lower than the LD₅₀ reported, because LD₅₀ tests normally don't give the experimental animals several years to die.
So, in conclusion, it seems like accurately comparing plutonium poisoning to poisoning by other heavy metals requires more knowledge than I have. Good thing the NRC's on the job.
