[...] toxicity measures you cite are for measuring poisons, not mutagens and/or carcinogens, many of which have 20-30 year latencies, or don't show their effects until the next generation. (Ever hear about thalidomide babies?) So, your toxicity argument is a sort of strawman, at least as a general argument.
On the topic of strawmen:
Thalidomide, it turns out, does not
cause birth defects. It
inhibits the spontaneous abortion of fetuses with certain, specific sorts of birth defects. I don't have the data ready to hand, but it is an important distinction to note.
Most of the very long-term effects of small exposure are difficult to trace, but in most cases, LD 50 data are useful, and, when used with other measurements can plot a curve of toxicity vs. dose that is useful for predicting too-small-to-have-effect levels. Very few substances are extremely persistent in the body; even PCBs fade away over time (10-15 years for typical exposures, but based, of course, on initial exposure levels and ongoing contact).
...Of course, if you endorse homeopathy, we ought to all be very, very dead, or perhaps totally immune....
PCBs are an interesting case. Polychlorinated Biphenols are no more toxic per unit volume than aspirin (which is, hey-la, worse than you think, so
don't eat a bottle of aspirins, please). But burn them in a specific, alas, pretty wide range of temperatures, and you get polychlorinated bi
furans, PCFs, which are quite nasty indeed. ...The problem here being that the traditional source of bad ol' "PCB contamination" is burned-up powerline hardware, transformers and switchgear, usually containing PCFs as a result of the failure that made it into junkyard fodder. The PCB oil is just the soda water -- it's that shotglass of PCFs that gives it the kick.
Moral of the story: read the fine print. Don't juggle blowtorches, but don't confuse flashlights with blowtorches, either.
Oh, parting thought: because humans are no longer mostly dead at 30, we live long enough to die of all sorts of unexpected, nasty things. Please remember the dear, sweet Momma Nature only cares that you live long enough to reproduce and get your young old enough to more or less fend for themselves. Anything past that is bonus time. Every year since 30 is sweet to me, doubly so since in a "state of nature," I would have died many times over before hitting even the minimum! How 'bout you -- appendix okay? Eyesight good? Teeth sound? Had any of the once-fatal childhood diseases? Tsk, think of the "tampering with nature" it took to get you this far!
--Herself