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by derefr
1066 days ago
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My assumption in writing the above was that non-soluble elemental lead metal (the thing the sheathing is made out of, and that Roman aqueducts were made out of, and the thing that soil could easily trap and filter out) is the "problem" with lead poisoning; while the lead ions in lead compounds are mostly safe. Like it is with mercury, where mercury amalgams are perfectly fine to use as dental fillings, but getting even a little metallic mercury past your skin will kill you. Looking into it, though, apparently lead metal and lead ions are both toxic, through independent mechanisms. And that the toxicity of e.g. lead-based paint is due to the toxicity of lead compounds, rather than the toxicity of metallic lead. Still: is there cause to believe that metallic lead from lead sheathing in cables, would react with something in the ground to form soluble lead compounds, rather than remaining particulate metal and therefore coming to rest in the soil? Things don't oxidize underground, right? And groundwater is usually pH-neutral enough to not create an environment amenable for reduction reactions involving e.g. chromium or sulfur, right? I say this because several people above have mentioned that there are other metallic-ion "natural pollutants" in groundwater — but I've still never heard of groundwater with high natural lead levels. |
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Elemental mercury is very difficult to absorb, and even in vapor form the LD50 is quite high. It typically requires extended exposure to even vapor from mercury to have any issues. Even a drop of organic mercury on a glove (let alone skin) can kill.
Historically, even periodically drinking liquid elemental mercury was relatively harmless and didn’t poison anyone. You’d have to do it a lot. The Louis and Clark expedition used it for its laxative effects, and it’s allowed historians to confirm which campsites were theirs or not, for instance.
Most compounds and salts of mercury, especially organic compounds, are incredibly toxic. [https://emergency.cdc.gov/agent/mercury/mercorgcasedef.asp]
Many of those compounds form when metallic/elemental mercury is around certain microorganisms, like those in many ponds and lakes, or when man made.
Lead isn’t dissimilar. Lead poisoning (or measurable uptake) from elemental lead almost always requires extended ingestion or inhalation of lead, or ingestion/exposure to a salt or compound which allows easier intake.
The most common forms of lead poisoning usually involve things like habitual smoking or eating while having lead dust covered hands, or persistent ingestion of lead containing substances (like contaminated water) or breathing in of lead contaminated dust.
It takes a surprising amount of persistent exposure, unless someone is really stupid. Like doing oxyacetylene cutting of lead sheet without PPE, or cleaning a shooting range then not washing their hands after.