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.
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.