[derefr]

I understand how lead-lined Roman aqueducts would put lead into drinking water — there's nowhere for the lead to go but to stay in the water, since the lead lining is below the water.

But I'm unclear on how lead that had leached into groundwater would remain in groundwater. Shouldn't the lead, being heavier than water, drop out of the groundwater and get caught up in the soil? Isn't this the primary filtering function we expect of soil — the reason aggregate is used as a filtering medium in wastewater treatment?

If not, wouldn't you expect to hear about water tables that have problematically-high natural levels of this or that heavy metal? Wouldn't you expect that it'd be deadly to drink groundwater that had ever flowed through any underground ore deposits?

[retrac]

Elemental lead is fairly reactive - it forms a number of compounds, some of which are soluble in water. Dissolved compounds may precipitate but they don't always "fall out" simply because the elements in them are heavier.

> you expect to hear about water tables that have problematically-high natural levels of this or that heavy metal?

That does happen. Cadmium is probably the most common culprit.

> In groundwater in Pakistan, mean Cd concentrations of 10 μg/L originated from Jurassic sulfide-bearing sedimentary rocks (Naseem et al., 2014). In Germany, background Cd concentrations in groundwater range from 0.11 μg/L in loess aquifers below arable land to 2.7 μg/L in sandy aquifers below forested lands [1]

The limit in the USA and EU is 5 ug/L. It's quite possible to drill a well with natural cadmium levels above the generally accepted safe level. Lead, arsenic, chromium, barium, and copper are other common culprits. In particular, chronic arsenic poisoning from naturally-occurring arsenic in ground water and aquifers affects many millions of people around the world.

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7147761/

[whatshisface]

Virtually everything that dissolves in water is heavier than an H2O molecule, and a lot (most?) soluble salts are denser than water. If you want an example, table salt sinks to the bottom before dissolving. Also, yes, some ground waters are naturally high in different metals. Before drinking water from a well you drilled you usually have to get the well's water tested.

[derefr]

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.

[lazide]

You have mercury all wrong, and lead mostly so.

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.

[LTL_FTC]

Currently worried about this. My employer asked me to help the production team with some assembly of the product which involved a good amount of soldering. Turns out it’s leaded solder and the owner doesn’t believe in venting the solder smoke to the exterior of the building. The tiny fans used are a joke. I’m in software and won’t be doing this regularly but it’s still incredibly worrisome as I don’t see employees washing their hands after handling it so it could be everywhere.

[teraflop]

As I understand it, the "solder smoke" produced during hand-soldering does not actually contain metallic solder itself, except maybe in trace amounts. It primarily consists of vaporized organic compounds from the rosin flux core of the solder wire.

It's still not good to inhale (chronic exposure can cause asthma and other respiratory issues) but it's not really an issue of leaded vs. lead-free.

And for what it's worth, I've always anecdotally heard that solder paste is what you really want to be worried about, rather than solder wire, because it's much easier for small amounts to get smeared onto objects/surfaces and contaminate them.

[AnimalMuppet]

If you're in the US, you might consider dropping a word to OSHA.

[rightbyte]

> cleaning a shooting range then not washing their hands after

Care to elaborate? Even handling bullets should be no more posionus than handling diver weights?

[genmud]

Also, depending on how the bullets get caught at the range (shredded tires vs sand vs steel backstops), they tend to produce a lots of fine lead dust[1].

[1] - https://youtu.be/QfDoQwIAaXg

[lazide]

I love those slow-mo bullet impact videos!

Also, be aware that most primers usually have some kind of heavy metal in them (lead azide, lead styphnate, mercury fulminate) though there are newer compositions using strontium and tetrazine starting to get traction. [https://en.m.wikipedia.org/wiki/Mercury(II)_fulminate]

Additionally, non-jacketed bullets (common with rim fire, low power pistol, blackpowder, and some other random stuff) will blast lead off the back of the bullets at the muzzle or forcing cone and into the air.

If the area is adequately ventilated it’s not really an issue. Some indoor ranges are not! Sometimes significant amounts of fine particulates can end up at shooting stations from it, or be inhaled.

That said, just wash your hands and don’t hang out in ranges that get Smokey and you’ll be fine. If you’re cleaning up a range with bad ventilation, wear a respirator rated for metal dust.

I’ve done all the high risk activities (including a decent amount of soldering with gasp leaded solder) for over 3 decades, have done that, and have tested ‘non-detectable’ for lead and mercury every time I felt like checking.

I’ve had friends who didn’t that ended up on Chelation therapy. Don’t be like them. They’re miserable.

[lazide]

If you wash your hands with soap and water before sticking them in your mouth after any of these activities, you’ll be fine. If you don’t, I wouldn’t recommend making whatever it was a habit.

If you handled a lot of powdered/pulverized lead powder, and then stick your hands in your mouth and lick your fingers - it could conceivably cause a measurable body burden of lead even if you did it once, maybe. So don’t do that.

[rightbyte]

Ok ty.

[lalopalota]

"not washing their hands" being the key part. it isn't dangerous to handle diver weights or clean up a shooting range. if the traces aren't cleaned off your hands before touching the face/eyes, eating, smoking cigarettes, etc, the lead will get into the body and cause problems.

[bigbillheck]

> If not, wouldn't you expect to hear about...

I've certainly heard about such:

https://www.usgs.gov/mission-areas/water-resources/science/a...

> lead, being heavier than water, drop out of the groundwater

Sodium chloride is over twice as heavy as water, and yet doesn't 'drop out' of it.

[anthonyu]

A bit of a bad analogy as, in water, the sodium and chloride are not bound together; rather, the ions are separately distributed throughout and wouldn't have the same density that they would have in a dry, crystal, ionically bound form.

[gwbas1c]

> wouldn't you expect to hear about water tables that have problematically-high natural levels of this or that heavy metal?

Where I live, I get periodic water quality reports in the mail, with the test results for all kinds of different contaminants.

The reports always list the typical source of contaminants; and naturally-occurring metals in the ground is very common.

Interesting artifact: A well near my childhood home has unusually high levels of chromium for the town. It's believed to be from when someone was running a car repair shop near the watershed; and they left some brake drums or similar car parts outside.

[FreshStart]

It's usually not that. It's usually the car repair shop pouring left-over chrome containing colors and derusting solutions into the ground.