What is it specifically about substances like mercury and lead that kills you?



I understand something like Carbon Monoxide which physically takes up space that should have oxygen there but what about lead in my blood kills me? Is it a chemical reaction that steals nutrients? Does it puncture blood cells?

In: Chemistry

Many proteins in your body incorporate atoms/molecules of specific metals like iron, copper, manganese etc. Those metals are crucial to how those proteins function. Heavier metals, like mercury can be put into those proteins by mistake. This means the protein will no longer work. Depending on what the protein does normally, that can cause lots of problems.

Heavy metals kinda sorta look like other atoms that are useful to your body enough to take their place in organic compounds your body tries to make, but the end result doesn’t work. For example, lead can pass for calcium to get brought to your brain and put into calcium’s place, but once there it can’t do what calcium can and whatever nerve cells it ends up being built into start failing.

>I understand something like Carbon Monoxide which physically takes up space that should have oxygen there

That’s not quite accurate. It’s not that Carbon Monoxide takes up space where oxygen should be, but that chemically, your blood has a greater affinity for carbon monoxide than oxygen. That is, given the choice between the two, it actively chooses carbon monoxide over oxygen.

The problem with heavy metals is that once they get into the body they don’t usually have a way to get out. So there is no amount of them that is ‘safe’ because it will always be with you. Lead from gasoline you were exposed to as a kid is still in your body today.

Lead and mercury damage the body in several ways but they tend to attack the mind first. You’ve heard the expression “mad as a hatter” and it comes from the fact that prior to the removal of mercury from many industries, hat makers were routinely exposed to mercury fumes from felting and hat making. These attacked the brain leading to erratic behavior and in some cases madness. Liquid mercury isn’t that bad and people used to drink it as a laxative. But the vapors that come off liquid mercury are really bad and because the vapor pressure of mercury makes it fume constantly, there isn’t a safe way to handle it outside of a fume hood.

If you look at violent crime in the united states decade by decade you will see that it was climbing in most places up to the 80’s, and then it began to drop and is still dropping year by year.

One of the explanations for this is lead exposure from leaded gasoline. It got everywhere, in the air we breathed, the surfaces we touched, in our food, in our water. Lead also attacks the brain and leads to problems like poor impulse control, dementia. It has been linked to the increase in violent crime in the 60’s and 70’s and poor impulse control in criminals.

There is also evidence that the use of lead in the Roman empire might have played a part in Rome’s decline and eventual downfall. They used to add lead oxide to wine to make it taste sweeter. Lead pitchers, lead plumbing, all contributed.

Basic chemistry lesson here.

All chemical interaction depend on the electrons around the nucleus. These form essentially the shape of the atom, and as you may know the shape of a tool determines what’s it’s good at, or a uniform true you the basic skill set of the person wearing it.

Lead is the same class of atom as carbon (same column on periodic table). It behaves very similar to carbon, it can easily combine with lots of elements into complex chains. The issue is that it is similar, not exactly the same.

To go with the uniform analogy carbon is dressed as a doctor, and so is lead. However one is an internist (adult medicine) the other is a pediatrician.

For a lot of tasks they are indistinguishable, and with just fine. And at a casual review (all the protein enzymes are capable of) they are identical. But once you really start working on the task, differences in skill sets start make a difference. Perhaps the pediatrician gets the job done, but it takes longer. Or sometimes makes a diagnosis that’s similar, but not the actual cause. The result is it is only partially treated.

Lead and carbon in the body work the same way. The lead gets integrated into a protein that now performs the task almost correct. It may take longer. Or might trigger a bit differently.

The body can’t really tell them apart, they both appear identical in most cases, and so they aren’t sorted out easily.

Many functions within the body rely on little worker molecules called enzymes that fit to specific other molecules like a lock and key – the enzyme being the lock.

The lock molecule holds the key molecule while it transforms it according to what the body needs to do with it.

There are 2 ways to stop the lock molecule working properly. One is to trick it with a similar key molecule (like carbon monoxide looks like oxygen). It doesn’t stop the lock molecule from working but depending on how many fake keys there are it can be a problem.

The other way is to deform the lock so the key doesn’t work. That’s what lead and mercury do. They bind to the lock (usually somewhere away from the actual keyhole) and distort it so the keyhole is all wonky, and the key won’t fit.

This is generally irreversible and the more lead or mercury poisoning the more it builds up with more locks being distorted.