- There it is.

This is iron, and iron is what's called a heavy metal.

And it's added to cereal on purpose, which people were freaking out   about on TikTok a few months back.

And I kind of get why.

I mean, heavy metals have a reputation for being dangerous or unhealthy.

- Some popular fruit juices may contain heavy metal.

- Many baby foods have dangerous levels of toxic heavy metals.

- And if this were a heavy metal like lead or mercury, it would be a huge problem.

So why is it that some heavy metals make you sick or even kill you, but others, you can just eat?

♫ Chime Sound Effect ♫ Alright, let's get into this.

First off, heavy metals are heavy because they have a high atomic mass and density.

And despite their reputation, they're not all bad.

You can put them on a "necessary to keep you alive", to "will kill" you spectrum which total disclaimer is not exact.

There's a lot of variability here, depending on   how much of a heavy metal we're talking about,  what other elements it might be combined with.

You get it.

But let's start in the middle with gold.

Elemental gold, what's in gold leaf,  is inert.

Meaning it's generally not going to react with other stuff like oxygen in the air or   acid in your stomach.

That's why a lot of jewelry  is made out of gold.

It won't get discolored or   rusty like a bunch of other metals do.

The fact  that it's inert is also why you can eat it.

[ inaudible ] I probably should  have done this shot last.

Your body can't digest it, so it'll just   pass right on through.

But keep in mind that the gold leaf I ate was 24-karats.

Karats is the measurement of the proportion of gold out of 24 parts total.

So what I ate was pure gold.

18 karat gold is only 18 out of 24 parts  gold.

So six of the 24 parts are other   metals like nickel or copper, which do react  with stuff.

And that could be a problem.

So that's the heavy metal gold.

Heavy metals like mercury and lead are a totally different story.

In the case of lead, our brains will mistake it  for calcium, and that's bad.

Your brain needs   calcium to send messages between neurons.

So lead  competing with calcium can mean two major things.

The calcium that should be getting into your  neurons and triggering that message isn't,   or neurons that aren't supposed to be active  start randomly sending messages.

Too much or   too little signaling in your brain can make it  harder for you to process information and cause   a bunch of behavioral changes.

By the way, there's some speculation that those behavioral changes   are part of what brought down the Roman  Empire.

But that's another video altogether.

Now, as for mercury, it comes in a few different  forms, and organic mercury, when it's combined   with carbon, is the most toxic.

In part  because it can soak right through your skin.

You've probably eaten organic mercury before in seafood, in the form of methylmercury.

But in that case, it's in such small amounts that you don't really need to worry about it, at least not in the short term.

But when you're exposed to organic mercury in larger amounts, all at once,   it can be really, really bad.

And there's a story  about just that that has always stuck with me.

In August 1996, a chemistry professor at  Dartmouth named Karen Wetterhahn was in   the lab doing research, and she spilled a few  drops of dimethylmercury onto her latex glove.

A glove similar to this one.

She wasn't worried because she was taking what were at the time, considered the right safety precautions.

What people didn't realize was that dimethylmercury can soak through latex gloves — to your skin — in something like 15 seconds.

Fast forward, a few months later, and Dr.  Wetterhahn is really sick.

She's experiencing   a bunch of different neurological symptoms,  like losing her balance and slurring her   words.

And not long after, she falls into  a coma.

Dr. Wetterhahn died in June 1997,   less than a year after first spilling  dimethylmercury on her glove.

Those neurological symptoms she was experiencing  make sense because mercury accumulates in your   central nervous system, including your brain.

The  only way to remove mercury is through something   called chelation therapy, where you're given  a drug that can bind to metals in your blood.

Even though Dr. Wetterhahn was given chelation  therapy, it was a few months after her exposure.

And so, her health continued to rapidly  deteriorate.

Today, people working with   organic mercury are told to wear multiple  pairs of gloves that it can't soak through.

Now let's go back to the beginning and  talk about a heavy metal that you need, iron.

Iron is a heavy metal but also an  essential nutrient.

It's so essential that   we need it to breathe.

So in your red blood  cells, you have a protein called hemoglobin   that carries oxygen throughout your body.

In  hemoglobin, there are molecules called heme   that use iron to bind oxygen molecules.

No iron means no oxygen flowing throughout your body.

In 1941, companies started adding elemental  iron and some other essential nutrients to   cereals and other grain products.

That's what  the word fortified refers to.

And obviously,   they're still fortifying grain products today.

I mean, I just pulled iron out of my cereal.

But what's interesting is that elemental  iron powder has a low bioavailability,   meaning your body can't actually absorb and  use most of it.

There are chemists working on   changing that, but TBD on when and if that change  might happen.

So heavy metals can be good for you,   but also deadly, but also somewhere in between.

So I have some news to share.

This is actually my last video for Reactions.

The past two and a half  years of writing and hosting this show have been   a ton of fun and also sometimes challenging,  especially when a pandemic hit, and we needed   to adapt almost instantly.

I'm going to miss this  amazing team of producers that I've worked with   and who have become my friends.

And I'll  miss all of you giving us really awesome,   sometimes unique feedback that's truly  helpful and also makes us laugh sometimes.

But I'm excited to be starting something new, a  podcast from the American Chemical Society called   Tiny Matters.

It's about things that are small  in size but big in impact.

And I think you're   going to like it.

We just released our trailer,  and I've left a link to it in the description.

If you can subscribe, rate, and review, that's  how it'll get on the charts and that people   will be able to learn about it.

I would be  incredibly grateful to get your support.

And although I won't be a part of it, the  Reactions team still has a whole lot more   in store for you.

And I know I can't wait to see the new videos they put out.

Thanks, everyone.