I think this was the plot of an episode of CSI (don't recall which sub-series, maby Miami?) in the 2000's. Eventually they determine a guy dies of lead poisoning and they figure out he ate massive amounts of chocolate candy. Conclusion: leaded gas used in other countries caused lead buildup on coco plants there and eventually gets shipped back to US chocolate makers.

Yup, this is Season 3 Episode 1 of CSI Vegas, titled: "Revenge is Best Served Cold."

I assume the heavy metals are coming from the soil. Arsenic is a common one in a lot of crops because of historic use of arsenic pesticides. Where is the lead and cadmium coming from? Road dust?

I've read a previous hypothesis that quite a bit of cocoa pod processing is done outside and beans may collect such dust during drying or fermenting stages.

Couple of other HN threads perhaps of interest,

https://news.ycombinator.com/item?id=34014515 ("Research reveals ways lead and cadmium in chocolate may be reduced", 82 comments)

https://news.ycombinator.com/item?id=38038465 "A third of chocolate products are high in heavy metals", 201 comments)

I was eating ~handful of dark chocolate chips a day for a couple years as my only dessert. Wonder how many IQ points that cost me.

"97.2% (70 of 72) fall below US FDA IRL limits established for Pb"

So you're probably fine but you might want to do more research on the particular brand(s) you're buying.

I could not find where their data is. No mention of what products and what respective concentrations. Anyone know?

Not the same study (I think) but there are brands and concentrations here (expressed as % above California's limits) : https://www.consumerreports.org/health/food-safety/a-third-o...

"Notably, 'organic' products were significantly more likely to demonstrate higher levels of both lead and cadmium"

Bummer. How widespread is this problem in other organic foods?

I found this reddit comment. It may be that West African cocoa is all conventionally grown (by a cartel) while American cocoa, where heavy metals are more common, is more likely to be organic.

You are falling for a scam. The truth is that West Africa retains a monopoly scaring you consumers with talk of “lead” and “cadmium”. To begin with, Cadmium is not heavily present in West Africa. It is very common in volcanoes soil like Guatemala, Ecuador, Peru, Venezuela, and Colombia. That said, this fear is conveniently promoted by big chocolate companies because their cocoa is all from West Africa. As for “lead”, this is from pesticides or private aviation. That said, cocoa pods are thick and it is questionable how much of this actually gets into your final product given the thick skin of the cocoa pod. Our concerns should be more focused on the poor farmers many of which are children that get sprayed or exposed to the pesticides and not so much the end consumer in this case. You might want to buy better chocolate. That Lindt is definitely west African cocoa and it is conventional so it gets sprayed. You don’t need to buy organic to get pesticide free chocolate. You just need to buy chocolate from chocolate makers who work with small family farms.

That seems not entirely persuasive. In particular:

> As for “lead”, this is from pesticides or private aviation. That said, cocoa pods are thick and it is questionable how much of this actually gets into your final product given the thick skin of the cocoa pod.

The commenter might have been discussing a different study, but this one appears to have tested the final product. If it found lead, people are eating lead.

I saw that. I’m not sure it invalidates the rest of the comment

The rest of the comment is just not what I care about. They're telling me the companies raising the alarm about heavy metals are doing so out of commercial interest. Okay, but that's just an ad hominem argument. It doesn't mean they're wrong.

I'd rather hear "actually, these levels of cadmium, arsenic, and lead are well within safe limits unless you're eating nothing but chocolate all day" (with matching data of course), which would better reassure me about the fancy South American organic chocolates. And/or if the commenter is trying to say that the more mass-produced West African conventional chocolates are worse, what are the specific health dangers (to the workers, apparently) posed by their pesticides that I should actually be concerned about?

In eggs this is also a problem. The chickens are required to eat natural foods but in certain cases the natural foods contain way more bad chemicals than if they were simply synthesized and added as a food additive to their regular food. Which is how it's done for regular eggs (because it's cheaper).