You May Be Ingesting Chromium-6: Don’t Panic | Vol. 3 / No. 47.4

Chromium trioxide, a Cr(VI) compound | Image: BXXXD, CC BY-SA 2.0

“‘Erin Brockovich’ Carcinogen In Tap Water Of More Than 200 Million Americans” reads the press release from EWG, the Environmental Working Group. It’s a headline that’s been adopted by a number of respectable news sources, like the Guardian US whose headline reads “Chromium-6: ‘Erin Brockovich’ chemical threatens two-thirds of Americans.” CNN’s reads “New report finds ‘Erin Brockovich’ chemical in US drinking water.” It sounds super scary, with quotes like the following:

Nearly 200 million Americans across all 50 states are exposed to unsafe levels of chromium-6 or hexavalent chromium, a heavy metal known to cause cancer in animals and humans, according to a new report released Tuesday by the nonprofit research and advocacy organization Environmental Working Group (EWG).

But as with every bit of attention-gathering fearmongering we see on the internet or news, it’s always important to back up and ask “wait, what?” So, here we go:

What is chromium-6?

Chromium-6 (aka hexavalent chromium, chromium(VI), Cr(VI), Cr6+, etc.) is a form of the element chromium that shows up in a number of compounds that are used fairly commonly in industrial applications as well as dyes and paints.

Is it in my water?

If the EWG’s data is good — and they claim it’s “federal data from drinking water tests,” so maybe it is —  then it might well be. They have an interactive map you can check.

Does chromium-6 cause cancer?

Yes. It absolutely does cause cancer.

Why don’t you look worried?

Aha. Well, that’s the thing. If you inhale it, it’s a pretty good carcinogen (as far as things can be good that cause cancer). But ingestion studies are few and far between. The one the EWG is primarily relying on is this one, which gave mice and rats water laced with high doses of the stuff (in the form of sodium dichromate dissolved in water) for two years and watched as many of them got cancer.

But remember, as ever, the dose makes the poison. And right now we don’t actually know what a “safe” long-term consumption level of Cr(VI) is. Here’s some numbers for scale:

The lowest dose in the mouse and rat study was the equivalent of 5 parts per million, or 5000 parts per billion.

The amount the folks in Hinkley (the Erin Brockovitch thing) were drinking was 0.58 ppm, or 580 parts per billion.

The highest legal amount in drinking water in California is 0.01 ppm, or 10 parts per billion.

The highest level EWG found in their data analysis was 0.007853 ppm, or 7.853 parts per billion (in Phoenix).

The non-binding California health goal for chromium-6 in drinking water (what the EWG uses for their definition of “safe”) is 0.00002 ppm, or 0.02 parts per billion.

In Massachusetts, the amounts detected were between zero and 0.059 parts per billion. Yeah, that’s three times California’s goal, but it’s also almost four orders of magnitude less than the amount in the water in Hinkley, and even with those numbers they couldn’t build a totally convincing case that it was causing an unusually high incidence of cancer.

What if you lived in Phoenix, would you be worried?

I don’t know about worried, but I might be interested in talking to my state representative about why Arizona doesn’t even have a legal limit on Cr(VI) in drinking water, or what steps it might try taking to lower those figures.

Wouldn’t you be outraged?

Ah. So, no. Look, maybe I should be, but at this point I’m all out of outrage. Thirty thousand people die in America each year by being shot. Our wasteful overuse of carbon-spewing energy is screwing up the planet not just for “our children’s children” but for us, now, today. We had 13.1 million children living in food insecure households last year. Are we doing anything about those? No, we’re passing laws to put labels on GMO crops, and fighting tooth and nail to stop the spread of diseases we should have wiped out decades ago. And don’t get me started about the options in the federal election.

Yeah, I don’t like a slightly increased cancer risk, but I also choose to drink alcohol and eat bacon and spam, both of which raise my cancer likelihood from “god you’ve got terrible genes you’ll probably get cancer if you live long enough” to “god you’ve got terrible genes and you drink and eat bad food so you’ll definitely get cancer if you live long enough.”

I just don’t have it in me to jump into an outrage when people generally known for peddling outrage tell me to.

Wait, “generally known for peddling outrage”?

Yeah, it’s basically EWG’s modus operandi. They’re the ones behind the ever-dubious “dirty dozen” list each year of scary pesticides in your produce. They’re the ones still hammering on about cellphones causing brain cancer. Hell, at the bottom of this latest press release in giant orange letters it reads “ARE YOU OUTRAGED? US TOO. TAKE ACTION TODAY!” with a little box for your e-mail address so they can send you more things to be outraged about, I suppose.

So you’re okay with this chromium stuff in your water?

I’m not happy about it. I just don’t know that the levels in my local water supply are really that upsetting. Massachusetts does a pretty good job with these things. Your mileage may vary. I’d probably make some phone calls if I lived in Phoenix, if only to reassure myself, but that’s about where I’d be on this. We’re not talking Flint’s lead crisis here.

Do you have more questions? Ask me, or better yet, find a scientist and ask her. Expert opinions are where it’s at.


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Richard Ford Burley is a human, writer, and doctoral candidate at Boston College, as well as an editor at Ledger, the first academic journal devoted to Bitcoin and other cryptocurrencies. In his spare time he writes about science, skepticism, feminism, and futurism here at This Week In Tomorrow.