Almost none, and far less than the fish most people eat. Antarctic krill feed on phytoplankton and live two to six years, so they never accumulate the mercury that builds up in long-lived predator fish — measured concentrations in wild Antarctic krill run around 0.006 to 0.071 parts per million, against the roughly 1.0 ppm that puts swordfish and shark on the FDA’s avoid list. The heavy metal actually worth asking a krill oil company about is not mercury. It is lead, and we will get to why.
Why krill are a bad place for mercury to end up
Mercury does not become dangerous because it exists in seawater. It becomes dangerous because it biomagnifies — each step up the food chain concentrates what the step below already carried, and each extra year of life adds to the total. A swordfish is a big predator that eats other predators for a decade or more. That is the whole mechanism.
Antarctic krill (Euphausia superba) break that mechanism in both directions: they eat phytoplankton and small protists, near the base of the food web rather than the top, and they are short-lived, so there is not much time on the clock for anything to build up.
The measurements bear this out. Seco and colleagues, writing in Environmental Pollution in 2019, sampled krill across three locations in the Scotia Sea and reported total mercury of roughly 0.006 to 0.071 µg/g — lowest in adult males from South Georgia, highest in juveniles from the South Orkney Islands. Krill from the South Orkneys carried five to seven times more than krill from South Georgia, which is a useful reminder that “krill” is not one uniform thing; where the boat is matters.
A parallel finding from Sontag, Steinberg and Reinfelder in Science of the Total Environment (2019, vol. 688) is that juvenile krill consistently carried more methylmercury than adults — the opposite of the pattern in fish, and further evidence that krill are not accumulating over a lifetime the way a tuna does.
One honest caveat on the comparison, because nobody else will give it to you: those krill figures are reported on a dry-weight basis, while the FDA’s fish numbers are wet weight. Krill is mostly water. Corrected properly, the gap is wider than the raw numbers suggest, not narrower. We are pointing that out against our own interest in keeping the math simple.
What actually shows up in the finished bottle
Wild krill is one thing. The oil in a capsule is another — it has been through a factory, a supply chain and a bottling line, and that is where contamination usually enters.
The reassuring result: when ConsumerLab tested fish, krill and algal oil supplements using a cold-vapor method, no detectable mercury turned up in any product tested. Their own summary was blunt — you will get more contamination from eating fish than from these capsules.
The unflattering finding, and the reason this article exists: a 2021 study in the Kocatepe Veterinary Journal (Erden Kızılırmak et al., 14(4):408–414) bought 11 krill oil brands off pharmacy shelves and sent them to an accredited lab. Mercury and cadmium came back inside Codex Alimentarius limits in every sample. But all 11 exceeded the EU tolerable limit for lead (0.08 mg/kg), and only one of the 11 came in under the arsenic limit (0.1 mg/kg). Peroxide values — a freshness measure — ranged from 10 to 30 meq O₂/kg.
Read that carefully, because the headline and the finding point in different directions. The metal people worry about is fine. The metals nobody asks about are the ones that failed.
The limits of that study, stated plainly
It was 11 brands from Turkish pharmacies, not a global survey, and it is a single small paper. It also measured total arsenic. Most arsenic in marine organisms is arsenobetaine, an organic form the body largely passes through unchanged, and a total-arsenic test cannot tell that apart from the toxic inorganic form. So the arsenic column is much weaker evidence than the lead column. The lead result is the one that should make you ask a question, and it is the one we would want asked of us.
What “heavy metal tested” on a label actually means
Scan any krill oil listing and you will see it: lab tested, heavy-metal tested, mercury-free. Those phrases are not regulated and mostly mean the company ran a test at some point. Two questions separate a real answer from a sticker.
Tested for what, exactly? Mercury is the cheap, easy, reassuring one — and, as the Kocatepe data shows, the one least likely to fail. A panel that stops at mercury is testing for marketing. Lead, cadmium and arsenic are where the interesting answers live.
Will they show you the paperwork? “Documentation available on request” only counts if the documentation actually arrives when you request it.
How we handle it, and what we will not claim
Captains Krill Oil™ is pressed mechanically from fresh-caught Antarctic krill, on the boat, in the Southern Ocean. No hexane. No chemical solvents. That matters here for a plain reason: every processing step and every added chemical is another opportunity for something to enter the oil, and we removed most of the steps by doing the extraction where the krill is caught rather than shipping meal halfway around the world first. If you want the long version, we wrote it up in is krill oil extracted with hexane.
We test lots at random, and they come back strong. Documentation is available on request — ask and we will send it. What we will not tell you is that we document every single lot, because we do not, and a company claiming a paper trail that complete is either a much bigger operation than ours or is telling you a story. It is a natural catch from a small family business that has been doing this for twenty years, and it varies a little lot to lot. That is what a real product looks like.
You might not need us
If mercury is your only reason for considering krill over fish oil, the honest answer is that you are solving a problem you probably do not have. Good fish oil from a reputable brand also tests clean for mercury — ConsumerLab found the same thing across the whole category. Mercury is not a reason to pay more for krill.
And if you eat fatty fish twice a week, you do not need a supplement at all, from us or anyone. The FDA’s own guidance is to eat fish, choosing lower-mercury species like salmon, sardines and pollock over swordfish and tilefish. That advice is free and it works. If you are pregnant, mercury exposure is worth real attention — and that is a conversation for your doctor, not a supplement company’s blog post.
The better reasons to choose a krill oil are the phospholipid form the omega-3 arrives in and how the oil was made and kept. Freshness is a bigger practical risk than any metal: rancid oil is far more common than contaminated oil, and you can often taste it. We covered that in does krill oil expire. On the sourcing question that usually comes next, see is krill endangered.
Frequently asked questions
Does krill oil have less mercury than fish oil?
In the raw material, yes, and by a wide margin — krill sit far lower on the food chain than the fish used for most fish oil. In the finished capsule the difference largely disappears, because refining removes mercury from fish oil too. ConsumerLab found no detectable mercury in either category.
Is krill oil safe during pregnancy?
Mercury is not the concern with krill that it is with predator fish, and unlike cod liver oil, krill carries no preformed vitamin A load. That said, pregnancy is exactly the situation where you should ask your OB or midwife rather than a supplement label, and we would rather you did.
What about lead, cadmium and arsenic in krill oil?
Cadmium has consistently tested within Codex limits. Lead is the one with a real finding against it — all 11 brands in the 2021 Kocatepe study exceeded the EU tolerable limit of 0.08 mg/kg. Ask any brand you are considering for lead results specifically, not a general “heavy metal tested” claim.
Do I need a certificate of analysis before buying krill oil?
It is a fair thing to ask for, and any brand should be able to produce testing documentation on request. Be skeptical of a company that will not, and equally skeptical of one promising a level of documentation that no small natural-product operation could actually maintain.
Can you taste or smell contamination in krill oil?
No. Metals have no taste at these concentrations. What you can taste is rancidity — a sharp, paint-like, old-fish note that means the oil has oxidized. That is the far more common defect, and your nose is a genuinely useful instrument for it.
Honest answer, not a pitch. — captainskrilloil.com