Lead, Arsenic, and Mercury in Cat Food: What We Know

If you're reading about heavy metals in cat food, one question comes first: are these hurting my cat? It's easy to land on two answers. Either the metals are in everything, so they can't matter, or they're in everything, so everything is a problem. The research points somewhere in between, and it looks a little different for each metal.

The short answer

The FDA's report on heavy metals in animal food says these metals are found in air, water, and soil, so they can't always be kept out of animal food entirely, and that high levels can be toxic. In its sampling, most results were below maximum tolerable levels. So the useful questions are how much, which form, and for how long. Below, each metal gets the same three parts: what it does, where it shows up, and what the evidence does and doesn't show.

Mercury

What it does. The Merck Veterinary Manual describes mercury as a problem mainly for the nervous system and the kidneys. It also notes that the nervous systems of young, developing animals are especially susceptible to organic mercury, which is one reason kittens come up in this conversation.

Where it shows up. Mercury builds up as it moves through aquatic food chains, so larger predatory fish carry more of it. Merck notes that commercial fish-based products have been linked to chronic mercury toxicosis in cats. As labeled background for people, the FDA says nearly all fish and shellfish contain trace amounts of methylmercury.

What the evidence does and doesn't show. Fish isn't the whole story. In the FDA's sampling, a herring meal was among the highest results for mercury, but so was a poultry mineral mix. In a 2021 Scientific Reports study, mercury was above the tolerable level in every cat food tested, though the authors suggest it may not have been methylmercury, the more toxic form. In that study, beef meal and chicken by-products had the highest mercury of the protein sources, while no fish meal sample was above the detection limit. A 2021 study from Spain found mercury among the highest hazard indexes, especially in cat food, and suggested fish ingredients as a possible reason. Its authors also note that cats are particularly sensitive to organic mercury. What these studies can't tell you is what any one food is doing to any one cat.

Arsenic

What it does. Arsenic comes in inorganic and organic forms, and the Merck overview explains that its toxicity depends on the form, the species, and how long exposure lasts. Merck's page on inorganic arsenic lists cats as the most sensitive of the species it covers to inorganic trivalent arsenicals.

Where it shows up. Merck notes that groundwater can carry inorganic arsenic. In the FDA's animal food sampling, an imported fish meal was among the three highest results for arsenic. As background from human food, the FDA says current research indicates inorganic arsenic is more dangerous than organic arsenic.

What the evidence does and doesn't show. In a UK study by Davies and colleagues, arsenic rose with fish content, and mercury tracked along with it. The authors raised a question about arsenic and kidney health in cats, but left it as something still to be determined. The Spain study found arsenic among the highest hazard indexes in cat food. Here's the catch: most of these studies measure total arsenic. A total number doesn't tell you how much is the inorganic form that Merck flags as most toxic to cats.

Lead

What it does. The Merck Veterinary Manual says lead mainly affects the nervous system, the gut, and the blood. There's no established toxic dose for cats.

Where it shows up. Food is only part of the picture. Merck names renovation of older homes as a common route in small animals, and it has been reported in cats that swallow dust from sanded lead paint while grooming. Ceramic glazes on bowls are another listed source. In the FDA's sampling, a poultry mineral mix was among the highest lead results.

What the evidence does and doesn't show. In the Scientific Reports study, lead was above tolerable levels in some cat foods. A 2026 study from Turkey in Veterinary Research Communications looked at both the food and the cats eating it. The measured toxic metals stayed below regulatory limits in the diets, and the researchers saw no consistent build-up in the cats by protein source or feeding time. Cats on poultry diets had lower blood lead than the other groups, but all values were within normal ranges. The authors are clear that their design can't rule out long-term build-up or risk.

What the research doesn't tell us yet

These studies are small, and most of them sampled foods outside the US. Finding a metal in a food is not the same as showing harm to the cats who eat it, and only one study here measured the cats themselves. The FDA has no set limits for these metals in animal food and instead acts case by case when testing finds a problem. Cadmium shows up in some of the same studies, and we'll cover it in a future post. If a company shares test results with you, our guide on how to read a heavy metal COA can help, and if you're unsure which metals count as heavy, see Is Iron a Heavy Metal?

What this means for you

For each metal, the honest answer is that it's worth paying attention to, but the research can't yet say what a given food means for your cat. If you'd like a simple way to ask brands better questions, try our 5-minute heavy metals check for cat food. Talk to your vet about your cat's diet, especially if it's fish-heavy or you're feeding a kitten. For the people side of the story, see our human-food guide to heavy metals in food.

FAQ

Is there mercury in cat food? Studies have found it. The FDA's sampling found most animal food results below maximum tolerable levels, while a 2021 study found mercury above tolerable levels in all the cat foods it tested, and its authors suggest it may have been a less toxic form.

Is arsenic in fish cat food the toxic kind? Not necessarily. Arsenic comes in organic and inorganic forms, and Merck notes the inorganic form is the one cats are most sensitive to. Most pet food studies report total arsenic, which doesn't show how much of each form is present.

Does lead in cat food mean my cat has lead poisoning? No. Detecting lead in a food doesn't mean your cat has lead poisoning, and lead can also come from household sources like old paint dust. If you're worried, see your vet.

Are tuna-based foods a problem? The research can't say that about any one food. Merck notes mercury builds up through aquatic food chains and that fish-based products have been linked to chronic toxicosis in cats. The Spain study, which included tuna and salmon cat foods, found higher hazard indexes in cat food and pointed to fish ingredients as a possible reason. Your vet can help you weigh this for your cat.

This article is general information, not veterinary advice. If you have questions about your cat's health, contact your veterinarian.

Curious whether a brand tests for heavy metals? Heavy Metal Tested is a certification program that helps brands share their independent results with owners. Learn how Heavy Metal Tested certification works.