A recent investigation has found that several popular commercial dog food products contain "dangerous levels" of heavy metals, plastic-based contaminants, and acrylamide—a potentially cancer-causing substance that forms when foods are processed at high temperatures.

“The amounts of heavy metals and other contaminants we detected are deeply concerning,” said Molly Hamilton, executive director of the Clean Label Project, the nonprofit that led the study. The Colorado‑based organization tests consumer goods for purity and certifies products that meet stringent safety benchmarks.

“Pet owners care for their dogs as much as parents care for their children,” Hamilton added. “They should be able to purchase dog food without fearing it could harm their pet.”

According to the report, dog foods tested contained three to thirteen times more heavy metals than human foods evaluated by the Clean Label Project over the past decade. These figures align with earlier research conducted by Dr. Joseph Wakshlag, a veterinary nutrition professor at Cornell University College of Veterinary Medicine.

“In a 2018 paper, we compared heavy metal intake per calorie between humans and dogs,” said Wakshlag, who co‑authored that study but was not involved in the new investigation. “We found that, relative to people, dogs consumed three to seven times more heavy metals daily.”

Laboratory tests showed that dry dog food, or kibble, had the highest concentrations of heavy metals and other contaminants, followed by air‑dried and freeze‑dried formulas. Fresh and frozen dog foods contained the lowest levels.

The report did not identify specific brands or products.

“More than 85% of dog owners feed dry food, and most dogs eat the same type of food every day, often for their whole lives,” Hamilton noted. “If kibble is all they eat, heavy metal buildup could be contributing to dogs’ higher cancer rates.”

Research indicates heavy metals can accumulate in a dog’s kidneys and liver, potentially leading to chronic illness. Exposure to lead and cadmium has been linked to canine cancer, a leading cause of death in dogs. The American Veterinary Medical Association estimates about one in four dogs will develop cancer.

The Pet Food Institute, which represents dog food manufacturers, told CNN it will review the Clean Label Project’s findings. “PFI and U.S. pet food makers continuously monitor ingredients to support the health and safety of dogs and cats,” a spokesperson said.

Fewer Contaminants in Fresh and Frozen Formulas

Clean Label Project purchased 79 top‑selling samples of fresh, frozen, kibble, and dried dog foods. A federally certified lab performed over 11,000 tests for plastics, pesticides, lead, arsenic, mercury, cadmium, and acrylamide.

Fresh and frozen dog foods—which entered the mainstream market around 2006—showed the lowest contamination. Lead and mercury levels in dry food were about 21 times higher than in fresh or frozen options. Kibble also contained over 13 times more arsenic and six times more cadmium.

One explanation, according to Wakshlag, is that “fresh and frozen dog foods are at least 70% water, and water carries far fewer heavy metals than a dense piece of kibble.” (Wakshlag also consults for a dog food company.) He added, “But you can’t just compare numbers directly, because a dog must eat about three cups of fresh food to get the same calories as one cup of dry. So overall exposure may still increase.”

A 2021 study also found elevated heavy metals in dog foods, with 81% of samples exceeding mercury limits and 100% surpassing lead limits set for animal feed.

Safety Standards and Knowledge Gaps

There is no established safe level of lead for humans, according to the EPA, which does not set thresholds for dogs. Safety limits for animal feed are developed by the Association of American Feed Control Officials and the National Research Council, based on the most sensitive species.

“The challenge is that NRC and AAFCO guidelines aren’t specific to dogs—pet food is grouped with livestock feed,” Hamilton explained. “The industry assumption is that dogs tolerate heavy metals better than people, but the basis for that is debatable.”

Wakshlag pointed out that few long‑term studies track how chronic contaminant exposure affects dogs. “We don’t really know the impact of consistently high levels over years. We need studies that follow dogs on different diets to find out,” he said. He suggests companies could test products routinely and share results, but that would raise costs: “If you want that transparency, expect to pay $3‑4 more per bag.”

Acrylamide and Plastic Chemicals

Acrylamide levels in dry dog food averaged 24 times higher than in fresh or frozen products, with one sample reaching 780 parts per billion. “That’s exceptionally high—like a person eating five servings of fries every day in terms of acrylamide exposure,” Wakshlag remarked.

Acrylamide forms in starchy foods cooked at high temperatures and is classified as likely carcinogenic to humans. It is also found in tobacco smoke and used to produce paper, dyes, and plastics.

The investigation also measured bisphenols (BPA and BPS) and the phthalate DEHP. Again, dry dog food contained the highest levels; fresh and frozen had the lowest.

While no dog‑specific studies exist, a 2025 study linked DEHP exposure to over 10% of heart‑disease‑related deaths globally among adults aged 55‑64. BPA is associated with fetal abnormalities, low birth weight, developmental issues, diabetes, heart disease, and cancer. BPS, often used as a BPA substitute, may similarly disrupt reproductive and cellular function.