In 2020, Aflatoxin-Contaminated Kibble Killed Over 130 Dogs in the United States
Pet food contamination is not a fringe concern or a theoretical risk. In late 2020 and early 2021, Midwestern Pet Foods recalled multiple product lines after aflatoxin contamination killed at least 130 dogs and sickened hundreds more. The FDA investigation found aflatoxin levels as high as 558 parts per billion (ppb) in some lots — more than 25 times the 20 ppb FDA action level for pet food.
This was not an isolated incident. Bischoff and Rumbeiha (2018) reviewed the history of pet food contaminants and found that major contamination events occur repeatedly: melamine in 2007 (killing thousands of pets), pentobarbital residues in rendered ingredients, Salmonella contamination, and chronic low-level mycotoxin exposure that never triggers recalls but accumulates over months and years.
The uncomfortable reality is that pet food regulation provides a safety floor, not a guarantee. Understanding what contaminants are routinely found in commercial dog food — and at what levels — helps owners make more informed feeding decisions.
Mycotoxins: The Grain-Based Threat
Mycotoxins are toxic secondary metabolites produced by molds (Aspergillus, Fusarium, Penicillium) that grow on grains during cultivation, harvest, or storage. The primary mycotoxins of concern in pet food:
Aflatoxins
Produced by Aspergillus flavus and A. parasiticus, primarily on corn, peanuts, and cottonseed. Aflatoxin B1 is the most potent:
- Mechanism: Metabolized by the liver to a reactive epoxide that binds DNA, causing mutations and hepatocellular damage
- Acute effects: Liver failure, coagulopathy, death. Dogs are more sensitive to aflatoxins than most livestock species.
- Chronic effects: Low-level chronic exposure causes progressive liver damage, immune suppression, and increased cancer risk
- FDA action level: 20 ppb in finished pet food
- Testing gap: FDA does not routinely test pet food for aflatoxins. Testing occurs primarily after adverse event reports.
Deoxynivalenol (DON / Vomitoxin)
Produced by Fusarium species on wheat, barley, and corn:
- Acute effects: Vomiting, feed refusal, diarrhea
- Chronic effects: Intestinal barrier disruption, immune modulation, reduced nutrient absorption
- Prevalence: Gazzotti et al. (2015) detected DON in 76% of commercial extruded dog foods tested in Italy, though most were below advisory levels
Ochratoxin A
Produced by Aspergillus and Penicillium species:
- Target organ: Kidney. Causes nephrotoxicity and is classified as a possible human carcinogen.
- Chronic exposure in dogs: May contribute to progressive kidney disease, though canine-specific dose-response data is limited.
Fumonisin
Produced by Fusarium on corn:
- Mechanism: Disrupts sphingolipid metabolism
- Effects: Hepatotoxicity, potential carcinogenicity
The Co-Exposure Problem
In practice, dogs eating grain-based kibble are rarely exposed to a single mycotoxin. Gazzotti et al. (2015) found that most contaminated foods contained multiple mycotoxins simultaneously. Co-exposure can produce additive or synergistic toxic effects even when individual mycotoxin levels are below regulatory thresholds. Current safety limits are set for individual toxins, not combinations.
Heavy Metals
Lead
- Sources: Contaminated ingredients, environmental exposure during manufacturing, contaminated water in ingredient processing
- Effects: Neurotoxicity, GI disturbance, kidney damage, behavioral changes
- Dogs are more sensitive to chronic lead exposure than humans due to higher bone turnover rates (lead accumulates in bone)
- Multiple pet food surveys have detected measurable lead in commercial products, though levels are generally below FDA limits
Arsenic
- Sources: Rice-based ingredients (rice concentrates arsenic from soil and irrigation water), contaminated water
- Inorganic arsenic is a known carcinogen
- Dogs eating rice-heavy diets may receive higher arsenic exposure than those on grain-free or non-rice formulations
Mercury
- Sources: Fish-based ingredients, particularly tuna and other large predatory fish
- Stern et al. (2010) analyzed mercury in canned fish-based pet foods and found methylmercury levels that, for some products and feeding regimens, could exceed safe exposure estimates for dogs
- Chronic mercury exposure affects the nervous system, kidneys, and developing puppies
Cadmium
- Sources: Organ meats (liver, kidney), certain grains, contaminated soils
- Cadmium accumulates in the kidney and liver with chronic exposure
- Long-lived dogs receiving organ-meat-heavy diets over years may accumulate meaningful cadmium burdens
BPA and Packaging Contaminants
Bisphenol A (BPA) — an endocrine-disrupting chemical used in can linings and some packaging — has been detected in canned dog food at levels that raise concern:
- BPA acts as an estrogen mimic, potentially disrupting thyroid function, reproductive development, and metabolic regulation
- Canned wet foods generally contain higher BPA levels than dry kibble, due to direct contact with can linings
- Some manufacturers have transitioned to BPA-free linings, though replacement chemicals (BPS, BPF) may carry similar endocrine-disrupting potential
- Dogs receiving exclusively canned diets over long periods may accumulate higher BPA exposure than those on dry or fresh food diets
What Owners Can Do
Ingredient and Brand Selection
- Diversify protein and grain sources. Rotating foods reduces chronic exposure to any single contaminant. A dog eating corn-heavy kibble exclusively for years faces more mycotoxin risk than one whose diet includes multiple grain sources or grain-free options.
- Choose brands with published quality testing. Some premium and prescription brands conduct routine mycotoxin, heavy metal, and contaminant testing on incoming ingredients and finished products. Brands that publish test results or COAs (certificates of analysis) provide more transparency.
- Consider fresh or minimally processed options for part of the diet. Fresh food diets bypass many of the contamination risks associated with long-term grain storage and high-heat extrusion processing, though they carry their own food safety considerations (bacterial contamination if raw).
- Limit fish-based diets for small dogs. Mercury bioaccumulates, and smaller dogs receive higher mg/kg exposure from the same food compared to larger dogs.
Storage and Handling
- Store dry food properly. Keep kibble in the original bag, sealed, in a cool dry location. Do not pour kibble into plastic storage containers, which can harbor rancid fat residues and mold spores from previous bags.
- Check lot numbers during recalls. The FDA recall database is the authoritative source for pet food recalls. Sign up for recall alerts.
- Inspect food before feeding. Discolored, off-smelling, or visibly moldy kibble should be discarded.
Monitoring
- Annual bloodwork including liver enzymes (ALT, AST, ALP) and kidney values (BUN, creatinine, SDMA) can detect early organ damage from chronic contaminant exposure.
- Watch for unexplained symptoms. Chronic vomiting, diarrhea, decreased appetite, increased thirst/urination, or lethargy without obvious cause may warrant investigation of dietary factors.
Limitations
- Regulatory testing of pet food is complaint-driven, not proactive. Many contamination events are discovered only after dogs are harmed.
- Chronic low-level exposure to mycotoxins and heavy metals is poorly studied in companion dogs. Safety limits are largely extrapolated from livestock and laboratory animal data.
- “Natural” and “organic” labels do not guarantee absence of contaminants. Organic grains can harbor mycotoxins; organic produce can contain soil-derived heavy metals.
- The relative risk of contamination across food formats (kibble, canned, raw, fresh) has not been systematically compared in a single controlled study.
Frequently Asked Questions
How common is pet food contamination?
Low-level mycotoxin contamination is common. Gazzotti et al. (2015) detected mycotoxins in over 75% of commercial dog foods tested. Most levels were below regulatory limits, but chronic exposure and co-exposure effects are poorly understood. Major contamination events causing acute illness are less common but occur multiple times per decade.
Is grain-free dog food safer from mycotoxins?
Grain-free formulations reduce mycotoxin exposure from corn, wheat, and barley. However, they substitute other carbohydrate sources (potatoes, legumes, tapioca) that carry their own considerations. Grain-free diets have been investigated by the FDA for a potential association with dilated cardiomyopathy in some breeds, though causality remains unestablished.
Can I test my dog’s food at home?
Consumer-level mycotoxin test kits exist but have limited accuracy and scope. Professional laboratory testing (ELISA, HPLC) is accurate but expensive and impractical for routine use. Choosing brands with established quality control programs is a more practical approach.
Should I stop feeding canned food because of BPA?
The BPA concern is real but should be weighed against the nutritional benefits of wet food (higher moisture content, often higher protein, lower carbohydrate). If BPA is a concern, look for brands using BPA-free can linings, or alternate between canned and other food formats.
Bottom Line
Pet food contamination — mycotoxins, heavy metals, BPA, and processing byproducts — is a real and underappreciated risk factor in canine health management. Chronic low-level exposure accumulates over a dog’s lifetime and may contribute to liver disease, kidney dysfunction, immune suppression, and cancer risk. Practical mitigation includes dietary rotation, brand quality vetting, proper storage, and annual bloodwork monitoring to detect early organ effects.