When you hear the word heavy metal what comes to your mind? Large slabs of iron? A block of gold? A genre of music? In the nutritional realm heavy metals aren’t exactly any of those things. To be specific, heavy metals are classified as minerals that have a density five times greater than the density of water. They also have a high atomic weight, which is the mass of a single atom. Heavy metals are a concern to health since heaviness and toxicity are interrelated. The heavier the metal, the more likely it is to induce toxicity at a low dose. Heavy metals can have serious implications on health when humans, or dogs, are chronically exposed to them. They have the potential to disrupt cell functioning and therefore cause harm to many important organs.
Many minerals (including metals) are added to dog foods to ensure proper nutrition. These are considered essential macrominerals and essential microminerals. Essential macrominerals include calcium, phosphorus, magnesium, potassium, sodium and chloride. Essential microminerals include iron, copper, manganese, selenium, iodine and zinc.
Heavy metals on the other hand are not added to pet foods to meet nutritional needs, but end up there from the ingredients that are exposed to them. Arsenic, cadmium, lead and mercury are four of the heavy metals that are of most concern when it comes to toxicity in dogs.
Due to bioaccumulation (gradual accumulation of a chemical in an organism from the air, soil or water) animal products have high levels of heavy metals. This could be influenced by where the animal lives and the environmental pollution it is exposed to. Farm raised animals tend to live longer and therefore are more likely to bioaccumulate heavy metals. Fish is the most concerning ingredient when it comes to heavy metal content due to the increasing levels of arsenic, cadmium and mercury bioaccumulation of aquatic environments.
Dog food is more likely to have higher levels of these potentially harmful heavy metals than human food because they contain 4D meats; dead, dying, diseased, and disabled animals. It is against federal law to use these meats for human grade. However, the FDA allows 4D meats to make their way into our pets’ food. This is because the use of 4D food is legal at a state level.
Bioaccumulation of heavy metals typically occurs in the organs of an animal, such as the heart, liver, kidneys, bones, intestines, and gizzards (poultry). While specific organ accumulation differs between species, most of these organs are discarded for human grade foods but are added to pet grade foods. However, these assumptions have not been heavily researched to determine the exact cause of dog food having higher levels of heavy metals.
Unfortunately, toxic limits for these metals have not been set for dogs as they are for humans. AAFCO (Association of American Feed Control Officials) and the NRC (National Research Council) have only established maximum intake levels for calcium, phosphorus, iodine and selenium. They also state that they take into consideration information provided by the NRC and AAFCO, which we find concerning since neither organization has set tolerance levels. Although the AAFCO does have a set level, they are not available to the public without purchase and there are some heavy metals that have no set limit.
While it is important to understand that there is a concern for toxicity involving these metals, it is also just as important to know that a diet excluding minerals could be just as harmful.
