Some consumers consider “contaminants” to be all artificial compounds in the product, including those added unintentionally or accidentally such as pesticides, drug residues, and metals, as well as intentionally (preservatives, vitamins, and minerals). Micro amounts (ppm or ppb) of pesticides, drugs, and industrial chemicals are intensely feared.
Unintentional contaminants can be found on occasion in food products, although every effort is made to eliminate, or at least minimize, these residues.
Major pet food manufacturers routinely scan and test all ingredients for many known or suspected contaminants before accepting delivery. It is far less costly to test and control the ingredients before production than to have a faulting product. The massive pet food recall during the spring of 2007 was due to an intentionally added previously unknown contaminant.
Pet owners may elect to feed a homemade food to their pets in order to avoid all types of contaminates. However, ingredients used in homemade foods may themselves be contaminated—in other words, making a food at home does not ensure against unintentional contaminates.