The purpose of this study was to examine pet foods from a variety of sources to determine if potentially toxic elements were present in the foods. A range of " budget " to " premium " grade pet food samples were donated by pet owners or purchased in several different stores. The food samples were ground in a cryogenic freezer mill (dry samples) or blender (wet samples), digested with concentrated nitric acid, and analyzed for trace metal content by inductively coupled plasma-mass spectrometry (ICP-MS)Results were then compared to both Environmental Protection Agency Reference Dose (RfD) values and World Health Organization Tolerable Daily Intake (TDI) values, which are considered the daily oral exposure limits for the human population. Many of the pet foods sampled showed significant concentrations of various toxic metals. In many cases, the concentrations exceeded the extrapolated human limit values calculated to pet-size dosages. Part I of this article focuses on the raw materials that are used in pet food manufacturing processes and all the potential sources of contamination. Part II of the article will discuss how the data relate to the dietary exposure of toxic metals in those pet foods when calculated for the daily intake of an average-sized dog and cat. To get a better understanding of the impact on the health of the pets, the daily intake of toxic metals will compared to EPA and WHO human risk assessment guidelines.

P.Atkins, L.Ernyei, W.Driscoll, R.Obenauf, and R. Thomas

In the past decade, consumers have doubled their spending on pet-related products. According to the American Pet Products Association (APPA), in 2009, pet owners in the United States spent more than $17 billion dollars on pet food (1). Along with this increased spending, there has been increased controversy. The melamine pet food scare of 2007 affected millions of people and their pets as well as the pet food industry. The supplementation of protein sources with materials containing melamine and cyanuric acid killed hundreds of pets and sickened many others. The pet food scare highlighted the potential for contaminants and controversial ingredients that could be contained in pet food. In addition to organic chemical contaminants and additives, there is also the possibility of toxic elemental contamination from protein sources, fillers, and manufacturing processes. The search for healthy pet food therefore goes beyond the choice of a name-brand food or seemingly nutritious ingredients on a label.

According to the Pet Food Recall Product List on the U.S. Food and Drug Administration (FDA) website, there have been almost 1000 pet food recalls since 2006. These recalls have increased awareness of the inadequate testing of ingredients used in the pet food industry (2). Pet food is a multibillion dollar per year business controlled by four or five large corporations that produce 80% of U.S. pet food and a number of smaller, premium-brand pet food companies that produce the remaining 20%. Because the pet food industry is not as well regulated as is food for human consumption, the quality of many of the ingredients used for pet food often is considered to be inferior. The major claim of the manufacturers of premium brands is that of superior quality with superior ingredients. However, because regulations have not been defined as to the quality of pet foods, claims of superior quality ingredients are very subjective and not always supported by the information stated on the product label.

Pet Food Manufacture

Figure 1: The manufacturing process of dry pet food (3).

The manufacture of pet food is a multistage process that exposes the ingredients to many potential contamination sources. Many of the same processes used to make food for human consumption are also used to make pet food. Dry pet food in the form of "kibble" accounts for more than 60% of all cat and dog food sales in the United States, whereas the most familiar form of wet pet food is sold in cans, trays, and pouches (3). The most common way to make dry pet food is extrusion. This process was adapted for making pet food in the 1950s based upon technology used to make breakfast cereals. Figure 1 illustrates the process of extrusion.

To make an extruded dry pet food, wet and dry ingredients are brought together in a mixer to form a moist dough. The dough is heated in the preconditioner and then is introduced into a large grinder, where the primary cooking phase for dry extruded pet food products occurs. The dough is cooked under intense heat and pressure as it moves toward the open end of the extruder. The hot dough passes through a shaping die and knife where the small pieces expand rapidly into kibble. The food is dried in an oven until its moisture content is low enough to make it shelf stable, similar to a cookie or cracker. After cooling, dry food may pass through a machine that sprays on a coating, which is generally a flavor enhancer. The final result is a bag, box, or package of dry pet food or treats.

Pet food companies are required to follow the same federal regulations for making wet pet food products that human food companies must follow (4). The process is described in CFR Title 21, Part 113. Ingredients are incorporated into a mixer. Clean empty containers (cans, pouches, trays, and so forth) are filled to meet the weight advertised on the label. Sealed containers are cooked at a specified temperature to destroy any bacteria, viruses, or mold that could otherwise grow in the sealed container. After the containers have cooled, labels are applied to containers, resulting in the finished wet food products.