Analysis of Toxic Trace Metals in Pet Foods Using Cryogenic Grinding and Quantitation by ICP-MS, Part II

Feb 11, 2011
Volume 26, Issue 2

This article is the second part of a study that examines pet foods from a variety of sources to determine if there were potentially toxic elements present in the foods and also whether more expensive foods with higher quality ingredients equated to lower levels of toxic elements. A range of "budget" to "premium" grade pet foods 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-metals content by inductively couples plasma-mass spectrometry (ICP-MS). Results were then compared to 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. Human limits were scaled to the weight of a 50-lb dog or 10-lb cat to gain perspective of an animal's potential exposure. 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 (1) focused on the raw materials that are used in the pet food manufacturing processes, all the potential sources of contamination, and, in particular, how the FDA regulates the pet food industry for trace-metal contamination. It also discussed the analytical methodology used to determine the trace-element content of the pet food samples, including the sample preparation steps and the optimum inductively coupled plasma–mass spectrometry (ICP-MS) instrumental conditions for the analysis.

Table I: A dogs daily intake (μg) of toxic elements from consuming five cups (500 g) of dry dog food
Part II of the article carries on from Part I and 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 size dog and cat. To get a better understanding of the impact to the health of the pets, the daily intake of toxic metals are then compared to EPA and WHO human risk assessment guidelines. Finally, conclusions will be drawn based on the comparison to these guidelines and in particular how they relate to the cost of the individual pet foods.

Dietary Exposure of Toxic Metals in Pet Food

Table II: A dogs daily intake (μg) of toxic elements from consuming one large can (375 g) of wet dog food
To understand what these toxic metal data mean in terms of impact on the health of an animal, they have to be related to the daily intake of food. For this study some generalities were made regarding the average size of a dog or cat and the amount the animal is fed in a day.

Table III: A cats daily intake (μg) of toxic elements from consuming one cup (100 g) of dry cat food
It was concluded that a medium to large size dog with a body weight of approximately 50 lb would typically be fed as much as 5 cups of dry dog food or one large can of wet dog food (or both) per day. An average-sized cat weighing approximately 10 lb typically could be fed as much as 1 cup of dry cat food or one small can or pouch of wet food (or both) per day.

Table IV: A cats daily intake (μg) of toxic elements from consuming one small can or pouch (175 g) of wet cat food
A cup of dry dog or cat food averaged about 100 g, whereas a large can of dog food typically weighed 375 g and an average-sized can of cat food weighed 175 g. From these standardized measurements, the element concentrations were calculated for each food serving. The three human protein servings (tuna, sardines, and chicken) were calculated for an average 100-g can.

Table V: A humans daily intake (μg) of toxic elements from consuming one can of tuna fish, sardines, or chicken (100 g)
For this exercise, we will focus on a smaller group of toxic elements including As, Be, Cd, Hg, Pb, Sb, Tl, and U, which are known to exhibit severe toxicity effects on the human population. Nickel was included with the toxic elements not because of acute toxicity but due to the large concentrations found in the various types of pet food, which over time could possibly become a health hazard. Tables I–V show the calculated concentrations of elemental exposure per serving for each type of food.

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