An Inside Look at Heavy Metals in Pet Food

The safety of commercial pet food has been under intense scrutiny since the 2007 melamine scandal, which caused thousands of pet illnesses and deaths worldwide.¹ Beyond organic contaminants, there is a growing concern regarding toxic elemental contamination originating from protein sources, fillers, and manufacturing processes.¹ To understand these risks, scientists utilize advanced spectroscopic techniques to identify and quantify heavy metals that may pose long-term health risks to companion animals.^1–3

In this Q&A article, we highlight the role that spectroscopy is playing in making pet food safer for animals.

Q: How do researchers use spectroscopic analysis to detect these contaminants?

The two main techniques researchers use to detect contaminants in pet food are inductively coupled plasma–mass spectrometry (ICP-MS) and inductively coupled plasma–optical emission spectroscopy (ICP-OES).^1-4 Both techniques offer specific advantages. For example, ICP-MS is ideal for trace element determination because of its high sensitivity and ability to filter out interferences.^1,2 Meanwhile, ICP-OES is often used to determine macro-elemental compositions to identify potential matrix interferences.³ Sample preparation is a critical first step, often involving cryogenic milling to grind the food into a uniform powder, followed by microwave digestion with nitric acid to break down the organic matrix.^1,2 In modern studies, instruments like the Agilent 7900 ICP-MS and the PerkinElmer ICP-OES are deployed to measure elements such as arsenic, lead, nickel, and uranium with high precision.^1,3

Q: Have heavy metal levels in pet food improved over the last decade?

Surprisingly, a 10-year follow-up study conducted in 2019 revealed that levels of several heavy metals have not significantly decreased, and in some cases, have increased.^1,2 Although we have seen that lead levels decreased from a maximum of 5.9 ppm in 2009 to 0.5 ppm in 2019, other toxic elements increased.^1,2 For example, arsenic concentrations jumped from a 2009 maximum of 290 ppb to 690 ppb in 2019, and nickel increased from 3200 ppb to 5900 ppb.^1,2 Uranium levels also increased. Compared to the results of the 2009 study, uranium levels increased when measured in 2019, reaching up to 1.7 ppm in some dog and cat food samples.^1,2

Q: Why does dry kibble often show higher contamination levels than wet food?

Spectroscopic studies consistently find that dry pet foods contain significantly higher concentrations of most metals compared to wet varieties.⁴ There are several reasons that explain this observation. For one, the low moisture content (8–10%) of dry food compared to the 70–80% moisture in wet food plays a role.⁴ Additionally, dry foods often rely on fortified mineral premixes and high-heat processing, which can introduce contaminants from machinery. The inclusion of grains, legumes, and vegetable by-products in dry kibble also contributes, as these ingredients can accumulate metals from contaminated soil or irrigation water during cultivation.

Q: How does the choice of protein source influence metal content?

The relationship between protein and metal concentration is significant; meat-based pet foods, particularly those using red meats like beef or lamb, often contain higher levels of essential metals like iron and zinc.⁴ This is because larger muscle mass and higher blood volume increase heme-iron and associated metals.⁴ Furthermore, organ meats like liver and kidney, which are common ingredients, act as storage sites for both essential and toxic metals.^3,4 Although some fish can be high in mercury, many commercial fish-based foods use smaller species like sardines, which generally have lower mercury levels than large predatory fish.⁴

Q: What are the current regulatory challenges regarding these findings?

Currently, one of the major challenges identified by researchers is that current U.S. Federal Drug Administration (FDA) and European Pet Food Industry Federation (FEDIAF) regulations do not fully account for chronic, low-level exposure to heavy metals.³ Most existing standards focus on acute toxicity and are often extrapolated from livestock or human data rather than being species-specific for companion animals.^1,3 Despite the enactment of the Food Safety Modernization Act (FSMA), there are still no definitive limits for many toxic metals in pet food.¹ Consequently, researchers are often forced to use human reference dosages from the Environmental Protection Agency (EPA) or the World Health Organization (WHO) to estimate the risks pets face from daily consumption.^1,2

Q: What can pet owners do to mitigate these risks?

Based on spectroscopic findings, experts recommend a strategy of moderation and rotation.⁴ For example, pet owners should consider variety when selecting dry food for their pets. This means rotating between different protein sources and mixing wet and dry foods to minimize the cumulative exposure to any single metal found in a specific formulation.^3,4 Pet owners have many choices in pet food brands, so it is important that they select the right brand for their brand. Consulting with their veterinarian to tailor diets to a pet's specific life stage and health status can also help ensure long-term well-being.^3,4 And finally, consistent monitoring for subtle health changes is essential, as pets with smaller body mass or compromised organ function are most susceptible to metal toxicity.^3,4

References

1. Atkins, P.; Restivo, T.; Lockerman, B. Heavy Metals in Pet Food: Changes in Heavy Metal Contamination in Pet Food Over the Past Decade. Spectroscopy 2021, 36 (3). Available at: https://www.spectroscopyonline.com/view/heavy-metals-in-pet-food-changes-over-the-past-decade (accessed 2026-02-10).
2. Bush, L. An Update on Assessing Heavy Metals in Pet Food with ICP-MS. Spectroscopy. Available at: https://www.spectroscopyonline.com/view/assessing-heavy-metals-in-pet-food-with-icp-ms-an-update (accessed 2026-02-10).
3. Semerjian, L.; Wetzel, W. The Role of ICP-OES in Analyzing the Metal Content in Pet Food. Spectroscopy. Available at: https://www.spectroscopyonline.com/view/the-role-of-icp-oes-in-analyzing-the-metal-content-in-pet-food (accessed 2026-02-10).
4. Semerjian, L.; Wetzel, W. Wetzel, W. Pet Food in the United Arab Emirates: An Interview with Lucy Semerjian. Spectroscopy. Available at: https://www.spectroscopyonline.com/view/pet-food-in-the-united-arab-emirates-an-interview-with-lucy-semerjian (accessed 2026-02-10).