Assessing Heavy Metals in Pet Food with ICP-MS: An Update

In 2009, a group of researchers conducted a study, using inductively coupled plasma–mass spectrometry (ICP-MS), to determine if heavy metal contaminants were present in a variety of pet foods (1,2). Results were compared to 2009 EPA Reference Dose (RfD) and World Health Organization (WHO) Tolerable Daily Intake (TDI) levels, scaled to the sizes of pets. In the intervening decade, the U.S. Food Safety Modernization Act (FMSA) was enacted, and pet food became one of the targets of scrutiny. The team conducted a follow-up study in 2019, revisiting the pet food brands first analyzed in 2009 as well as new brands that have emerged since, to see if anything changed significantly in the intervening decade. The new study used updated cryogenic and microwave technologies for sample preparation before ICP-MS analysis. We spoke to the study’s lead author, Patricia Atkins, a Senior Application Scientist at Spex CertiPrep, about this investigation.

You conducted a study in 2009 of inorganic contaminants in pet food (1,2). What prompted the original study, and what prompted you to update it? Was there any clinical evidence or suspicion that toxic materials exceeded calculated risk assessment guidelines?

I started at Spex CertiPrep in 2008 and was a new scientist there. Since I was, and am, tasked with creating new and interesting research projects, I often draw from my life experiences and interests for topics. In 2009, I was a grieving pet owner who felt that I fed my cats the best foods, but yet here I was with an animal who died from cancer. I wondered if the food was as good as purported. This time period was just a year or two after the melamine scandal in pet food, and I wondered if pet food was safer now. I found a lot of other employees were also wondering about their pet food and its safety. As I looked on-line, I realized that we were not alone in our questions, but I had the ability to do some testing, so I did.

Since that original study, which was very widely debated and remembered, ten years had passed and the FSMA had been enacted. It seemed time to revisit the study and see if anything had changed.

Did you have a targeted list of potential contaminants? If so, how did you determine what to include on that list?

I did want to target certain groups like heavy metals or wear metals, but since I work for a standards company, it gave me a lot of freedom to examine the entire periodic table. I did focus on toxic elements at first, then expanded to some of the more unusual findings. That rationale and approach let me see that some of my dog foods actually contained uranium.

You have looked at trace toxic metals. Are you aware of any studies assessing potential toxic organic contaminants, such as pesticides or industrial chemicals, in pet food?

I have seen references to some studies of pesticides in animal feed and veterinary drugs in some pet foods. Most of the work on pet food occurred around the time of the melamine crisis. Now most studies involve bacteriological contamination or cannabis use in pet foods.

Can you briefly summarize the study? What approaches or methods did you use for sampling, sample preparation, and analysis? Did you use internal standards? What types of pet food did you analyze and how many samples did you take? Were you able to determine that samples were not contaminated during handling?

In this study, we focused only on dry food, as opposed to wet and dry food of the first study. We primarily did that to basically unify our preparation and analysis. Our dry foods were purchased or donated by employees and ground using cryogenic milling. Each pet food was sampled three times, and run in triplicate with cleaning runs and blanks between samples. All replicates were examined by ICP-MS, and if one replicate appeared contaminated, it was either rerun or eliminated.

When you analyzed your results, how did you how did you calculate the risk assessment levels of these contaminants for pets? Is there a legal or regulatory standard for toxicity in daily dietary exposure in pets?

Back in 2009, we determined feeding levels by consensus, which was often questioned by other scientists once we presented our data. During this study, we used pet food manufacturers’ feeding guidelines for portions, and based the data on a standardized weight for a dog and a cat. There are no clear guidelines regarding limits of any particular metal in pet food; even the new guidelines just state that contaminants cannot be harmful and must be tested. In both the 2009 and 2019 studies, we based pet exposure on reference dosages of elements for humans.

What did you find overall? What were the contaminants that occurred most frequently across the samples? Which contaminants were present at the highest levels? Do pet owners need to be concerned? Which metal contaminants are of most concern to you?
 

Overall, we found that the levels of heavy metals had not significantly changed in ten years in the brands we looked at for this study. Both dog and cat foods had higher levels of arsenic and nickel than what had been found in 2009. Arsenic in 2009 had a maximum of 290 ppb, while in 2019 we saw it up to 690 ppb. Nickel in 2009 had a maximum of 3200 ppb, but in 2019 we found up to 5900 ppb. In our first study, we had surprisingly found uranium up to 0.9 ppm in our dog food samples; in this study, we have found cat and dog food samples containing up to 1.7 ppm of uranium. Any of the heavy metals are of concern, so arsenic is a problem as well as any of the other heavy metals.

Did you see any significant changes since the first study? Have you changed your sample preparation or analysis method over time?

The levels of lead overall in the 2019 samples had decreased compared to 2009 from a maximum of 5.9 ppm to 0.5 ppm. Our sample preparation and analysis methods over the decade have change some with new advances in microwave and ICP-MS technologies. Our instruments are more sensitive, and see smaller amounts with the ability to filter out interferences, which in turn increases accuracy. 

The first study, as I recall, attracted a bit of attention. Did you get any significant pushback from it, such as from pet food manufacturers? Was there any response from any governmental bodies that regulate pet food? Do you expect any additional response from this study? Is there any further action that can be taken by consumers?

Yes, the first study did receive a lot of attention, both good and bad. I spoke with many pet food manufacturers at conferences, and while they would not publicly comment, many personally agreed with our findings. We also had the Royal Military College of Canada request our pet food samples to try analysis with a new type of instrumentation. We shared our samples, and, overall, their results corresponded with ours. Some of the governmental bodies, including the FDA, did have some feedback. I take these responses and any that may come from our current study as helpful criticism to create better studies in the future. Some requests from this current study was to bring back the wet food studies and include these new frozen or refrigerated pet foods.

Have you had any regulatory group or pet food supplier criticize your work on a scientific basis, such as critical errors, sampling issues, or assumption or calculations of calculated risk assessment guidelines?

There were a few points of contention from the FDA in our 2009 study, based upon how we chose to prepare samples and compare them to feeding amounts and regulatory limits. The criticisms focused around calculating for dry weight of wet food samples, and the amount we standardized to feed pets and using human limits for pets. They wanted us to use Association of American Feed Control Officials (AAFCO) feeding guidelines and studies on exposure of cows and sheep. So, in this study, we focused only on dry food, used pet food manufacturer feeding guidelines, but still kept the human reference dosage models.

What are your next steps in this work, if any?

We are not entirely finished with this work. There are a few outlier samples we want to test again, and we may expand the study to see if we can detect adulteration or over-addition of fillers to the pet food. It will depend on timing how much further we will delve into the topic, but I do hope there is some room for further analysis.

References

1.    P. Atkins, L. Ernyei, W. Driscoll, and R. Thomas, Spectroscopy 26(1), 46-68. (2011). http://www.spectroscopyonline.com/analysis-toxic-trace-metals-pet-foods-using-cryogenic-grinding-and-quantitation-icp-ms-part-i?id=&pageID=1&sk=&date=

2.    P. Atkins, L. Ernyei, W. Driscoll, R. Obenauf, and R. Thomas, Spectroscopy 26(2), 42–59 (2011). http://www.spectroscopyonline.com/analysis-toxic-trace-metals-pet-foods-using-cryogenic-grinding-and-quantitation-icp-ms-part-ii

Patricia Atkins is a Senior Application Scientist at Spex CertiPrep’s Certified Reference Material’s division. She spends her time researching industry trends and new reference materials. She is a frequent conference speaker and contributor to scientific journals and magazines on chemical and scientific topics. Atkins received her degrees from Rutgers University. Before joining Spex in 2008, Atkins was a chemist supervisor at Ciba Specialty Chemicals in the Water Treatment Division and a laboratory manager and researcher at Rutgers University in the Civil and Environmental Engineering Department where she was involved in air pollution research.