Contamination of Synthetic Minerals with Heavy Metals in Pet and Agricultural Feed

 The use of synthetic minerals in pet and agricultural feed has been a topic of concern due to potential contamination with heavy metals. Several studies and regulatory bodies have highlighted the presence of heavy metals in synthetic mineral supplements, raising alarms about their safety and long-term impact on animal health.

General Research –

Numerous studies have documented the contamination of synthetic minerals with heavy metals. For example, a study published in the Journal of Agricultural and Food Chemistry found that synthetic feed-grade zinc and copper supplements often contain significant levels of lead and cadmium. The study analyzed various samples and concluded that the manufacturing processes for these synthetic minerals frequently introduce heavy metals as contaminants.(1)


Regulatory Body Reports –

The European Food Safety Authority (EFSA) has reported on the presence of heavy metals in mineral supplements. In their assessments, EFSA noted that synthetic sources of minerals, such as those used in animal feed, often contain higher levels of contaminants like arsenic, lead, and mercury compared to natural sources. These findings are based on extensive testing and monitoring programs across the European Union.(2) The majority of synthetic supplements used in animal feed in the United States are sourced from Europe or China (or are Chinese supplements sold to Europe then purchased by American companies).


Manufacturing Processes –

The process of manufacturing synthetic minerals involves multiple chemical reactions and the use of reagents. These processes can introduce heavy metals and other impurities. A study by the United States Geological Survey (USGS) found that the reagents and catalysts used in the synthesis of minerals like iron, zinc, and manganese often contain heavy metals, despite purification.(3)

The primary source of raw materials for synthetic minerals is mining operations. These ores are naturally contaminated with heavy metals. Additionally, mining areas are frequently exposed to environmental pollutants, which can further introduce heavy metals into the raw materials. During extraction and refinement, chemical reagents and solvents are used to separate and purify the minerals. These chemicals can themselves be contaminated with heavy metals or can cause heavy metals to leach from the ores. A review article in Environmental Science & Technology highlighted that high-temperature smelting and roasting, used to extract metals from ores, can release heavy metals into the air and eventually deposit them back onto the minerals being processed in the form of dust and emissions.(4) The processes used to synthesize isolate minerals, such as precipitation and crystallization, can introduce impurities if the reagents or solvents used are contaminated with heavy metals. Catalysts and other chemical additives used during synthesis can contain trace amounts of heavy metals. Additionally, residues of heavy metals from previous batches can contaminate subsequent batches of synthetic minerals.

Inadequate regulatory oversight and quality control measures can further contribute to higher levels of contamination being overlooked or tolerated in the final products.


Regulatory Statements Regarding the “Typical Contamination” Levels of Isolate Minerals

The Association of American Feed Control Officials (AAFCO) provides a resource in its Official Publication (OP) with the page titled “Approximate Dilution Factors and Typical Contamination Levels of AAFCO-Defined Mineral Feed Ingredients.” This page clarifies extent of heavy metal contamination in synthetic minerals and the significant dilution required to mitigate their toxicity in animal feed.

The chart on this page offers a detailed overview of the typical heavy metal contamination levels for various minerals and the necessary dilution factors to ensure safety. It highlights the pervasive nature of heavy metal contamination in synthetic minerals. The need for extensive dilution stresses the significant contamination issue inherent in synthetic mineral production.(5)

Guidelines on Contaminant Levels in Mineral Feed Ingredients

The AAFCO OP also includes a chart titled “Official Guidelines Suggested for Contaminants In Individual Mineral Food Ingredients.” This chart provides guidelines on the maximum tolerance levels for various heavy metals in complete feed, helping to manage and control the risks associated with their presence.


The chart details the following aspects for each contaminant: (6)



Maximum Tolerance Level in Complete Feed (ppm)

Total Level of Group Permitted Without Labeling (collectively ppm)

Labeling Required Between Indicated Range (collectively ppm)

Use Prohibited at Levels Above (collectively ppm)






Avg amount consumed per kg* of body weight per day at that level

~0.004 mg

= ~0.05mg


= ~12mg

*based on 85 k factor – the suggested regulatory base of an “average” dog.


The accepted canine mercury toxicity threshold is <0.1 mg/kg of body weight. The fact that the “prohibited at levels above” threshold is set at 120x the toxicity level raises significant concerns. This large gap suggests that regulatory bodies may be allowing higher levels of mercury exposure before taking action. FOIA (Freedom of Information Act) documents indicate that there is a significant lack of oversight on heavy metals in feed, thus placing a heavy responsibility on manufacturers to self-regulate to ensure their products are safe.  When safety control is predominantly in the hands of manufacturers, the risk of negligence or lack of thorough testing increases. Companies that do not prioritize safety might cut corners, potentially leading to harmful products in the market.


Laboratory Analysis of Popular Dog Foods

In alignment with the AAFCO OP charts, a laboratory analysis of five popular dog food brands confirmed the AAFCO charts’ accuracy. The average iron content of the tested foods was 293 ppm, with one product showing an iron level of 1,200 ppm. Notably, this product also had a lead level more than double that of the other samples – as indicated in the AAFCO chart. The food with the highest manganese and zinc had the second highest lead level, while the one with the lowest copper and manganese had the lowest arsenic content. Again, both of these were in alignment with the “typical contamination” levels identified in the AAFCO OP.  These correlations highlight the concern that higher mineral concentrations likely indicate increased heavy metal contamination.

MSDS Report for Animal Feed Mineral Premix

The Material Safety Data Sheet (MSDS) for “Animal Feed Mineral Premix” references that the standard “complete and balanced premix” blend contains “some or all” of multiple minerals, each of which may be present at levels of 1-99% of the product. The blend is considered toxic and is sold with a skull and crossbones. This is likely largely due to the levels of copper, cobalt, manganese, and zinc which are noted by AAFCO to be “typically contaminated” with the high contamination of heavy metals.(7)


Statistical Data from HTMA Profiles

Statistical data on Hair Tissue Mineral Analysis (HTMA) profiles from ParsleyPet, which includes hundreds of dogs, has further confirmed the accuracy of these regulatory charts. The data shows that dogs consuming diets containing synthetic, isolate minerals have a higher risk of heavy metal toxicity compared to those consuming formulated diets without synthetic mineral supplements. Specific heavy metal toxicities align with minerals listed in the AAFCO “typical contamination” chart. For instance, dogs with elevated selenium levels are at a higher risk of mercury toxicity.* The AAFCO chart indicates that selenium is “typically contaminated” with 10-1,000 ppm of mercury, highlighting the critical need for careful monitoring and regulation of synthetic mineral supplements in pet food.

*Assuming normal thyroid function.


  1. Journal of Agricultural and Food Chemistry: Study on synthetic zinc and copper supplements and their heavy metal content.
  2. European Food Safety Authority (EFSA): Reports on heavy metal contamination in mineral supplements.
  3. United States Geological Survey (USGS): Research on the manufacturing processes of synthetic minerals and associated contaminants.
  4. Environmental Science & Technology: Review article on contamination pathways of heavy metals in synthetic minerals.
  5. AAFCO OP 2019, pg 306
  6. AAFCO OP 2019, pg 307
  7. chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/





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