Kalicharan et al. 2025 — Heavy metal contamination in pet food, South Africa
Kalicharan and colleagues measured As, Cd, Co, Cu, Fe, Pb, Hg, Ni, and Zn in 31 commercially available extruded cat and dog food brands from the South African market, split between premium brands (n=14) and supermarket brands (n=17) and across protein formulation types (red meat, poultry, fish, meat medley). Analysis used ICP-OES for most metals and hydride generation AAS (HGAAS) for mercury, with microwave digestion. The study is classified C-tier for this wiki because the matrix is pet food rather than human food; however, the methodology is rigorous and the findings on protein-type-dependent metal accumulation have indirect relevance to the wiki’s ingredient and supply-chain scope.
Note on scope classification: This paper does not belong on HMT&C-scope product pages. It is ingested here as a methodological and supply-chain cross-reference only, not as direct evidence for human food occurrence data.
Key concentration data
Mean concentrations reported across all extruded dog food brands (mg/kg, as-is basis):
| Metal | Dog food (mean mg/kg) | Cat food (mean mg/kg) |
|---|---|---|
| As | 7.47 | 2.92 |
| Cd | 6.23 | 3.15 |
| Co | 4.01 | 2.44 |
| Ni | 16.72 | 4.26 |
| Pb | 3.99 | 7.24 |
| Hg | 0.47 | 0.16 |
| Cu | 35.59 | 38.08 |
| Fe | 529.53 | 389.14 |
| Zn | 25.25 | 195.12 |
Canine brands exceeded the applicable maximum tolerable limits (MTLs from FDA/NRC/FEDIAF) more frequently than feline brands. Red meat protein formulations contained the highest total heavy metal levels, followed by poultry, fish, and mixed-meat formulations — a protein-source-dependent pattern with direct parallels to human food ingredient risk (animal by-products, offal, and organ meats as metal accumulation sites).
Methodological relevance
The ICP-OES and HGAAS methods used are standard for multi-element food analysis. The microwave digestion protocol with concentrated nitric acid is essentially the same as used in human food heavy metal studies. The multi-element standard preparation from 1,000 ppm mono-element standards is consistent with ISO 17294-2 and US EPA Method 6020 approaches. This methodological consistency means the concentration values are directly comparable in kind (if not in matrix) with human food occurrence data reported by other sources in this wiki.
The finding that red meat formulations carry higher metal loads than poultry or fish formulations (except for mercury) is consistent with the known biology: large muscle and organ tissue in ruminants concentrates Cd, Pb, and As through longer bioaccumulation pathways than poultry.
Supply-chain cross-relevance
The study’s protein-type dependency is useful context for the wiki’s supply-chain section on animal-derived ingredients. Organ meats and animal by-products — which appear in some human food products as protein concentrates or flavor enhancers — are the same materials driving elevated metal levels in pet food here. The by-product-as-accumulation-site mechanism is the same regardless of the intended consumer species.
Limitations
This is a pet food study, not a human food study. The South African regulatory framework (and the MTLs cited from FDA/NRC/FEDIAF for pet food) differs from the regulatory frameworks applicable to human food. The n=31 sample is small. Brand-specific data are not reported (aggregate only), which is appropriate for this wiki’s brand-firewall rules.
Implications
Supply chain: relevant context for index discussion of animal by-product protein as a heavy metal accumulation site.
Testing: the ICP-OES + HGAAS dual-method approach is a well-validated reference for multi-element analysis in complex protein matrices.