Overview
Hobbie, Kamerud, and Anderson presented a Society of Toxicology 2014 poster examining how stainless-steel grade, cooking time, and repetitive cooking cycles affect nickel and chromium leaching from cookware into tomato sauce. Using three NIST stainless-steel reference materials, a high-purity nickel SRM, and a commercial grade-316 saucepan, the authors cooked four commercial tomato sauces under simulated home-cooking conditions and quantified nickel (Ni) and chromium (Cr) in the finished sauce by ICP-MS. After six hours of cooking, Ni and Cr concentrations in tomato sauce rose up to 26-fold and 7-fold respectively versus sauce cooked without stainless steel; at 20 hours the increases reached approximately 34-fold for Ni and 35-fold for Cr. Leaching declined with sequential cooking cycles but did not eliminate; by the tenth cycle a single 126 g serving still contributed an average of 88 µg Ni and 86 µg Cr.
Key numbers
| Finding | Source-reported value |
|---|---|
| Stainless-steel materials tested | NIST 121d (grade-304 equivalent, Cr 17.50%, Ni 11.18%); NIST 123c (grade-304 equivalent, Cr 17.40%, Ni 11.34%); NIST 160b (grade-316 equivalent, Cr 18.34%, Ni 12.35%); NI-131 (Ni 99.9%); commercial grade-316 saucepan (Cr 16-18%, Ni 10-14%, range from Atlas Steel 2000) |
| Cooking trials covered | three stainless-steel grades, one commercial grade-316 saucepan, cooking times of 2-20 h, ten consecutive cooking cycles, and four commercial tomato sauces |
| Replicates | n=4 (cooking-time and cooking-cycle trials with NIST 123c); n=5 (stainless-steel-grade and commercial-tomato-sauce trials) |
| nickel (Ni) fold-increase after 6 h cooking | up to 26-fold over sauce cooked without stainless steel (grade-dependent) |
| chromium (Cr) fold-increase after 6 h cooking | up to 7-fold over sauce cooked without stainless steel (grade-dependent) |
| nickel (Ni) fold-increase after 20 h cooking | approximately 34-fold over no-stainless-steel control |
| chromium (Cr) fold-increase after 20 h cooking | approximately 35-fold over no-stainless-steel control |
| Tenth-cycle nickel (Ni) contribution per 126 g tomato-sauce serving | average 88 µg Ni |
| Tenth-cycle chromium (Cr) contribution per 126 g tomato-sauce serving | average 86 µg Cr |
| Seasoning effect | leaching decreased with sequential cooking cycles and stabilized after the sixth cycle, though significant contributions persisted |
| Commercial-sauce variation | the four commercial tomato sauces did not show significant differences in Ni or Cr leaching |
| Cited nickel (Ni) reference values | estimated U.S. adult daily intake 162 µg/day (ATSDR 2005); Tolerable Upper Intake Level 1000 µg/day (Trumbo et al. 2001) |
| Cited chromium (Cr) reference values | adequate-intake level 45 µg/day (ATSDR 2012); lowest dose reported to cause allergic contact dermatitis 2500 µg/day (Veien et al. 1983) |
Methods (brief)
Sample preparation followed EPA Method 3050 acid digestion with 3 mL HNO3 and heat in the absence of nitrogen oxides; the authors used 1 g metal, 3 g sauce per cook, with cook process and sauce-separation steps. Finished tomato sauce was analyzed for Ni and Cr by ICP-MS. The poster reports replicate sample structure (n=4 for cooking-time and cooking-cycle trials with NIST 123c; n=5 for stainless-steel-grade comparisons and commercial-sauce comparisons). The poster does not disclose ICP-MS instrument model, LOD/LOQ, blank handling, certified reference materials for QA recovery, or full digestion-blank treatment. Cooking-time conditions were 2 h, 6 h, and 20 h; cooking-cycle conditions were the 1st, 3rd, 6th, and 10th sequential cooks of the same stainless-steel material in fresh sauce. The “saucepan” reference values for the commercial grade-316 saucepan Ni and Cr mass fractions were taken from Atlas Steel 2000 rather than measured directly.
The “no stainless steel” baseline values for the four commercial tomato sauces are reported as the sauces without any added stainless-steel material, providing the leaching-versus-baseline contrast. Cr is total chromium by ICP-MS; the poster does not speciate hexavalent chromium (Cr-VI) from Cr-III.
Implications
This source documents stainless-steel cookware as a quantitatively non-trivial dietary contributor of nickel and chromium during home cooking of acidic foods, especially tomato-based sauces and especially during long simmer times. The 88 µg Ni and 86 µg Cr per 126 g serving at the tenth cooking cycle are large fractions of the cited reference intakes (Ni daily intake estimate 162 µg/day; Cr adequate-intake level 45 µg/day), and the magnitude depends on stainless-steel grade, cooking duration, and how many prior cooks the cookware has seen. For product-contact pages, this is direct migration evidence from a cookware-grade alloy into a finished food matrix and is routeable to cookware-metal-alloy and tomato-sauce.
Because the source is a conference poster with limited methods detail and no peer-reviewed publication referenced on the poster face, the values should be carried as B-tier conference-abstract evidence and corroborated against the peer-reviewed literature on stainless-steel-to-acidic-food metal migration before they drive any threshold synthesis.
Related evidence
- Metal and alloy cookware (cast iron, stainless steel, aluminum)
- Tomato Sauce — REDIRECT (Cat 7 sub-variant of Canned foods, general)
- Tomato
- Nickel
- Chromium
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