Stainless steel leaches nickel and chromium into foods during cooking

Abstract

Toxicological studies show that oral doses of nickel and chromium can cause cutaneous adverse reactions such as dermatitis. Additional dietary sources, such as leaching from stainless steel cookware during food preparation, are not well characterized. This study examined stainless steel grades, cooking time, repetitive cooking cycles, and multiple types of tomato sauces for their effects on nickel and chromium leaching. Trials included three types of stainless steels and a stainless steel saucepan, cooking times of 2-20 h, 10 consecutive cooking cycles, and four commercial tomato sauces. After a simulated cooking process, samples were analyzed by ICP-MS for Ni and Cr. After 6 h of cooking, Ni and Cr concentrations in tomato sauce increased up to 26- and 7-fold, respectively, depending on the grade of stainless steel. Longer cooking durations resulted in additional increases in metal leaching, where Ni concentrations increased 34-fold and Cr increased approximately 35-fold from sauces cooked without stainless steel. Cooking with new stainless steel resulted in the largest increases. Metal leaching decreases with sequential cooking cycles and stabilized after the sixth cooking cycle, although significant metal contributions to foods were still observed. The tenth cooking cycle resulted in an average of 88 μg of Ni and 86 μg of Cr leached per 126 g serving of tomato sauce. Stainless steel cookware can be an overlooked source of nickel and chromium, where the contribution is dependent on stainless steel grade, cooking time, and cookware usage.

Figure 1. Metal Released from Stainless Steel into Tomato Sauce

(A) Nickel and chromium concentrations (mg/kg) in commercial tomato sauce cooked for six hours in the absence of stainless steel, with stainless steel SRMs, nickel pellets or a stainless steel saucepan (n=5). (B) Nickel and chromium concentrations (mg/kg) in commercial tomato sauce cooked in the absence of stainless steel or with NIST 123c, the equivalent of 304 stainless steel (n=4). Two, six and twenty hour cooking times are shown. Also the first, third, sixth, and tenth cooking cycles (n=4) each shown. (C) Nickel and chromium concentrations (mg/kg) in four commercially obtained tomatoes sauces (sauce A–D) cooked in absence of stainless steel (n=4), and with NIST 123C, the equivalent of SS grade 304 (n=5). *Indicates statistical difference at p=0.05 or less. **A twenty hour cook time was used while testing the SS grade 316 saucepan.

Figure 2. Total Daily Intake for Ni and Cr and Potential Contributions from Cooking Scenarios

Potential (A) nickel (μg) and (B) chromium (μg) from one serving (126 g) of tomato sauce from various cooking scenarios in addition to estimated maximum daily nickel intakes for U.S. adults (162 μg/day) (7) and adequate chromium intake level of a healthy individual, 45 μg/day (14). Nickel levels are compared with the Tolerable Upper Intake Level (UL) (1000 μg/day) (6) and chromium levels are compared with the lowest dose known to cause ACD, 2500 μg/day (13).