Stainless Steel Leaches Nickel and Chromium into Meals Throughout Cooking (2013)

Stainless Steel Leaches Nickel and Chromium into Meals Throughout Cooking (2013)

J Agric Food Chem. Creator manuscript; accessible in PMC 2015 Jan 5.

Printed in final edited invent as:

PMCID: PMC4284091



Toxicological reviews existing that oral doses of nickel and chromium can trigger cutaneous adverse reactions akin to dermatitis. Additional dietary sources, akin to leaching from stainless metal cookware for the length of meals preparation, are no longer effectively characterized. This glimpse examined stainless metal grades, cooking time, repetitive cooking cycles, and a pair of kinds of tomato sauces for their results on nickel and chromium leaching. Trials incorporated three kinds of stainless steels and a stainless metal saucepan; cooking times of 2 to 20 hours, ten consecutive cooking cycles, and 4 industrial tomato sauces. After a simulated cooking course of, samples were analyzed by ICP-MS for Ni and Cr. After six hours of cooking, Ni and Cr concentrations in tomato sauce increased as a lot as 26- and 7-fold respectively, relying on the grade of stainless metal. Longer cooking periods resulted in extra will increase in metal leaching, where Ni concentrations increased 34 fold and Cr increased roughly 35 fold from sauces cooked without stainless metal. Cooking with contemporary stainless metal resulted in essentially the most attention-grabbing will increase. Steel leaching decreases with sequential cooking cycles and stabilized after the sixth cooking cycle, even though most valuable metal contributions to meals were aloof noticed. The tenth cooking cycle, resulted in a median of 88 μg of Ni and 86 μg of Cr leached per 126 g serving of tomato sauce. Stainless metal cookware would be an overpassed source of nickel and chromium, where the contribution will rely on stainless metal grade, cooking time, and cookware utilization.

Keywords: Chromium, Nickel, Stainless Steel, Contact Dermatitis, Allergic Sensitivity, Food Security


Over the final several a few years the occurrence of allergic contact dermatitis (ACD) has vastly increased (1, 2). Nickel and to a less extent chromium are regarded as as a frequent trigger of ACD. Each and each metals contemporary many numerous ability sources. Nickel is a model metal that happens naturally in soils, water, vegetation, and animals. Though Ni is known to be a must must the health of some species, it has no longer been proven to be a must must the health of different folks (3). There are no longer any known human enzymes or cofactors dependent on Ni for customary feature (4). With out reference to its unknown essentiality, other folks are uncovered to Ni via the diet. Meals high in nickel encompass peanuts, peas, oatmeal, and milk chocolate; 956, 699, 495, 871 μg/kg respectively (5). In 2001, the Tolerable Upper Intake Stage (UL) of Ni became lowered to 1,000 μg per day (6). Adults in the U.S. are estimated to ingest a median of 69 to 162 μg of Ni per day (7).

Toxicological reviews existing that a single oral dose of Ni as diminutive as 67 μg can trigger recurrence of ACD, flare up eczema, or lead to systemic dermatitis in other folks sensitive to nickel (8, 9). Evaluate hang proven the severity of dermatitis has a dose dependent relationship to oral doses of nickel (8). Approximately 10% of different folks are by systemic dermatitis from nickel exposures which is extra prevalent in ladies folk (9). Whereas there are some reviews on the delivery of nickel from stainless metal jewelry (10) there would possibly possibly be less facts accessible on diversified publicity routes akin to from cookware (2, 11, 12).

Address Ni, Cr can trigger ACD. A single oral dose of 2500 μg of Cr can trigger dermatitis in sensitized other folks (13). Humans are uncovered to Cr via meals and drinking water. Chromium stages in meals are most steadily estimated to be low, about 10–1300 μg/kg (14). Chromium concentrations in U.S. drinking waters range from 0.2–35 μg/L, and the US EPA has predicament a most contamination stage at 100 μg/L for drinking water (14). Low stages of Cr (III) are a need to hang for human health and metabolism of glucose, protein, and rotund; alternatively adverse results of oral Cr exposures, akin to dermatitis, are furthermore known (14). The contemporary each day consumption of chromium in the US inhabitants has been estimated at 76 μg while the US FDA instructed each day consumption is 120 μg Cr (14). It’s instructed that folk sensitive to metals decrease their publicity (8, 9, 15). On the other hand, an overpassed source of Cr would be leaching from stainless metal dilapidated for the length of cooking processes (1618).

Stainless steels are dilapidated in the meals and beverage commercial on account of their thermal conductivity and resistance to corrosion. Stainless metal grades 304 and 316 are essentially the most steadily dilapidated in the meals and beverage commercial (19). These SS grades differ by their chemical compositions of metals at the side of nickel and chromium. SS grade 304 accommodates roughly 18–20% mass half chromium, and eight–12% nickel, whereas SS grade 316 accumulate roughly 16–18% chromium, and 10–14% nickel; diversified metals would possibly per chance furthermore fluctuate all the method in which via the grades (20). Stainless steels most steadily withhold inform and prolonged contact with meals for the length of cooking and manufacturing processes.

Outdated study performed on the delivery of metals from stainless metal for the length of cooking procedures hang most steadily handiest examined one SS grade and of these reviews few diversified the meals or conditions (1518, 21). Often non-acidic meals were examined, akin to, dried fruits and traditional soups, or they examined non-meals matrices like single chemical ingredient acidic solution, (1518, 21). Acidic alternate options, like acetic acid, couldn’t be sufficiently a comparable to acidic meals which are serene of a complex array of chemistries. Whereas total, results recommend that Ni and Cr are leached from stainless metal into non-meals acidic alternate options and foodstuffs for the length of cooking processes (1518), the estimated Ni or Cr contribution from cookware to a serving of acidic meals is no longer effectively characterized. In addition, the reviews reached contradicting conclusions pertaining to the severity and significance of metal leaching and the components, akin to SS grade and cooking time, which make a contribution to metal leaching. Outcomes between reviews were furthermore highly inconsistent. This would possibly possibly well be on account of adaptations in experimental conditions akin to meals variety, cooking length, and diversified uncontrolled variables.

The targets of this glimpse were to quantify the amount of Ni and Cr leached from stainless steels actual into an trusty acidic meals, for the length of realistic simulated cooking procedures, and to identify contributing cooking conditions to metal leaching. In this glimpse, three stainless steels a comparable to these dilapidated in the meals commercial and cooking wares and a stainless metal cooking pot were examined in a bunch of systematic simulated cooking scenarios. Cooking scenarios were established to take a look at grade of stainless metal, cooking apparatus, cooking length, cooking cycles and tomato sauce producers for their results on metal leaching.


Reagents and Take a look at Offers

Plasma grade elemental customary alternate options from Alfa Aesar (Ward Hill, MA) and Fisher (Pittsburgh, PA) Optima grade concentrated nitric acid were dilapidated in all experiments. Three stainless metal Long-established Reference Offers (SRMs), NIST 121d, NIST 123c, and NIST 160b, from Nationwide Institute of Requirements and Expertise (Gaithersburg, MD) were dilapidated. The SRMs are a comparable in Ni and Cr mass half to stainless metal (SS) grades incessantly dilapidated in cookware; diversified constituents were furthermore nominally the a comparable, Desk 1. All SRMs were in chip invent and had the a comparable range of particle dimension and ground put. The stainless metal chips dilapidated in this glimpse had particle dimension ranging between 0.5 and 1.18mm millings. Subsamples were sparsely taken to carry out sure representativeness. Pure Ni pellets, Ni-131, from Atlantic Gear Engineers (Bergenfield, NJ) were dilapidated as a sure engage a watch on for Ni leaching. One commercially received grade 316 stainless metal saucepan became examined. The stainless metal saucepan became washed with water and cleansing soap ahead of use as instructed by the producer and then three extra 18M-Ohm-cm rinses were conducted. Four outmoded model commercially received tomato sauces (TS) were evaluated because the meals matrix (tomato sauce A–D) and were manufactured by diversified firms and at diversified manufacturing locations. The acidity of the tomato sauces examined ranged between 4.17–4.3 pH.

Desk 1


Steel materials uncovered to tomato sauce for the length of cooking processes.

SRM Description Stainless Steel Equivalent Grade Chemical Composition (% mass)
Ni Cr
NIST 121d 304 11.18 ± 0.21 17.50 ± 0.15
NIST 123c 304 11.34 ± 0.15 17.40 ± 0.15
NIST 160b 316 12.35 ± 0.22 18.37 ± 0.21
Ni-131 99.9
Saucepan* 316 10 – 14 16 – 18


Samples were digested the use of an Environmental Explicit AutoBlock (Charleston, SC). A Perkin Elmer (Norwalk, CT) Sciex Elan 6000 Inductively Coupled Plasma Mass Spectrometry (ICP-MS) with a Ryton spray chamber and Crossflow nebulizer with GemTips, and a PE AS91 auto sampler became dilapidated to investigate pattern extracts. ICP-MS parameters incorporated: nebulizer gas waft, 0.91L/min; twin detector mode; peristaltic pump charge, roughly 2.5mL/minute; PTFE tubing; 3 replicates, 1 learning/replicate, 30 sweeps/learning; pattern flush extend, 35s; read extend, 15s; wash extend, 45s. Quantitation became according to Ni60 and Cr52 with Ge74 dilapidated as an inner customary. To determine on instrument detection limits (IDLs) and the restrict of quantitation (LOQ), the bottom calibration customary that resulted in a signal to noise ratio larger than 3:1 became discovered for every metal. The bottom calibration customary became incessantly analyzed (n≥7), and a outmoded deviation became calculated for every metal. IDLs were sure by multiplying the resulting customary deviation estimates with the pupil t-charge akin to the top diploma of freedom and 99% self perception (22). The limits of quantitation (LOQ) for nickel and chromium were sure to be 0.085μg/L and nil.807μg/L respectively.

Sampling and Preparation

To simulate dwelling cooking scenarios, the next sampling course of became established. For every take a look at, 5g of tomato sauce became weighed into high density polyethylene digest tubes. Tomato sauce background samples contained no take a look at metal, while sure Ni leaching controls contained 1g of Ni pellets. All SS publicity samples contained 1g of stainless metal NIST chips, Desk 2. All samples were then cooked in the AutoBlock at 85°C. This temperature became maintained for the given experimental cook time for dinner. The TS became separated from the take a look at metal pattern via quantitative switch into neat digest tubes.

Desk 2


Cooking scenarios with materials dilapidated to take a look at experimental variable with Ni and Cr results in p.c leached from SRM.

Experimental Variable n SRM SS Grade Equivalent Cook Time (hours) Cooking Cycles Tomato Sauce Mean %Ni Leached Mean %Cr Leached
Stainless Steel Grade 5 NIST 121d 304 6 1 Sauce A 2.85% 1.32%
5 NIST 123c 304 6 1 Sauce A 5.10% 3.25%
5 NIST 160b 316 6 1 Sauce A 4.20% 2.61%
5 Ni-131 6 1 Sauce A 6.60%
5 Saucepan 316 20 1 Sauce A

Cooking Time 4 NIST 123c 304 2 1 Sauce A 4.26% 3.35%
4 NIST 123c 304 6 1 Sauce A 4.94% 3.71%
4 NIST 123c 304 20 1 Sauce A 6.59% 4.00%

Cooking Cycle 4 NIST 123c 304 6 1 Sauce A 5.10% 3.25%
4 NIST 123c 304 6 3 Sauce A 1.28% 1.11%
4 NIST 123c 304 6 6 Sauce A 0.48% 0.30%
4 NIST 123c 304 6 10 Sauce A 0.48% 0.34%

Tomato Sauce 5 NIST 123c 304 6 1 Sauce A 5.10% 3.25%
5 NIST 123c 304 6 1 Sauce B 5.08% 3.25%
5 NIST 123c 304 6 1 Sauce C 5.11% 3.16%
4 NIST 123c 304 6 1 Sauce D 4.62% 2.67%

A contemporary SS grade 316 saucepan became examined for metal leaching the use of ~751g of TS cooked for 20 hours. The sauce pan became positioned on a hotplate and became heated to 85°C, and the temperature became maintained for a cook time for dinner of 20 hours. This time level became chosen as an instance a realistic but high publicity disaster.

All TS samples were then homogenized and digested the use of an adapted US EPA skill 3050b. Temporarily, the TS samples were positioned into AutoBlock, 2 mL of nitric acid became added and left to react at room temperature overnight. An additional mL of nitric acid became added and the samples were heated to 85°C, most steadily for 12 hours. Samples were diluted to 10 mL with 18MΩ-cm water, vortexed, and filtered with PALL (Port Washington, NJ) 0.45μm polyvinylidene difluoride membrane filters. 0.25 mL of pattern extracts were blended with an inner customary solution of Ge, and diluted to 5 mL in 1% nitric acid. The samples were then analyzed by ICP-MS.

Every cooking disaster and examined situation are listed and outlined in Desk 2. Take a look at conditions encompass four stainless steels/take a look at metals and a cooking pot, four cooking times, ten cooking cycles, and 4 tomato sauces every in replicates of four to 5.

Optimistic Regulate

Optimistic engage a watch on (QC) samples were employed all the method in which via the glimpse, accounting for 30% of all samples analyzed. QC samples incorporated blanks, pre-digestion fortifications of nickel and chromium, persevering with calibration verifications (CCV) and licensed reference materials. A six level calibration with a regression coefficient of 0.998 or larger for both nickel and chromium became dilapidated in examining samples with ICP-MS. CCV requirements and instrument blanks were analyzed ahead of and submit sequence and at in any case every ten samples for the length of every sequence in bid to carry out sure instrumentation accuracy. The CCVs were 96 to 111% recovery, and all instrument blanks were below detection limits. Fortification samples ranged from 102–107% for Ni and 101–109% for Cr, Desk 3.

Desk 3

Optimistic Regulate results for Ni and C

Concentration (ug/L) Ni Mean %Restoration
Sample Form n Ni ± SD
Instrument Clean 16 BDL
Reagent Clean 16 BDL
10 ug/L Check Long-established 9 10.4 ± 0.572 96.0%
20 ug/L Check Long-established 5 21.2 ± 0.399 106%
Pre-digest Fortification 3 52.1 ± 1.01 104%
Concentration (ug/L) Cr Mean %Restoration
Sample Form n Cr ± SD
Instrument Clean 16 BDL
Reagent Clean 16 BDL
10 ug/L Check Long-established 8 9.64 ± 0.870 96.4%
20 ug/L Check Long-established 8 22.2 ± 0.566 111%
Pre-digest Fortification 3 52.3 ± 1.91 104%

Statistical Analysis

Differences in metal concentrations between experimental samples were evaluated for statistical significance the use of R (23). For customary facts, a one skill prognosis of variance (ANOVA) for pairwise a pair of comparability course of became performed. Generalized linear regression prognosis became conducted to discover if experimental variables were correlated with leaching. Regression coefficients and ANOVAs were regarded as as to be statistically most valuable at p≤0.05.


Grade of Stainless Steel

Four metal SRMs were examined, three are a comparable to stainless metal grades, one became a nickel metal, Desk 1. Tomato sauce samples, cooked in the absence of stainless metal, were discovered to hang on realistic 0.130 mg/kg Ni, and nil.200 mg/kg Cr. This agrees effectively with outdated reviews of Ni in tomatoes that ranged from 0.04 mg/kg to 1.21 mg/kg (24). Tomato sauce uncovered to Ni pellets for the length of the simulated cooking course of contained vastly increased concentrations of Ni than all diversified samples at 66.0 mg/kg. Tomato sauce cooked with NIST 123c contained 5.93 mg/kg Ni and 5.75 mg/kg Cr, Resolve 1A. After six hours of cooking TS with NIST123c there became a 26-fold amplify in Ni in contrast with the engage a watch on TS and an nearly 30-fold amplify in Cr. Tomato sauce cooked with NIST 160b resulted in 5.32 mg/kg Ni and 4.88 mg/kg Cr. Cooking tomato sauce with NIST160b resulted in a 24-fold and a 26-fold amplify in Ni and Cr over the engage a watch on TS. Tomato sauce samples cooked with NIST 121d were discovered to hang the smallest amount of Ni and Cr leached, averaging 3.34 mg/kg and 2.39 mg/kg respectively. Cooking TS for six hours with NIST121d resulted in a 15- and 12-fold amplify in Ni and Cr over the engage a watch on TS. There became a diminutive distinction between the final amount of Ni and Cr leached into tomato sauce between NIST 123c and 160b: alternatively, both were vastly increased than NIST121d. The contemporary percentage of Ni leached from the stainless steels for the length of the 6 hr experiments were 2.78, 4.13, and 5.04% for NIST 123c, 160b and 121d respectively. The contemporary Cr leached for the length of the 6 hr experiments became 1.37, 2.66 and 3.30% for NIST 123c, 160b, and 121d, Desk 2. All SS a comparable samples resulted in most valuable will increase in both Ni and Cr concentrations in TS for the length of simulated cooking scenarios.

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Steel Released from Stainless Steel into Tomato Sauce

(A) Nickel and chromium concentrations (mg/kg) in industrial tomato sauce cooked for six hours in the absence of stainless metal, with stainless metal SRMs, nickel pellets or a stainless metal saucepan (n=5).

(B) Nickel and chromium concentrations (mg/kg) in industrial tomato sauce cooked in the absence of stainless metal or with NIST 123c, the a comparable of 304 stainless metal (n=4). Two, six and twenty hour cooking times are proven. Also the predominant, third, sixth, and tenth cooking cycles (n=4) every proven.

(C) Nickel and chromium concentrations (mg/kg) in four commercially received tomatoes sauces (sauce A–D) cooked in absence of stainless metal (n=4), and with NIST 123C, the a comparable of SS grade 304 (n=5).

*Indicates statistical distinction at p=0.05 or less.

A twenty hour cook time for dinner became dilapidated while attempting out the SS grade 316 saucepan.

Cooking Time

Resolve 1B illustrates the results of cooking time on Ni and Cr leaching into tomato sauce. We discovered no most valuable will increase in metal leached between a two and 6 hr cooking time. On the other hand, after twenty hours of cooking, Ni concentrations reached 7.63 mg/kg, roughly a 95-fold amplify from TS cooked in the absence of stainless metal. Equally, after twenty hours of cooking, Cr concentrations averaged 7.06 mg/kg, nearly a 9-fold amplify from the engage a watch on TS. This records reveals that most valuable will increase in Ni and Cr leaching occur with increased cooking times.

Cooking Cycles

Ten cooking cycles were performed in bid to take a look at the results of repeated stainless metal utilization on metal leaching. All samples uncovered to SS for the length of cooking resulted in vastly increased concentrations of Ni and Cr in contrast with the engage a watch on TS no topic the selection of cooking cycles. Nickel and chromium concentrations were top in the predominant cooking cycle. Sequential cooking cycles resulted in lowered Ni and Cr notify; after three cooking cycles, samples contained 1.61mg/kg of Ni and 2.03 mg/kg of Cr. Whereas this represents about a 65% reduction in Ni from the predominant cook dinner cycle, it is aloof about a 20-fold amplify from unexposed tomato sauce. Equally, by the third cooking cycle Cr lowered about 35% from the predominant cooking cycle, but aloof became 2.5-fold above the unexposed tomato sauce. Steel contributions from the stainless metal perceived to succeed in a actual situation after 6 cooking cycles; there became no statistical distinction between the 6th and 10th cooking cycle for either Ni or Cr. Nonetheless, after the sixth cooking cycle, Ni and Cr contributions were aloof vastly above the engage a watch on TS. There became roughly an 8-fold amplify in Ni and 3-fold amplify in Cr noticed above the unexposed engage a watch on TS. Although the amount of metal leaching in the origin lowered with cooking cycles, most valuable amounts of both Ni and Cr continue to leach after a pair of cooking cycles and appear to succeed in a fixed situation.

Industrial Tomato Sauce (TS)

Four diversified commercially received tomato sauces were analyzed for their quit on metal leaching when cooked in the presence of NIST123c stainless metal. All tomato sauces had a comparable preliminary Ni and Cr concentrations when cooked in the absence of stainless metal, starting from 0.090–0.224 mg/kg Ni, and nil.200–0.275 mg/kg Cr. All four tomato sauces were discovered to hang a comparable results on the total amount of Ni and Cr leached. Mean Ni concentrations of tomato sauces cooked with stainless metal ranged from 5.86–6.14 mg/kg, and resulted in roughly 64- to 68-fold will increase in Ni in contrast with the engage a watch on TS. Mean Cr concentrations of TS cooked with stainless metal ranged from 4.87–5.96 mg/kg, and resulted in roughly 21-fold will increase in Cr in contrast with the unexposed TS. The four TS were no longer vastly diversified for either Ni or Cr. With a a comparable matrix and pH, as expected, all tomato sauces had a comparable results on metal leaching despite originating from diversified industrial tomato sauce manufacturing firms.

SS Saucepan

A two quart SS 316 grade saucepan, identical outdated of dwelling cookware, became dilapidated to in an instant estimate metal leaching into tomato sauce. The Ni focus in TS cooked in the saucepan increased to 3.84 mg/kg after a 20 hr cook time for dinner, Resolve 1A. This represents nominally a 50-fold amplify in Ni focus in TS cooked in the saucepan. Whereas less dramatic, Cr furthermore increased vastly in TS from 0.200mg/kg to 0.6mg/kg, nominally a 3-fold amplify when cooked in a SS saucepan.

After 20 hours of cooking, TS cooked with the a comparable SS SRM, NIST123c, had about twice the focus of Ni as that existing in TS cooked with the saucepan, Figures 1A and 1B. Likewise, Cr concentrations were decrease in saucepan (0.536 mg/kg) TS than when cooked with NIST123c (7.06 mg/kg). The sauce to ground put ratio became diversified between the 2. The ratio of tomato sauce to ground put of the saucepan fervent with the tomato sauce (roughly 486 cm2) became roughly 1:0.62. In distinction, the NIST stainless metal chips had a ground put of roughly 25.0 cm2, the tomato sauce to ground put ratio became 1:5. The distinction in ratio of sauce to ground areas between the saucepan and the NIST SS is about a component of 10.


Stainless Steels and Cooking Scenarios

We discovered that diversified SS grades hang diversified leaching properties in tomato sauce. The mass of Ni in stainless steels did no longer correlate with the amount leached. NIST 160b has a better Ni mass half than the diversified SS examined; alternatively, we noticed that it did no longer hang essentially the most attention-grabbing amount of Ni leached brooding about both Ni mass or %Ni leached, Desk 2. Extra illustration, is that NIST 121d and 123c hang a comparable Ni notify, however the amount of Ni and Cr leached became vastly diversified. NIST 123c leached about 56% extra Ni and 42% extra Cr than NIST 121d but both are a comparable to SS grade 304. Diversified constituents beyond Ni notify in SS make a contribution to Ni leaching. As an illustration, it has been reported that an increased chromium oxide layer on the ground of SS is known to hang maintaining properties against corrosion (19). A chromium oxide protection layer is in step with our findings, NIST160b has the top Cr notify and Ni notify, but does no longer hang the top nickel leaching, suggesting that Cr alone or with potentially diversified constituents reduces Ni leaching. No longer all SRM hang certified values for all parts, but for folk that were accessible for all three SS, (C, Cr, Mn, Ni, Cu and Mo) no single ingredient correlated with the Ni or Cr leaching inclinations noticed.

Longer cook dinner times in the predominant cooking cycle produced statistically increased Ni and Cr leaching concentrations at 20 hrs in step with findings for diversified metals and cookware. It has been demonstrated that Pb in glazed cookware and storage containers can leach with take a look at acidic alternate options and increased with length of contact (25). Seasoning of the samples, via a pair of cook dinner cycles diminished the amount of Ni and Cr leached, even though it did no longer put away with either. The reduction of metal leached in the later cooking cycles became no longer on account of less metal left in the topic topic, as handiest a truly diminutive percentage (

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