The Release of Nickel
from Stainless Steel
into Cooked Foods
Kristin Kamerud¹ Kim Anderson²
College of Agricultural Sciences¹, Environmental and Molecular Toxicology²
Oregon State University
 Soils, plants, and animals
 5th most abundant element (by weight)
 84 mg/kg in crust
 15-20 µg/L in surface waters
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 Ubiquitous in environment
November 26th 2012
Nickel in the Environment
 Widely used in industry
 Production of stainless steel and other
nickel alloys
2
 Weathering of rocks/soil, volcanic
emissions, vegetation fires
 Combustion of fossil fuels, tobacco
smoke, industry and recycling
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 Natural and anthropogenic releases of
nickel
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Nickel in the Environment
3
Global Nickel Production
Nickel (Tons)
250000
200000
2009
150000
2010
100000
50000
0
Australia
Canada
Indonesia
Philippines
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300000
November 26th 2012
Global Nickel Mine Production
Russia
Total global nickel production:
1,550,000 tons
4
U.S. Geological Survey, Mineral Commodity Summaries, January 2011
 Not yet proven for humans
 Oral exposures through food and
drinking water
 Estimated Intakes: up to 900 µg/day
 Tolerable upper intake level (UL):
1000 µg/day
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 Essential for some species
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Pathways of Human Exposure
5
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November 26th 2012
Dietary Exposure to Nickel
6
Flyvholm, M.-A., G. D. Nielsen, et al. (1984). "Nickel content of food and estimation of dietary intake." Zeitschrift
für Lebensmitteluntersuchung und -Forschung A 179(6): 427-431.
• 0.09% of nickel metal
• Distribution targets
• Kidney, cardiovascular system, blood,
immune system
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• Absorption dependent on form of
nickel
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Nickel Toxicokinetics
• Metabolism not well understood
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 10% of population
 Allergic Contact Dermatitis (ACD)
 Oral doses of 3000µg
 Recommended to lower
Nickel intake
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 Nickel Sensitivity
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Effects of Nickel Exposure
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Kreciz, Beata. "Systemic Contact Dermatitis to Nickel Present in Cocoa
in 14-Year-Old Boy." Pediatric Dermatology 28.3 (2011): 335-36.
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 Commonly used in food and beverage
industry
 316, 304, 420
 Chromium oxide surface
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Stainless Steel Background
9
Stainless Steel
Grade
Chromium Mass
Fraction (%)
Nickel Mass
Fraction (%)
316
304
420
16-18
17-19
12-14
10-14
8-10.5
<0.6
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 Chemical composition Ni containing
stainless steels
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Stainless Steel Background
10
Atlas Steels. "Stainless Steel Grade Chart.“ SPECIALTY STEELS PRODUCT REFERENCE MANUAL.
Atlas Steels, n.d. Web.
Variables Tested:
 Grade of stainless steel
 Cooking time
 Cooking cycles (usage “seasoning”)
 Commercial tomato sauces
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 Is nickel released into foods?
 Is the amount significant?
 What factors contribute to nickel leaching?
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Research Questions:
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 Nickel released increases with cook time
 Nickel released is constant over multiple
cook cycles
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 Nickel released is inversely proportional to
grade of stainless steel
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Hypotheses:
 Nickel content is constant for multiple
commercial tomato sauces
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Identification
Number
Stainless
Steel Grade
Equivalence
316a
NIST 121d
316
17.50
11.18
316b
NIST 123c
316
17.40
11.34
304
NIST 160b
304
18.37
12.35
Nickel Pellet
NI-131
Saucepan

Chemical
Composition (mass
fraction %)
Cr
Ni
99.9
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Description
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Materials Used
316
Four commercially obtained tomato
sauces (pH 4.17-4.3)
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November 26th 2012
Study Design
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Sampling
Acid Digest
• EPA method
3050b
• 3mL HNOз
• Heat
• Absence of NO2
• Sample
preparation
• Data analysis
ICP-MS
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• 1g metal
• 5g sauce
• Cook process
• Sauce separated
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Methods
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 Tomato leave, oyster tissue, soils and
sediment matrices
 0.25g of each CRM was digest and analyzed
for 16 metals including Ni
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 Acid digest and ICP-MS analysis validated
with Certified Reference Materials
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Multi-Matrix Method Validation
 Conducted over three different days
 Replicates of three each day
 Quality Control Samples
 Pre-digest fortification
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 Average nickel % recovery: 91.3%
 %RSD: 1.35
 Average pre-digest sample fortification %
recovery: 103%
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 Precision & Accuracy
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Method Validation
 Limit of Quantification: 0.085µg/L

 n=7
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• Meet QC data quality objectives
Sample Type
Concentration (µg/L)
% Recovery
n Total
Instrument Blank
BDL
―
16
Reagent Blank
BDL
―
16
10µg/L Check Standard
10.4
±
0.572
96.0
9
20µg/L Check Standard
21.2
±
0.399
106
5
Pre-digest Fortification
52.1
±
1.01
104.2
3
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• Quality Control Samples
November 26th 2012
Quality Control Results
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5g of Tomato Sauce
1g 1g
NIST
316a
121d
(11.18% Ni)
1g1g
NIST
316b
123c
(11.34% Ni)
1g 1g
NIST
304
160b
(12.35% Ni)
1g NI
131
(99.9% Ni)
Blank
Tomato
Sauce
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November 26th 2012
Grade of Stainless Steel
Samples were refluxed at 85°C for six hours.
Tomato sauce then underwent acid digestion and analysis by ICP-MS.
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*
60
8
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Nickel Concentration (mg/kg)
70
6
*
4
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Stainless Steel Grade
2
*
0
Tomato
Sauce
SS 316b
SS 304
SS 316a
Stainless Steel Grade
n=5; samples deemed significant at p=<0.05
* Statistical difference between one or more samples
NI 131
20
*
Nickel Concentration (mg/kg)
70
 Results show 316b
and 304 equivalent
 Protective
properties of Cr
60
8
6
*
4
2
*
0
Tomato
Sauce
SS 316b
SS 304
SS 316a
Stainless Steel Grade
NI 131
November 26th 2012
 Expectations:
 316a and 316b
about equal
 304 high
response
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Discussion
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Chemical Composition
(mass fraction %)
Cr
Ni
Average Ni
Leached
(µg)
% Ni
Leached
316a
17.50
11.18
3.11
2.78
316b
17.40
11.34
5.71
5.04
304
18.37
12.35
5.1
4.13
Nickel Pellet
―
99.9
65.8
6.59
 Grade of stainless steel experimental
samples
 n=5
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Experimental
Tomato Sauce
Sample
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Percent Nickel Released
22
1g 1g
NIST
123c
316b
(11.34% Ni)
Blank
Tomato
Sauce
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5g of Tomato Sauce
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Cooking Time
Samples were refluxed at 85°C for two, six, or twenty hours.
Tomato sauce then underwent acid digestion and analysis by ICP-MS.
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*
8
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Ni Concentration (mg/kg)
10
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Cooking Time
6
4
2
0
Tomato Sauce
2 Hours
6 Hours
Cook Time (Hours)
n=4; samples deemed significant at p=<0.05
* Statistical difference between one or more samples
20 Hours
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1g1g
NIST
123c
316b
(11.34% Ni)
Blank
Tomato
Sauce
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5g of Tomato Sauce
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Cooking Cycles
Samples were refluxed at 85°C for six hours.
Tomato sauce was washed off, and replaced with fresh sauce.
Tomato sauce from the third, sixth, and tenth cooking cycle underwent acid
digestion and analysis by ICP-MS.
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November 26th 2012
*
6
4
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Nickel Concentration (mg/kg)
Cooking Cycles
*
2
0
Tomato 1st
Sauce Cycle
3rd
Cycle
6th
Cycle
Cooking Cycle
n=4; samples deemed significant at p=<0.05
* Statistical difference between one or more samples
10th
Cycle
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1g 1g
NIST
316b
123c
(11.34% Ni)
Blank
Tomato
Sauce 1-4
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5g of Tomato Sauce
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Commercial Tomato Sauces
Samples were refluxed at 85°C for six hours.
Tomato sauce then underwent acid digestion and analysis by ICP-MS.
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Commercial Tomato Sauce
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8.00
Tomato Sauce
Tomato Sauce & SRM 123c
6.00
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Nickel Concentration (mg/kg)
C.
4.00
0.25
*
0.00
Sauce A
Sauce B
Sauce C
Sauce D
Commercial Tomato Sauce
n=4; samples deemed significant at p=<0.05
* Statistical difference between one or more samples
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Grade 316
Stainless Steel
Saucepan
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571g of Tomato Sauce
November 26th 2012
Saucepan
Sauce was refluxed at 85°C for twenty hours.
5g aliquots were taken and underwent acid digestion and analysis by ICP-MS.
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Saucepan
Nickel Concentration (mg/kg)
70
60
8
6
4
*
*
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November 26th 2012
*
2
*
0
Tomato
Sauce
SS 316b
SS 304
SS 316a
Stainless Steel Grade
n=5; samples deemed significant at p=<0.05
* Statistical difference between one or more samples
** 20 hour cook time
NI 131
Saucepan **
(316)
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Grade 316:
 ~50% less nickel leached from saucepan
than 316b
 However, tomato sauce to stainless steel
surface area ratios different
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 Would have expected similar nickel
concentrations
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316b and Stainless Steel Saucepan
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Saucepan
 Avg. nickel released after
20h cook time:
7.63mg/kg
 Avg. nickel released after
20h cook time:
3.84mg/kg
 ~50% less than 316b
 Sauce : Stainless steel
ratio
 1:5
 Sauce : Stainless steel
ratio
 1:0.6
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316b
November 26th 2012
Surface Area
 Would expect a nearly a 10 fold difference,
but we observed only a 2 fold difference
 Stainless steels used a good surrogate for
cookware and cooking variable assessment
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Ni per Serving of Tomato Sauce
2000
Estimate Daily
Nickel Intakes3
Nickel (µg)
1600
1200
Daily UL2
800
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November 26th 2012
Nickel per Serving of Tomato Sauce
Contribution to Total Nickel Intake
400
0
Tomato
Sauce
Saucepan
(20 Hours)
20 Hours
Cooking Time
1st Cycle
10th Cycle
Cooking Cycles
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 Nickel is leached into tomato sauce
 316b and 304 showed no statistical
difference
 Protective properties of Cr
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 Hypothesis: Nickel released is inversely
proportional to grade of stainless steel
November 26th 2012
Conclusions
 316a statistically different than 316b and
304
 316b showed greatest response
 Dependent on chemical composition
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 Nickel increase with cook time
 Hypothesis: Nickel released is constant over
multiple cook cycles
 Nickel is still leaching after 10 cook cycles but the
amount is less than the early cook cycles
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 Hypothesis: Nickel released increases with
cook time
November 26th 2012
Conclusions
 Hypothesis: Nickel content is constant for
multiple commercial tomato sauces
 No significant difference were seen between
multiple commercial tomato sauces in their effect
on nickel leaching
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 Avoidance of stainless steel cookware
may decrease total nickel exposure
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 Stainless steel cookware contributes to
total nickel intakes
November 26th 2012
Conclusions
36
Kristin Kamerud
Kim Anderson, Ph.D.
 Kate Field, Dan Sudakin
 FSES
 Kevin Hobbie, Norman Forsberg
 Friends & Family

November 26th 2012
Acknowledgements
37
November 26th 2012
Kristin Kamerud
Thank you for your attention.
Any Questions?
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