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Food Additives & Contaminants
ISSN: 0265-203X (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/tfac19
The release of nickel and other trace elements
from electric kettles and coffee machines
Torsten Berg , Annette Petersen , Gitte Alsing Pedersen , Jan Petersen &
Charlotte Madsen
To cite this article: Torsten Berg , Annette Petersen , Gitte Alsing Pedersen , Jan Petersen &
Charlotte Madsen (2000) The release of nickel and other trace elements from electric kettles and
coffee machines, Food Additives & Contaminants, 17:3, 189-196, DOI: 10.1080/026520300283441
To link to this article: https://doi.org/10.1080/026520300283441
Published online: 10 Nov 2010.
Submit your article to this journal
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Citing articles: 21 View citing articles
The release of nickel and other trace elements from electric
kettles and coŒee machines
To rst en B erg{*, Annette Petersen{, Gitte A lsing
Pe dersen{, Jan P ete rsen{a nd C harlo tt e Madsen {
{Danish V eterinary and Food Adm inistration , Mù rkh ù j Bygad e 19,
DK-286 0 S ù borg, D enm ark; {Odense Regional L aborat ory , L ille
T ornbje rgve j 24 , DK-52 20 O den se S é , Denm ark
(R eceived 14 M ay 1999; revised 20 A ugust 1999; accepted 30
November 1999 )
T he release of nickel, chrom ium an d lead from electric
kettles to water under conditions simulating regular
house hold use was i nvestig ated. T en out o f 26 k ettles
sold on the Danish market released more than 50 ·g/l
nick el to water, whereas neither lead nor chrom ium was
released in any signi®can t am ount . Fifty ·g/l of nickel
in water was chosen as the threshold of action, because
concentrations below this value were considered un-
likely to provide outbreaks of eczem a f or thos e con-
sum ers su ering from contac t allergy to nickel, who are
also sensitiv e to the conten t of nickel in the diet. T his
®rst part of the study was f ollow ed up by a dialogue
between th e kettle producer s and the Danish auth-
oritie s, leading to a change of construction or design
for those kettles that did not com ply with the criteria.
As a f ollow -up study another ten kettles were studied to
check whether complianc e was improved . T wo of these
ten k ettles still released more than 50 ·g/l nickel to
water unde r the test conditions . T hese two kettles,
howe ver, were subsequently withdrawn f rom the mar-
ket . Co ee machines tested similarly did not release
alum inium , lead, chro mium or nickel in quantitie s of
any signi®cance.
Ke yw ords : nickel (Ni) , chromium (Cr), lead (Pb),
aluminium (Al), electric kettles, co ee machines
Introd uction
In general , nickel is not a particularl y toxic trace
element (Nielsen 1977 ). Some consumers, however,
already su ering from contact allergy to nickel may
get systemic reactions, e.g. eczema, from ingestion of
fairly small amounts of nickel from foodstu s rich in
nickel, or from food and drink contaminated by food
contact materials which release nickel. Nickel allergy
may arise when the skin remains in contact with
nickel-containing items such as jewellery or buttons,
but does not arise from ingestion of nickel com-
pounds (Christensen and Mù ller 1975 , Veien and
Menne
Â1990 , Bertram 1992 , Nielsen and Menne
Â
1992, Menne
Âet al. 1994) . An estimate d 10±15% of
the populatio n su ers f rom nickel allergy , 10% of
which may be sensitive to the content of nickel in the
diet (Veien et al. 1 993) .
There is no Joint FAO/WHO Expert C ommittee on
Food Additives and Contaminants (JECFA) evalua-
tion of the toxicity of nickel, but the World Health
Organizatio n (WHO) has laid down a Tolerable Daily
Intak e (TDI) of 0.005 mg/kg bodyweight f or the
intak e from drinking water. This has led to a guide-
line level of 20 mg/l for drinking water (WHO 1993) .
The European Union (EU) directive on drinking
water in f orce has a limit of 50 mg/l for nickel in
drinking water (EEC 1980) based upon considera-
tions other than nickel allergy. It has recently been
decided that this limit will be reduced to 20 mg/l in
2002 (EU 1998). Moreover , the EU f ramework direc-
tive on materials and articles intended to come in
contact with foodstu s states that such materials and
articles may not under normal or foreseeabl e con-
ditions of use transfer their constituent s to f oodstu s
in quantities which could endanger human health
(E EC 1 989) .
Nickel is a ubiquitou s element , and the average daily
intak e of nickel is approximate ly 200 mg (150 ±700 mg).
It comes from a numbe r of foodstu s, including
mainly cereal products , in particular bran , muesli
Food Add itiv es and C ont aminants , 20 00, V ol. 17 , No. 3, 1 89 ±196
* To who m corresponden ce sh ould b e a ddressed .
Food A dditiv es and C ontam inant s ISSN 0265±203X p rin t/IS SN 146 4±5122 online #200 0 Taylo r & Franci s Ltd
http ://w ww .tan df. co. uk/j ourna ls/tf /02652 03 X. html
and similar products, pulses, legumes and oilseeds,
including cocoa beans (National Food A gency 1990a,
1995, Codex 1995). Nuts, seeds, chocolate products
and bivalve molluscs may contain high concentra -
tions of nickel (Codex 1995). These product s should
not be consumed excessively by consumers sensitive
to nickel in the diet.
Foodstu s such as drinks that are often consumed in
large quantities are of particular interest, as they may
contribut e a fairly large single dose of nickel, even
though the concentration does not seem excessive.
Moreover, nickel dissolved in water is more bioavail-
able than nickel in f oods (Solomons et al. 1982,
Sunderman et al. 1989 , Nielsen et al. 1999). Further-
more, the release of nickel from f ood contac t
materials and articles may contribute to the daily
intake of nickel.
Because co ee machines and electric kettles are
widely used for the preparation of co ee, tea and
instant co ee, the question arose whether such kit-
chen utensils might leach metals to the ® nal product
in quantitie s that could endanger huma n health. The
present study was designe d to test co ee machines
and electric kettles sold in Denmark f or possible
release of lead, chromium and nickel under conditions
that simulated normal household use. For co ee
machines , the release of aluminium w as also deter-
mined. The choice of test conditions , including the use
of a standardized drinking water, is of special rele-
vanc e in Denmark, as the large majority of drinking
water used is ground water of considerable hardness,
due to the geological nature of the country.
Materials an d methods
Co ee machine s and electric kettles
In the ® rst part of th e study 26 di erent brands of
electric kettles and 15 brands of co ee machines
produced in Denmark and other European countries
were sampled by local food inspectors in production
or import facilities. The models sampled largely cov-
ered the Danish market in late 1994. Information
concerning the composition of the heating element
was obtained from producers or importers. A ll kettles
were tested for release of lead, chromium and nickel,
and the co ee machines were also tested for release of
aluminium.
The second part of the study focused on electric
kettles. Ten brands of kettles, including those that
released more than 50 mg/l nickel in the ® rst study and
remained available in 1996 were tested for nickel only.
All samples were new, and prior to testing they were
treated as described in the manufacturers’ directions
for use.
Extraction
Extracts were produced under conditions that simu-
late normal household use. As the composition of
drinking water in Denmark varies considerably, a
standardize d drinkin g water f or extractio n was pre-
pared by dissolving 50 mg/l sodium chloride and
50 mg/l calcium carbonate in de-ionized water, essen-
tially free from these ions. A ir was blown through the
solution until saturatio n and pH adjuste d to 6.6 using
carbon dioxide or air (Markussen 1996, personal
communication). This standardized drinkin g water
corresponds with respect to sodium, calcium and
chloride to a typical Danish drinkin g water sample.
If the standardized water was to be used af ter the day
of prep aratio n , pH w as re -adjust ed t o 6. 6 bef or e use.
The standardized drinking wate r was also used as a
blank throughout the experiments.
All extracts were produced by boiling 500 ml of the
standardize d drinking water in the kettle until auto -
matic switch o or until the co ee machine reservoir
was emptied. A fter cooling to room temperature ,
100 ml of this solution was transferred to a poly-
ethylene container which had been thoroughly rinsed
with nitric acid, and 2 ml of suprapu r nitric acid was
added. This extract was used for further analysis.
For each co ee machin e or electric kettle six extracts
were produced. The ® rst three were produced as
described, one after another, and the content of trace
elements in each of them was subsequently measured.
Then the co ee machine or the electric kettle was
descaled, i.e. calcareous deposits on the heating ele-
ment were removed, using either the method pre-
scribed by the producer, or by using a boiling 3%
(w/v) citric acid solution, which was left for 30 min.
For the co ee machines a similar descaling procedure
was applied. A f ter descaling, the following two ex-
tracts were discarded. The next three extracts (nos
4±6) were submitted to chemical analysis.
190 T . B erg et al.
Extracts 3 and 6 were used to decide whether the
co ee machine or electric kettles complied with the
acceptance criterion.
Methods of analysis
In the ® rst part of the study, the content of lead,
chromium and nickel in the extracts from electric
kettles was determined by graphite furnace atomic
absorptio n spectrophotometry (GF-AA S), using a
Perkin Elmer Zeeman 3030 instrument. Measure -
ments were performed in accordanc e with a standar d
method ( National Food Agency 1990b), using
platform atomization and appropriate chemical
modi® ers. In the second part of the study a Perkin
Elmer 1100 B instrument and deuterium background
correction was used, and a similar measuring routine
was applied.
Calibratio n was performed according to the method
of standard additions. A ll extracts were initially meas-
ured to establish the level of metal ions, and then a
certi® ed reference material was measured (see Quality
Assurance , below). Extracts were appropriately
diluted and standar d additions of 30 mg Ni/l, 20 mg
Cr/l and 30 mg Pb/l were made to the extracts. All
extracts were then determined, using a standar d curve
comprising the blank and the standard additions. The
standards were prepared using 1000 mg/l Titrisol p.a.
ampoules from Merck.
For the co ee machines the release of aluminium (Al),
and f or som e models also nickel (Ni) , chromium (Cr)
and lead (Pb), was determined by an ICP±MS Perkin
Elmer ELAN 5000 instrument. The analyses were
performed using a total-quant multi-element scanning
method.
Quality assurance
The accuracy of the analyses was assessed using
certi® ed reference materials , i.e. the reference waters
LL 1 and LL 2 f rom the Water Quality Institut e VKI
in Hù rsholm, Denmark. The reference materials were
measured several times in each analytical series.
Each series of analysis by GF-AAS comprised ten
samples, each determined twice by double injections,
and included one blank. The blanks were standard-
ized drinking water, as used f or the extractions, to
which suprapur nitric acid was added. The detection
limits, equivalent to three times the standard devi-
ation of the blanks, were 1 mg Ni/l, 0.5 mg Cr/l and
1mg Pb/l. The detection limit f or ICP±MS analysis of
aluminium was 5 mg A l/l.
If a kettle released more than 50 mg nickel/l, the
measurement was repeated . When con® rmed, a new
kettle of the same brand was sent to another labora-
tory f or an independent veri® cation of extraction and
analysis. In all cases the ® rst results were con® rmed.
Results and discuss ion
Co ee machine s
In 13 out of 15 co ee machines included in the study,
the heating elements were made of aluminium, and
they did release f rom 137 to 765 mg/l aluminium to the
third extract, and from 50 to 76 0 mg/l aluminium to
the sixth extract (table 1). These levels of aluminium
were considered not to contribute signi® cantly to the
daily intake of aluminium and not to constitute any
health hazard. In the two remaining co ee machines
the heating elements were made from copper or a
copper/stainless steel combination. No release of
aluminium from these two kettles could be detected .
Five co ee machines , including the two that did not
release aluminium, were tested for release of chro-
191Release of trac e elem ents from k ettles
T abl e 1. Re lease of a lum iniu m f rom co ee m achi nes
(·g/1)in 1994.
Heating element Extr act no. 3 Extract no. 6
Al uminium 137 63
Al uminium 212 100
Al uminium 211 190
Al uminium 198 108
Al uminium 196 421
Al uminium 337 80
Al uminium 279 400
Fib re glass and copper ± ±
Al uminium 303 139
Al uminium 281 199
Al uminium 765 760
Stainless s teel an d copper ± ±
Al uminium 368 50
Al uminium 312 226
Al uminium 346 235
±: Release of aluminium below detection limit of 5 mg/l.
mium and nickel, and two were tested for lead. The
results were all below the limit of determinatio n
except for one co ee machine which released 54 mg/l
nickel to extract number 6, i.e. after descaling.
The release of aluminium f rom co ee machines before
and after descaling was followed. Figure 1 shows the
release for two machines. The results generally show a
decrease before descaling. This may be explained by
the f ormation of deposits on the aluminium surf ace.
Just after descaling , a minor increase followed.
Electric kettles
The 26 electric kettles studied in the ® rst part of this
investigatio n were classi® ed according to the metals
of the heating elements. Ten had nickel-plated heating
elements made of copper and seven had chromium-
plated copper heating elements. Five had heating
elements of stainless steel, whereas the heating
elements were gold-plated for three kettles and
Te¯ on-coated for one.
Only one of the 26 electric kettles released chromium
(6. 7 mg/l) to extract number 3 to an extent which
exceeded the limit of detection of 0.5 mg/l. Two out
of 26 electric kettles released 1 and 5 mg/l lead,
respectively, to extract number 3, and the latter also
released 1 mg/l to extract number 6. None of the
remaining kettles released measurable amounts of
chromium or lead under the test conditions.
The release of chromium and lead f rom the electric
kettles studied is considered to be insigni® cant and
not to contribute to any substantial degree to the
intak e of chromium or lead from the diet.
The release of nickel f rom the 26 electric kettles to
extracts 3 and 6 is presented in table 2. All ten kettles
having nickel-plated heating elements released
measurable quantities of nickel to the standardized
water extracts, as did two out of seven kettles having
chromium-plated heating elements and one with a
stainless steel heating element. Those kettles that had
192 T . B erg et al.
Figure 1. Relative release of aluminium f rom co ee m achines in 1994 com pared to extract 1.
heating elements covered with gold (with one
exception discussed below) or Te¯ on released no
nickel, or only small and insigni® cant quantitie s of
nickel during the test.
For seven out of the ten electric kettles having nickel-
plate d heating elements made out of copper the
concentration of nickel found in extract number 3
exceeded 50 mg/l. A f ter descalin g a similar trend was
found , as seven out of ten kettles, though not quite
the same seven as before, again did not comply with
the criterion. The concentrations of nickel released
to the extract varied considerably from product to
product. The variation between kettles of di erent
brands may be caused by di erences in design and in
particular in technology applied f or nickel plating.
For the seven kettles having chromium-plated copper
heating elements, two released quantities of nickel in
excess of 50 mg/l, whereas ® ve released quantities close
to the limit of determination. Quite frequently
chromium plating on copper includes a nickel coating
of the copper as a ® rst step, which enables the sub-
sequent chromium plating to stick more e ciently to
the heating element. This technology may explain the
large release of nickel from some chromium-plated
heating elements.
One electric kettle with a gold-plated heating element
released nickel af ter descaling. The reason for this
unexpected ® nding was subsequently identi® edÐ a
small disk that formed part of the constructio n was
coate d with nickel. The design was then change d and
the disk replaced. The Te¯ on-coated aluminium heat-
ing element used in one electric kettl e did not release
any measurable amount of the elements being studied.
In general, electric kettles with heating elements made
of stainless steel did not release substantial quantities
of nickel when exposed to the test in this study. One
kettle, however, with a heating element of stainless
steel released nickel, probably due to the use of other
parts made of or coated by nickel or due to use of a
steel quality that could release nickel.
Following the conclusion of the ® rst part of this study
the Nationa l Veterinar y and Food A dministration
entered into a dialogue with the importers and pro-
ducers of the ten electric kettles that released nickel in
quantities exceeding 50 mg/l. These electric kettles
were found to release nickel to an extent that may
endanger human health by provoking an attack of
nickel eczema in consumers already having acquired
a nickel allergy and being sensitive to the content of
nickel in the diet. Whereas this criterion was consid-
ered fairly strict by some producers, arguing that
attack s of eczem a had only been provoked by sub-
stantially larger quantities in medical experiments
(Dubois 1995 , personal communication), it was gen-
erally accepted that nickel allergy was a widespread
and serious problem for Danish consumers. More-
over, it was considered that any changes in construc-
tion of these electric kettles that could remove the
possibility of such kettles being a risk f actor for
nickel-allergic consumers would be to the bene® t of
both consumers and industry. It was also generally
recognized that nickel ions in aqueous solution might
well be more easily bio-available than nickel in f ood
and hence more prone to cause attacks . The industry
therefore agreed to undertake construction changes to
eliminate the problem . The Danish authorities conse-
quently decided systematically to inform consumers
about the problem, including publishing names and
models of all the products studied, rather than using
193Release of trac e elem ents from k ettles
T abl e 2. Re lease of n icke l f ro m ele ctric k ettle s (mg/l)in
1994.
Heating element Extrac t no. 3 Extr act no. 6
Nickel-plated 268 522
102 297
212 152
23 25
129 88
167 77
182 381
19 63
84 35
13 44
Chromium-plated 154 187
110 154
2 1
3±
2±
2±
± ±
Stainless s teel 30 31
± ±
± ±
± ±
± ±
Gold plated ± ±
2 20
1±
Te¯ on coated aluminium ± ±
±: R elease of nickel below det ection limit o f 1 mg/l.
bans and withdrawal of the products (Berg et al.
1995) .
Criteria for acceptable nickel release
Several studies are published where patients with
chronic nickel eczema have been orally challenged
with nickel sulphate in capsules resulting in ¯ are-up
of symptoms ( reviewed in Veien and Menne
Â1990) .
Studies with low doses (400±600 mg nickel) have
showed con¯ icting results. These variation s may well
stem from the fact that: ( i) patients were not asked to
keep a diet low in nickel in the challenge and in the
placebo period, (ii) the possible nickel release from
electrical kettles used by the patients was unknow n
and (iii) in the study by Gawkrodge r et al. (1986) the
patients were asked to ingest the nickel prior to
breakfast. When nickel is ingested in w ater , af ter an
overnight fast, 30 min or 1 h prior to a meal of
scrambled eggs, peak nickel concentration in serum
is 13-fold higher than in cases when nickel-containing
water and scrambled eggs is ingested simultaneously
(Nielsen et al. 1999). If the nickel intake is not
standardized in relation to food intake substantial
variations may be expected.
Two studies have show n ¯ are-up of dermatitis after a
single oral dose of 600 mg nickel (Kaabe r et al. 1979,
Cronin et al. 1981) and one study af ter two weekly
doses of 500 mg nickel ( Jordan and King 1979).
According to the existing knowledge, 600 mg nickel is
the lowest adverse e ect level, i.e. the lowest dose
resulting in ¯ are-up of dermatitis in sensitive subjects.
The low e ect level is based on a single dose . It is
likely that nickel intake from water will be accumu-
lated , as the median nickel half-times found in the
Nielsen study was 19. 9±26.7 h (Nielsen et al. 1999) .
There is no established no-e ect level.
If a kettle releases 400 mg nickel/l boiled water, and
1.5 l water is consumed daily (the mean liquid intake
of an adult) , the total daily intake equals the low
e ect level of 600 mg. Hence there is a safety factor of
eight from the current EU limit f or nickel in drinking
water of 50 mg/l to the 400 mg/l. A s the low e ect level
is establishe d in the most sensitive humans , a safety
factor of eight is considered appropriate to adjust for
a possible cumulative e ect , and from e ect level to
no-e ect level. Fifty mg/l was therefore chosen as the
threshold of action.
Second part of the studyÐ the f ollow-up
Two years later the study concerning possible release
of nickel from electric kettles was repeated. This was
done to verify whether industry had changed the
kettles to comply with the release criterion estab-
lished. Ten brands of kettles were sampled , including
two that had been included in the previous study, and
eight with heating elements made of nickel-plated
copper or chromium-plated copper. In general, kettles
with heating elements made from stainless steel or
plate d with gold or Te¯ on were not sampled in this
part of the study as they were considered to comply
with the criterion based upon the experience f rom the
® rst part of the study.
The results show that eight of the ten electric kettles
sampled in this part of the study complied with the
criterion, seven of which had heating elements
made of chromium-plated coppe r and one out of
stainless steel. The two remaining had heating ele-
ments of respectively nickel-plated copper, and cop-
per coated with a nickel±chromiu m alloy and both
released nickel in quantities above 50 mg/l. A model,
which did not release nickel subsequently replaced
one of these, and marketing of the other w as dis-
continued.
The second part of the study was again followed up
by informatio n f rom the authorities to the consumers .
This was done because even if all electric kettles sold
on the Danish market could be considered harmless,
even for consumers su ering from nickel allergy and
sensitive to small quantities of nickel in the diet, there
would still for several years ahead remain electric
kettles in general household use, which did not com-
ply with the criterion established .
This part of the study included following the release
of nickel during 25 extractions af ter descaling, again
to simulate norma l household use. Two kettles with
nickel-plated heating elements releasing substantial
quantities of nickel in the ® rst extract af ter descaling
were studied. After 10±15 extractions, the release of
nickel dropped to less than 20% of the release in the
extract number 6, i.e. the third af ter descaling, see
® gure 2. Therefore, it is advisable that consumers do
not descale their kettles too frequently , and it is
recommended that water is boiled and discarded
several times after descaling prior to the use of the
kettle for food purposes.
194 T . B erg et al.
Com parison with other studies
Studies published on the release of chromium and
nickel from stainless steel kitchen utensils (Vrochte et
al. 1991 , Flint and Packirisam y 1995 , 1997 ) showed
that, in general and with the occasional exception of
the ® rst use of a utensil , insigni® cant quantitie s of
chromium and nickel were release d to the food f rom
utensils made of the grade of stainless steel that is
normally used f or such utensils .
One study focused on the release of nickel from nine
electric kettles ( Helmers 1998). Helmers found that
the release of nickel from nine electric kettles that had
not been descaled varied f rom the limit of detection to
55 mg/l, while the release after descaling varied from
170 to 640 mg/l. Moreover, Helmers showed that the
release decreased again after descaling to approach
the limit of detection of 5 mg/l af ter 100 extractions.
Our results are in accordance with both these ® nd-
ings.
Conclus ions
The study has shown that, during experiments
that simulate normal household practice in
Denmark, electric kettles with nickel-plated or chro-
mium-plated heating elements may release nickel to
water. The quantities released f rom some new kettles
and f rom some kettles after descaling may cause
problems for those consumers with nickel allergy
who are sensitive to nickel in the diet. For other
consumers the water boiled in electric kettles may
be an additional source of nickel, but not one posing
any health hazard.
Electric kettles with heating elements made of
stainless steel, or with elements e ciently coated by
gold or Te¯ on , did not release nickel in quantitie s of
any signi® cance , whereas kettles with elements of
nickel-plated copper and some of chromium-plated
copper did.
195Release of trac e elem ents from k ettles
Figure 2. Relative release of nickel f rom two di erent kettles com pare d to extract 3 after descaling .
The repeated study as well as subsequent inspections
by the municipal food inspection authorities showed
that electric kettles of the types that did release
substantial quantities of nickel were removed from
the market during 1996. The strategy applied by the
authorities to reduce the nickel exposure consisted
of dialogu e with the producers and importers of
electric kettles in order to make them use more
suitable materials in the kettle-manu facturing pro-
cess. At the same time the consumer s were informed
to be cautious. This had the desired e ect on the
market.
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