Number 122 August 1997
MAFF UK - SURVEY OF LEAD AND TIN IN CANNED FRUITS AND VEGETABLES
Index to MAFF UK Food Surveillance Information
Sheets, 1997
See also:
146: MAFF UK - Concentrations of
Metals and Other Elements in Selected Snack and Convenience Foods (March
1998)
149: MAFF UK - 1994 Total Diet
Study (Part 2) Dietary Intakes of Metals and Other Elements (May 1998)
150: MAFF UK - Metals and Other
Elements in Cows' Milk and Vegetables Produced Near Industrial Sites
(May 1998)
151: MAFF UK - Concentrations of
Metals and Other Elements in Marine Fish and Shellfish (May 1998)
152: MAFF UK - Summaries of Food
Surveillance Papers - 'Lead, Arsenic and Other Metals in Food' and
'Cadmium, Mercury and Other Metals in Food' (June 1998)
155: MAFF UK - Lead in Dried
Fruit (August 1998)
166: MAFF UK - Metals and Other
Elements in Vegetarian Foods (November 1998)
179: MAFF UK - Tin in Canned Tomato
Products (June 1999)
182: MAFF UK - Tin in Canned
Pineapples (July 1999)
193: MAFF UK - Duplicate Diet
Study of Vegetarians - Dietary Exposures to 12 Metals and Other Elements
(January 2000)
Summary
A survey of lead and tin in canned fruits and vegetables was carried out
between August 1996 and February 1997 on behalf of the Ministry of
Agriculture, Fisheries and Food (MAFF) by Campden and Chorleywood Food
Research Association. The aim of this survey was to determine the
concentrations of lead and tin in a range of retail canned fruit and
vegetable foods on sale in retail outlets in the UK. Concentrations of
lead (mean 0.04 mg/kg, range <0.01 - 0.13 mg/kg) were similar to those
previously reported for these foods and below the statutory limit for lead
in all samples. Tin concentrations (mean 58 mg/kg, range 0.02 - 242 mg/kg)
were broadly similar to previous results and, in all but two samples of
gooseberries, below the statutory limit for tin. Relatively high levels of
tin, still below the statutory limit, were found in some samples of other
foods including asparagus, tomatoes, apricots and grapefruit. MAFF is
planning a further study of individual cans of the products found to have
higher tin contents in this study, to investigate the factors that
influence their tin contents. Composite samples were analysed and it is
not therefore possible to give results for individual branded samples.
Background
Lead
High levels of lead have, in the past, been found in canned foods, as a
result of the use of lead-containing solder to seal can seams. However,
since the 1980s this practice has been progressively phased out in the UK
and in much imported produce, in favour of sealing by welding or, for
certain foods, tin solder. This action was accompanied by a marked decline
in lead content of canned foods,1 and
canned foods now make only a minor contribution to overall dietary lead
intakes. Intakes of lead from consumption of canned vegetables, estimated
from the Total Diet Study (TDS), fell from 0.007 mg/day in 1982 to less
than 0.001 mg/day in 1991. The intake of lead from fruit products fell
from 0.005 mg/day to 0.001 mg/day over the same period. Samples from the
present survey were analysed for lead to provide current data to monitor
this trend.
The Lead in Food Regulations 1979,2
as amended, set a general limit for lead in foods of 1 mg/kg, with
specific limits for certain foods which are listed in the Schedule to the
Regulations. The Joint Food and Agriculture Organisation/World Health
Organisation Joint Expert Committee on Food Additives and Contaminants
(JECFA) has set a Provisional Tolerable Weekly Intake (PTWI) for lead of
0.025 mg/kg body weight.3 This
corresponds to approximately 0.21 mg/day for a 60 kg adult. The dietary
intake of lead estimated from the 1991 TDS was 0.028 mg/day, well below
the PTWI.4
Tin
Tin is present naturally in foods although the tin content is generally
below 1 mg/kg. The major dietary source of tin is canned foods, which
often contain higher concentrations of tin than the unprocessed food,
usually as a result of the dissolution of the tin coating of the can. The
Tin in Food Regulations 1992 set a maximum permissible tin content of
200 mg/kg in foods for sale in or import to the UK.5
Previous MAFF surveys of tin in canned foods have shown that the majority
of canned foods on sale in the UK comply with this limit, but with
typically a few percent of samples containing in excess of 200 mg/kg tin.1
JECFA has set a PTWI for inorganic tin of 14 mg/kg body weight, which
applies to chronic exposure. This is equivalent to 120 mg/day for a 60 kg
adult.6 Tin in canned foods is likely to
be present predominantly if not entirely in the inorganic form.
The most recent estimate of the dietary intake of tin from the typical
UK diet was reported in 1994, for analysis of samples from the 1991 UK
Total Diet Study.4 The estimated average
intake was 5.3 mg/day. Although still well below the PTWI, this value was
significantly higher than estimates for previous years (e.g. 2.0 mg/day in
1987 and 2.2 mg/day in 1985). The increase was mainly attributable to an
increase in the tin content of canned vegetables samples (93 mg/kg in 1991
compared with 26 mg/kg in 1987, and 24 mg/kg in 1985). Canned vegetables
contributed 66 per cent of the total tin intake in 1991, with fruit
products (including canned fruits) contributing a further 25 per cent. In
view of these results, the Food Advisory Committee recommended that
further work be undertaken to identify the foods and mechanisms
responsible for the apparent increase in the tin content of canned
vegetables.
Campden and Chorleywood Food Research Association were commissioned to
undertake this survey. Samples of a wide range of canned fruit and
vegetable products were purchased from retailers for analysis and these
are listed in Table 2. Foods were purchased from
retail outlets in the North, Midlands and South of England to identify any
regional variations in the concentrations of lead and tin present.
Method
Composite samples of each of 33 food types were analysed from three
regions (North, Midlands and South of England). One composite sample of
pasta sauce was also analysed. This brought the total number of samples to
100. The food types analysed are listed in Table 2.
Each composite sample consisted of up to eight different brands of the
same type of food.
To prepare each composite sample, the individual brands making up a food
type were blended separately then added together in equal weights and
blended further. Before blending each food was prepared following normal
domestic practices (e.g. brine was drained from canned vegetables, etc.),
but were not cooked. Analyses for lead and tin were carried out using
procedures accredited by the United Kingdom Accreditation Service (UKAS),
based on atomic absorption spectrophotometry by a flame method or, for
samples containing low levels of tin, by hydride generation. Limits of
determination of 0.01 mg/kg for lead and 0.05 mg/kg for tin were achieved.
All samples were analysed in duplicate and the results reported as the
means of duplicate analyses. Mean results were accepted only if the
individual results remained within the following tolerances from the mean
value: for lead, ±0.03 mg/kg; for tin, ±0.05 mg/kg (values below
5 mg/kg), ±5 mg/kg (values below 100 mg/kg) or ±5 per cent
(values over 100 mg/kg).
Results
The lead and tin concentrations in composite samples are summarised in
Table 2. Results are given for composite samples
from each region and as a mean over the three regions. There was no
significant regional variation in concentrations of lead and tin in foods
purchased from the North, Midlands and South of England.
Interpretation
Lead
The lead concentrations in all samples were below the appropriate
statutory limits. The mean lead content of canned vegetables was 0.02
mg/kg (range <0.01-0.05 mg/kg) and that of canned fruits 0.05 mg/kg
(range <0.01-0.13 mg/kg). These values are similar to previous data,
for example those from the 1991 TDS for canned vegetables (mean 0.02
mg/kg, range 0.01-0.04 mg/kg) and fruit products (which includes canned
fruits; mean 0.03 mg/kg, range 0.01-0.06 mg/kg).
Tin
The tin contents of two composite samples of gooseberries were over 200
mg/kg, so one or both of the two individual cans that made up each of
these samples will have exceeded the statutory limit. Some composite
samples of other foods, for example tomatoes, asparagus, apricots and
grapefruit, contained relatively high levels of tin (i.e. mean across all
three regions >100 mg/kg), though still below the limit. It is possible
that one or some of the individual cans making up these composite samples
could have exceeded the statutory limit. All these foods are known to be
relatively aggressive to tin and high values have been reported in
previous work.1 The overall spread of
results and the proportion of samples that exceed the statutory limit in
this survey is also similar to those found in 1983-87.1
The mean tin concentration in canned vegetables was 44 mg/kg (range
0.02-165 mg/kg). This is somewhat lower than the value of 93 mg/kg (range
23-218 mg/kg) found for canned vegetables in the 1991 TDS (and which
prompted this study), and is closer to values from earlier TDS. The mean
tin content for canned fruits in the present study was 67 mg/kg (range
7.6-242 mg/kg), higher than that found for fruit products in the 1991 TDS
(mean 32 mg/kg, range 7.6-86 mg/kg).
As the number and type of different foods sampled and their preparation
in this study were different from those from the TDS, it is not possible
to state with certainty whether the present results for tin reflect a
trend since 1991. A project to analyse samples from the 1994 TDS for tin
(and other elements) will be completed and reported this year and should
help to clarify whether the results from the 1991 TDS were anomalous. The
present study does however provide current data on the levels of tin in a
wide range of canned fruits and vegetables. MAFF is considering a further
study of individual cans of the products found to have higher tin contents
in this study, to elucidate further the factors that influence their tin
contents.
No significant differences were seen between the lead and tin contents
of fruits packed in juice compared with the same fruits packed in syrup.
Intakes of lead and tin
Dietary intakes of lead and tin by mean and high-level adult consumers
have been estimated, assuming that all canned fruits and canned vegetables
contain lead and tin at the highest levels reported for these foods in the
current study, and that all other foods contain lead and tin at the mean
levels found in the 1991 TDS. These estimates are shown in
Table 1. This scenario is very unlikely,
especially for long-term consumption, and therefore represents an extreme
worst-case estimate of intakes. Nevertheless, total dietary intakes of tin
estimated even on this basis, while higher than corresponding estimates
based on the 1991 TDS alone, remain well below the PTWI. Intakes of lead
do not differ significantly from those estimated from the 1991 TDS alone,
and again are well within the PTWI. Therefore the levels of lead and tin
found in this study do not represent a long-term risk to consumers.
Acute effects due to tin have been reported following consumption of
canned foods, especially acid fruit juices, with tin contents above 250
mg/kg. These effects are due to gastric irritation. Any such products on
sale in the UK would of be in breach of The Tin in Food Regulations
1992. All samples in the present study contained less than 250 mg/kg
tin, although as these are composite samples it is not possible to state
whether this value was exceeded in individual cans making up the composite
samples with the highest tin contents.
The results of this survey have been circulated to the Local Authorities
Co-ordinating Body on Trading Standards (LACOTS) for information. MAFF
will also be circulating this Information Sheet to trade, retail and
consumer groups on publication, and inviting their comments.
References
- Meah, M.N., Smart, G.A., Harrison, A.J.,
Sherlock, J.C. (1991). Lead and tin in canned foods: Results of the UK
survey 1983-1987. Food Additives and Contaminants, 8,
485.
- The Lead in Food Regulations 1979 (S.I.
[1979] No. 1254), as amended by The Lead in Food (Amendment)
Regulations 1985 (S.I. [1985] No. 912). HMSO.
- World Health Organisation (1993). Evaluation of
Certain Food Additives and Contaminants. Forty-First Report of the Joint
FAO/WHO Expert Committee on Food Additives. WHO Technical Report
Series No.837. WHO, Geneva.
- MAFF Food Safety Directorate (1994). Food
Surveillance Information Sheet Number 34: 1991 Total Diet Study.
- The Tin in Food Regulations 1992 (S.I.
[1992] No. 496). HMSO.
- World Health Organisation (1989). Evaluation of
Certain Food Additives and Contaminants. Thirty-Third Report of the
Joint FAO/WHO Expert Committee on Food Additives. WHO Technical
Report Series No. 776. WHO, Geneva
Contact Point
Further information can be obtained from:
Dr Patrick Miller
MAFF, Joint Food Safety and Standards Group
Food Contaminants Division
Room 238
Ergon House, c/o Nobel House
17 Smith Square
London, SW1P 3JR.
Tel: +44 (0)20 7238 5751
Fax: +44 (0)20 7238 5331
Return to Index to Surveillance Information Sheets, 1997 page
Go to top of page
These pages were last updated on July 31st 1997
