Number 71 July 1995
MAFF UK - DIOXINS IN FOOD - UK DIETARY INTAKES
Index to MAFF, UK Food Surveillance Information
Sheets, 1995
See also:
88: MAFF, UK - Dioxins in Human Milk
(May 1996)
89: MAFF, UK -
Polychlorinated Biphenyls in Food - UK Dietary Intakes (May 1996)
105: MAFF, UK: Dioxins and Polychlorinated
Biphenyls in Foods and Human Milk (June 1997)
106: MAFF, UK: Dioxins and Polychlorinated
Biphenyls in Fish Oil Dietary Supplements and Licensed Medicines (June 1997)
143: MAFF UK - Dioxins and PCBs in Cows'
Milk from the Bolsover Area Collected in October and November 1997 (March 1998)
145: MAFF UK - Dioxins and PCBs in Farmed
Trout in England and Wales (March 1998)
184: MAFF UK - Dioxins and PCBs in UK and
Imported Marine Fish (August 1999)
Summary
MAFF has recently carried out a survey of dioxins in Total Diet Study
samples collected in 1982 and 1992. Results show that dietary intakes of
dioxins by average and high level UK consumers have fallen substantially over
recent years, and are now considerably below the Tolerable Daily Intake for this
group of chemicals.
Background
'Dioxins' is the generic term given to polychlorinated dibenzo-p-dioxins
and dibenzofurans. Concern over dioxins arose initially because one particular
dioxin, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), was found to produce
clinical effects (chloracne) in workers exposed to it through industrial
accidents. It is also toxic to some species of laboratory animals. The other
dioxins which also contain chlorine at positions 2,3,7 and 8 of the molecule are
thought to be less toxic and concentrations of these compounds are multiplied by
a weighting factor reflecting their relative toxicities to give a total dioxins
content in terms of 'Toxic Equivalents' (TEQs).1
The vast majority of dioxins do not contain chlorine at positions 2, 3, 7 and 8
of the molecule and are thought to have no biological activity.
Dioxins are very persistent chemicals produced during various combustion and
incineration processes and are also unwanted by-products in the manufacture of
certain chemicals. As a result, dioxins are ubiquitous environmental
contaminants and are generally present at very low concentrations in all foods,
especially fatty foods and cows' milk.
Previous surveillance results for dioxins in a range of foods were published
in Food Surveillance Paper No. 31, 'Dioxins in Food'.2
These included the results for two sets of Total Diet Study (TDS) samples
collected in 1988. Each TDS food group consists of retail food products,
prepared as for consumption, then combined in amounts reflecting their relative
importance in the average UK diet and stored under controlled conditions so as
to be stable for many years.3,4
From these samples, the dietary intake of dioxins by the average UK consumer
was estimated to be 125 pg TEQ/person/day, the largest contribution being made
by animal products and other fatty foods. This estimate was based on a very
limited data set owing to the high cost of analysis for dioxins. A more
extensive survey has been undertaken to provide a more reliable estimate of
average UK dietary intakes of dioxins and to investigate trends in dioxins
intake over recent years.
In the current survey, TDS samples of eleven food groups from 24 locations
in the UK which had been collected in 1982 and 1992 were analysed for dioxins.
The eleven food groups included those foods expected to make the major
contribution to dietary intakes of dioxins. In addition, bread was analysed as
it is a staple item of most people's diet. For each food group, the material
analysed was a composite of samples from all locations included in the TDS in
that year. The average UK dietary intake of 125 pg TEQ/person/day estimated for
TDS samples collected in 1988 was based on a different set of food groups. It
included a contribution of 15 pg TEQ/person/day from fruit and vegetables. This
was a conservative estimate and the actual contribution of fruit, vegetable and
other non-fatty foods to total dioxins intake is likely to be low. For this
reason these food groups were not analysed in the current survey.
Results
Both sets of food samples were analysed in 1994/1995 by high resolution gas
chromatography-high resolution mass spectrometry at CSL Food Science Laboratory,
Norwich. The laboratory has participated in interlaboratory trials of
measurement of dioxins in human milk and human blood organised by the World
Health Organization and has recognised expertise in the analysis of foods for
dioxins.
The analysis of the very low concentrations of dioxins found in foods is
exceptionally demanding and involves a chain of steps, most of which have to
operate at the limit of performance. The coefficient of variation for the
analytical data is a measure of the difference that may be expected between
individual analyses of the same sample. This coefficient was difficult to
establish for most of the food groups because of the limited numbers of samples
analysed. Based on previous work, the coefficient of variation for milk was
approximately 10 percent.2 The coefficient for
other foods is likely to have been similar, as long as all of the important
congeners were detectable.
The concentrations (ng TEQ/kg on a fresh weight basis) of dioxins in each
sample are shown in Table 1. As expected,
dioxins were found in highest concentrations in fatty foods, whilst in bread
most congeners were present below the limit of detection (LOD). The average
intake of dioxins from each of the food groups was calculated by multiplying the
concentration of dioxins in that food group sample by the amount of that food
group eaten in a day by an average UK consumer for the relevant year. The types
and quantities of foods that make up the TDS groups are largely based on
household consumption data from the National Food Survey (NFS), supplemented by
import and trade statistics. For neither year was account taken of food
consumed outside the home. Total dietary intakes were obtained by summing the
contributions of all eleven food groups. The average UK dietary intakes were
estimated to be 240 pg TEQ/person/day in 1982 and 69 pg TEQ/person/day in 1992 (Table 1). These intakes were calculated assuming
that congeners present at concentrations below the LOD were present at the LOD.
These are therefore upper bound intakes and will tend to overestimate
the actual intakes.
The dietary intakes of dioxins have also been estimated for average and high
level (97.5th percentile) UK consumers using food consumption data from the
dietary and nutritional survey of British adults. 5
In this study all food eaten in a 7 day period by each of over 2000 adults was
recorded. Estimates of the intakes from food groups which were not analysed
have been included by assuming that each congener was present at the reporting
limit of 0.01 ng/kg. Using this method to calculate intakes, the estimated mean
UK dietary intake of dioxins has fallen from 250 pg TEQ/person/day in 1982 to 88
pg TEQ/person/day in 1992. High level intakes have also decreased considerably,
from 442 pg TEQ/person/day in 1982 to 156 pg TEQ/person/day in 1992 (Figure 1). The dietary and nutritional survey of
British adults included food consumed outside the home. This, plus the
contributions from food groups not analysed, will account for most of the
differences between the estimates generated by the two methods.
Interpretation
The estimated dietary intakes of dioxins by average and high level UK
consumers have fallen sharply over the decade 1982-1992 (Figure 1). A Tolerable Daily Intake (TDI) of 10
pg/kg body weight/day for 2,3,7,8-TCDD was recommended by an expert group
convened by the World Health Organization Regional Office for Europe in 19906. The UK Committee of Toxicity of Chemicals in Food,
Consumer Products and the Environment (COT) endorsed this TDI in 1992 and
recommended that it could be regarded as equivalent to an intake of 600 pg
TEQ/day for a 60 kg adult. Average and high level UK dietary intakes of dioxins
between 1982 and 1992 were considerably below this TDI. Thus there appears to
be no risk to human health from the levels of dioxins in the UK diet. It should
be noted that the COT is currently reviewing the most recent data on the
toxicity of dioxins, including that referred to in a draft report by the US
Environmental Protection Agency, and is considering whether it is necessary to
revise the TDI agreed in 1992. The estimated average UK dietary intake of
dioxins in 1992 is similar to estimates of 60 pg TEQ/person/day in the
Netherlands7 and 92 pg TEQ/person/day (lower
bound estimate) in Canada.8
In all food groups except bread and cereal products, the concentrations of
dioxins were lower in samples collected in 1992 than in samples collected in
1982. The small apparent increases in concentrations of dioxins in bread and
cereal products between 1982 and 1992 may have resulted from the degree of
uncertainty inherent in assigning a value to any congeners that were not present
at the LOD. The use of upper bound estimates may significantly
overestimate total dioxins concentrations in those samples where most congeners
are not present at the LOD. The concentrations of most congeners in the cereal
products samples from 1992 and in both bread samples were below the LOD.
Inspection of the data reveals that the relative contributions of the
various food groups to the estimated UK average dietary intakes of dioxins have
changed over the decade (Figure 2). The
contributions made by the fats and oils and the milk products groups have fallen
from 1982 to 1992, whilst those from the cereal products and the milk groups
have increased.
The composition of some of the food group samples will have been changed
between 1982 and 1992 to reflect changes in household consumption. This
provides an excellent basis for estimating dietary intakes but the samples do
not necessarily provide a quantitative comparison of environmental levels of
dioxins over this time. Analysis of the composite food groups shows that the
average fat content of many foods fell between 1982 and 1992. The total amount
of fat in that part of the average UK daily diet made up of the eleven food
groups fell from 92 g in 1982 to 72 g in 1992. As dioxins are primarily found
in fat, the fall in the fat content of the diet will have contributed to the
observed decrease in average dietary intakes. Other changes in dietary habits,
for example the increase in the proportion of dietary fat that is of vegetable
rather than animal origin, may also have contributed to the observed decrease in
dietary intakes, as animals can accumulate dioxins as a result of environmental
exposure whilst uptake of dioxins by plants is known to be low.
REFERENCES
- NATO/Committee on the Challenges of Modern Society
(1988) International Toxicity Equivalency Factor (I-TEF) method of risk
assessment for complex mixtures of dioxins and related compounds. Pilot study
on international information exchange on dioxins and related compounds. CCMS
Report Number 176, Environmental Protection Agency, Washington D.C.,
USA.
- Ministry of Agriculture, Fisheries and Food (1992)
Dioxins in Food. Food Surveillance Paper No. 31, HMSO, London.
- Peattie, M.E., Buss, D.H., Lindsay, D.G., and Smart,
G.A. (1983) Reorganisation of the British total diet study for monitoring food
constituents from 1981. Food Chem. Toxic. 21, 503-507.
- Ministry of Agriculture, Fisheries and Food (1994)
The British Diet: finding the facts. Food Surveillance Paper No. 40,
HMSO, London.
- Gregory, J., Foster, K., Tyler, H. and Wiseman, M.
(1990) Dietary and nutritional survey of British adults, HMSO, London.
- World Health Organization, Regional Office for Europe
(1991) Summary report. Consultation on Tolerable Daily Intake from food of
PCDDs and PCDFs. Bilthoven, Netherlands, 4-7 December 1990. EUR/ICP/PCS
030(S) 0369n, WHO Regional Office for Europe, Copenhagen.
- Theelen, R.M.C., Liem, A.K.D., Slob, W. and van
Wijnen, J.H. (1993) Intake of 2,3,7,8 chlorine substituted dioxins, furans, and
planar PCBs from food in the Netherlands: median and distribution. Chemosphere
27, 1625-1635.
- Birmingham, B., Thorpe, B., Frank, R., Clement, R.,
Tosine, H., Fleming, G., Ashman, J., Wheeler, J., Ripley, B.D. and Ryan, J.J.
(1989) Dietary intake of PCDD and PCDF from food in Ontario, Canada. Chemosphere
19, 507-512.
Contact point
For further information, please contact:
Mr Steven Wearne
Food Safety and Science Group
Food Contaminants
Division
Ministry of Agriculture, Fisheries and Food
Room 238, Ergon
House, c/o Nobel House
17 Smith Square
London SW1P 3JR
Tel: +44 (0) 171 238 6227
Fax: +44 (0) 171 238 5331
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