Number 52 February 1995
MAFF UK - Surveillance for pyrrolizidine alkaloids in honey
Index to MAFF UK Food Surveillance Information
Pyrrolizidine alkaloids (PAs) form a large group of natural toxicants which
occur in some plants of the families Boraginaceae, Compositae, Leguminosae and
Ranunculaceae. Some plant species of the genera Heliotropium (family
Boraginaceae) and Senecio (family Compositae) are found in the UK. PAs
have been shown to cause hepatic (liver) damage and hepatocellular cancer in
experimental animals. PAs have also been linked to veno-occlusive disease and
chronic hepatic damage in humans at high doses.
Humans may be exposed to PAs directly, for example by the ingestion of
herbal teas and herbal products. Humans may also be indirectly exposed to PAs
in foods, such as milk, from animals which have consumed PA-contaminated feed.
MAFF has previously instigated studies on the levels and types of PAs present in
herbal products and carried out surveillance for PAs in milk.
Concern has also been raised over the possibility of foraging bees making
honey from the nectar of tansy ragwort (Senecio jacobaea) which may
contain PAs. Therefore, MAFF has carried out a small survey to determine the
levels of PAs in UK honey produced by bees with access to ragwort. UK produced
honey represents about 10 percent of the total UK honey market.
This survey was designed to obtain samples of honey during the ragwort
flowering period. One hive was situated at each of three sites adjacent to
where ragwort was growing. A sample of honey was taken from unsealed combs
prior to the 1994 ragwort flowering season (1 sample) and at intervals during
the flowering season (12 samples). Eight farmgate samples were obtained from
small local producers to coincide with sampling from study hives. It was not
possible to establish the sites of hives of the farmgate producers, the time at
which these samples were bottled and whether the samples had been blended. In
addition, two samples of a dark, waxy honey were donated by a small independent
producer. This waxy honey was unpalatable and not suitable for blending with
In order to determine whether the bees had foraged on ragwort, analysis of
the pollen content of the honey samples was carried out on 12 out of 13 study
hive samples and all farmgate and donated samples (22 samples in total). The
samples found to contain ragwort pollen were further analysed for jacoline,
jacozine, jacobine, seneciphylline and senecionine, the five major PAs in
ragwort, at CSL Food Science Laboratory, Norwich. Two samples, which did not
contain ragwort pollen, were also analysed for PAs. The analysis for PAs is
particularly difficult because, for example, pure standards are not available.
However, a satisfactory method of analysis was developed at CSL Food Science
Laboratory during this project.
Eight honey samples (5 samples from study hives, 1 farmgate sample and 2
dark, waxy samples donated by a small honey producer) were found to contain
ragwort pollen. The percentage of pollen which originated from ragwort ranged
between 0.1 and 8.9. Ten samples of honey were analysed for PAs (6 study hive
samples, 2 farmgate, 2 dark, waxy honey) of which 8 were the samples containing
ragwort pollen. The results of this analysis are detailed in
PAs were detected in 6 of the 8 samples containing ragwort pollen, at total
concentrations ranging from 0.01 to 1.5 mg/kg. The 2 dark, waxy honey samples
contained the highest total alkaloid concentrations, at 0.4 and 1.5 mg/kg
respectively. Coincidentally, these dark, waxy honey samples were unpalatable
and unlikely to enter the food supply through blending with other honeys. PAs
were not present at detectable levels in the 2 samples which did not contain
ragwort pollen grains. PAs were not detected in any of the retail samples
obtained at the farmgate.
The presence of ragwort pollen grains in some samples indicates that bees
will visit ragwort flowers. The presence of ragwort pollen grains in honey was
usually associated with detectable levels of the PAs found in ragwort, but this
was not always the case.
Estimates of intake of total PAs from honey have been made by assuming the
maximum amount of honey consumed on any one occasion for adults (93g)1, schoolchildren (60g)2
and infants (32g)3 and are based on the highest
detected level of total PAs (0.06 mg/kg) which would be likely to enter the food
chain (see Table 2, below).
|Table 2: Estimates of maximum intakes of PAs derived from
ragwort from the maximum consumption on one occasion of edible honey containing
total PAs at the highest level detected during surveillance (0.06 mg/kg).|
Maximum honey consumption on any one occasion kg/person/day
Estimated intake of total PAs mg/ person /day
When considering comfrey, the Committee on the Toxicity of Chemicals in
Food, Consumer Products and the Environment (COT) concluded that there was
sufficient evidence linking the intake of comfrey to toxic effects in humans to
warrant recommending that people should not consume preparations of comfrey
which contain high levels of PAs. Comfrey tablets and capsules have been
voluntarily withdrawn from sale by the health food trade but comfrey leaves for
use in tea infusions are still available. Tea made from comfrey leaves contains
low levels of PAs. Small amounts of PAs from this source are unlikely to do any
harm. For the adult consumer, estimated daily intake of total PAs from the most
contaminated, edible honey (0.006 mg/person/day) was one tenth of that from one
cup of comfrey leaf tea infusion (0.06 mg/cup) and is no cause for concern.
Estimated total PA intakes from the honey for schoolchildren and infants were
less than for adults.
Little is known about the relative toxicities of PAs and their metabolism in
humans. A MAFF-funded project on this subject is currently in progress.
However, the data from this survey suggest that, compared with the ingestion of
PAs from comfrey leaf tea, PA consumption from locally produced honeys is not a
cause for concern, even when hives are situated near to ragwort plants. Indeed,
the honey samples with the highest levels of PAs were coincidentally dark, waxy,
unpalatable and unsuitable for retailing or blending with other honeys.
- Gregory, J. Foster, K., Tyler, H. & Wiseman, M.
(1990). The Dietary and Nutritional Survey of British Adults. (HMSO).
- Report on Health and Social Subjects, No. 36: The
Diets of British Schoolchildren. (HMSO).
- Mills, A. & Tyler, H. (1992). Food and Nutrient
Intakes of British Infants Aged 6-12 months. (HMSO).
Further information can be obtained from:
Mrs Chelvi Leonard
Food Safety and Science Group
Food Contaminants Division
Ergon House, c/o Nobel House
17 Smith Square
London SW1P 3JR
Tel: +44 (0) 171 238 5734
Fax: +44 (0) 171 238 6591
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