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Source of this page: http://www.food.gov.uk/science/surveillance/fsis2001/bisphenols
4apr2006
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This survey was carried out in the UK , to see if there is leaching of the substances BPA and BPF into canned food. BPA (bisphenol A) and BPF (bisphenol F) are chemical components of resins used to coat some cans. BPF did not leach into food but BPA did. BPA was found in some canned foods (e.g. some vegetables but not infant formulae).
Independent scientists have advised the Agency that the levels of BPA found in this survey are unlikely to be of concern to health, and there is no reason for consumers to change their source of foodstuffs as a result of these findings. The Food Standards Agency is consulting consumer groups, industry, environmental organisations and others on methods of managing the scientific uncertainties about this substance.
This survey was carried out to establish whether migration of BPA or BPF occurs into retail samples of canned foods in the UK.
Food cans often have an internal polymeric coating to stop metal from the can corroding and migrating into the can's contents. The coating is applied to the component parts of the can which is then assembled and filled. The can and contents are then processed, usually by heating, to ensure that the canned food is not bacterially-contaminated.
Polymeric coatings used on the insides of cans are usually highly cross-linked, thermoset resins capable of withstanding processing conditions (typically 1.5 hours at 121°C for canned foods). Where food is heated in the can to ensure preservation, the most widely-used types of internal coating for cans are epoxyphenolic resins, PVC organosols and cross-linked polyester resins. Epoxyphenolic resins are the most important, being used widely for both can bodies and ends for 2- and 3-piece constructions, although more usually for shallow draw cans in the case of 2-piece products. Epoxy resins used for beverage can bodies are commonly modified so that the resins can be dispersed in water, rather than in organic solvents, before they are applied.
BPA is used to make most types of epoxy resins. These are cross-linked before being applied to the insides of cans. BPA is not generally used for cross-linking as this could lead to more migration. This substance may also be present in PVC organosol coatings, if they contain bisphenol A diglycidyl ether (BADGE) to scavenge for hydrogen chloride. There may be some unreacted BPA in the BADGE. But an excess of epichlorohydrin is reacted with BPA to produce BADGE. Indeed residual epichlorohydrin appears to be at most a minor contaminant of can coatings as a previous survey did not detect it in retail canned foods.1
BPA migrates from can coatings into food simulants.2 The amount of migration may increase if coated cans are heated under pressure.3 But migration from can coatings into simulants is not an exact guide as to whether there will be migration into food and drink and if so how much. For example BPA migrates from polycarbonate bottles into simulants, but when samples of feed for infants were tested in the UK there was no detectable migration from bottles.4
There is surprisingly little in the refereed scientific literature on BPA migration into canned food and drink. This substance has been reported at up to 0.033 mg per can in the liquid from cans of vegetables purchased in Spain and the USA, in some samples of canned tea or coffee and one of sake in Japan, in samples of infant formulae liquid concentrates in the USA and in samples of canned vegetables and fruit in Japan.3,5,6,7,8
BPF is also used to make epoxy resins, but the resins are rarely used in food contact materials. There may be some residues of BPF in Novolak glycidyl ethers which are used to scavenge for hydrogen chloride in some PVC organosol coatings. BPF is a mixture of three isomers (2,2'-, 2,4'-, and 4,4'-dihydroxydiphenylmethane). Extensive searches of the literature, carried out in reviewing the work reported below, found no evidence of work to test whether BPF isomers migrate from can coatings into food.
BPA is being reviewed under the EU Regulation on Existing Substances (793/93/EEC) for which, in the UK, the Health and Safety Executive is carrying out a health risk assessment. This includes reviewing human exposure to this substance via chemical migration into food and other routes. Other possible sources of human exposure to BPA include some wood varnish and fillers.
As BPA may migrate into food and its toxicological status is unclear, UK industry has been taking steps to find ways of reducing its migration and to find possible alternative substances. Given the role that coatings have in ensuring the microbiological and chemical safety of canned food, industry has been taking great care to ensure that reducing BPA levels or replacing it with another substance does not allow bacterial or metallic contamination of canned food.
Samples
The following canned products were analysed (Table 1):
Fifty-one of these samples were from the same retail batches of canned foods as those tested for BADGE and related substances in another survey.9 Samples were tested in both surveys to examine whether BPA and/or BPF were present with BADGE, BFDGE or their reaction products.
Three cans of each sample, all bearing the same batch number, were purchased from retail outlets in the south of England. The distribution of types of samples tested in this survey is similar across the UK. Collection of samples was weighted approximately 80 per cent from supermarkets and included about 40 per cent 'own brand' foods to approximately reflect consumer shopping habits.
Samples were stored sealed at room temperature. After cans were opened the total contents of each can were homogenised and an aliquot taken for analysis. The remaining contents of each can were then frozen and stored in a freezer.
Calibration materials
BPA (more than 99 per cent), and BPF isomers 2,2'-dihydroxydiphenylmethane (95 per cent) and 4, 4'-dihydroxydiphenylmethane (98 per cent) were obtained from Sigma-Aldrich. 2,4'-Dihydroxydiphenylmethane (97 per cent) was obtained from TCI, Japan. BPA-d16 (98 atom per cent D) was obtained from Sigma-Aldrich and converted to BPA-d14 by dissolution in aqueous sodium hydroxide and reprecipitation by acidifying with dilute sulphuric acid. This BPA-d14 was used as an internal standard.
Analytical methodology
Published methods for determining BPA in food were not considered suitable as the survey reported here was on a wide range of foodstuffs. No methodology was found in the literature for the determination of BPF in foods. Therefore, a method was developed to measure these analytes simultaneously using gas chromatography-mass spectroscopy (GC/MS), with deuterated BPA as an internal standard, in which BPA and the BPF isomers were acylated using acetic anhydride after isolation from the food.
The entire contents of a can were homogenised using a food mixer. Twenty grams (g) of sub-sample was taken and an aliquot of internal standard added. Each sample was blended with 20 ml n-heptane (for fat removal) and 20 ml acetonitrile. After filtering into a Buchner flask through a GF/C filter, the residue and heptane layer were returned to the sample jar for a further extraction with a fresh 20 ml of acetonitrile. The filtrate was treated with anhydrous sodium sulphate and decanted to a measuring cylinder. The second extraction was filtered and treated in the same way and combined with the first extract. For samples with a low fat content, for example vegetables, soup, desserts and pasta, heptane was omitted from the procedure above. The solution was evaporated under nitrogen to approximately 5 ml and then diluted to 50 ml with water. The sample was transferred to a 250 ml separating funnel for the derivatisation step. Ten ml of 72 per cent w/v potassium carbonate and 10 ml of methanol were added and swirled to mix. Ten ml of acetic anhydride was added and swirled gently after reaction had subsided. The solution was left to stand for 15 minutes with occasional swirling and then extracted with 5 ml n-heptane. The heptane layer was collected and analysed by GC-MS. For the analysis of infant formulae, 10 g formula were extracted with 20 ml of acetonitrile by shaking vigorously in a 40 ml vial for one minute. The layers were allowed to settle. The acetonitrile portion was then filtered through a GF/C filter. The residue was shaken with a further 10 ml of acetonitrile and filtered. The combined solutions were evaporated under nitrogen and derivatised as described above. For the analysis of beverages, the samples were opened and allowed to degas. 50 ml was measured into a 250 ml separating funnel and derivatised as described above.
Quantitative results were obtained using the GC-MS results by comparison against external standards prepared in water and derivatised as before. For each analytical run, a further portion of a sample was 'spiked' with a known quantity (circa 0.1 mg/kg) of BPA and BPF isomers and then processed in exactly the same fashion as described above. The results for this sample were used to estimate the method recovery for the respective batch and check that the method was 'in control'. A solvent blank was also prepared and run alongside the samples.
In all cases, calibration curves were constructed for the analytes by injection of derivatised external standards containing the same addition of the internal standard. Concentrations were obtained from the graphs by interpolation and the concentrations in the food in mg/kg were calculated by multiplying by the final volume of extract and dividing by the mass of food taken.
GC-MS conditions
The following GC-MS conditions were used:
| Column | HP-5MS (5 per cent phenylmethyl siloxane), 30m x 0.25 mm, 0.25 microns film. | |
| Carrier gas | Helium @ 5 psi | |
| Injector | Splitless 270°C | |
| Oven program | 90°C hold 2 minutes (min) Ramp to 250°C at 5°C/min Ramp to 300°C at 10°C/min Hold 2min |
|
| Ions | BPA diacetyl | m/z 228;213 |
| BPF diacetyl isomers | m/z 200 | |
| BPA d14 diacetyl | m/z 224 | |
| Retention times | BPA diacetyl | 32.5min |
| 2,2-BPF diacetyl | 26.6min | |
| 2,4-BPF diacetyl | 28.8min | |
| 4,4-BPF diacetyl | 30.9min | |
| BPA d14 diacetyl | 32.4min | |
Analytical performance
Limits of detection for BPF isomers and BPA were defined by calculating concentrations equivalent to three times the signal to noise on analysis. The detection limits were 0.002 mg/kg for BPA, 0.005 mg/kg for the 2,2' and 2,4' isomers of BPF and 0.01 mg/kg for the 4,4' isomer of BPF. Limits of quantification were calculated from the concentration of BPA or BPF giving a signal equal to ten times the signal to noise on analysis.
The results were corrected for recovery using values obtained for control samples. The calibration graphs had correlation coefficients of 0.995 or better. The mean relative recoveries obtained for BPA were in the range 81 to 103 per cent. For BPF isomers the mean relative recoveries obtained were in the range 61 to 128 per cent. In all cases where BPA was quantified (greater or equal to 0.007 mg/kg) the peak identity was confirmed by checking also for the m/z ion at 213.
Quality assurance
The following procedures were used:
To ensure that results obtained by the laboratory carrying out the survey - Pira International, Leatherhead - were of acceptable accuracy, samples of baked beans and canned fish were 'spiked' with known levels of BPA and BPF isomers by an independent laboratory (Central Science Laboratory [CSL], York) and delivered together with the unfortified samples to Pira International for 'blind' analysis. Quantitative results were within 90 to 120 per cent of the values for levels of BPA and BPF added by CSL.
An estimate of the repeatability (95 per cent probability level) of the analytical method was made by conducting six replicate analyses on the homogenised contents of a can of salmon. The results were very similar (0.011 mg/kg for three analyses and 0.01 mg/kg for the other three).
Reporting
Brand names were reported as this survey was carried out in accordance with guidelines for reporting survey results published in the Food Safety Information Bulletin in September 1997. The absence of a particular brand from Table 1 means only that the brand was not included in the survey.
The analytical methodology proved to be acceptably precise and the results should be reproducible, within the constraints of inter-sample and inter-batch variation.
No BPF isomers were detected in any of the samples. BPA was detected (Table 1) at up to 0.07 mg/kg in 37 samples, and at 0.35 to 0.42 mg/kg in one sample (limit of detection: 0.002 mg/kg; limit of quantification: 0.007 mg/kg). There are few data from previous surveys of food or drink for BPA with which to compare the results. However levels of BPA in canned vegetables were similar to those reported previously. 3,8
The main reason for BPA contamination is likely to be migration of monomer left in polymerised epoxy resins coatings used on the insides of cans. However the result of 0.35 to 0.42 mg/kg for one sample probably reflected the use of BPA as a cross-linking agent in the resin used to coat the can. It is very unlikely that the presence of BPA in food samples in this survey was caused by the use of BADGE as a scavenger in PVC organosol coatings. The pattern of BPA contamination did not correlate with that for BADGE reaction products in a previous survey which looked at many of the same samples.9 Samples from only two batches out of 51 contained both BPA and BADGE reaction products in these two surveys.
Intake was estimated at 0.00036 to 0.00038 mg/kg bodyweight/day for adults and 0.00083 to 0.00087 mg/kg bodyweight/day for infants. These estimates were made using the data in Table 1, 97.5 percentile values for daily consumption of the foods that were tested,10,11 mean values of bodyweight (60 kg and 8.8kg for adults and infants respectively)12 and a mean contaminant level. Upper and lower bound values were calculated for the mean contaminant level to take account of results that were less than the limits of quantification or detection. These estimates of intake are considerably less than the Tolerable Daily Intake (TDI) of 0.05 mg/kg bodyweight/day set by the Scientific Committee on Food.13
The toxicology of BPA has been the subject of debate. For example the TDI is being reconsidered in the light of work to establish whether BPA is an in vivo endocrine-modulator (i.e. in laboratory animals and hence in humans) and if so how potent it is in vivo. Experts have debated whether this substance has measurable effects at low levels in vivo. Therefore this survey was submitted for consideration by the independent Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment (COT). Their statement on this survey is in Annex 1 (PDF). The COT acknowledges the uncertainties that exist in the scientific understanding of potential endocrine effects of BPA. Nevertheless, on present evidence they conclude that the levels of BPA identified in canned foods analysed in this survey are unlikely to be of concern to health, and that there is no reason for consumers to change their source of foodstuffs as a result of these findings. The Food Standards Agency is consulting consumer groups, industry, environmental organisations and others on methods of managing the uncertainties noted by the COT.
Dr David Watson
Food Standards Agency
Chemical Safety and Toxicology Division
Room 516C, Aviation House
125 Kingsway
London WC2B 6NH
Tel: +44 (0) 20 7276 8537
Fax: +44 (0) 20 7276 8514
E-mail: david.watson@foodstandards.gsi.gov.uk
A copy of the full report of this survey is available by e mail from David Watson or from the Food Standards Agency library in Aviation House, 125 Kingsway, London WC2B 6NH (Tel. No. +44 (0)20 7276 8181/8182), at a cost of £7.50 plus £1.50 postage and packing.
source: http://www.foodstandards.gov.uk/fsainfsheet/2001/no13/13bisp.htm
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