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MAFF UK - DIOXINS IN COWS' MILK FROM FARMS CLOSE TO INDUSTRIAL SITES

Index to MAFF UK Food Surveillance Information Sheets, 1997

Summary

MAFF is carrying out a survey of dioxins in samples of cows' milk from individual farms in the vicinity of potential sources of dioxins in the UK. This survey is in response to a recommendation by the Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment that food from around known emission sources should be monitored. A progress report on this survey was published in the Food Safety Information Bulletin in October 1996. This report presents the results for all samples taken during the period 1993-1995. Further samples were taken from around other industrial sites in 1996, and the results are expected later this year. For all but two of the farms sampled during 1993-1995, concentrations of dioxins were within the normal range (1.7-7.1 ng TEQ/kg milk fat, or 0.04-0.27 ng TEQ/kg whole milk) previously established for cows' milk from individual farms in the UK. The two farms were in the Huddersfield area in 1995 and contained concentrations of dioxins of 9.2 and 11 ng TEQ/kg milk fat, or 0.36 and 0.38 ng TEQ/kg whole milk respectively. Further samples were taken from these two farms and additional farms in this area in October 1996. Milk from one farm has now fallen from 9.2 ng TEQ/kg milk fat (0.35 ng TEQ/kg whole milk) to 4.6 ng TEQ/kg milk fat (0.20 ng TEQ/kg whole milk) (within the normal range), while that from the other has fallen only slightly (now 8.6 ng TEQ/kg milk fat, or 0.37 ng TEQ/kg whole milk). The concentrations of dioxins in milk from a third farm not previously sampled was slightly outside the normal range (7.8 ng TEQ/kg milk fat, or 0.30 ng TEQ/kg whole milk). The results from these and all other farms included in the survey are well below the Maximum Tolerable Concentration (MTC) of 0.7 ng TEQ/kg whole milk (17.5 ng TEQ/kg milk fat) agreed with the Department of Health. The dioxins levels in the milk from the farms tested do not therefore pose a risk to human health.

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 very toxic to some species of laboratory animals. The sixteen other dioxins which also contain chlorine at positions 2, 3, 7 and 8 of the molecule are considered 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 significant biological activity.

Dioxins are produced during various combustion and incineration processes and are also unwanted by-products in the manufacture of certain chemicals. Dioxins are chemically very stable and so are ubiquitous in the environment and are generally present at very low concentrations in all foods, especially fatty foods including cows' milk.

MAFF began the first surveys of cows' milk for dioxins in 1989, analysing samples taken from farms in rural and in urban/industrial areas of the UK. From these surveys it was found that concentrations of dioxins were usually in the range 1.1-1.5 ng TEQ/kg milk fat (0.04-0.06 ng TEQ/kg whole milk) in milk from farms in rural areas and 3.0-7.1 ng TEQ/kg milk fat (0.09-0.27 ng TEQ/kg whole milk) in milk from farms in urban/industrial area.² This sampling was undertaken in response to a recommendation from the Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment (COT) that samples of foods known to accumulate dioxins, taken from around known emission sources, should be investigated.³ In 1995 the COT recommended that continuing major sources of dioxins should be identified with a view to reducing further inputs of dioxins to the environment.⁴

Although the concentrations of dioxins in most of the samples analysed were within the expected range established from samples taken in 1989 and 1990, in 1991 it was found that the concentrations of dioxins in milk from three farms in the Bolsover area of Derbyshire were above the current Maximum Tolerable Concentration (MTC),² although with the exception of one farm the concentrations have now fallen to within the normal range.^5-9 This farm kept a suckler herd and did not supply milk for human consumption. In the case of the two other farms, the former Milk Marketing Board stopped accepting their milk as it did not meet the standard conditions for sale because the levels of dioxins exceeded the MTC of 0.7 ng TEQ/kg whole milk⁵ (17.5 ng TEQ/kg milk fat). The mtc is an expert assessment by scientists and advisors in MAFF and the Department of Health of the highest level of dioxins that could be present in milk without an individual who drinks even a large amount of milk exceeding the internationally agreed safe level of dioxins intake. It is based on the Tolerable Daily Intake of 10 pg 2,3,7,8-TCDD/kg bodyweight/day set by the World Health Organization in 1990¹⁰ and endorsed by the COT in 1992 as 10 pg TEQ/kg bodyweight/day for mixtures of dioxins. The upper limit of the normal range of dioxins concentrations in milk in the UK is about one-third of this MTC. Concentrations of dioxins in retail milk purchased in 1988 from various areas of the UK were at the lower end of the normal range. This is expected as milk from a number of farms is blended in the dairy prior to sale. Concentrations of dioxins in milk from dairies supplied by farms in the Bolsover area were also very low.²

Following the findings of elevated concentrations of dioxins in milk from farms in the Bolsover area, and in line the recommendation of the COT, samples of milk have been collected during the period 1993-1995 from 93 farms in the vicinity of 29 industrial sites throughout England which are potential sources of dioxins. Additional samples were taken from 12 farms in the Huddersfield area in 1996. These sites included municipal, clinical and chemical waste incinerators, coal-fired power stations, landfill sites, a secondary metal refiner, a manufacturer of chlorinated chemicals and a cement kiln. A list of the sites included in the monitoring programme is included in Table 1. Cows' milk was chosen for investigation because cows graze relatively large areas and any dioxins present on grass eaten by the cows would concentrate in the milk fat. Milk is also an important food and a significant source of dioxins in the diet and is a relatively easy matrix to analyse for dioxins.

Under the Environmental Protection Act 1990 (EPA), all prescribed processes require authorisations from the regulatory authorities before operations can start. Regulations made under the Act, The Environmental Protection (Prescribed Processes and Substances) Regulations 1991, SI 472 (as amended) describe the processes and substances that require control. Under these Regulations processes are divided into Part A and Part B. Part A processes are those that have the greatest potential for pollution to the three (air, land and water) environmental media and are controlled under Integrated Pollution Control (IPC) of the Act. Part B processes have less serious potential to pollute and are controlled by local authorities for air pollution. The Act and Regulations do not place numerical limits on pollutants that can be emitted. However they do require that in operating a process, an operator uses Best Available Techniques Not Entailing Excessive Costs to prevent or minimise the release of prescribed substances and to render harmless any such substances which are released.

Municipal waste incinerators have been the major source of dioxins emissions in the UK. These plants came under IPC control in August 1992 and were required to meet new plant standards defined in the Community Directive (89/429/EEC) by 1 December 1996. The Directive did not set a dioxins limit but a limit of 1 ng/m³ was set by the Environment Agency. The same limit was also applied to other types of incinerators, e.g. clinical waste, chemical waste, sewage sludge. A practical effect of this limit, which became binding from 1 December 1996, is that municipal waste incinerators will no longer be the major source of dioxins. Her Majesty's Inspectorate of Pollution estimated in 1995 that these incinerators produced 460-580 g/year. This will reduce to less than 10 g/year from now on. Other sources of dioxins emissions which are projected to fall significantly by the year 2000 are clinical waste incineration, sewage sludge incineration, iron, steel and non-ferrous metal processes, and chemical waste incineration.¹¹

As a statutory consultee, the Ministry receives copies of all Integrated Pollution Control applications submitted to the Environment Agency. These applications contain details of dioxins emissions and this information was used to select industrial sites for inclusion in the current survey where there were dairy farms within 7 km of the site. Using dispersion models it is possible to predict the area of maximum deposition of dioxins and milk from dairy farms which lay within such an area was selected for analysis.

Methods

All samples, together with appropriate analytical blanks, were analysed at the CSL Food Science Laboratory, Norwich. Milk was freeze-dried, spiked with ¹³C₁₂ labelled internal standards and extracted with dichloromethane/cyclohexane. The extract was passed through beds of silica gel and base-modified silica, then fractionated using a column containing activated carbon dispersed on glass fibres. Details of the fractionation process have been published.¹² The fraction containing dioxins was recovered by eluting the column by reversed flow with toluene, and purified by chromatography on acid-modified and base-modified silicas and on Florisil. Dioxins were determined by high resolution gas chromatography/high resolution mass spectrometry at 7000 resolution.

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. Based on previous work, the coefficient of variation for the analysis of dioxins in milk was approximately 10 percent.²

The results complied with published acceptance criteria.¹³ These criteria lay down general conditions for use of internal standards and specification of limits of detection. They also cover the following more specific areas:

Validation: extraction efficiency; average and repeatability for blanks and recovery; selection of appropriate GC column and MS resolution; repeatability of relative response factors and isotope ratios; and absence of suppression effects;

Quality control: adequate blanks; check sample extraction; recovery of internal standards; chromatographic separation; MS calibration, tuning and sensitivity; and

Data acceptance: validated and quality controlled procedures; criteria for identification as a dioxin or furan; criteria for assignment as specific isomer; and criteria for acceptance of quantification.

For Quality Control purposes a reference sample with known concentrations of dioxins congeners was included in the batches of samples analysed. The sample was of powdered milk, and the dioxins content had been analysed by several laboratories in an interlaboratory study carried out by BCR. The concentrations found in the current survey were within the confidence interval of the concentrations accepted by BCR.

Results

The concentrations of dioxins found in the samples from the various sites are summarised in Table 1. The concentrations of dioxins were in the range 0.87-11 (mean 2.7) ng TEQ/kg milk fat, or 0.03-0.38 (mean 0.10) ng TEQ/kg whole product.

Interpretation

In all but two of the samples taken during the period 1993-1995, the concentrations of dioxins were within or below the normal range of 1.1-7.1 ng TEQ/kg milk fat previously established for milk from individual farms in the UK in 1989. The two samples of milk which had slightly elevated concentrations of dioxins were both taken in 1995 from farms in the Huddersfield area. The largest potential source of dioxins in this area at that time was probably the Vine Street Municipal Waste Incinerator which closed down on 1 December 1996 as it did not meet the new plant emission standards (i.e. dioxins emissions limit of 1 ng TEQ/m³). As with any urban/industrial area, there are also other potential sources of dioxins.

MAFF had previously given a commitment to undertake further investigations if the surveillance uncovered concentrations of dioxins outside the normal range. Accordingly, a total of 12 further samples were taken from these and additional farms in the Huddersfield area in October 1996. The results show that milk from one farm has fallen from 9.2 ng TEQ/kg milk fat (0.35 ng TEQ/kg whole milk) to 4.6 ng TEQ/kg milk fat (0.20 ng TEQ/kg whole milk) and is now within the normal range, while that from the other has not fallen to such a large extent (now 8.6 ng TEQ/kg, or 0.37 ng TEQ/kg whole milk). The concentration of dioxins in milk from a third farm not previously sampled (7.8 ng TEQ/kg milk fat, or 0.30 ng TEQ/kg whole milk) is slightly outside the normal range. MAFF is discussing these results with the local authority for the area. The concentrations of dioxins in milk from the other farms (1.9-5.5 ng TEQ/kg milk fat, or 0.08-0.24 ng TEQ/kg whole product) are all within the normal range. The results from all the farms in Huddersfield and all other areas included in the survey are well below the Maximum Tolerable Concentration of 0.7 ng TEQ/kg whole milk (17.5 ng TEQ/kg milk fat), and there is no risk to human health from consumption of milk from any of the farms.

The concentrations of dioxins (all on a fat basis) are similar to those found in the Netherlands (up to 13.5 ng TEQ/kg) in milk from cows grazing close to incinerators in the Lickebaert area and to those found in the Tyrol region of Austria (up to 8.6 ng TEQ/kg milk fat) in milk from cows grazing close to a metal reclamation plant,¹⁴ and cows grazing near potential sources in Bavaria (up to 5.6 ng TEQ/kg milk fat).¹⁵ Higher concentrations (13.5-37.0 ng TEQ/kg milk fat, using German TEF system) have been reported in milk from cows grazing in the vicinity of a metal reclamation plant in Germany.¹⁶ The results of a more recent survey in Germany confirm expectations that dioxins emissions from newer incinerators are lower: concentrations of dioxins in milk from farms close to an incinerator built in 1993 were up to 0.8 ng TEQ/kg milk fat.¹⁷ All the incinerators targeted in the MAFF survey were built well before this time and the existence of IPC controls, so it is reasonable to expect that concentrations of dioxins in milk in the UK will fall further.

In September 1996, the survey was extended to include samples of cows' milk taken from the vicinity of other potential sources of dioxins (steel and non-ferrous metals plants). These samples are currently being analysed, and the results will be published in the Food Safety Information Bulletin when available.

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, publ. Environmental Protection Agency, Washington D.C., USA.
Ministry of Agriculture, Fisheries and Food (1992) Dioxins in Food. Food Surveillance Paper No. 31, publ. HMSO.
Department of the Environment (1989) Dioxins in the environment. Pollution Paper No. 27, publ. HMSO.
Department of Health (1995) Statement by the Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment on the US EPA draft health assessment document for 2,3,7,8-tetrachlorodibenzo-p-dioxin and related compounds, publ. Department of Health, London.
Ministry of Agriculture, Fisheries and Food (1992) Report of Studies on Dioxins in Derbyshire carried out by the Ministry of Agriculture, Fisheries and Food.
Ministry of Agriculture, Fisheries and Food (1992) Further Report of Studies on Dioxins in Derbyshire carried out by the Ministry of Agriculture, Fisheries and Food.
Ministry of Agriculture, Fisheries and Food (1992) Third Report of Studies on Dioxins in Derbyshire carried out by the Ministry of Agriculture, Fisheries and Food.
Ministry of Agriculture, Fisheries and Food (1994) Dioxins in cows milk. Food Surveillance Information Sheet 43.
Ministry of Agriculture, Fisheries and Food (1995) Dioxins in cows' milk from the Bolsover area. Food Surveillance Information Sheet 75.
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, publ. WHO Regional Office for Europe, Copenhagen.
Her Majesty's Inspectorate of Pollution (1995) A review of dioxin emissions in the UK. Research Report No DoE/CPR2/41/1/38.
Krokos, F., Creaser, C.S., Startin, J.R. and Wright, C. (1996) Congener-specific method for the determination of ortho-chlorobiphenyls, non-ortho-chlorobiphenyls, PCDDs and PCDFs in foods by carbon-column fractionation and gas chromatography-isotope dilution mass spectrometry. Fresenius Journal of Analytical Chemistry (in press).
Ambidge, P.F., Cox, E.A., Creaser, C.S., Greenberg, M., Gem, M.G. de M., Gilbert, J., Jones, P.W., Kibblewhite, M.G., Levey, J., Lisseter, S.G., Meredith, T.J., Smith, L., Smith, P., Startin, J.R., Stenhouse, I. and Whitworth, M. (1990) Acceptance criteria for analytical data on polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans. Chemosphere 21, 999-1006.
Liem, A.K.D., Hoogerbrugge, R., Kootstra, P.R., van der Velde, E.G. and de Jong, A.P.J.M. (1991) Occurrence of dioxins in cow's milk in the vicinity of municipal waste incinerators and a metal reclamation plant in the Netherlands. Chemosphere 23, 1675-1684.
Lassek, E., Jahr, D., and Mayer, R. (1993) Polychlorinated dibenzo-p-dioxins and dibenzofurans in cows milk from Bavaria, FRG. Chemosphere 27, 519-534.
Riss, A. and Hagenmaier, H. (1989) Environmental monitoring of PCDD/PCDF in the vicinity of a metal reclamation plant in Tyrol/Austria. Paper presented at the 9th International Symposium on Chlorinated Dioxins in the Environment, Ontario, Canada, 17-22 September 1989.
Hippelein, M., Kaupp, H., Dörr, G. and Hutzinger, O. (1996) Baseline contamination assessment for a new resource recovery facility in Germany. Part III: PCDD/Fs, HCB and PCBs in cow's milk. Chemosphere 32, 1617-1622.

Contact Point

For further information, please contact:

Dr Nigel Harrison
MAFF, Food Safety and Science Group
Food Contaminants Division
Room 234, Ergon House
17 Smith Square
London SW1P 3JR

Tel: +44 (0) 171 238 6235
Fax: +44 (0) 171 238 5331

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These pages were last updated on 31 January 1996