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PCDFs from board products
Chemosphere, Voi.23, Nos.ll-12, pp1561-1568, Printed in Great Britain
1991
0045-6535/91 $3.00 + 0.00 Pergamon Press plc
DISTRIBUTION OF PCDD/PCDFs IN PE-COATED PAPERBOARDS AN EXPLANATION FOR MIGRATION OF PCDD/PCDFs FROM BOARD PRODUCTS V.H.Kitunen* and M.S.Salkinoja-Salonen University of Helsinki Department of General Microbiology Mannerheimintie 172, Finland
ABSTRACT Distribution of polyehlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) in polyethylene (PE) coated paperboards was studied. PCDDs/PCDFs were found in the PE-layer of the board whenever they were found in the base board. The migration of PCDDs/PCDFs most probably occurred during the coating operation of the board.
INTRODUCTION Chlorine and chlorine containing chemicals have been used for bleaching since the 19th century. However, since the late 1980"s some these conventional bleaching processes have been shown to be a source of highly toxic organic chemicals including PCDDs/PCDFs. PCDDs/PCDFs formed during the bleaching were found both in products and effluents (Rappe et al. 1987; Kuehl et al. 1987; Beck et al. 1988; Swanson 1988; Amendola et al. 1989; Clement et al. 1989; Kitunen and Salkinoja-Salonen 1989). Due to their low water solubility PCDDs/PCDFs were adsorbed effectively onto cellulose fibres. Remarkable amounts (20-70%, Amendola et al. 1989) were retained in the cellulose and therefore consequently found from the final products. Although PCDDs/PCDFs are effectively adsorbed to the fibres, they may also release from fibres. Migration of PCDDs/PCDFs from paperboards to food are shown by several authors (Ryan et al 1988; Beck et al. 1989; Startin et al. 1989; Rappe et al. 1990). Our interest was focussed on the mechanisms by which the migration of PCDDs/PCDFs migth be possible. We studied the effect of different stages of PE-coating of the paperboard, distribution of PCDDs/PCDFs in the PE-coated board, and effect of temperature to the PCDDD/PCDF content of the PE-film.
EXPERIMENTAL Unused and used paperboards and paperboard packagings produced in US, Canada and Finland were analysed. Samples were taken during the years 1987 to 1990. 100 to 200g of pulped PE-coated or uncoated paperboard were extracted 24 to 48 hours in a Soxhlett extractor with 1 to 1,5 1 of acetone, ethanol (99%) or toluene. The peeled PE-films (20 to 40g) were extracted 24 hours in a Soxhlett extractor with acetone or ethanol (99%). 1561
1562
Before extraction all samples were spiked with the mixture of '3C,2-1abelled standard solution (2378-TCDD, 12378-PeCDD, 123678-HxCDD, 1234678-HpCDD, OCDD, 2378-TCDF, 12378-PeCDF, 23478-PeCDF, 123678-HxCDF and 1234678-HpCDF) purchased by Wellington Laboratories (Guelph, Canada) or Cambridge Isotope Laboratories (Woburn, MA). ';C,2-1abelled 1234-TCDD was used as an injection standard. Quantitative standard containing all unlabelled 2378-substituted standards was from Cambridge Isotope Laboratories. Qualitative standard was used for identification of other than 2378-substituted congeners. All solvents except ethanol were of HPLC grade (Rathburn, Walkerburn, UK). Ethanol (99%), which was also used for washing of glassware, was from OY Alko AB, Finland. Sample clean-up was carried out as described earlier (Kitunen and Salkinoja-Salonen, 1989) with minor modifications or when automated clean-up system (Fluid Management Systems,Watertown, MA) was used, according to Lapeza et al. (1986) with minor modifications. GC-MS analysis was carried out by Hewlett-Packard 5890 gas chromatograph connected to Hewlett-Packard 5970 B mass selective detector operating with SIM-detection. Injection technique used was all glass solid injector (Chrompack, Middelburg, Netherlands) operating with splitless mode at 270 or 280°C. Polar SP-2331 (60m x 0,25mm x 0,2#m, Supelco, Inc., Bellefonte, Switzerland) or NB-9C (50m x 0,2mm x 0,2#m, HNUNordion OY Ltd, Finland) and apolar HP-5 (25m x 0,2ram x 0,3#m, Hewlett-Packard, Avondale, PA) fused silica capillary columns were used in the GC-runs. The temperature program used for analysis for polar columns was as follows: 3 min at 60°C followed by 50°C/min to 180°C and then 5°C/min to 265°C and isothermal 265°C for 30 minutes. For apolar column the program was 3 minutes at 60°C followed by 50°C/rain to 200°C and then 5°C/min to 300°C and isothermal at 300°C for 10 minutes. Analysis was carded out by following the three most intense ions of molecular pattern (e.g. for TCDDs; 320, 322, 324). Detection limits with polar columns were as follows; lppt for tetra to hexa chlorinated PCDD/PCDF congeners, 2ppt for hepta chlorinated congeners and 2 to 10 ppt'for OCDD and OCDF. For apolar columns detection limit were as follows: 0,1 to 0,5 ppt for tetra to hepta chlorinated congeners and 1 to 5 ppt for OCDD and OCDF. RESULTS
PCDDs/PCDFs in PE-coatim, The roles of different stages and treatments during PE-coating on the PCDD/PCDF content of the paperboard were studied. Hot (340°C) PE-melt is extruded on the base board. To obtain better attachment of PE to the paperboard, an open flame may be used to "activate" (e.g. produce carbonyl groups) the cellulose matrix. Electric corona treatment of PE-coated surface may also be done to increase adhesion of electrically charged dyes. Provided that suitable precursors are present there is a possibility of formation of PCDDs/PCDFs.
1563
Figure 1. shows the anlytieal results of the paperboards at the different stages of PE-coating. The typical milk cartridge board (295g/m2) contained 14g of PE per m2 at the outside face and 26g per m2 at the inside face of the cartridge. Comparison of the PCDD/PCDF content of the board at the subsequent phases did not show any significant differences. The distribution between the isomers shown in Figure 1 was practically same at all phases. According to these results PE-coaling did not generate PCDD/PCDFs.
PCDD/PCDF content of paperboards 20-- / 16-12--
8--
:5 ¢-
4--
O
o/ 1
Test 1
2378-TCDD
Test 3
Test 2
I-~ 2378-TCDF
Test 4
Test 5
Test 6
I 1 123678-HxCDD~]] 123789-HxCDD~
Figure 1. The PCDD/PCDF content of paperboard at different phases of the process of PE-eoating. Description of the phases of board treatment is in Table 1.
Table 1. Description of paperboards taken from different PE-coating operation. Board sample
Test 1
Test 2
Test 3
Test 4
Test 5
Test 6
Flame treatment Corona treatment
No No
No One side
Both sides No
Both sides One side
Both sides No
Both sides One side
PE-coating
No
No
No
No
Both sides
Both sides
Behaviour of PCDD/PCDFs in PE-coated board Mierographs of a typical milk packaging board are shown in Figure 2. The figure shows that the PE-films are evenly spread but have not penetrated into the board. The thicker PE-film faces inside and thinner PE-film faces outside in the packaging.
1564
Figure 2. Micrographs of two different magnifications of the structure of PEcoated board studied in this paper.
Distribution of PCDD/PCDFs in PE-coated board.
Uncoated board
25"
P E - e o a t e d board "~ 20-
I
~15
I
d~o-
I
0
t 5-
IAmW Base board
PE-film inside
PE-film outside
PE-film washed
PE g r a nulates
Base board surface
Base board inside
Ill
1111 2378,-TCDD
Figure 3. The distribution of the major toxic PCDD/PCDF congeners in uncoated and PE-coated packaging board. The four groups of columns on the left are PEcoated board and two groups of columns on the right represent uncoated board. Base board -- the board between PE-layers, PE-fflm inside = inside face of the food package, PE-film outside = outside face of the food package, PE-film washed = celluse-free PE-film, washed with distilled water, PE-granulates = PE raw material, Base board surface = surface leaflet (0.1ram) of the uncoated board and Base board inside = interior of the uncoated board, thickness 0.3mm. Concentrations in ppt (pg/g).
1565
To establish the location of PCDD/PCDFs in PE-coated board, the PE-films were peeled off and analysed separately. A portion of the separated PE-fdms was cleaned with cold water until translucent and practically free of cellulose fibres. Results of the analysis of the fully coated packaging board (see Figure 3) shows that a significant part of the board contained PCDD/PCDFs which were located in the PE-layers. Figure 3 also shows that PE raw material (PE-granulates) contained no detectable ( < 0.5pp0 amount of PCDD/PCDFs and that the PCDD/PCDFs were evenly distributed in the base board before it was PE-coated. The PCDD/PCDF contents of the water-washed cellulose-free PE-films and unwashed PE-films were similar. The isomeric distribution was roughly the same as that of the base board. The results obtained from different brands of board are shown in Figure 4. Figure 4 shows the PCDD/PCDF content of PE-films of two brands of coffee cups. The total amount of the PCDD/PCDFs in the PE-film aligning the coffee cups was smaller than that of milk cartridge, probably because of the smaller amount of PE. Comparison between these two brands of coffee cup shows that the PCDD/PCDF content of the PE-films differed significantly from each other. In the case of coffee cup 1 2378-TCDF seemed clearly of better mobility as compared to that of 123678-HxCDD and 123789-HxCDD.
Distribution f'^'~ . . . . .
of PCDD/PCDFs '
15 -/
C'3 12 £3C-
cardboards Coffee cup 2
16
°
in different
12 9-
-
d cO
6,3-Base board
PEfilm
(l
2378-TCDD
Whole board
[-7 2378-TCDF
O-/~Base board
12~TS-IIzCDD ~
PEfilm
Whole board
123759-HxCDD~
Figure 4. Distribution of the major toxic PCDD/PCDF congeners in the singleside-PE-coated coffee cups. Base board = the body of the board without PE-film, PE-film -- PE-film from the surface of the board and Whole board = both PEfilm and the board analysed together. Concerations in ppt (pg/g).
1566
The effect of tem_t3erature to fully PE-eoated board To study the effect of thermal treatment of the board on the migration of the PCDD/PCDFs in board the same fully coated milk cartridge board shown in Figures 1, 2 and 3 was heated at 50oc (1 hour), 100oc (5 minutes and 1 hour) and 150oc (5 minutes and 1 hour). Visual inspection of heated films revealed no change at 50°C or during a short period at 100oc. One hour at 100oc and even shorter period at 150°C turned the board yellowish and induced typical smell of the PE-melt. One hour heating at 150°C caused more severe effects to the board such as brownish colour and bubbling of the PE-film. Figure 5 shows the results of the analysis of the PE-films after different thermal treatments. These visual changes changed little of the PCDD/PCDF contents of the PE-film on attached to the board.
PCDD/PCDF content of heated PE-film 25-
20-
15c~
e-
~; 1 0 o
.
.
50C, l h
(11 237s-tODD
10012, $min Jlt .
100C, l h .
[~ ~'~t~Dr
.
.
1$0C, 5rain
.
LIE ...........
I
123~S-mCDB ~
15012, l h
1~9-m~
3
Figure 5. Recovery of PCDD/PCDFs after thermal treatment of a fully PE-coated food packaging board.
The only clear change was observed at 150°C apparently causing "internal migration" of the PCDD/PCDFs.
1567
DISCUSSION PCDD/PCDFs have high affinity to the pulp and fines (Swanson, 1988; Rappe et al. 1989) due to low water solubility of these compounds (Friesen et al. 1990; Friesen and Webster 1990). Therefore, once formed, these compounds were also found in the products (Amendola et al. 1989; Kitunen and Salkinoja-Salonen 1989 and 1990). Although the PCDD/PCDFs were effectively adsorbed by the fiber, they were desorbed leading to migration of the PCDD/PCDFs from the paper into food as reported by several authors (Ryan et al. 1988; Beck et al. 1989; Startin et al. 1989; Rappe et al. 1990). Our interest focused on the mechanisms by which PCDD/PCDF contamination may occur. To get get an insight to this problem the micro-distribution of PCDD/PCDFs in food packaging boards was studied. The results revealed that a significant portion of the PCDD/PCDFs may reside in the PE-films of the boards. Studies of boards of different origins showed that the PCDD/PCDF contribution of PE-films varied from a few percent to tens of percent. Our results thus indicated that the PE-films acted like a sorbent rather than like a barrier against PCDDIPCDFs. The sorbent PE acted as a reservoir, releasing PCDD/PCDFs to the adjacent food such as milk or cream. The "internal migration" or relocation of the PCDD/PCDFs from the base board to the PE-film seemed to occur during the extrusion process, when the hot PE-melt is spread on the base board. Heat vaporized the PCDD/PCDFs in the board and induced purging from the base board arid dissolved them in the PE-fluid. Enrichment of the PCDD/PCDFs in the PE-film facing to the board may explain migration from package into food. It seems that PCDD/PCDFs of the PE-coating are able to migrate further and those located in cellulose matrix are immobile and thus less significant for further migration. The migration of PCDD/PCDFs into food, observed by other workers, was quantitavely similar to what we found as PCDD/PCDF content of the PE-films aligning on the boards. So these facts suggest a causal relationship. No migration towards the surface was observed in the uncoated boards. Therefore the availability of PCDD/PCDFs in uncoated boards seems actually smaller than that in PE-coated boards. Thermal treatment after PE-coating did not induce significant migration PCDD/PCDFs into the PE-films facing the board. However, thermal treatment may mobilize the PCDD/PCDFs from the PE-film to food. Therefore heating of food in contaminated packagings should be avoided.
CONCLUSIONS PE-coating process did not generate PCDD/PCDFs, but the PE-film faced on the board acted like a reservoir and not as a harder against the PCDD/PCDFs. Migration of PCDD/PCDFs into the food therefore can be avoided only by using PCDD/PCDF-free board. This principle has already been put in practice in the industry.
1568
Rappe C., Andersson R., Bergquist P.-A., Brohede C., Hansson M., KjeUer L.-O., Linstrtm G., Marklund S., Nygren M., Swanson S.E., Tysldind M. and Wiberg K. (1987). Overview on environmental fate of chlorinated dioxins and dibenzofurans. Sources, levels and isomeric pattern in various matrices. Chemosphere, 16:16031618. Rappe C., Linstrtm G., Glas B., Lundstrtm K. and Borgstrtm S. (1990). Levels of PCDDs and PCDFs in milk cartons and in commercial milk. Chemosphere, 20:1649-1656. Rappe C., Swanson S., Glas B., Kringstad, K.P., DeSousa F., Johansson L. and Abe Z. (1989). On the formation of PCDDs and PCDFs in the bleaching of pulp. Pulp Paper Can. 90:42-47. Ryan J.J., Panopio L.G. and Lewis D. (1988). Bleaching of pulp and paper as a source of PCDDs and PCDFs. 8th International Symposium On Chlorinated Dioxins And Related Compounds. August 21-26, Umet, Sweden. Startin J.R., Rose M., Wright C., Parker I. and Gilbert J. (1989). Surveillance of British food PCDDs and PCDFs. Chemosphere, 20:.793-798. Swanson S.E. (1988). Dioxins in the bleach pulp. Thesis, University of Umefi, Umefi.
1991
0045-6535/91 $3.00 + 0.00 Pergamon Press plc
DISTRIBUTION OF PCDD/PCDFs IN PE-COATED PAPERBOARDS AN EXPLANATION FOR MIGRATION OF PCDD/PCDFs FROM BOARD PRODUCTS V.H.Kitunen* and M.S.Salkinoja-Salonen University of Helsinki Department of General Microbiology Mannerheimintie 172, Finland
ABSTRACT Distribution of polyehlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) in polyethylene (PE) coated paperboards was studied. PCDDs/PCDFs were found in the PE-layer of the board whenever they were found in the base board. The migration of PCDDs/PCDFs most probably occurred during the coating operation of the board.
INTRODUCTION Chlorine and chlorine containing chemicals have been used for bleaching since the 19th century. However, since the late 1980"s some these conventional bleaching processes have been shown to be a source of highly toxic organic chemicals including PCDDs/PCDFs. PCDDs/PCDFs formed during the bleaching were found both in products and effluents (Rappe et al. 1987; Kuehl et al. 1987; Beck et al. 1988; Swanson 1988; Amendola et al. 1989; Clement et al. 1989; Kitunen and Salkinoja-Salonen 1989). Due to their low water solubility PCDDs/PCDFs were adsorbed effectively onto cellulose fibres. Remarkable amounts (20-70%, Amendola et al. 1989) were retained in the cellulose and therefore consequently found from the final products. Although PCDDs/PCDFs are effectively adsorbed to the fibres, they may also release from fibres. Migration of PCDDs/PCDFs from paperboards to food are shown by several authors (Ryan et al 1988; Beck et al. 1989; Startin et al. 1989; Rappe et al. 1990). Our interest was focussed on the mechanisms by which the migration of PCDDs/PCDFs migth be possible. We studied the effect of different stages of PE-coating of the paperboard, distribution of PCDDs/PCDFs in the PE-coated board, and effect of temperature to the PCDDD/PCDF content of the PE-film.
EXPERIMENTAL Unused and used paperboards and paperboard packagings produced in US, Canada and Finland were analysed. Samples were taken during the years 1987 to 1990. 100 to 200g of pulped PE-coated or uncoated paperboard were extracted 24 to 48 hours in a Soxhlett extractor with 1 to 1,5 1 of acetone, ethanol (99%) or toluene. The peeled PE-films (20 to 40g) were extracted 24 hours in a Soxhlett extractor with acetone or ethanol (99%). 1561
1562
Before extraction all samples were spiked with the mixture of '3C,2-1abelled standard solution (2378-TCDD, 12378-PeCDD, 123678-HxCDD, 1234678-HpCDD, OCDD, 2378-TCDF, 12378-PeCDF, 23478-PeCDF, 123678-HxCDF and 1234678-HpCDF) purchased by Wellington Laboratories (Guelph, Canada) or Cambridge Isotope Laboratories (Woburn, MA). ';C,2-1abelled 1234-TCDD was used as an injection standard. Quantitative standard containing all unlabelled 2378-substituted standards was from Cambridge Isotope Laboratories. Qualitative standard was used for identification of other than 2378-substituted congeners. All solvents except ethanol were of HPLC grade (Rathburn, Walkerburn, UK). Ethanol (99%), which was also used for washing of glassware, was from OY Alko AB, Finland. Sample clean-up was carried out as described earlier (Kitunen and Salkinoja-Salonen, 1989) with minor modifications or when automated clean-up system (Fluid Management Systems,Watertown, MA) was used, according to Lapeza et al. (1986) with minor modifications. GC-MS analysis was carried out by Hewlett-Packard 5890 gas chromatograph connected to Hewlett-Packard 5970 B mass selective detector operating with SIM-detection. Injection technique used was all glass solid injector (Chrompack, Middelburg, Netherlands) operating with splitless mode at 270 or 280°C. Polar SP-2331 (60m x 0,25mm x 0,2#m, Supelco, Inc., Bellefonte, Switzerland) or NB-9C (50m x 0,2mm x 0,2#m, HNUNordion OY Ltd, Finland) and apolar HP-5 (25m x 0,2ram x 0,3#m, Hewlett-Packard, Avondale, PA) fused silica capillary columns were used in the GC-runs. The temperature program used for analysis for polar columns was as follows: 3 min at 60°C followed by 50°C/min to 180°C and then 5°C/min to 265°C and isothermal 265°C for 30 minutes. For apolar column the program was 3 minutes at 60°C followed by 50°C/rain to 200°C and then 5°C/min to 300°C and isothermal at 300°C for 10 minutes. Analysis was carded out by following the three most intense ions of molecular pattern (e.g. for TCDDs; 320, 322, 324). Detection limits with polar columns were as follows; lppt for tetra to hexa chlorinated PCDD/PCDF congeners, 2ppt for hepta chlorinated congeners and 2 to 10 ppt'for OCDD and OCDF. For apolar columns detection limit were as follows: 0,1 to 0,5 ppt for tetra to hepta chlorinated congeners and 1 to 5 ppt for OCDD and OCDF. RESULTS
PCDDs/PCDFs in PE-coatim, The roles of different stages and treatments during PE-coating on the PCDD/PCDF content of the paperboard were studied. Hot (340°C) PE-melt is extruded on the base board. To obtain better attachment of PE to the paperboard, an open flame may be used to "activate" (e.g. produce carbonyl groups) the cellulose matrix. Electric corona treatment of PE-coated surface may also be done to increase adhesion of electrically charged dyes. Provided that suitable precursors are present there is a possibility of formation of PCDDs/PCDFs.
1563
Figure 1. shows the anlytieal results of the paperboards at the different stages of PE-coating. The typical milk cartridge board (295g/m2) contained 14g of PE per m2 at the outside face and 26g per m2 at the inside face of the cartridge. Comparison of the PCDD/PCDF content of the board at the subsequent phases did not show any significant differences. The distribution between the isomers shown in Figure 1 was practically same at all phases. According to these results PE-coaling did not generate PCDD/PCDFs.
PCDD/PCDF content of paperboards 20-- / 16-12--
8--
:5 ¢-
4--
O
o/ 1
Test 1
2378-TCDD
Test 3
Test 2
I-~ 2378-TCDF
Test 4
Test 5
Test 6
I 1 123678-HxCDD~]] 123789-HxCDD~
Figure 1. The PCDD/PCDF content of paperboard at different phases of the process of PE-eoating. Description of the phases of board treatment is in Table 1.
Table 1. Description of paperboards taken from different PE-coating operation. Board sample
Test 1
Test 2
Test 3
Test 4
Test 5
Test 6
Flame treatment Corona treatment
No No
No One side
Both sides No
Both sides One side
Both sides No
Both sides One side
PE-coating
No
No
No
No
Both sides
Both sides
Behaviour of PCDD/PCDFs in PE-coated board Mierographs of a typical milk packaging board are shown in Figure 2. The figure shows that the PE-films are evenly spread but have not penetrated into the board. The thicker PE-film faces inside and thinner PE-film faces outside in the packaging.
1564
Figure 2. Micrographs of two different magnifications of the structure of PEcoated board studied in this paper.
Distribution of PCDD/PCDFs in PE-coated board.
Uncoated board
25"
P E - e o a t e d board "~ 20-
I
~15
I
d~o-
I
0
t 5-
IAmW Base board
PE-film inside
PE-film outside
PE-film washed
PE g r a nulates
Base board surface
Base board inside
Ill
1111 2378,-TCDD
Figure 3. The distribution of the major toxic PCDD/PCDF congeners in uncoated and PE-coated packaging board. The four groups of columns on the left are PEcoated board and two groups of columns on the right represent uncoated board. Base board -- the board between PE-layers, PE-fflm inside = inside face of the food package, PE-film outside = outside face of the food package, PE-film washed = celluse-free PE-film, washed with distilled water, PE-granulates = PE raw material, Base board surface = surface leaflet (0.1ram) of the uncoated board and Base board inside = interior of the uncoated board, thickness 0.3mm. Concentrations in ppt (pg/g).
1565
To establish the location of PCDD/PCDFs in PE-coated board, the PE-films were peeled off and analysed separately. A portion of the separated PE-fdms was cleaned with cold water until translucent and practically free of cellulose fibres. Results of the analysis of the fully coated packaging board (see Figure 3) shows that a significant part of the board contained PCDD/PCDFs which were located in the PE-layers. Figure 3 also shows that PE raw material (PE-granulates) contained no detectable ( < 0.5pp0 amount of PCDD/PCDFs and that the PCDD/PCDFs were evenly distributed in the base board before it was PE-coated. The PCDD/PCDF contents of the water-washed cellulose-free PE-films and unwashed PE-films were similar. The isomeric distribution was roughly the same as that of the base board. The results obtained from different brands of board are shown in Figure 4. Figure 4 shows the PCDD/PCDF content of PE-films of two brands of coffee cups. The total amount of the PCDD/PCDFs in the PE-film aligning the coffee cups was smaller than that of milk cartridge, probably because of the smaller amount of PE. Comparison between these two brands of coffee cup shows that the PCDD/PCDF content of the PE-films differed significantly from each other. In the case of coffee cup 1 2378-TCDF seemed clearly of better mobility as compared to that of 123678-HxCDD and 123789-HxCDD.
Distribution f'^'~ . . . . .
of PCDD/PCDFs '
15 -/
C'3 12 £3C-
cardboards Coffee cup 2
16
°
in different
12 9-
-
d cO
6,3-Base board
PEfilm
(l
2378-TCDD
Whole board
[-7 2378-TCDF
O-/~Base board
12~TS-IIzCDD ~
PEfilm
Whole board
123759-HxCDD~
Figure 4. Distribution of the major toxic PCDD/PCDF congeners in the singleside-PE-coated coffee cups. Base board = the body of the board without PE-film, PE-film -- PE-film from the surface of the board and Whole board = both PEfilm and the board analysed together. Concerations in ppt (pg/g).
1566
The effect of tem_t3erature to fully PE-eoated board To study the effect of thermal treatment of the board on the migration of the PCDD/PCDFs in board the same fully coated milk cartridge board shown in Figures 1, 2 and 3 was heated at 50oc (1 hour), 100oc (5 minutes and 1 hour) and 150oc (5 minutes and 1 hour). Visual inspection of heated films revealed no change at 50°C or during a short period at 100oc. One hour at 100oc and even shorter period at 150°C turned the board yellowish and induced typical smell of the PE-melt. One hour heating at 150°C caused more severe effects to the board such as brownish colour and bubbling of the PE-film. Figure 5 shows the results of the analysis of the PE-films after different thermal treatments. These visual changes changed little of the PCDD/PCDF contents of the PE-film on attached to the board.
PCDD/PCDF content of heated PE-film 25-
20-
15c~
e-
~; 1 0 o
.
.
50C, l h
(11 237s-tODD
10012, $min Jlt .
100C, l h .
[~ ~'~t~Dr
.
.
1$0C, 5rain
.
LIE ...........
I
123~S-mCDB ~
15012, l h
1~9-m~
3
Figure 5. Recovery of PCDD/PCDFs after thermal treatment of a fully PE-coated food packaging board.
The only clear change was observed at 150°C apparently causing "internal migration" of the PCDD/PCDFs.
1567
DISCUSSION PCDD/PCDFs have high affinity to the pulp and fines (Swanson, 1988; Rappe et al. 1989) due to low water solubility of these compounds (Friesen et al. 1990; Friesen and Webster 1990). Therefore, once formed, these compounds were also found in the products (Amendola et al. 1989; Kitunen and Salkinoja-Salonen 1989 and 1990). Although the PCDD/PCDFs were effectively adsorbed by the fiber, they were desorbed leading to migration of the PCDD/PCDFs from the paper into food as reported by several authors (Ryan et al. 1988; Beck et al. 1989; Startin et al. 1989; Rappe et al. 1990). Our interest focused on the mechanisms by which PCDD/PCDF contamination may occur. To get get an insight to this problem the micro-distribution of PCDD/PCDFs in food packaging boards was studied. The results revealed that a significant portion of the PCDD/PCDFs may reside in the PE-films of the boards. Studies of boards of different origins showed that the PCDD/PCDF contribution of PE-films varied from a few percent to tens of percent. Our results thus indicated that the PE-films acted like a sorbent rather than like a barrier against PCDDIPCDFs. The sorbent PE acted as a reservoir, releasing PCDD/PCDFs to the adjacent food such as milk or cream. The "internal migration" or relocation of the PCDD/PCDFs from the base board to the PE-film seemed to occur during the extrusion process, when the hot PE-melt is spread on the base board. Heat vaporized the PCDD/PCDFs in the board and induced purging from the base board arid dissolved them in the PE-fluid. Enrichment of the PCDD/PCDFs in the PE-film facing to the board may explain migration from package into food. It seems that PCDD/PCDFs of the PE-coating are able to migrate further and those located in cellulose matrix are immobile and thus less significant for further migration. The migration of PCDD/PCDFs into food, observed by other workers, was quantitavely similar to what we found as PCDD/PCDF content of the PE-films aligning on the boards. So these facts suggest a causal relationship. No migration towards the surface was observed in the uncoated boards. Therefore the availability of PCDD/PCDFs in uncoated boards seems actually smaller than that in PE-coated boards. Thermal treatment after PE-coating did not induce significant migration PCDD/PCDFs into the PE-films facing the board. However, thermal treatment may mobilize the PCDD/PCDFs from the PE-film to food. Therefore heating of food in contaminated packagings should be avoided.
CONCLUSIONS PE-coating process did not generate PCDD/PCDFs, but the PE-film faced on the board acted like a reservoir and not as a harder against the PCDD/PCDFs. Migration of PCDD/PCDFs into the food therefore can be avoided only by using PCDD/PCDF-free board. This principle has already been put in practice in the industry.
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Rappe C., Andersson R., Bergquist P.-A., Brohede C., Hansson M., KjeUer L.-O., Linstrtm G., Marklund S., Nygren M., Swanson S.E., Tysldind M. and Wiberg K. (1987). Overview on environmental fate of chlorinated dioxins and dibenzofurans. Sources, levels and isomeric pattern in various matrices. Chemosphere, 16:16031618. Rappe C., Linstrtm G., Glas B., Lundstrtm K. and Borgstrtm S. (1990). Levels of PCDDs and PCDFs in milk cartons and in commercial milk. Chemosphere, 20:1649-1656. Rappe C., Swanson S., Glas B., Kringstad, K.P., DeSousa F., Johansson L. and Abe Z. (1989). On the formation of PCDDs and PCDFs in the bleaching of pulp. Pulp Paper Can. 90:42-47. Ryan J.J., Panopio L.G. and Lewis D. (1988). Bleaching of pulp and paper as a source of PCDDs and PCDFs. 8th International Symposium On Chlorinated Dioxins And Related Compounds. August 21-26, Umet, Sweden. Startin J.R., Rose M., Wright C., Parker I. and Gilbert J. (1989). Surveillance of British food PCDDs and PCDFs. Chemosphere, 20:.793-798. Swanson S.E. (1988). Dioxins in the bleach pulp. Thesis, University of Umefi, Umefi.