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The content of heavy metals in food packaging paper: an atomic absorption spectroscopy investigation
Food Corm/,
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PAPER
The content of heavy metals in food packaging paper: an atomic absorption spectroscopy investigation Marcel0 E. Conti* and Francesco Botri: The levels of four representative heavy metals-Cd, C’q Pb and Hg- have been measured by atomic absorption spectroscopy (AAS) in 12 different samples of paper: 7 different kinds of food packaging papel; commonly employed in Italy (brown and white bread bags, brown and white bakery paper; white bakery bag, butcher’s paper and salami paper), and 5 samples of non-food paper (two newspapers, one weekly magazine, one blue and one yellow notebook), assayed, for comparative purposes, in the same experimental conditions. The levels of heavy metals have been measured in all the samples according to two different procedures: i) after immersion in distilled water for 24 h at T = 23%; and ii) after immersion in 3% v/v acetic acid for 24 h at T = 40°C. The results of the present investigation show that all samples of food packaging paper contain concentrations of heavy metals that are generally lower than those detected in samples of common paper Moreovel; our results show that there is a remarkable difference among the levels of heavy metals depending on the procedure of sample pretreatment. Our observation points out that the pretreatment usually indicated as ‘migration test’ (pegormed in 3% v/v acetic acid at T = 4O”C), being remarkably more drastic than the ‘extraction test’ (per$ormed in distilled water at T = 23”C), should be requested in all those cases in which a direct contact occurs between the food and the paper packaging. 0 1997 Elsevier Science Ltd.
INTRODUCTION The strong need of the food industry for suitable and inexpensive raw materials to be used for the production of food packagings has always been, at least partially, satisfied by cellulosic fibres. Paper and paper derivatives are indeed one of the primary sources of food packagings all over the world, and their use is promoted not only by economical factors lstituto di Merceologia, Universita ‘La Sapienza’, Via de1 Castro Laurenziano 9, 00161 Roma, Italy. *To whom correspondence should be addressed. Tel: (+39-6)-49766516. FAX: (+39-6)-4941621 E-Mail: CONTIM@AXRMA. UNIROMAI .IT.
(paper packagings are extremely inexpensive) but also by their safety of use (Bureau and M&on, 1996). Food packaging represents a very important sector of paper packaging, accounting for around 62% of the total packaging produced in Italy. In the last few years, environmental and economic driving forces have been strongly promoting the use of secondary cellulose fibres, in addition to virgin fibres, for the production of paper-based products, including paper packaging and, among them, those needed by the food industry. This trend has forced both the scientific and political communities to reconsider the safety of food paper packaging, and to define standards of quality for the secondary cellulose
Food Control 1997 Volume 8 Number 3
131
Heavy metals in packaging paper by AAS: M.E. Conti and F. Botre
fibres to be employed for the production of food packaging. In Italy, the use of secondary fibres for the production of papers and paper derivatives has been regulated since 1973. (Ministerial Decree, 1973). Almost 25 years ago, the regulation imposed the use of virgin fibres for the production of food packaging, with a limited number of exceptions; later on, in 1979 (Ministerial Decree, 1979), three main toxicological parameters were defined to assess the overall quality of secondary fibres: i) polychlorinated aromatic hydrocarbons, and more specifically polychlorodiphenyls, whose levels should never exceed 10 ppm; ii) bleaching agents, whose presence should always be excluded; iii) lead, whose levels should never exceed 3 ug/dmz (Grammicioni, 1994). Although the European Union has not yet defined a specific regulation in this field, the problem is currently under investigation at the level of the European Council (Svennson, 1993). There is, however, a strong need for a more specific definition of paper quality, especially as far as the recycling of secondary fibres by the food packaging industry is concerned (Rossi, 1993). The direct contact of foods with paper packaging could in fact lead to the release of variable amounts of toxicants, which could, in turn, represent a definite threat to the health of the consumer. Recently, heavy metals other than Pb have been proposed as a valuable quality index for paper packagings. More precisely, to assess the overall quality of food packagings produced by secondary fibres, two main procedures have been proposed, the ‘extraction test’ and the ‘migration test’. The former, carried out in distilled water and at T = 23”C, presents safety limits that are markedly higher than the latter, carried out in 3% acetic acid at T = 40°C (see Table I). It is self evident that products satisfying the ‘extraction test’ could be used only for a limited range of applications, while those satisfying also the ‘migration test’ could be employed also for the production of packaging in direct contact with foods. The present investigation reports the results of an experimental survey carried out to determine, by atomic absorption spectroscopy (AAS), the levels of four representative heavy metals - cadmium, chromium, lead and mercury - in different paper samples. The method proposed here is similar to the Official Methods reported in the literature (CNR IRSA, 1980; AOAC, 1995) but some variations, regarding the thermal program and the sample ‘lhble 1. Heavy metals purity limits (mg/kg) Council of Europe (1992)
MATERIALS
The AAS system is constituted by a Perkin Elmer model 1100B atomic absorption spectrometer, equipped with an HGA-700 graphite furnace, a deuteriumarc background correction and a Perkin Elmer Model AS-70 autosampler (Perkin Elmer Italia SpA, Monza, Italy); the results have been recorded by an Epson EX-850 dot-matrix printer (Epson Italia S.p.A,, Milano, Italy). The detection of mercury, by the cold vapour technique, has been carried out by a Varian Techtron model AA-475 atomic absorption spectrometer (Varian Italia, Milano, Italy). Materials Samples of paper Samples of food packaging paper (No. l-7) and of reference non-food paper (No. 8-12) are listed in Table 2. All samples were purchased from local dealers, cut into square samples (10 x 10 cm) and stored at 4°C (humidity: 50-55%). Prior to the beginning of either the migration test or the extraction test, the samples were put in weighing bottles, desiccated in an oven at T = 105°C for 2 h and weighed every 30 min until constant weight was reached. The average mass was determined for all the 12 samples of packaging papers; all the values are reported in Table 2. Laboratory glassware,reagents and standards of heavy metals All the glassware used for the preparation of stock and standard solutions was decontaminated from the possible presence of heavy metals by overnight treatment with metal-free, concentrated HNO, (Merck, Darmstadt, Germany). Table 2. Samples of food and non food packaging papers tested for
heavy metals concentrations Sample
by the
Extraction test*
Migration test**
Cadmium Chromium VI Lead Mercury
0.5 0.05 3 0.3
0.005 0.05 0.01 0.005
*In distilled water, 24 h at T = 23°C. **In 3% acetic acid, 24 h at T = 40°C.
Food Control 1997 Volume 8 Number 3
AND METHODS
Instrumentation
1 as stated
Chemical element
132
pretreatment operations, have been introduced in order to optimize and to simplify the overall analytical procedure (Conti et al., 1996).
: 4 5 6 7 8 9 IO II I2
by Atomic Absorption Spectroscopy
Description
g/m?
brown bread bag white bread bag white bakery bag butcher’s paper, coupled to a PE film salami paper, coupled to a PE film brown bakery paper white bakery paper British newspaper Italian weekly magazine yellow pad notebook blue pad notebook Italian newspaper
48.9 42.4 59.6 53.6 59.4 21.4 31.3 46.3 75.7 103.6 112.4 45.5
Heavy metals
in packaging paper by AAS: M.E. Conti and F. Botre
All reagents were analytical grade. Acetic acid 96% (‘Merck Suprapur’, Lot-No.: B583255) was supplied by Merck (Darmstadt, Germany). Cadmium, chromium, lead and mercury standards were prepared by dilution with 2% HNO, from stock standard solutions of their respective nitric salts (1000 + 2 ppm in 0.5 M HNO,), supplied by Merck (Darmstadt, Germany); water ultrapure grade by Mini-Q from Millipore (Millipore Corporation USA) was used for the preparation of all solutions.
distilled water). Results of tests for the selective determination of chromium VI, performed only on those samples which had presented detectable levels of total chromium, are given in Table 11. All data are expressed both as ppm (ug of heavy metal per g of paper) and as ug/dm’. The analytical results are here discussed for each one of the considered analytes.
Extraction tests
Four out of seven samples of food-packaging paper have shown levels of lead that lie below the detection limit of the instrumental technique. For the other three samples the values varied from a minimum of 0.89 ug/g to a maximum of 3.88 ug/g. Only one of these values is above the limit stated by the Italian law (3.0 ug/g), but all of them are considerably higher than the guideline value suggested by the European Council (0.01 ug/g, see Table 2). It has to be pointed out that samples No. 4-5, although presenting a considerable concentration of lead, are not in direct contact with food, due to the presence of a ‘barrier layer’, represented by a polyethylene (PE) film. Samples of common paper (No. 8-12) generally presented higher levels of lead. In this respect, the remarkable amount of lead detected in samples of yellow (No. 10) and blue (No. 11) notepad paper can reasonably be traced to the high percentages of secondary fibres which are employed for their production.
Lead Test in 370 acetic acid
According to the guidelines given by the current regulation, 2 dmz of each sample (i.e. the two sides of 1 dm2 specimens) were kept in 100 ml of metals-free distilled water at T = 23°C for 24 h. At the end of this treatment, the solution was analyzed for heavy metal concentrations. Migration tests The procedure was the same as for the extraction test, with the difference that the samples were kept in 100 ml of a 3% v/v metal-free solution of acetic acid at T = 40°C for 24 h. Operative conditions in the spectrometric assays The quantitative determination of each analyte was carried out by applying the method of the linear regression to the calibration plot following the addition of different aliquots of known standards to the samples under investigation. The determination of cadmium, chromium and lead has been carried out with the graphite furnace, while the determination of mercury has been carried out according to the cold vapour technique. Determination of Cr (VI) has been carried out by a spectrometric method employing phenylcarbazide (CNR IRSA, 1980). The instrumental specification of the methods are given in Table 3, while the description of the thermal programs followed for the determination of each single metal are reported in Tables 4-6. Results of the recovery tests and of the precision tests are given in Tables 7 and Table 8, respectively.
RESULTS All results of the present study are reported in Table 9 (tests in 3% acetic acid) and Table IO (tests in
Test in distilled water
Five out of seven samples of food packaging paper have shown levels of lead that lie below the detection limit of the instrumental technique. However, the levels of lead in the remaining two samples lie below the guideline value suggested by the European Council (3.0 ug/g, Table I). Among all samples of common paper, lead has been detected only in the two newspaper samples (samples No. 8 and 12). Cadmium Test in 3% acetic acid
Three out of seven samples of food packaging paper have shown levels of cadmium that lie below the detection limit of the instrumental technique. For the other four samples the values were found to be higher than the guideline value suggested by the European Council (0.005 ug/g, Table 1).
Table 3. Operative conditions in the spectrometric analyses Element
Wavelength (nm)
Slit width (nm)
Matrix modifier
Graphite tubes
Cd Pb
228.8 283.3
0.7
Cr
357.9 253.7
0.7 0.5
0.2 mg NH,H,PO, (IO pl) 0.2 mg NH,H,PO, (IO 111) 0.05 mg Mg (NO,)? (IO pl) -
pyrolytic/coated pyrolytic/coated pyrolytic/coated
Hg
Food Control 1997 Volume 8 Number 3
133
Heavy metals
in packaging
by AAS: M.E. Conti and F. Botr&
paper
‘able 4. Furnace program for the determination Step
of Pb
Chromium
Temperature (“C)
Ramp (s)
Hold (s)
Argon flow (ml/min)
80 100 120 300 750 2000 2650 20
20 20 20 30 30 0
40 40 60 30 45 4 5 10
300 300 300 300 300 0 300 300
The atomization injected = 20 ~1.
1 1 occurs
at
step
6;
volume
of
sample
All samples of common paper presented detectable levels of lead, generally higher than those measured in samples of food packaging paper Testin distilledwater Only two samples of food-packaging paper presented levels of cadmium higher than the detection limit of the instrumental technique. All samples of common paper presented levels of cadmium that lay below the detection limit of the instrumental technique.
Table 5. Furnace program for the determination Step
Temperature (“C)
Ramp (s)
1 2 3 4 5 6
120 350 600 2100 2650 20
20 10 10 0 1 1
The atomization injected = 10 ~1.
occurs
at
step
Hold (s)
Argon flow (ml/min)
10 3
300 300 300 0 300 300
4;
volume
Table 6. Furnace program for the determination Temperature (“C)
Step
of Cd
of
Hold (s)
Argon flow (mUmin)
20 10
::
300
: 5 6 7
1650 450 2500 2700 20
10 0 1 5
20 :
Z
The atomization injected = 15 111.
occurs
sample
Ramp (s)
300 120
at
5 step
5;
volume
0 300 300 of
Testin distilledwater All the samples considered in this study, both of food-packaging paper and of common paper, presented levels of chromium that lay below the detection limit of the instrumental technique. Mercury All the samples considered in this study, both of food packaging paper and of common paper, presented levels of mercury that lay below the detection limit of the instrumental technique, no matter the nature of the sample pretreatment (3% acetic acid or distilled water).
DISCUSSION
of total Cr
:
Testin 3% acetic acid Four out of seven samples of food-packaging paper and two out of five samples of common paper have shown levels of chromium that lie below the detection limit of the instrumental technique. The remaining six samples (three of food packaging paper and three of common paper) were also assayed for the specific determination of Cr (VI). These last values, listed in Table IO, were always higher than the guideline value suggested by the European Council (0.05 pglg, Table 1).
sample
European countries are promoting the recycling of cellulose fibres, and this trend is particularly evident in The Netherlands, where the production of secondary cellulose fibres reaches 71% of the total production of cellulose fibres, in the UK 62%, and in Germany 56.4% On the contrary, primary cellulose fibres are still intensively used in countries where wood is one of the main natural resources (i.e. in the Scandinavian countries). According to data respective to 1994 (Pavesi, 1996), the Italian paper industry utilizes secondary fibres in a percentage oscillating around 50% of total (the ratio secondary fibres/virgin fibres was 2.997l2.850.10” tons in 1993 and 3.300/3.400*10” tons in 1994). Among the secondary fibres, nearly 70% comes from domestic collection. Secondary fibres are destined to very different final products: so, for instance, 80% of fibres utilized for the production of packagings comes from recycled paper, while the production of graphic paper utilizes only 10% of secondary fibres as starting materials.
lsble 7. Recovery tests Element
No. of tests
Concentration (w/l) .._
Recovery mean (%) + SD( %)
Pb Cd Cr Hg
9 8 8 7
IO I 5 2
95.6+2 97.4+3 98.0 k 2 96.8+3
134
Food Control 1997 Volume 8 Number 3
Heavy metals in packaging
found to match the requirements stated by the Italian regulation for paper destined to food packaging), several samples presented values exceeding the limits indicated by the European Council. Therefore, these particular samples should be considered as a potential risk to the human health incase they could ever be re-employed, without any kind of pretreatment, as a source of cellulose secondary fibre in the production of packaging to be used in direct contact with food products. Furthermore, it has to be pointed out that the values of heavy metal concentrations (again, apart from Hg) obtained by both the migration and the extraction test have always been lower for paper samples employed as food packaging in direct contact with food, with respect to samples coupled to a protective PE film and to paper samples employed for other uses. Finally, it seems worthwhile for us to highlight the marked decrease in the levels of heavy metals, shifting from the migration test to the extraction test. This evidence shows that the potential risks to health are in principle dependent not only on the nature of
The newspaper industry lies in an intermediate position, utilizing about 50% of secondary fibres, even if the use of secondary fibres is continuously growing. It is worthwhile to highlight that usually the assessment of the quality of food packagings does not include paper packagings among the possible sources of food contamination (Bureau and Multon, 1996). The investigation shows that a significant amount of heavy metals are present in some of types of paper; for indeed, apart from mercury (whose concentration always lay below the instrumental limits of the analytical technique applied in the present study) and lead (whose levels have been Table 8. Precision tests*
Element Pb Cd Cr Hg
No. of tests
(@l)
Variation coefficient %
IO II 12 9
4.2 1.0 3.4 2.0
6.1 3.ti 4.1 8.4
Concentration
paper by AAS: M.E. Conti and F. Botr&
*Assays of Pb, Cd and Cr have been carried out by the automatic sampler.
Table 9. Results of the migration tests (3% acetic acid). Data are expressed as both pg of metal per g of paper and pg of metal per dm’ of paper. Each value is the mean of five independent sample preparations Lead Sample 1 2 3 4 5 6 : 9 IO 11 12
Chromium
Cadmium
Mercury
pg/dm’
@g
l@dm’
&g
pg/dm’
Wg
Ltg/dm’
Wg
0.72 n.d. n.d. 0.51 n.d. 1.20 n.d. 2.63 1.12 6.71 12.81 0.27
1.47 n.d. n.d. 0.95 n.d. 4.38 n.d. 5.68 1.47 6.47 11.39 0.59
0.01 0.05 n.d. n.d. 0.04 0.02 n.d. 0.03 0.04 0.04 0.09 0.10
0.02 0.11 n.d. n.d. 0.06 0.07 n.d. 0.06 0.05 0.03 0.08 0.22
n.d. n.d. n.d. 0.28 0.24 n.d. n.d. n.d. 0.32 0.28 0.40 n.d.
n.d. n.d. n.d. 0.52 0.40 n.d. n.d. n.d. 0.42 0.27 0.35 n.d.
n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.
n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.
n.d: not detectable ([Pb] <4 &I,
[Cd] ~0.1 @I,
[Cr] ~4 pgil, (Hg] < 1 Itgil in the contact liquid).
Table 10. Results of the extraction tests (distilled water). Data are expressed as both pg of metal per g of paper and pg of metal per dm’ of paper. Each value is the mean of five independent sample preparations Lead Sample I
Cadmium
Chromium
Mercury
@dm’
&Yg
l@dm’
@g
@dm’
l&g
@dm’
I&g
n.d. 0.23 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.
n.d. 0.54 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.
n.d. n.d. 0.05 0.05 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.
n.d. n.d. 0.08 0.09 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.
n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.
n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.
n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.
n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.
n.d.: not detectable ([Pb] <4 @I,
[Cd] ~0.1 @I, [Cr) <4 @I, [Hg] <
I &I in the contact liquid).
Food Control 1997 Volume 8 Number 3
135
Heavy metals in packaging paper by AAS: M.E. Conti and F. Botrl!
‘lbble 11. Results of the migration tests (3% acetic acid) for Cr VI. Data are expressed as both pg of metal per g of paper and pg of metal per dm’ of paper. Each value is the mean of five independent sample preparations Chromium VI Sample
pgldm’
@g
4 5 9 IO II
0.12 0.07 0.10 0.12 0.13
0.22 0.13 0.13 0.11 0.12
*The listed data have been obtained by concentrating acetic acid extract. The used specimens had a contact surface of 4 dm’.
5:l the
the packaging, but also, to a relevant extent, on the nature of the packaged food. This finding also stresses the primary role played by the storage conditions of the system packaging/packaged, since various environmental agents (temperature, humidity, volatile acids and so on) could markedly affect the release of various components of the packaging into the food. Additional experiments are presently in progress in our laboratories, in order to extend the sampling to a more relevant number of geographic areas, and to compare the results of the present work with those obtained by a biological approach. The same investigation reported in this work is also being carried out for other paper derived food-packaging materials (paper boards).
136
Food Control 1997 Volume 6 Number 3
ACKNOWLEDGEMENTS This work has been supported in part by a grant of the Italian National Research Council (CNR). REFERENCES Bureau, G. and Multon, J. L. (1996) Food Packaging Technology, Vol. 1-2 VCH, Weinheim. CNR IRSA, (1980) Metodi Analitici per le Acque, Rome, Italy. Conti, M. E., Boccdcci Mariani, M., Milana, M. R. and Gramiccioni, L. (1996) Heavy Metals and Optical Whitenings as Quality Parameters of Recycled Paper for Food Packaging. Journal of Food Processingand Preservation20, I- 11. Gramiccioni, L. (1994) Caratteristiche Qualitative di Carte e Cartoni per Uso Alimentare. In Libera Circolazione e Qualit& dei Prodotti net Mercato Unico Europeo, ed. F. Botrt: and E. lannucci, vol 11, pp. 625-630. Kappa, Roma. Italian Ministerial Decree, dated 21.3.1973, published Cl,@no 104, 20.4.1973.
on Gaze.
Italian Ministerial Decree, dated D. M. 18.61979, published on Gazz. Ufl no 180, 3.7.1979. ‘Official Methods of Analysis of AOAC International. In AOAC International,ed. P. Cunniff, Vol XVI, Arlington (VA), USA. Pavesi, F. (1996) Pianeta carta lmpresa e ambiente 5, 26-35. Rossi, L. (1993) The Status of the Food Packaging Regulation at the Beginning of the Internal Market and Future Perspectives. In Proceedings of the International Conference on: Materialsfor Food Packaging, Gothenburg, (Sweden). Svennson, K. (1993) Work of the Council of Europe in the Area of Paper and Board used in Food Contact Applications. In Proceedings of the International Conference on: Materials for Food Packaging,Gothenburg (Sweden).
Vol. X. No. 3, pp. 131-136. 0 IYY7 Elscvicr
All rights rcscrvcd. ELSEVIER
PII: SO956-7135(97)00004-2
Printed
OYXI-7l.wY7
1YY7
Scicncc
in Great
Ltd
Britain
$17.tH)+0.00
PAPER
The content of heavy metals in food packaging paper: an atomic absorption spectroscopy investigation Marcel0 E. Conti* and Francesco Botri: The levels of four representative heavy metals-Cd, C’q Pb and Hg- have been measured by atomic absorption spectroscopy (AAS) in 12 different samples of paper: 7 different kinds of food packaging papel; commonly employed in Italy (brown and white bread bags, brown and white bakery paper; white bakery bag, butcher’s paper and salami paper), and 5 samples of non-food paper (two newspapers, one weekly magazine, one blue and one yellow notebook), assayed, for comparative purposes, in the same experimental conditions. The levels of heavy metals have been measured in all the samples according to two different procedures: i) after immersion in distilled water for 24 h at T = 23%; and ii) after immersion in 3% v/v acetic acid for 24 h at T = 40°C. The results of the present investigation show that all samples of food packaging paper contain concentrations of heavy metals that are generally lower than those detected in samples of common paper Moreovel; our results show that there is a remarkable difference among the levels of heavy metals depending on the procedure of sample pretreatment. Our observation points out that the pretreatment usually indicated as ‘migration test’ (pegormed in 3% v/v acetic acid at T = 4O”C), being remarkably more drastic than the ‘extraction test’ (per$ormed in distilled water at T = 23”C), should be requested in all those cases in which a direct contact occurs between the food and the paper packaging. 0 1997 Elsevier Science Ltd.
INTRODUCTION The strong need of the food industry for suitable and inexpensive raw materials to be used for the production of food packagings has always been, at least partially, satisfied by cellulosic fibres. Paper and paper derivatives are indeed one of the primary sources of food packagings all over the world, and their use is promoted not only by economical factors lstituto di Merceologia, Universita ‘La Sapienza’, Via de1 Castro Laurenziano 9, 00161 Roma, Italy. *To whom correspondence should be addressed. Tel: (+39-6)-49766516. FAX: (+39-6)-4941621 E-Mail: CONTIM@AXRMA. UNIROMAI .IT.
(paper packagings are extremely inexpensive) but also by their safety of use (Bureau and M&on, 1996). Food packaging represents a very important sector of paper packaging, accounting for around 62% of the total packaging produced in Italy. In the last few years, environmental and economic driving forces have been strongly promoting the use of secondary cellulose fibres, in addition to virgin fibres, for the production of paper-based products, including paper packaging and, among them, those needed by the food industry. This trend has forced both the scientific and political communities to reconsider the safety of food paper packaging, and to define standards of quality for the secondary cellulose
Food Control 1997 Volume 8 Number 3
131
Heavy metals in packaging paper by AAS: M.E. Conti and F. Botre
fibres to be employed for the production of food packaging. In Italy, the use of secondary fibres for the production of papers and paper derivatives has been regulated since 1973. (Ministerial Decree, 1973). Almost 25 years ago, the regulation imposed the use of virgin fibres for the production of food packaging, with a limited number of exceptions; later on, in 1979 (Ministerial Decree, 1979), three main toxicological parameters were defined to assess the overall quality of secondary fibres: i) polychlorinated aromatic hydrocarbons, and more specifically polychlorodiphenyls, whose levels should never exceed 10 ppm; ii) bleaching agents, whose presence should always be excluded; iii) lead, whose levels should never exceed 3 ug/dmz (Grammicioni, 1994). Although the European Union has not yet defined a specific regulation in this field, the problem is currently under investigation at the level of the European Council (Svennson, 1993). There is, however, a strong need for a more specific definition of paper quality, especially as far as the recycling of secondary fibres by the food packaging industry is concerned (Rossi, 1993). The direct contact of foods with paper packaging could in fact lead to the release of variable amounts of toxicants, which could, in turn, represent a definite threat to the health of the consumer. Recently, heavy metals other than Pb have been proposed as a valuable quality index for paper packagings. More precisely, to assess the overall quality of food packagings produced by secondary fibres, two main procedures have been proposed, the ‘extraction test’ and the ‘migration test’. The former, carried out in distilled water and at T = 23”C, presents safety limits that are markedly higher than the latter, carried out in 3% acetic acid at T = 40°C (see Table I). It is self evident that products satisfying the ‘extraction test’ could be used only for a limited range of applications, while those satisfying also the ‘migration test’ could be employed also for the production of packaging in direct contact with foods. The present investigation reports the results of an experimental survey carried out to determine, by atomic absorption spectroscopy (AAS), the levels of four representative heavy metals - cadmium, chromium, lead and mercury - in different paper samples. The method proposed here is similar to the Official Methods reported in the literature (CNR IRSA, 1980; AOAC, 1995) but some variations, regarding the thermal program and the sample ‘lhble 1. Heavy metals purity limits (mg/kg) Council of Europe (1992)
MATERIALS
The AAS system is constituted by a Perkin Elmer model 1100B atomic absorption spectrometer, equipped with an HGA-700 graphite furnace, a deuteriumarc background correction and a Perkin Elmer Model AS-70 autosampler (Perkin Elmer Italia SpA, Monza, Italy); the results have been recorded by an Epson EX-850 dot-matrix printer (Epson Italia S.p.A,, Milano, Italy). The detection of mercury, by the cold vapour technique, has been carried out by a Varian Techtron model AA-475 atomic absorption spectrometer (Varian Italia, Milano, Italy). Materials Samples of paper Samples of food packaging paper (No. l-7) and of reference non-food paper (No. 8-12) are listed in Table 2. All samples were purchased from local dealers, cut into square samples (10 x 10 cm) and stored at 4°C (humidity: 50-55%). Prior to the beginning of either the migration test or the extraction test, the samples were put in weighing bottles, desiccated in an oven at T = 105°C for 2 h and weighed every 30 min until constant weight was reached. The average mass was determined for all the 12 samples of packaging papers; all the values are reported in Table 2. Laboratory glassware,reagents and standards of heavy metals All the glassware used for the preparation of stock and standard solutions was decontaminated from the possible presence of heavy metals by overnight treatment with metal-free, concentrated HNO, (Merck, Darmstadt, Germany). Table 2. Samples of food and non food packaging papers tested for
heavy metals concentrations Sample
by the
Extraction test*
Migration test**
Cadmium Chromium VI Lead Mercury
0.5 0.05 3 0.3
0.005 0.05 0.01 0.005
*In distilled water, 24 h at T = 23°C. **In 3% acetic acid, 24 h at T = 40°C.
Food Control 1997 Volume 8 Number 3
AND METHODS
Instrumentation
1 as stated
Chemical element
132
pretreatment operations, have been introduced in order to optimize and to simplify the overall analytical procedure (Conti et al., 1996).
: 4 5 6 7 8 9 IO II I2
by Atomic Absorption Spectroscopy
Description
g/m?
brown bread bag white bread bag white bakery bag butcher’s paper, coupled to a PE film salami paper, coupled to a PE film brown bakery paper white bakery paper British newspaper Italian weekly magazine yellow pad notebook blue pad notebook Italian newspaper
48.9 42.4 59.6 53.6 59.4 21.4 31.3 46.3 75.7 103.6 112.4 45.5
Heavy metals
in packaging paper by AAS: M.E. Conti and F. Botre
All reagents were analytical grade. Acetic acid 96% (‘Merck Suprapur’, Lot-No.: B583255) was supplied by Merck (Darmstadt, Germany). Cadmium, chromium, lead and mercury standards were prepared by dilution with 2% HNO, from stock standard solutions of their respective nitric salts (1000 + 2 ppm in 0.5 M HNO,), supplied by Merck (Darmstadt, Germany); water ultrapure grade by Mini-Q from Millipore (Millipore Corporation USA) was used for the preparation of all solutions.
distilled water). Results of tests for the selective determination of chromium VI, performed only on those samples which had presented detectable levels of total chromium, are given in Table 11. All data are expressed both as ppm (ug of heavy metal per g of paper) and as ug/dm’. The analytical results are here discussed for each one of the considered analytes.
Extraction tests
Four out of seven samples of food-packaging paper have shown levels of lead that lie below the detection limit of the instrumental technique. For the other three samples the values varied from a minimum of 0.89 ug/g to a maximum of 3.88 ug/g. Only one of these values is above the limit stated by the Italian law (3.0 ug/g), but all of them are considerably higher than the guideline value suggested by the European Council (0.01 ug/g, see Table 2). It has to be pointed out that samples No. 4-5, although presenting a considerable concentration of lead, are not in direct contact with food, due to the presence of a ‘barrier layer’, represented by a polyethylene (PE) film. Samples of common paper (No. 8-12) generally presented higher levels of lead. In this respect, the remarkable amount of lead detected in samples of yellow (No. 10) and blue (No. 11) notepad paper can reasonably be traced to the high percentages of secondary fibres which are employed for their production.
Lead Test in 370 acetic acid
According to the guidelines given by the current regulation, 2 dmz of each sample (i.e. the two sides of 1 dm2 specimens) were kept in 100 ml of metals-free distilled water at T = 23°C for 24 h. At the end of this treatment, the solution was analyzed for heavy metal concentrations. Migration tests The procedure was the same as for the extraction test, with the difference that the samples were kept in 100 ml of a 3% v/v metal-free solution of acetic acid at T = 40°C for 24 h. Operative conditions in the spectrometric assays The quantitative determination of each analyte was carried out by applying the method of the linear regression to the calibration plot following the addition of different aliquots of known standards to the samples under investigation. The determination of cadmium, chromium and lead has been carried out with the graphite furnace, while the determination of mercury has been carried out according to the cold vapour technique. Determination of Cr (VI) has been carried out by a spectrometric method employing phenylcarbazide (CNR IRSA, 1980). The instrumental specification of the methods are given in Table 3, while the description of the thermal programs followed for the determination of each single metal are reported in Tables 4-6. Results of the recovery tests and of the precision tests are given in Tables 7 and Table 8, respectively.
RESULTS All results of the present study are reported in Table 9 (tests in 3% acetic acid) and Table IO (tests in
Test in distilled water
Five out of seven samples of food packaging paper have shown levels of lead that lie below the detection limit of the instrumental technique. However, the levels of lead in the remaining two samples lie below the guideline value suggested by the European Council (3.0 ug/g, Table I). Among all samples of common paper, lead has been detected only in the two newspaper samples (samples No. 8 and 12). Cadmium Test in 3% acetic acid
Three out of seven samples of food packaging paper have shown levels of cadmium that lie below the detection limit of the instrumental technique. For the other four samples the values were found to be higher than the guideline value suggested by the European Council (0.005 ug/g, Table 1).
Table 3. Operative conditions in the spectrometric analyses Element
Wavelength (nm)
Slit width (nm)
Matrix modifier
Graphite tubes
Cd Pb
228.8 283.3
0.7
Cr
357.9 253.7
0.7 0.5
0.2 mg NH,H,PO, (IO pl) 0.2 mg NH,H,PO, (IO 111) 0.05 mg Mg (NO,)? (IO pl) -
pyrolytic/coated pyrolytic/coated pyrolytic/coated
Hg
Food Control 1997 Volume 8 Number 3
133
Heavy metals
in packaging
by AAS: M.E. Conti and F. Botr&
paper
‘able 4. Furnace program for the determination Step
of Pb
Chromium
Temperature (“C)
Ramp (s)
Hold (s)
Argon flow (ml/min)
80 100 120 300 750 2000 2650 20
20 20 20 30 30 0
40 40 60 30 45 4 5 10
300 300 300 300 300 0 300 300
The atomization injected = 20 ~1.
1 1 occurs
at
step
6;
volume
of
sample
All samples of common paper presented detectable levels of lead, generally higher than those measured in samples of food packaging paper Testin distilledwater Only two samples of food-packaging paper presented levels of cadmium higher than the detection limit of the instrumental technique. All samples of common paper presented levels of cadmium that lay below the detection limit of the instrumental technique.
Table 5. Furnace program for the determination Step
Temperature (“C)
Ramp (s)
1 2 3 4 5 6
120 350 600 2100 2650 20
20 10 10 0 1 1
The atomization injected = 10 ~1.
occurs
at
step
Hold (s)
Argon flow (ml/min)
10 3
300 300 300 0 300 300
4;
volume
Table 6. Furnace program for the determination Temperature (“C)
Step
of Cd
of
Hold (s)
Argon flow (mUmin)
20 10
::
300
: 5 6 7
1650 450 2500 2700 20
10 0 1 5
20 :
Z
The atomization injected = 15 111.
occurs
sample
Ramp (s)
300 120
at
5 step
5;
volume
0 300 300 of
Testin distilledwater All the samples considered in this study, both of food-packaging paper and of common paper, presented levels of chromium that lay below the detection limit of the instrumental technique. Mercury All the samples considered in this study, both of food packaging paper and of common paper, presented levels of mercury that lay below the detection limit of the instrumental technique, no matter the nature of the sample pretreatment (3% acetic acid or distilled water).
DISCUSSION
of total Cr
:
Testin 3% acetic acid Four out of seven samples of food-packaging paper and two out of five samples of common paper have shown levels of chromium that lie below the detection limit of the instrumental technique. The remaining six samples (three of food packaging paper and three of common paper) were also assayed for the specific determination of Cr (VI). These last values, listed in Table IO, were always higher than the guideline value suggested by the European Council (0.05 pglg, Table 1).
sample
European countries are promoting the recycling of cellulose fibres, and this trend is particularly evident in The Netherlands, where the production of secondary cellulose fibres reaches 71% of the total production of cellulose fibres, in the UK 62%, and in Germany 56.4% On the contrary, primary cellulose fibres are still intensively used in countries where wood is one of the main natural resources (i.e. in the Scandinavian countries). According to data respective to 1994 (Pavesi, 1996), the Italian paper industry utilizes secondary fibres in a percentage oscillating around 50% of total (the ratio secondary fibres/virgin fibres was 2.997l2.850.10” tons in 1993 and 3.300/3.400*10” tons in 1994). Among the secondary fibres, nearly 70% comes from domestic collection. Secondary fibres are destined to very different final products: so, for instance, 80% of fibres utilized for the production of packagings comes from recycled paper, while the production of graphic paper utilizes only 10% of secondary fibres as starting materials.
lsble 7. Recovery tests Element
No. of tests
Concentration (w/l) .._
Recovery mean (%) + SD( %)
Pb Cd Cr Hg
9 8 8 7
IO I 5 2
95.6+2 97.4+3 98.0 k 2 96.8+3
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Food Control 1997 Volume 8 Number 3
Heavy metals in packaging
found to match the requirements stated by the Italian regulation for paper destined to food packaging), several samples presented values exceeding the limits indicated by the European Council. Therefore, these particular samples should be considered as a potential risk to the human health incase they could ever be re-employed, without any kind of pretreatment, as a source of cellulose secondary fibre in the production of packaging to be used in direct contact with food products. Furthermore, it has to be pointed out that the values of heavy metal concentrations (again, apart from Hg) obtained by both the migration and the extraction test have always been lower for paper samples employed as food packaging in direct contact with food, with respect to samples coupled to a protective PE film and to paper samples employed for other uses. Finally, it seems worthwhile for us to highlight the marked decrease in the levels of heavy metals, shifting from the migration test to the extraction test. This evidence shows that the potential risks to health are in principle dependent not only on the nature of
The newspaper industry lies in an intermediate position, utilizing about 50% of secondary fibres, even if the use of secondary fibres is continuously growing. It is worthwhile to highlight that usually the assessment of the quality of food packagings does not include paper packagings among the possible sources of food contamination (Bureau and Multon, 1996). The investigation shows that a significant amount of heavy metals are present in some of types of paper; for indeed, apart from mercury (whose concentration always lay below the instrumental limits of the analytical technique applied in the present study) and lead (whose levels have been Table 8. Precision tests*
Element Pb Cd Cr Hg
No. of tests
(@l)
Variation coefficient %
IO II 12 9
4.2 1.0 3.4 2.0
6.1 3.ti 4.1 8.4
Concentration
paper by AAS: M.E. Conti and F. Botr&
*Assays of Pb, Cd and Cr have been carried out by the automatic sampler.
Table 9. Results of the migration tests (3% acetic acid). Data are expressed as both pg of metal per g of paper and pg of metal per dm’ of paper. Each value is the mean of five independent sample preparations Lead Sample 1 2 3 4 5 6 : 9 IO 11 12
Chromium
Cadmium
Mercury
pg/dm’
@g
l@dm’
&g
pg/dm’
Wg
Ltg/dm’
Wg
0.72 n.d. n.d. 0.51 n.d. 1.20 n.d. 2.63 1.12 6.71 12.81 0.27
1.47 n.d. n.d. 0.95 n.d. 4.38 n.d. 5.68 1.47 6.47 11.39 0.59
0.01 0.05 n.d. n.d. 0.04 0.02 n.d. 0.03 0.04 0.04 0.09 0.10
0.02 0.11 n.d. n.d. 0.06 0.07 n.d. 0.06 0.05 0.03 0.08 0.22
n.d. n.d. n.d. 0.28 0.24 n.d. n.d. n.d. 0.32 0.28 0.40 n.d.
n.d. n.d. n.d. 0.52 0.40 n.d. n.d. n.d. 0.42 0.27 0.35 n.d.
n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.
n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.
n.d: not detectable ([Pb] <4 &I,
[Cd] ~0.1 @I,
[Cr] ~4 pgil, (Hg] < 1 Itgil in the contact liquid).
Table 10. Results of the extraction tests (distilled water). Data are expressed as both pg of metal per g of paper and pg of metal per dm’ of paper. Each value is the mean of five independent sample preparations Lead Sample I
Cadmium
Chromium
Mercury
@dm’
&Yg
l@dm’
@g
@dm’
l&g
@dm’
I&g
n.d. 0.23 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.
n.d. 0.54 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.
n.d. n.d. 0.05 0.05 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.
n.d. n.d. 0.08 0.09 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.
n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.
n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.
n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.
n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.
n.d.: not detectable ([Pb] <4 @I,
[Cd] ~0.1 @I, [Cr) <4 @I, [Hg] <
I &I in the contact liquid).
Food Control 1997 Volume 8 Number 3
135
Heavy metals in packaging paper by AAS: M.E. Conti and F. Botrl!
‘lbble 11. Results of the migration tests (3% acetic acid) for Cr VI. Data are expressed as both pg of metal per g of paper and pg of metal per dm’ of paper. Each value is the mean of five independent sample preparations Chromium VI Sample
pgldm’
@g
4 5 9 IO II
0.12 0.07 0.10 0.12 0.13
0.22 0.13 0.13 0.11 0.12
*The listed data have been obtained by concentrating acetic acid extract. The used specimens had a contact surface of 4 dm’.
5:l the
the packaging, but also, to a relevant extent, on the nature of the packaged food. This finding also stresses the primary role played by the storage conditions of the system packaging/packaged, since various environmental agents (temperature, humidity, volatile acids and so on) could markedly affect the release of various components of the packaging into the food. Additional experiments are presently in progress in our laboratories, in order to extend the sampling to a more relevant number of geographic areas, and to compare the results of the present work with those obtained by a biological approach. The same investigation reported in this work is also being carried out for other paper derived food-packaging materials (paper boards).
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Food Control 1997 Volume 6 Number 3
ACKNOWLEDGEMENTS This work has been supported in part by a grant of the Italian National Research Council (CNR). REFERENCES Bureau, G. and Multon, J. L. (1996) Food Packaging Technology, Vol. 1-2 VCH, Weinheim. CNR IRSA, (1980) Metodi Analitici per le Acque, Rome, Italy. Conti, M. E., Boccdcci Mariani, M., Milana, M. R. and Gramiccioni, L. (1996) Heavy Metals and Optical Whitenings as Quality Parameters of Recycled Paper for Food Packaging. Journal of Food Processingand Preservation20, I- 11. Gramiccioni, L. (1994) Caratteristiche Qualitative di Carte e Cartoni per Uso Alimentare. In Libera Circolazione e Qualit& dei Prodotti net Mercato Unico Europeo, ed. F. Botrt: and E. lannucci, vol 11, pp. 625-630. Kappa, Roma. Italian Ministerial Decree, dated 21.3.1973, published Cl,@no 104, 20.4.1973.
on Gaze.
Italian Ministerial Decree, dated D. M. 18.61979, published on Gazz. Ufl no 180, 3.7.1979. ‘Official Methods of Analysis of AOAC International. In AOAC International,ed. P. Cunniff, Vol XVI, Arlington (VA), USA. Pavesi, F. (1996) Pianeta carta lmpresa e ambiente 5, 26-35. Rossi, L. (1993) The Status of the Food Packaging Regulation at the Beginning of the Internal Market and Future Perspectives. In Proceedings of the International Conference on: Materialsfor Food Packaging, Gothenburg, (Sweden). Svennson, K. (1993) Work of the Council of Europe in the Area of Paper and Board used in Food Contact Applications. In Proceedings of the International Conference on: Materials for Food Packaging,Gothenburg (Sweden).