Occurrence of organochlorine agrochemical residues in Spanish cheeses

Pestic. Sci. 1995,44, 177-182

Occurrence of Organochlorine Agrochemical Residues in Spanish Cheeses Antonio Bentabol & Manuela Jodral* Department of Food Science and Technology, Faculty of Veterinary Medicine, University of Cordoba, Av. Medina-Azahara 9,14005 Cordoba, Spain (Received 24 June 1994; revised version received 8 November 1994; accepted 8 February 1995)

Abstract: A total of 146 samples of different kinds of cheeses produced in Spain were analysed in order to ascertain the specific contamination pattern. The organochlorine compounds studied were those most commonly investigated in previous surveys : a-HCH, /?-HCH, y-HCH (lindane), 6-HCH, chlordane, aldrin, dieldrin, endrin, heptachlor, heptachlor epoxide, and the isomers and metabolites of DDT. a-HCH, /3-HCH, y-HCH, chlordane, p,p‘-DDT, and p,p’-DDE were found in more than 76% of samples; p,p’-DDE and y-HCH were the most frequently detected, with frequencies of 100 and 97.9% respectively. 6-HCH, aldrin, dieldrin, heptachlor, heptachlor epoxide, o,p‘-DDT, p,p’-DDD and o,p‘-DDD were observed at lower frequencies. No residues of endrin were detected in any sample. Insecticides exceeding the maximum residue limits (MRLs) were chlordane, /?-HCH, a-HCH and 7-HCH, with 42, 20, eight and six samples respectively. Mean residues of organochlorines found were as follows (pg kg- butterfat): a- HCH = 46.3; /?-HCH = 46.5; y-HCH = 54.2; 8-HCH = 16.9; aldrin = 16.7; dieldrin = 9-7; heptachlor = 15.9; heptachlor epoxide = 14.8; chlordane = 50.2; o,p’-DDT = 5.1; p,p’-DDT = 12.4; o,p’-DDD = 19.6; p,p’-DDD = 46.7; 0,~’-

DDE = 6.9; p,p‘-DDE = 40.7 (ZDDT = 55.0). Estimated dietary intakes (EDIs) from cheese consumption were compared to

acceptable daily intakes (ADIs) for the pesticides where residues exceeded the MRL. EDIs calculated were in all cases below ADIs, and, therefore, based on the ADIs, there is no health risk involved in the consumption of cheese from Spain arising from organochlorine residues.

Key words : organochlorine residues, Spanish cheeses.

1 INTRODUCTION other dairy products has great relevance because these values are convenient indicators of environmental con-

Organochlorine pesticides have been massively tamination by organochlorine pesticides. The employed in the past decades against vegetal pests and occurrence of these compounds in milk and dairy pro- vector-borne diseases. These uses have led to extensive ducts has been recently reported by different authors in contamination of the environment and food chain. Spain’-6 and other pointing out in all Owing to their lipophilic properties, organochlorines cases the decreasing levels with respect to previous are primarily stored in fat-rich tissues and fluids of surveys as a consequence of the restriction or banning humans and animals. Milk is one of the ways these pro- of these insecticides. A few studies include cheeses in the ducts are excreted, dissolved in butterfat, and they can group of dairy products analysed. accumulate in fat-rich dairy products, such as cheeses; The present survey was undertaken to follow up the this fact is specially relevant because milk and dairy observed trends and to evaluate actual organochlorine’ products play a central role in human nutrition. Moni- pesticide residues levels in cheeses in Spain, to contrib- toring the levels of pesticides present in cheese and ute to the knowledge of the present status of Spanish

foods with respect to organochlorines, and to assess the * To whom correspondence should be addressed. possible associated health risks. There will be an

177 Pestic. Sci. 0031-613X/95/$09.00 0 1995 SCI. Printed in Great Britain

178 Antonio Bentabol, Manuela Jodral

increased interest from regulatory agencies in reviewing the incidence and levels of residues in cheeses from different countries as international markets are opened further by EU, NAFTA and GATT.

2 MATERIALS AND METHODS

2.1 Samples

One hundred and forty-six samples of cheeses produced in Spain were collected from Spanish markets in ordi- nary commercial outlets, usually located near the pro- duction zone, during 1991. Cheeses analysed represented different kinds of cheeses commonly con- sumed in Spain. These cheeses used milk of different animal origins and were made by different processes. Samples were kept at 4°C until analysis or frozen at -20°C when it was not possible to analyse them imme- diately.

2.2 Analytical procedures

Samples were analysed by a multi-residue technique described by Bentabol and Jodral." In this technique, the fat extracted from the cheeses was subjected to two simultaneous processes of extraction and clean-up, one with sulfuric acid and the other by means of potassium hydroxide-ethanol solution, complementing the previous process. The behaviour of the different organochlorine pesticides in the two treatments enabled us to identify and confirm them. The analytical method- ology for the analysis of cheeses was based on four key factors: (a) isolating the fat from the cheese, (b) extracting the chlorinated pesticides from the fat by acid treatment with concentrated sulfuric acid, (c) extracting chlorinated pesticides from the fat by basic treatment with potassium hydroxide-ethanol solution (100 g litre- I) and (d) comparison between the behaviour of the different pesticides in the two chromatograms obtained, after GC analysis.

2.2.1 Fatty matter extraction Fat contained in cheeses was separated from the rest of the product by a liquid-liquid partitioning method, according to the standard NBN V21-017 of the Belgian Institute for Normalization," employed successfully by Pozo et aL3 in previous surveys. Anhydrous sodium sulfate was added to a sample of cheese (45 g) and triturated, so that, after mixing, a dry friable mass was obtained. Acetone (200 ml) was added and mixed with a blender, followed by light petroleum distillate (100 ml) and further mixing. The liquid phase was poured off carefully into a 500-ml separation funnel and shaken with water (100 ml). After phase separation, the aqueous layer was discarded, and the supernatant phase

decanted through anhydrous sodium sulfate and glass wool. The solvent was evaporated under vacuum, leaving the fat, which was transferred to a glass vial and kept at - 20°C until analysis.

2.2.2. Fatty matter determination The percentage of fatty matter contained in the cheese samples was determined using an acid-butyrometric method according to Van Gulik, corresponding to the I S 0 3432 standard, in which triturated cheese (3 g) was digested at 65°C with sulfuric acid (p = 1-84) in glass butyrometers (Dr N. Gerber, Original, Zurich, Switzerland). The determinations were made in dupli- cate for each sample and the results expressed as a mean of the observations. The differences between the two readings did not exceed 0.5 g of fatty matter 100 g-' of cheese.

2.2.3 Clean-upextraction Fat was subjected to a two-way clean-up-extraction procedure, with concentrated sulfuric acid and potassium hydroxide-ethanol solution.

2.2.3.1 Acid treatment. Fat (2.0 g) was placed in a 25-ml screw-topped glass tube, hexane (20 ml) added and mixed to total fat dissolution. Concentrated sulfuric acid (1 ml) was added, the tube closed and shaken for 30 s in an orbital shaker. The mixture was centrifuged at 3000 rev. min-' for 10 min to separate the two phases. Seventeen samples of the upper phase (10 ml), containing the pesticides dissolved in hexane, were transferred to gauged glass vials and concentrated to 2.5 ml on a 40°C sand bath. The concentrates were then ready for GC analysis.

2.2.3.2 Alkaline treatment. Fat (2.0 g) was placed in a 100-ml dilution flask, freshly prepared ethanolic potassium hydroxide (100 g litre-'; 10 ml) added, and mixed to dissolution. The mixture was heated on a 60°C water bath for 30 min for saponification, with periodic shaking. The mixture was cooled, bidistilled water (10 ml) added and shaken to total dissolution of the soap formed. Equal parts were poured into two 25-ml glass tubes, hexane (10 ml) added to each tube and mixed in a shaker for 30 s. The tubes were centrifuged for 10 min at 3000 rev. min-'. Five millilitres of the upper phase of each tube were combined in a gauged glass vial. After concentration to 2.5 ml, the extract was ready for GC separation.

2.2.4 GC determination The two extracts obtained for each sample were investigated separately by gas chromatography in a gas chro- matograph (Hewlett-Packard model 5890) with 63Ni electron-capture detector, and equipped with a 2 m x 2 mm ID x inch (6 mm) OD glass column packed with 5% QF-1 on 80-100 mesh Chromosorb@

Organochiorine Agrochemical Residues in Spanish Cheeses 179

W-AW analytical column. Inject ion volume: 5 p1. Separation was carried out under isothermal condi- tions: oven 190"C, injector and detector 225°C; carrier gas : argon-methane. Samples were injected manually. Linearity of the response of the detector was demon- strated (r > 0.999) for every one of the standards. Retention times and comparative behaviour to both treatments were used for identification of the pesticides. When necessary, another column of different polarity, SE-30, was used for confirmation purposes.

For the calculation of the total recoveries of the method, from fat extraction to GC analysis, cheese (32% fat rich; 45 g) of known chlorinated residues content was homogenized with endrin (50 pg) and 10 pg of each of the other pesticides. The method was applied in quadruplicate to the fortified cheeses; results are shown in Table 1. Pesticide standards were supplied by Supelco Inc. (Bellefonte, USA).

3 RESULTS AND DISCUSSION

Table 2 shows levels obtained for the different organochlorine residues in analysed cheeses. All samples contained residues of pesticides. HCH, chlordane and DDE were the most frequent chlorinated pesticide contaminants detected in the cheeses analysed.

Frequency distribution of organochlorine residues obtained in the analysed cheeses are shown in Table 3.

3.1 Hexachlorocyclohexane

HCH, as one or more of its isomers, was detected in all the samples analysed. y-HCH was the isomer most frequently found and with the highest concentrations of all HCHs. On the other hand, 8-HCH was detected in only 9.6% of samples, with a mean concentration of 16-9 pg kg-' fat basis, the lowest in this group. In 13.7% of cases, levels of P-HCH exceeded the maximum residue limits (MRLs), established by European Cornm~nity'~ for dairy products containing 2% or more fat. It is followed by a-HCH in 5.5%, and y-HCH in 4.1% of the samples. Although y-HCH is still in current use in Spanish agriculture, primarily as seed treatment and for cowshed clearing of insects, technical HCH, including also the rest of its isomers, was banned from agricultural purposes in Spain in the later 1970s. We have found higher frequencies and lower concentrations in Spanish milk and dairy products than those reported in the 1970 decade14-16 even though the presence of some of the HCH isomers was not reported in any of these previous surveys. Our results agree with those of Barcelo and Garcia-Puignou4 and De la Riva and Anadbn' obtained recently in Spain. The most probable explanation for these facts is improved meth- odology, including better detection limits, or this perhaps indicates the use of y-HCH preparations which do not possess the required level of purity and which contained larger quantities of other isomers than those authorized. The high frequencies detected for this group

TABLE 1 Average Recoveries of Organochlorine Pesticides after Sulfuric Acid and Potassium Hydroxide-Ethanol Treatments"

Sulfuric acid treatment Potassium hydroxide-ethanol treatment

Pesticide Recovery (%)b SD Ret. time" Recovery (%)b SD Ret. time" Degrad. prod.

a-HCH B-HCH y-HCH 6-HCH Aldrin Dieldrin Endrin Chlordane Heptachlor Heptachlor epoxide o,p'-DDT p,p'-DDT o,p'-DDD p,p'-DDD o,p'-DDE p,p'-DDE

103.4 99.9

113.9 118.0 87.6 D D

101.1 95.5 84.6

100.7 91.7

106.2 119.7 102.5 101.6

17.7 13.3 21.7 19.3 9.1 -

-

7.9 7.1

14.2 9.4 6.4 6.8

16.7 4.7 4.7

0.65 0.9 1 0.80 1.10 1.00 N N

1.68 0.88 1.75 2.41 3.54 2.28 3.22 1.49 1.91

D D D D

109.1 95.7 99.6 97.2 90.9 86.3 T T T T

100.5 98.9

N N N N

1 .oo 2.66' 6-02 1-68 0.88 1.76

( 1.49)' (1.91) (1.25) (3.05) 1.49 1-91

N N N N

o,p'-DDE p,p'-DDE o,p'-DDMU p,p'-DDMU

a D = destroyed; T = transformed; N = no GC peaks observed. Expressed as mean for four replicates. Retention times relative to aldrin (2.28 min). In parenthesis, retention times of the degradation products relative to aldrin.


TABLE 2 Percentage of Positive Samples, Mean, Absolute Residue Concentration Range and Number of Samples

Exceeding Legal Tolerances (MRL) of Organochlorine Pesticides in Spanish Cheeses (n = 146)

No. samples Detection Positive exceeding

Pesticide limit“ (%) Mean” Range MRLb M R L

a-HCH fi-HCH y-HCH 6-HCH ZHCH‘ Aldrin Dieldrin Aldrin + dieldrin Endrin Chlordane Heptachlor Heptachlor epoxide Heptachlor + H. epoxide o,p’-DDT p,p’-DDT o,p’-DDD p,p’-DDD o,p’-DDE p,p’-DDE ZDDT~ Z Pesticides‘

0.50 1 .00 0.25 1 .00

85.7 77.4 97.9 9.6

100.0 6.1

21.2 26.7 0

94.5 12.3 6.8

19.2 4.8

34.2 4.8 7.5

76.7 100.0 100.0 100.0

46.32 46.50 54.20 16.93

130.50 16.67 9.67

14.74

50.22 15.94 14.80 15.54 5.14

12.42 19.57 46.73

6.94 40.77 55.05

249.20

-

2-1644 2-615 1-1071 3-53 3-1913 1-34 3-63 1-63 -

7-962 3-55 4 2 4 3-55 1-8 2-58 3-78 2-119 1-101 4345 4 4 0 6

27-2 1 39

100 75

200 -

8 20 6 -

0.50 0.50 -

150 20 50

15.00 1 .00 0.50 1 .00

0.50 1 .00 0.50 1 .00 0.50 0.50 -

0

Expressed as pg kg-’ on fat basis.

ZHCH, sum of a-HCH, p-HCH, y-HCH and 6-HCH. ZDDT, sum of o,p’-DDT, p,p’-DDT, o,p’-DDD, p,p’-DDD, o,p’-DDE and p,p‘-DDE.

* MRL issues in Directive 86/363 of the European Communities, expressed as pg kg-’ on fat basis.

‘ Sum of all the organochlorine residues.

TABLE 3 Frequency Distribution of Organochlorine Residues in Spanish Cheeses

Frequency distribution by content in fat (pg kg-’)”

Pesticide < I 1-10 11-20 21-30 31-40 41-50 51-70 71-100 101-200 201-300 >300

a-HCH P-HCH y-HCH 8-HCH Aldrin Dieldrin Endrin Heptachlor Heptachlor epoxide Chlordane o,p‘-DDT p,p’-DDT o,p’-DDD p,p‘-DDD o,p’-DDE p,p’-DDE

0 37 27 19 29

0 33 33 6 5

0 3 3 0 14 14

0 9 4 5 2 9 28

0 7 0 - 33 11 0 4 2

3 2 0 96 8 0 21 35

-

-

- - -

- -

-

18 9 20 10 28 12 1 1 1 2 2 0 0 0 2 1 3 0

24 24 0 0 1 3 0 0 0 1 5 1

35 17

9 10 8 7

13 4 1 1 0 0 0 1 0 0 1 0 0 0

11 24 0 0 1 1 0 0 0 1 0 1 5 12

6 10 7 0 0 0 0 0 0

10 0 0 1 3 0

12

5 7 7 0 0 0 0 0 0 5 0 0 0 1 1 5

1 0 1 0 0 0 0 0 0 2 0 0 0 0 0 2

2 3 5 0 0 0 0 0 0 1 0 0 0 0 0 2

a - = below detection limit specified in Table 2.

Organochlorine Agrochemical

of substances imply their environment.

3.2 Aldrin and dieldrin

Residues in Spanish Cheeses

great dispersion in the

Aldrin was detected in 6.2% of the samples, with a mean level of 16.7 pg kg-'. Dieldrin was found more frequently, 21.2%, with a mean concentration of 9-7 pg kg-'. The presence of aldrin in cheese implies direct contamination of milk or at least a recent contamination, as aldrin is quickly transformed into its epoxide, i.e. dieldrin, during animal metabolism. The MRL for these pesticides is 150 pg kg-' butterfat, expressed as combined aldrin and dieldrin; none of the samples exceeded this limit. Aldrin and/or dieldrin were present in 26.7% of the cheeses analysed, with an average concentration of 14.7 pg kg-' and values ranging between 1 and 63 pg kg-'.

3.3 Endrin

This insecticide was not detected in any of the samples analysed ; this agrees with many similar studies. Barcel6 and Garcia-Puignou? De la Riva and Anad6n,5 Garrido et aL6 in Spain; Frank et aL7 and Fytianos et a1.' in other countries did not find endrin in milk and dairy products analysed.

3.4 Heptachlor and heptachlor epoxide

Heptachlor was detected in 12.3% of the samples, and 6.8% of the samples contained heptachlor epoxide. The two compounds have not been detected together in any of the 146 samples of cheese analysed. The EC reports the MRL for these residues as a combination of the two; none of the samples exceeded the MRL. Our results, together with other recent surveys (Barcel6 and Garcia-Puignou: De la Riva and Anadon5), classify heptachlor and its epoxide as infrequent residues in Spanish milks, and therefore dairy products. This does not seem to occur in other countries, since Frank et aL7 detected heptachlor epoxide in 96% of their samples in Canada.

3.5 Chlordane

This insecticide was found in 94.5% of the samples. The average concentration detected was one of the highest found, 50.2 pg kg-'. This was the pesticide that most frequently exceeded the allowed limits; levels detected were greater than MRL in 28.8% of the samples. Our results show a decrease of approximately 25% in the

181

chlordane mean concentration from that reported by Garrido et aL6 The high frequencies and levels obtained suggest that, despite its prohibition in 1977, chlordane may still be widely used in Spanish agriculture.

3.6 ZDDT

ZDDT includes the residues of p,p'-DDT; p,p'-DDD; p$-DDE; o,p'-DDT; o,p'-DDD and o,p'-DDE, as described in the EC regulations. All the samples contained some isomer of DDT or its metabolites. The mean level of CDDT was 55.1 pg kg-', with a maximum of 406 pg kg-'. The individual values detected for the different components of this group are shown in Table 2. p,p'-DDE, o,p'-DDE and p,p'-DDT were the compounds of this family detected most frequently, with 100,76.7 and 34.2% respectively. The o,p'- isomers of these substances appeared with lower concentrations and frequencies than p,p' ones. This fact, according to Frank et ~ 1 . ~ and Garrido et a1.,6 is due to a lesser persistence of o,p'-isomers in the environment. Another cause could be that commercial DDT used as an insecticide normally contained > 70% p,p'-DDT, because the latter was the most insecticidally active isomer: the other components, including o,p'-DDT, were minorities or impurities. No sample exceeded lo00 pg kg-', which is the MRL established for CDDT. None of the authors consulted included the six components of this group in their studies, so no direct comparison with their results can be made: in general, levels of ZDDT detected were lower than those found in previous surveys. The prevalence of DDE residues over those of its precursor imply that these compounds appear as residues of treatments made with DDT before its prohibition in Spain.

3.7 Health risk evaluation

Table 2 illustrates the number of samples of cheese exceeding MRLs allowed in the EC for each one of the residues.

Estimated daily intakes (EDIs) of these compounds were calculated to evaluate the possible health risks which might be associated with the consumption of cheese containing organochlorine pesticides. Calcu- lations are based on the average per capita consumption of cheese reported by the Spanish Ministry of Foods, Agriculture and Fi~heries,'~ i.e. 5.4 kg cheese per year, which equals 14.3 g per day. We have to know the residue concentrations expressed as kg of product, instead of on a fat basis. The percentage of fatty matter in the samples ranged between 17 and >40%, with a mean of 33.7%. We have calculated the EDIs for every sample, taking into account its specific fatty matter content. We have calculated average EDIs from these


TABLE 4 Maximum, Minimum and Average Estimated Daily Intake (EDI), and Acceptable Daily Intake

(AD1)O of Some of the Organochlorine Insecticides Studied

ED1 AD1 (pg kg-' bw)

Pesticide (pg kg-' bw)b Maximum Minimum Average

y-HCH (Lindane) 10 5.55 1 0 - 2 5.94 x 10-5 3.79 x 10-3 Aldrin + dieldrin 1 3.65 1 0 - 3 4.30 x 1 0 - 5 9.45 x 10-4 Heptachlor + H. epoxide 5 4.28 10-3 2.52 x 10-4 1-10 x 10-3 ZDDT 20 2.66 1 0 - 3 2.10 x 10-4 3.71 x 10-3

(I Recommended by FAO/WHO. bw = body weight.

individual EDIs. These results are shown in Table 4 together with maximum and minimum EDIs obtained, as well as ADIs recommended by FAO/WH0.18 In all cases the EDIs obtained were less than 1% of ADIs recommended ; therefore the consumption of Spanish cheeses does not seem to be a risk for consumer health based on their content of organochlorine insecticides residues and actual recommendations. On the other hand, we cannot forget the possible long-term effects of pesticide accumulated in the human body, which are still not well known, and must be further investigated.

ACKNOWLEDGEMENTS

The authors wish to thank Ms Gloria Fernandez-Marin for her invaluable collaboration and analytical assist- ance during the development of this work.

This research is supported by the project ALI 92/0991 of the Interministerial Commission of Science and Technology of Spain.

REFERENCES

1.

2.

3.

4.

5.

Herrera, A., Pozo, R., Jodral, M. & Polo, L. M., Pesticidas organoclorados en leches evaporadas y en leches conden- sadas espaiiolas. Revista de Sanidad e Higiene Ptiblica, 40

Baluja, G., Hernandez, L. M., Gonzalez, M. J. & Rico, M. C., Presence of organochlorine pesticides, poly- chlorinated biphenyls and mercury in Spanish human milk samples. Bull. Environ. Contam. Toxicol., 28 (1982)

Pozo, R., Polo, L. M., Jodral, M., Jordano, R. & Zurera, G., Plaguicidas organoclorados en quesos espaiioles. Archioos de Zootecnia, 126 (1984) 143-61. Barcelo, D. & Garcia-Puignou, L., Residuos de plaguicidas en leches UHT espaiiolas determinados por cromatografia de gases de alta resolucion. Reo. Agroquim. Tecnol. Aliment., 27 (1987) 583-9. de la Riva, C. & Anadon, A., Organochlorine pesticides in cow's milk from agricultural region in northwestern Spain. Bull. Enoiron. Contam. Toxicol., 46 (1991) 527-33.

(1981) 1-12.

573-7.

6.

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

Garrido, M. D., Bentabol, A., Jodral, M. & Pozo, R., Pro- ceedings EuroResidue 11: Conference on Residue of Veteri- nary Drugs in Food, 1 (1993) 298-302. Frank, R., Braun, H. E., Sirons, G. H., Rasper, J. & Ward, G. G., Organochlorine and organophosphorus insecticides and industrial pollutants in the milk supplies of Ontario- 1983. J. Assoc. Ofi Anal. Chem., 48 (1985) 499-504. Fytianos, K., Vasilikiotis, G., Weil, L., Kavlendis, E. & Laskaridis, N., Preliminary study of organochlorine compounds in milk products, human milk and vegetables. Bull. Environ. Contam. Toxicol., 34 (1985) 504-8. Dogheim, S. M., Almaz, M. M., Kostandi, S. N. & Hegazy, M. E., Pesticide residue in milk and fish samples collected from upper Egypt. J . Assoc. Of. Anal. Chem., 71

Kaphalia, B. S., Takroo, R., Mehrotra, S., Nigam, U. & Seth, T. D., Organochlorine pesticide residues in different India1 cereals, pulses, spices, vegetables, fruits, milk, butter, deshi ghee, and edible oils. J. Assoc. Ofi Anal. Chem., 73 (1990) 509-12. Bentabol, A. & Jodral, M., Simple method for the determination of chlorinated pesticides: Application to cheese samples. J. Assoc. OH. Anal. Chem. (in press) (1994). Belgian Institute for Normalization, Melk en Zuivelpro- dukten bepaling von het gehalte aan organochlor-pesticide residus. NBN V21-017, 1977. European Communities, Directiva del Consejo de Ias Comunidades Europeas 86/363/CEE. Fijaci6n de conte- nidos maximos para 10s residuos de plaguicidas sobre y en 10s productos alimenticios de origen animal. Boletin Oficial de las Comunidades Europeas, 221 (1986) 43-7. Herrera, A., Pozo, R., Polo, L. M., Lopez, R., Jodral, M. & Iglesias, J., Investigaciones de plaguicidas organoclorados en mantequillas espaiiolas. Anales de Bromatologia, 28

Pozo, R., Herrera, A., Polo, L. M., Lopez, R., Jodral, M. & Iglesias, J., Niveles de plaguicidas organoclorados en leches esterilizadas espaiiolas. Anales de Bromatologia, 29

Martinez, I. & Juarez, M., Residuos de pesticidas organoclorados en leche y productos lacteos comerciales. Rev. Esparlola de Lecheria, 112 (1979) 59-73. Anon, El consumo alimentario en EspaAa. Ministry for Foods, Agriculture and Fisheries, Madrid, 1989, pp. 577-93. Anon, Consecuencias sanitarias del empleo de plaguicidas en la agricultura. World Health Organization, Geneva, 1992.

(1988) 872-4.

(1976) 409-40.

(1977) 305-60.

Documents

Occurrence of organochlorine agrochemical residues in Spanish cheeses