Fressenius J Anal Chem, 1991; 339: 376–383. 9. Waters Analysis Carbamate
System. Operator's Manual. 10. Ruprich J et al: The Health Risk Assessment of ...
Cent Eur J Publ Health 2004; 12 (4): 220–223
DETERMINATION OF N-METHYLCARBAMATES IN FOODS Borkovcová I., Janoušková E., Řehůřková I., Ruprich J.
The National Institute of Public Health in Prague, Division for the Hygiene of Food Chains in Brno, Czech Republic SUMMARY The multiresidue method using multisolvent extraction, SPE cleanup of the extract, HPLC with the use of OPA post-column reaction and fluorescence detection for the determination of N-methylcarbamate pesticides in food products was used. A matrix solid phase dispersion method of the isolation and extraction of carbamates was alternatively applied. In the introductory study 44 items of the food basket for the Czech Republic were analysed. In the major part of the studied samples, the considerable part of which was culinary treated, the concentration of the target carbamates was below the limit of the used detection method. In the concentration range of 10–100 μg/kg in the analysed samples of the studied analytes, aldicarb and its metabolites, e.g. methomyl and methiocarb were being found most frequently. Key words: N-methylcarbamates, food products, extraction, HPLC determination Address for correspondence: I. Borkovcová, National Institute of Public Health, Centre for the Hygiene of Food Chains, Palackého 3a, 612 42 Brno, Czech Republic. E-mail:
[email protected], www.chpr.szu.cz
INTRODUCTION Being both highly effective and having a broad spectrum of activity carbamate pesticides are extensively and world wide applied to protect crops and food from the ravages of pests. They exhibit herbicidic, fungicidic, acaricidic, nematocidic and rodenticidic effects. The number and quantity of N-methylcarbamate pesticides used in agriculture continue to increase, replacing the more environmentally stable organohalogen pesticides. Carbamates inhibit acetylcholinesterases, they are toxic for organisms, and they can attack nervous system giving a rise to the genetic damage. Due to their toxic nature and harmful effect on human organism a great attention is given to the monitoring of carbamates and their metabolites in the environment. Drinking water sources can be contaminated by agricultural runoff. After being applied to foods they can contain residues of both carbamates and their by-products and if harvested too soon after the application the above mentioned residues can remain in the produce. Both the development of the multiresidual method of N-methylcarbamate pesticides and the determination and monitoring of these compounds in foods of the food basket for the population of the Czech Republic were implemented in the Centre of Hygiene of Food Chains in Brno, National Institute of Public Health in Prague (1).
List of acronyms: GPC–Gel Permeation Chromatography; HPLC–High Performance Liquid Chromatography; LC–Liquid Chromatography; LOD–Limit of Detection; MSPD–Matrix Solid Phase Dispersion; SPE–Solid Phase Extraction; US–EPA–United States Environmetal Protection Agency
On the basis of the data on the reviewed carbamate pesticides occurrence and in consent with the regulations of the Czech Republic, the commodities in which the occurrence of these pesticides would be probable were selected. The commodities were mostly of the plant origin, e.g.: vegetables, fruits, vegetable and fruit products and cereals. The isolation of carbamate pesticides from the food matrix followed by HPLC assay was performed on eleven analytes specified in US-EPA method 5.3.1 and most frequently mentioned in the literature, e.g. on: aldicarb, aldicarbsulfoxide, aldicarbsulfone, methomyl, oxamyl, 3-hydroxycarbofuran, carbaryl, carbofuran, propoxur, pirimicarb and methiocarb (2–8). Considering that the ADI values are very low, they range from 0,1 to 1 μg.kg–1, it was necessary to work out the analytical method, the LOD of which could make the evaluation of the exposure to those carbamate pesticides in foods possible. PRINCIPLE OF THE DETERMINATION From the chemical point of view, N-methylcarbamates are derived from carbamic acid. Their characteristic feature is the hydrolyzable N-methylcarbamoyl moiety. The rest of the molecule is structurally different and its character limits subsequent analysis, determination and detection. Thus, it would be difficult to include all these above mentioned compounds into a multiresidue method using LC with UV detection and to achieve uniformly low detection limit for each analyte. The N-methylcarbamoyloximes – oxamyl, methomyl and aldicarb have UV extinction coefficients nearly 3–4 orders of magnitude lower than those of the aromatic ring containing
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Table 1. Validation parametres of the method for determining N-methylcabamates in foods Recovery (%)
SD (μg/kg)
RSD (%)
LOQ (μg/kg)
Aldicarbsulfoxide
92.0
8.6
9.4
0.9
Aldicarbsulfone
95.4
8.1
8.5
0.07
Oxamyl
96.1
7.2
7.5
1.0
Methomyl
94.1
8.6
9.2
4.8
3-hydroxycarbofuran
82.4
7.2
8.8
0.3
Aldicarb
80.1
7.5
9.4
0.7
Propoxur
58.1
3.7
4.4
0.5
Carbofuran
85.0
7.2
8.5
0.9
Carbaryl
82.0
7.4
9.1
0.8
Pirimicarb
88.2
8.5
9.6
0.5
Methiocarb
76.8
7.75
10.1
0.3
Analyt
SD = standard deviation, RSD = relative standard deviation, LOQ = limit of quantitation. LOQ was estimated via analysis of blank samples. Recoveries are valid for concentrations up to 400 μg/kg except for oxamyl (200 μg/kg). The validation parameters were obtained by means of EffiValidation 1.0 software. Table 2. Concentrations of N-methylcarbamates (μg/kg) in selected food samples Oxamyl
Methomyl
3OHCBF
Aldicarb
Propoxur
Carbofuran
Carbaryl
Methiocarb
Syrup
Samples
AldicarbSO AldicarbSO2 < 0.9
< 0.07
