Ethoxyquin (EMQ) residues in Atlantic salmon measured by fluorimetry and gas chromatography (GLC)

Salmons of two different sizes (group I; 22--30 g, group II; 600--1450 g) were tested for ethoxyquin (EMQ) residues after fed ad libitum a diet supplied with the therapeutic level of 900 ppm EMQ for 2 months. The sums of residues of EMQ and possible metabolites having similar fluorescence characteristics were determined by a fluorimetric method. The percentage of unmetabolized EMQ present was estimated using a gas chromatographic-mass spectrometric (GLC-MS) method measuring only unchanged EMQ. For both methods the detection limit was 0.1 ppm. EMQ residues were also fluorimetrically estimated in muscle tissue of small salmons fed a diet preserved with 150 ppm EMQ for 2 months. At termination of feeding the diet supplied with 900 ppm EMQ, residues measured fluorimetrically in muscle tissue of salmons in both groups were averaging 0.7 ppm. Approximately one third was unchanged EMQ. From salmons of group II blood, kidney and hepatic tissue were also analyzed at termination of feeding and residues averaging 0.3, 0.8 and 1.8 ppm respectively were estimated. The elimination of EMQ from muscle tissue is illustrated in Fig. 1. No residues could be detected 9 days following termination of feeding the therapeutic level of EMQ. In muscle tissue of salmons fed the diet preserved with 150 ppm EMQ, residues ranging from 0.1 to 0.3 ppm of EMQ and possible metabolites were found in 9 of 10 samples obtained from 20 salmons in group I. For an evaluation of EMQ used as a feed additive (150 ppm), further studies were recommended. The diets used in the experiment contained 88 and 830 ppm EMQ respectively measured fluorimetrically at the end of the experiment. Approximately 88% of the residues in the feed was unchanged EMQ. It is suggested that most information regarding the hygienic aspects of residues in muscle tissue is obtained by fluorimetry which is therefore recommended for determination of EMQ residues in tissues. The GLC-MS method, however, is recommended for estimation of EMQ levels in feed.