Xenobiotic clenbuterol in food producing male pigs: Various tissue residue accumulation on days after withdrawal

Using enzyme-linked immunosorbent assay (ELISA) and liquid chromatography tandem mass spectrometry (LC-MS/MS) the concentrations of clenbuterol (ng/g) were shown to be highest in choroid/pigmented retinal epithelium (choroid/PRE) (499.59 ± 26.36 ng/g), followed by hair (fair colored) (207.76 ± 86.88 ng/g), liver (25.06 ± 16.72 ng/g) and kidney (6.88 ± 3.52 ng/g) after 28 days of oral clenbuterol administration in a growth-promoting dose (10 μg/kg BW, twice daily) to food producing male pigs, with a high correlation coefficient between the two methods for all study matrices (r = 0.8800–0.9999). In the liver as an alimentary tissue and regulatory matrix for the control of clenbuterol abuse, the maximal allowed concentration of 0.5 ng/g was achieved in liver tissue (0.40 ± 0.12 ng/g) on day 14 and in the kidney (0.28 ± 0.10 ng/g) on day 7 after treatment withdrawal. In contrast, the concentration of residual clenbuterol in choroid/PRE (57.49 ± 6.13 ng/g) and hair (68.36 ± 3.35 ng/g) recorded on day 14 of withdrawal was 143- and 170-fold that measured in the liver, with a similar ratio persisting on day 35 of withdrawal (164:1 and 183:1, respectively). These findings indicated a high accumulation potential of clenbuterol residues in the hair and choroid/PRE as compared with the liver and kidney, pointing to the pig choroid/PRE and hair as useful new matrices in the control of clenbuterol abuse as a growth promotant in food production, especially after prolonged withdrawal.