Regarding group B, the lowest MDLs were observed for erythromycin at 0.0051 ng L -1 (MQL at 0.0169 ng L -1 ) and sulfamethoxazole with an MDL of 0.0163 ng L -1 (MQL of 0.0543 ng L -1 ). Higher MDLs were observed for the quinolone metabolites: hydroxy-norfloxacin at 108.7 ng L -1 and desmethylofloxacin at 31.8 ng L -1 .