Veterinary pharmaceuticals are potent environmental contaminants. Special attention has been paid to antibiotics because of their potential health risk. Research has been undertaken to understand their environmental fate and toxicity. However one very important phenomenon has been overlooked and it is that more than half of the drugs currently in use are chiral compounds. Chiral compounds can exist in the form of enantiomers, which have similar physicochemical properties but differ in their biological properties and, therefore, in their potency, toxicity and biodegradation. Because of the most of studies on chiral pharmaceuticals do not explicitly account for individual stereoisomers, they implicitly and incorrectly assumes that enantiomers have identical environmental behavior. Furthermore, there is also a lack of information concerning enantioselective toxicity of chiral pharmaceuticals in the environment. This might lead to a significant under- or overestimation of their toxicity, as well as, an incorrect environmental risk assessment.Trace analysis of pharmaceuticals in environmental samples is always challenging due to the complexity and diversity of sample matrices, and until today only few chiral analytical methods for environmental trace-level determinations have been developed being the most of them focus on a few pharmaceuticals, and none of them in a group of several veterinary pharmaceuticals of environmental relevance.The proposal concerns the development and validation of a method for enantiomeric analysis of a group of chiral veterinary medicines of environmental relevance in environmental matrices using microextraction techniques and determination by liquid chromatography coupled with tandem mass spectrometry, the study of their environmental fate and their toxicity effects towards different organisms and the evaluation of the environmental risk posed by these compounds.