[en] Emerging contaminants, such as pharmaceutical compounds constitute a latent danger in aquatic ecosystems, as their presence in these media may cause direct or indirect negative impacts on biota. This toxic potential effect is particularly worrying microalgae, organisms of great importance into aquatic ecosystems, since they are the begging of the energy flow and contribute to oxygen balance and through. Nowadays the antibiotic oxytetracycline is one of the most used in multiple sectors as in medicine, veterinary, livestock or pisciculture. In this study the possible toxic effect of emerging pollutant oxytetracycline (OTC) on freshwater microalgae Chlamydomonas reinhardtii was studied. C. reinhardtii cultures were exposed to different concentrations of oxytetracycline (1, 2.5, 5, and 10 mg l-1) for 24 h and parameters of growth, cell viability, cell contents of photosynthetic pigment chlorophyll a, weight dry cell were analyzed versus control cultures without antibiotic. Oxytetracycline exposure caused a significant decrease (p <0.05) of growth and the lost of cell viability in cultures of C. reinhardtii concentration dependent antibiotic, while the chlorophyll a content of microalgal cells only recorded a significant decrease (p <0.05) in cultures exposed to the highest concentration tested. In contrast, cell dry weight showed a significant increase (p <0.05), except in cultures with the lowest concentration of antibiotic. In parallel to these previus described assays, where the cultures were exposed at a light intensity of 70 μmol photon m-2 s-1, cultures with the same concentrations of oxytetracycline but exposed to an increasingly light intensity were carried out. These cultures were exposed to 200 μmol photon m-2 s-1, in order to study a potential interaction between antibiotic exposure and an increase in light intensity. The results suggest the existence of an antagonistic effect between the two factors, showing IC50 with higher values of growth rate and cell viability in cultures exposed to 200 μmol photon m-2 s-1 than in those exposed to 70 μmol photon m-2 s-1.

[gl] Os contaminantes emerxentes, entre os cales se atopan os compostos farmacéuticos, constitúen un perigo latente nos ecosistemas acuáticos, xa que a súa presenza nestes medios pode provocar impactos negativos directos ou indirectos sobre a biota, sendo particularmente preocupante un potencial efecto tóxico sobre as microalgas, organismos de grande relevancia para os ecosistemas, onde contribúen ó balance de osíxeno e grazas as cales se desencadea o fluxo de enerxía nos mesmo. Na actualidade, o antibiótico oxitetraciclina é un dos fármacos máis empregados en múltiples sectores como na medicina, veterinaria, gandeiría ou piscicultura. Neste traballo estudouse o posible efecto tóxico do contaminante emerxente oxitetraciclina (OTC) sobre a microalga doceacuícola Chlamydomonas reinhardtii. Os cultivos de C. reinhardtii expuxéronse a diferentes concentración de oxitetraciclina (1; 2,5; 5; y 10 mg l-1) durante 24 h e tamén se analizaron os parámetros de crecemento, viabilidade celular, contido celular do pigmento fotosintético clorofila a e o peso seco celular fronte ós cultivos control sen antibiótico. A exposición a oxitetraciclina provocou un descenso significativo (p < 0,05) do crecemento e unha perda da viabilidade celular nos cultivos de C. reinhardtii dependente da concentración do antibiótico, mentras que o contigo de clorofila a das células microalgales só rexistraron un descenso significativo (p < 0,05) nos cultivos expostos á concentración máis alta ensaiada. Pola contra, o peso seco celular, presentou un incremento significativo (p < 0,05), exceptuando o cultivo coa maior concentración de antibiótico. Paralelamente a estos ensaios, onde os cultivos se someteron a unha intensidade lumínica de 70 μmol fotón m-2 s-1, leváronse a cabo cultivos coas mesmas concentracións de oxitetraciclina pero sometidos a un incremento na intensidade lumínica, sendo expostos a 200 μmol fotón m-2 s-1, co fin de estudar unha potencial interacción entre a exposición ó antibiótico e un incremento da intensidade lumínica. Os resultados obtidos suxeren a existencia dun efecto antagonista entre ambos factores, observándose IC50 con valores superiores nos cultivos expostos a 200 μmol fotón m-2 s-1 que nos expostos a 70 μmol fotón m-2 s-1 para os parámetros taxa de crecemento e viabilidade celular.