[en] Emerging contaminants (EC), such as pharmaceuticals, pose a potential risk in aquatic environments since their presence in water media can induce toxic effects onto the environment's biota. This kind of compounds, not completely degraded after their use/application, can easily reach different water bodies, like lakes or oceans, given that many water treatment systems cannot efficiently eliminate them nowadays. Thus, it is of great concern the potential negative effect these compounds can cause on representative organisms of these environments, such as microalgae, given their essential role on the trophic net as primary productors. In recent years, advance oxidation processes (AOP) have been researched as promising mechanisms of remediation and elimination of these emerging contaminants from aquatic environments. In the present study several experiments were carried out in order to test the possible toxic effect of the antibiotic and emerging contaminant sulfamethoxazole (SMX) on the freshwater microalga Raphidocelis subcapitata. For that, several parameters, like proliferation, viability, vitality, photosystem II's quantum yield, oxidative stress, and potential of cytoplasmic and mitochondrial membrane were monitored through flow cytometry (FCM). The effective concentration of SMX that induces a 10% inhibition on the growth of the microalga was calculated (EC10). Furthermore, the toxicity of photolyzed SMX (PLSMX), obtained after exposure of SMX solutions at their EC10 to UV light, was also studied by monitoring of the same parameters. The results obtained demonstrated that exposure to both compounds, pure and photolyzed, significantly induces (p<0.05) great levels of cells with low vitality. Nevertheless, PLSMX also induces total cell growth inhibition and the decrease of daughter cells percentage. Further, the cells also show a loss in cell viability and a decrease on the quantum yield of their photosystem II. Moreover, R. subcapitata exposed to PLSMX also exhibited enhanced levels of intercellular reactive oxygen species (ROS) production and great values of cells with both cytoplasmic and mitochondrial depolarized membranes. From the results obtained it can be concluded that PLSMX showed a greater toxic effect on the studied microalga compared to pure SMX. This has great ecological relevance, since remediation of SMX by AOP could affect the aquatic environments in a more toxic manner compared to pure SMX, scenario aggravated by the fact that microalgae are the fundamental primary productors of these environments. Thus, further research on SMX remediation is needed.

[gl] Os contaminantes emerxentes (EC), coma os medicamentos, supoñen un potencial risco nos medios acuáticos dado que a súa presencia nestes ambientes pode inducir efectos tóxicos na biota do medio. Este tipo de compostos, os cales non se degradan completamente despois do seu uso/aplicación, poden alcanzar facilmente diferentes masas de auga, coma lagos ou océanos, dado que a día de hoxe os sistemas de tratado de auga non as poden eliminar de maneira eficiente. Polo tanto, é de elevada preocupación o potencial efecto negativo que estes compostos poden causar nos organismos representativos destes medios, coma as microalgas, dado o seu papel esencial na rede trófica coma produtores primarios. En anos recentes, os procesos de oxidación avanzada (AOP) foron investigados como mecanismos prometedores de remediación e eliminación destes contaminantes emerxentes en medios acuáticos. Neste estudo varios experimentos foro levados a cabo para comprobar o posible efecto tóxico do antibiótico e contaminante emerxente sulfametoxazol (SMX) na microalga de auga doce Raphidocelis subcapitata. Para iso, varios parámetros, coma a proliferación celular, a viabilidade, a vitalidade, o rendemento cuántico do fotosistema II, o estrés oxidativo, e o potencial das membranas citoplasmática e mitocondrial foron monitorizados por citometría de fluxo (FCM). A concentración efectiva de SMX que induce unha inhibición do 10% no crecemento da microalga foi calculada (EC10). Por outra parte, a toxicidade de SMX fotolizado (PLSMX), obtido logo da exposición de solucións de SMX na súa EC10 con luz UV, tamén foi estudiada por monitorización dos mesmos parámetros. Os resultados obtidos demostraron que a exposición de R. subcapitata a ambos compostos, puro e fotolizado, induce significativamente (p<0.05) elevados niveis de células con baixa actividade metabólica. Sen embargo, PLSMX tamén induce a inhibición total do crecemento celular e a redución da porcentaxe de células fillas. Ademais, as células tamén mostran unha perda da viabilidade celular e unha redución no rendemento cuántico do fotosistema II. Adicionalmente, R. subcapitata exposta a PLSMX tamén exhibiu niveles elevados de produción intracelular de especies reactivas de osíxeno (ROS) e de células con membrana citoplasmática e mitocondrial despolarizadas. Cos resultados obtidos pódese concluír que PLSMX mostrou un maior efecto tóxico na microalga estudiada en comparación con SMX puro. Isto é de gran relevancia ecolóxica, dado que a remediación de SMX con AOP pode afectar aos medios acuáticos dunha maneira máis tóxica ca SMX puro, escenario agravado polo feito de que as microalgas son os produtores primarios fundamentais destes medios. Polo tanto, maior investigación na remediación de SMX é necesaria.