[en] Human activities are known to generate large amounts of toxic substances, some of which are commonly known as emerging pollutants. These pollutants, to a greater or lesser extent, end up in the aquatic ecosystems endangering the natural balance of oceans and marine life. Primary producers such as microalgae are often used to evaluate the ecotoxicity of these harmful substances because of their particularly sensitivity to habitat perturbations and because they are the first to establish contact with the pollutant when it reaches the ecosystem. In the present study, we analyse the toxicity of the emerging contaminant benzalkonium chloride (BAC) on the marine diatom Phaeodactylum tricornutum. Cultures of P. tricornutum were exposed to concentrations of 0.025 - 0.05 and 0.10 mg L-1 of BAC and different physiological parameters were measured after 24 and 96 hours of exposure by spectrophotometry, cytometry, fluorometry and epifluorescence microscopy techniques in order to evaluate the toxicity of BAC. In addition, the median effective concentration (EC50) for this compound was calculated and, using the Comet assay, its genotoxic effect on the microalgal genetic material was determined. The results showed a cellular stress in response to the tested pollutant since parameters such as cell density, viability, photosynthesis and cellular protein concentration were significantly compromised, the most sensitive parameters being cell growth inhibition and increased photosynthetic activity. Changes in lipid peroxidation were observed, although they were not statistically significant. Finally, photosynthetic performance and membrane integrity were not affected.

[gl] Na actualidade, as actividades levadas a cabo polo ser humano xeran uhna gran cantidade de sustancias tóxicas, algunhas delas se coñecen como contaminantes emerxentes e chegan, en maior ou menor cantidade, ós ecosistemas acuáticos, poñendo en risco o equilibrio natural dos océanos e a vida mariña. Productores primarios, como as microalgas, utilízanse para avaliar a ecotoxicidade destas sustancias nocivas xa que, además de ser microorganismos especialmente sensibles ás perturbacións do hábitat, tamén son os primeiros en manter contacto có contaminante cando chega ó ecosistema. Neste estudo analizouse a toxicididade do contaminante emerxente cloruro de benzalconio (BAC) sobre a diatomea mariña Phaeodactylum tricornutum. Cultivos desta diatomea foron expostos a concentracións de 0,025 – 0,05 y 0,10 mg L-1 do BAC, e analizáronse distintos parámetros fisiolóxicos ás 24 e 96 horas de exposición mediante técnicas de espectrofotometría, citometría, fluorometría e microscopía de epifluorescencia, coa fin de avaliar a toxicidade do BAC. Ademáis, calculouse a concentratición efectiva media (EC50) para este composto e, por medio do ensaio do cometa, determinouse o seu efecto xenotóxico sobre o material xenético microalgal. Os resultados mostraron estrés celular en resposta a o contaminante ensaiado, xa que parámetros como a densidade celular, a viabilidade, a fotosíntese e a concentración celular de proteínas víronse significativamente alterados, sendo os parámetros máis sensibles a inhibición do crecemento celular e o incremento da actividade fotosintética. Observáronse cambios na peroxidación lipídica, aínda que non foron estatísticamente significativos. Por último, o rendimento fotosintético e a integridade de membrana non se viron afectados.