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The acute toxicity of three formulations of commercial detergent (ROMA Ò , FOCA Ò and BLANCA NIEVES Ò) was evaluated using the polychaete Capitella sp. C in static bioassays over a 48-h exposure period. The probit method was used to determine the median lethal concentration (LC 50) of each formulation as a whole as well as the LC 50 of the active ingredient, linear alkylbenzene sulfonate (LAS), using 95 % confidence intervals. The formulations and LAS showed LC 50 values of between 70.79 and 147.91 ppm and 15.48 and 22.38 ppm, respectively, at 48 h. FOCA Ò was the most toxic detergent, followed by BLANCA NIEVES Ò and finally ROMA Ò. The variation in the toxicity of the three detergents could have been caused both by differences in the relative concentrations of the anionic surfactant LAS contained in each formulation and the presence of other ingredients (enzymes, sodium silicate, sodium tripolyphosphate, bleachers and perfumes) which can also increase formulation toxicity. Correlation analysis revealed that percent mortality of Capitella sp. C increased with increase in the concentrations of the detergent over the 48-h exposure period. The risk quotient was greater than one for all three evaluated detergents, indicating that there is a high risk that they adversely affect the aquatic biota, particularly sediment-dwelling organisms such as the test species. Keywords Polychaeta Á Capitella Á Bioassays Á Acute toxicity Á Detergents To the memory of Jonatán Delgado Martínez, poet, composer, musician and rock drummer.

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