<p>Laboratories produce a large volume of wastewaters containing different chemical indicators, organic species for which there is no complete knowledge about their effects in the aquatic environment.</p>
<p>The aim of this work was to evaluate the ecotoxicity of four chemical indicator substances commonly used in titrations (sodium diphenylamine-4-sulfonate, phenolphthalein, methyl orange, and eriochrome black T) by applying two distinct bioassays that evaluated the growth inhibition of the microalga <em>Chlorella vulgaris</em> and the acute immobilization of the microcrustacean <em>Daphnia magna</em>.</p>
<p>All the indicators showed growth inhibition rates in the chronic test performed with the alga C. vulgaris. Only phenolphthalein and eriochrome black-T showed high immobilization rates on the acute test for D. magna. C. vulgaris showed higher sensitivity to the chemical indicators tested than D. magna. Eriochrome black T was the most toxic for both test organisms and, according to the effective concentration that causes inhibition on 50% of C. vulgaris population, it can be considered as “highly toxic to aquatic organisms”. Phenolphthalein and methyl orange may be classified as “toxic to aquatic organisms” and sodium diphenylamine-4-sulfonate is the least toxic, only being considered as “harmful”.</p>
<p>This work increases the awareness of the hazardous effects of these chemical indicators and reinforces the need of improved solutions to manage and treat laboratory effluents.</p>