John Wiley & Sons, Ltd.

Accounting for dissociation and photolysis: A review of the algal toxicity of triclosan

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Triclosan, an antimicrobial agent commonly used in down‐the‐drain consumer products, is toxic towards freshwater microalgae. However, the rapid photolysis and pH dependent dissociation of this compound may give rise to uncertainty in growth inhibition tests with freshwater microalgae, if these are not well characterized. This study presents methods to minimize these uncertainties by stabilizing pH with an organic buffering agent (bis‐tris) and by the application of UV covers to remove UV wavelengths. Toxicity tests with these methods were in compliance with the validity criteria of the OECD 201 test guidelines, and no negative effects were seen in controls relative to the unmodified method. Application of the methods enabled toxicity tests with triclosan at pH levels of 7.0, 8.0 and 8.5 yielding EC10 values of 0.5, 0.6 and 12.1 μg/L respectively. The observed change in toxicity with pH was proportional to the change in BCF as calculated using the cell model (a dynamic flux model based on the Fick‐Nernst‐Planck equations – in this case parameterised for an algal cell). Effect concentrations produced with the methods presented here offer robust data on which to base risk assessment, and it is suggested that similar approaches be used to minimize uncertainty when testing other compounds that dissociate and photolyse. Environ Toxicol Chem © 2014 SETAC

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