John Wiley & Sons, Ltd.

A toxicokinetic study of specifically acting and reactive organic chemicals for the prediction of internal effect concentrations in Scenedesmus vacuolatus

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The toxic potency of chemicals is determined well by using the internal effect concentration accounting for differences in toxicokinetic processes and mechanisms of toxic action. This present study examines toxicokinetics of specifically acting and reactive chemicals in the green algae Scenedesmus vacuolatus by using an indirect method. Concentration depletion in the exposure medium was measured for chemicals of lower (log Kow < 3: isoproturon, metazachlor, paraquat) and moderate (log Kow 4‐5: irgarol, triclosan, N‐phenyl‐2‐naphtylamine) hydrophobicity at seven time points over 240 min or 360 min. Uptake and overall elimination rates were estimated by fitting a toxicokinetic model to the observed concentration depletions. The equilibrium of exposure concentrations was reached within minutes to hours or was even not observed within the exposure time. Kinetics of bioconcentration cannot be explained by the chemical's hydrophobicity only, but influencing factors such as the ionization of chemicals, the ion‐trapping mechanism or the potential susceptibility for biotransformation are discussed. Internal effect concentrations associated to 50% inhibition of Scenedesmus vacuolatus reproduction were predicted by linking the bioconcentration kinetics to the effect concentrations and ranged from 0.048 to 7.61 mmol/kg wet weight for specifically acting and reactive chemicals. Knowing the time‐course of the internal effect concentration may help to understand toxicity processes like delayed toxicity, carry‐over toxicity or mixture toxicity in future studies. Environ Toxicol Chem © 2014 SETAC

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