Analyzing the Limitations and the Applicability Domain of Water–Sediment Transformation Tests like OECD 308

[Image: see text] The assessment of chemical degradation rates from water–sediment experiments like for instance OECD 308 is challenging due to parallel occurrence of processes like degradation, sorption and diffusive transport, at different rates in water and sediment or at their interface. To systematically and quantitatively analyze this limitation, we generated artificial experiment data sets using model simulations and then used these data sets in an inverse modeling exercise to estimate degradation half-lives in water and sediment (DegT50(wat) and DegT50(sed)), which then were evaluated against their true values. Results were visualized by chemical space diagrams that identified those substance property combinations for which the OECD 308 test is fundamentally inappropriate. We show that the uncertainty in estimated degradation half-lives in water increases as the process of diffusion to the sediment becomes dominant over degradation in the water. We show that in theory the uncertainty in the estimated DegT50(sed) is smaller than the uncertainty in the DegT50(wat). The predictive value of our chemical space diagrams was validated using literature transformation rates and their uncertainties that were inferred from real water–sediment experiments.