Quantification and Validation of Measurement Uncertainty in the ISO 8192:2007 Toxicity Assessment Method: A Comparative Analysis of GUM and Monte Carlo Simulation.

Reliable toxicity assessments are essential for protecting biological processes in wastewater treatment plants (WWTPs). This study focuses on quantifying the measurement uncertainty of the ISO 8192:2007 method, which determines the inhibition of oxygen consumption in activated sludge. Using the GUM guideline and Monte Carlo Simulation (MCS), up to 29 uncertainty contributions were evaluated in terms of oxygen consumption rate and percentage inhibition. The results reveal that temperature tolerance, measurement interval, and oxygen probe accuracy are dominant contributors, accounting for over 90% of the total uncertainty. The GUM results for oxygen consumption rates were validated by Monte Carlo Simulation, confirming their reliability. The percentage inhibitions showed asymmetric distributions and were underestimated by the GUM method, especially at lower toxicant concentrations. This highlights the necessity of simulation-based approaches for asymmetric systems. Notably, the consideration of correlations in the GUM analysis had minimal impact on outcomes. The findings emphasize the need for the precise recording of measurement time intervals, temperature control, the regular calibration of oxygen probes, and repeat measurements at low toxicant concentrations. Overall, this study enhances the robustness of ISO 8192:2007-based toxicity testing and provides practical guidance for reducing measurement uncertainty.