Are Fixed Acceptance Criteria Fit for Purpose? Rethinking Field Duplicate Evaluation in Environmental Sampling

Presented by Renan Lourenço de Oliveira Silva
Contact Information: [email protected]

ABSTRACT

Field duplicate samples are widely used as a quality control tool in environmental monitoring programs, commonly evaluated using fixed acceptance criteria such as relative percent difference (RPD). However, the application of a single acceptance threshold across different matrices, environmental conditions, concentration ranges, and analytical methods raises important questions regarding whether such criteria are truly fit for purpose. This presentation discusses practical limitations associated with the use of fixed acceptance criteria for field duplicates, based on observations from routine monitoring programs involving diverse environmental compartments, including heterogeneous matrices such as sediments and wastewater influent. In such systems, natural spatial and temporal variability may lead to large differences between duplicate results that do not necessarily reflect poor sampling or analytical performance. Conversely, in more homogeneous conditions, the same criteria may fail to detect relevant inconsistencies. In the context of ISO/IEC 17025, where laboratories are required to ensure the validity and appropriate interpretation of results, the use of fixed criteria without considering the combined effects of sampling variability and analytical uncertainty may lead to misleading conclusions. Rather than focusing on the adequacy of a specific metric, this presentation examines whether a universal acceptance criterion can be considered fit for purpose under varying conditions. Alternative approaches are discussed, including context-dependent evaluation based on matrix characteristics, concentration levels, historical variability, and the explicit consideration of analytical uncertainty alongside sampling-related variability. Additional factors such as project-specific objectives, data use, and decision-making context are also considered as part of a more technically justified evaluation framework. The objective is to promote a more technically sound and context-aware interpretation of field duplicate results, supporting the development of evaluation approaches that better reflect real-world environmental variability while maintaining data quality and confidence in decision-making processes.