 The study aimed to improve the reliability of marine contaminant data for assessment purposes under the MSFD by collecting detailed QA slash QC information using a questionnaire based on requirements from various organizations. Results indicate an overall good level of laboratory proficiency, but heterogeneities were observed in sampling protocols and analytical methods. The study highlights the importance of sharing detailed QA slash QC information associated with data to improve data reliability and reusability and support marine pollution assessment. This article was authored by Megan in French and Marina Leipheiser.