The shifting baseline of microplastic measurement: A comparison of methodologies used in estuarine-based studies and guideline recommendations

Microplastics are a ubiquitous contaminant of estuarine environments, threatening ecological health. However, the comparison and interpretation of data from microplastic studies is challenged by inconsistency in methods of detection and analysis. This study reviews the methods reported in historical estuarine-based microplastic studies and compares them with current guideline recommendations to identify aspects that need improvement. Our analysis was undertaken on a database of 175 studies conducted across 36 countries between 2013 and 2023. We show that the majority of database studies (71 %) use suitable identification methods; however, fewer studies report recommended analytical representation (47 %) and analytical proportions (40 %). Only 30 % of the studies in our database utilised methods that align with all current recommendations. We further examined the use of density separation methods, used to separate microplastics from sediment samples and found only a low proportion of these studies (8 %) adhered to current guideline recommendations. Our findings indicate that there has been little improvement in the methods used in historical estuarine-based studies over the last 10 years. This demonstrates the need for greater focus on considering and reporting analytical representation and proportions in future work to ensure microplastic prevalence is accurately measured.