Are we underestimating floating microplastic pollution? A quantitative analysis of two sampling methodologies.

Microplastics (MPs) are widespread in the water column of several aquatic ecosystems. Thus, the sampling methodology is considered as a basic factor influencing MPs abundance. In this baseline, a total of 67 investigations were chosen to conduct a quantitative analysis between two sampling methods: Trawl and bulk. The aim is to report a general overview of the MPs abundance and characteristic differences based on the sampling procedures and provide methodological recommendations. MPs abundance reported by bulk studies is 3500 higher than trawl studies. Furthermore, the morphological types and polymers abundances were statistically affected by the type of sampling tool. Conversely, MPs size ranges were significantly different between sampling procedures, suggesting that trawling underestimates the smaller MPs fractions. The analysis confirms that the sampling methods should be selected based on the research objectives. In this sense, it is recommended to combine both types of sampling procedures to obtain comprehensive data.