Sampling microplastics in estuarine environments: lessons learned from suspended sediment dynamics and perspectives.

Standardized sampling methods and protocols are essential to facilitate the comparison of studies on plastic pollution and to advance knowledge of this environmental issue. Several protocols for sampling microplastics in oceanic and coastal waters have been developed, compared and even harmonized for this purpose. However, these protocols may be not adapted for the study of estuarine environments, characterized by strong vertical, horizontal and temporal gradients.  In this work, microplastic sampling methods and strategies are discussed in relation to estuarine hydrodynamic processes. The analogies between the dynamical behaviour of microplastics and sediments make it possible to draw out recommendations for sampling microplastics based on several decades of research in estuarine hydro-sedimentary dynamics. In particular, we will discuss when, where, and how to sample microplastics in order to capture the most representative picture of microplastic pollution in these highly dynamic systems subject to strong anthropogenic pressures.