Microplastics in seawater: sampling strategies, laboratory methodologies, and identification techniques applied to port environment

Abstract

The European Interreg Italy-France 2014-2020 Maritime Project SPlasH! (Stop to Plastics in H₂O!) focused on the study of microplastics (MPs) in the marine port environment to evaluate their presence, abundance, and mechanisms of diffusion to the open sea. In the framework of this project, a worldwide review of 74 studies was carried out, providing an overview of MP investigation techniques, focusing on sampling strategies, laboratory methodologies, and identification of MPs collected in seawater, and specifically evaluating their applicability to the marine port environment. Nets were the most commonly used device for MP surface sampling, but their use can be difficult in narrow spaces within the port basins, and they must be coupled to discrete sampling devices to cover all port basins. In the laboratory, density separation (NaCl, ZnCl₂, NaI, sodium lauryl sulfate (SLS)), filtration (polycarbonate, polyamide, glass, cellulose, ANOPORE inorganic membrane filters), sieving, visual sorting, and digestion methods (acidic, enzymatic, alkaline, oxidative) were used to separate MPs from seawater. Digestion becomes essential with water samples with great inorganic and organic loads as deriving from a port. Although many studies are based only on visual MP identification under a microscope, analytical identification techniques unequivocally determine the particle nature and the identity of the plastic polymers and are necessary to validate the visual sorting of MPs. Fourier-transform infrared spectroscopy (FTIR) is the most used analytical identification technique.

Keywords: Analytical identification; Microplastics; Port environment; Sampling devices; Seawater monitoring; Visual sorting.

Fig. 1

Evolution in the published studies on microplastics in seawater from 2004 to 2018

Fig. 2

Distribution of areas where the studies analyzed in the present review are conducted and numbers of studies (from 1 to > 10) for each area showed by the colored circles

Fig. 3

(a) Number of reviewed studies expressed in percentage (%) in which different sampling devices are used. (b) Number of the reviewed studies expressed in percentage (%) in which different types of net are used; maximum percentage shown in the y-axis is equal to 50 instead of 100 to be able to appreciate the difference between each histogram

Fig. 4

Scheme of different steps of laboratory methodologies applied to separate microplastics from seawater in the studies analyzed in the present review

Fig. 5

Example of microplastic particles and their polymer type and their size (Galgani et al. 2013)