Sediment sampling allows benthic material from beaches, estuaries and the seafloor to be assessed for the presence of microplastics (Claessens et al., 2011). To separate any plastics from the benthic material, saline water or mineral salts can be added to the sediment samples to increase water density, permitting lower-density microplastics to be separated via flotation. Visible, denser plastic fragments can be removed by hand under a microscope (Andrady, 2011 and Thompson et al., 2004). A lipophilic dye (e.g. Nile Red) can then be used to stain the plastics to assist identification using a range of microscopy techniques (Andrady, 2011). Using Fourier-Transform Infrared

Spectroscopy (FT-IR), items of interest can then be confirmed as plastic by comparing spectra of the samples with that of known polymers LDK378 in vitro (Barnes et al., 2009 and Thompson et al., 2004). Microplastics within the water column can be collected by conducting a trawl along a transect Lapatinib (i.e. manta trawls for sampling surface water, bongo nets for collecting mid-water levels and benthic trawls to assess the seabed) using fine meshes (Browne et al., 2010, Ryan et al., 2009 and Thompson et al., 2004). The presence of microplastics can then be determined by examining the samples under a microscope, or allowing evaporation

of the seawater and investigating the residue left behind (Andrady, 2011). Despite the heterogeneous nature of plastics within the ocean, sufficient transects and

repeats allow for both spatial and temporal patterns in plastic abundance to be determined in a variety of marine ecosystems (Ryan et al., 2009). Typically, 330 μm aperture meshes have been used for many of the microplastic trawls documented in this review, but it is important to note that using meshes with different apertures can produce large variations in the quantity of microplastics collected: by utilising 80 μm meshes, Galeterone KIMO Sweden found microplastics at 100,000 times higher concentrations than when using 450 μm meshes (Lozano and Mouat, 2009). In contrast, an Algalita Marine Research Foundation survey of the North Pacific central gyre, conducted in 1999, identified 9,470 plastic fragments with a 1 mm mesh, but decreasingly smaller quantities of finer sized particles when using smaller-aperture meshes (4,646 microplastics with a 0.5 mm mesh, and just 2,626 microplastics using a 0.3 mm mesh) (Moore, 2008). Long-term data from Continuous Plankton Recorders (CPRs) are of particular benefit to determining microplastic abundance in the open ocean. These are specialised units designed to constantly sample plankton within 280 μm silkscreen-meshes, whilst being towed behind vessels along fixed routes (Thompson et al., 2004). Archived CPR samples, held by the Sir Alastair Hardy Foundation for Ocean Science (SAHFOS) have helped evaluate the prevalence of microplastics in the Northwest Atlantic throughout the past fifty years.