Microplastics Sampling and Abundance
The distribution of microplastics can be considered from several perspectives . The most apparent is perhaps the geographic distribution, which may be evaluated on a range of spatial scales, ranging from a few meters within a beach  to several kilometers between countries or continents [18,27]. The distribution of microplastics can also be categorized across environmental compartments, such as the quantity of microplastics along coastlines, at the sea surface, in the water column or on the sea bed (both subtidal and intertidal), and quantities in biota that have been accumulated by ingestion [16,31]. Temporal distribution, although less popular, can be used to assess the variation in marine debris over time and the effect of legislation to curb the release of microplastics into the environment. Smaller plastic debris (<0.5 mm in diameter) is considered a widely under-researched component of marine debris due to the difficulties in assessing the density, abundance, and distribution of this component within the marine environment [6,24]. A quantification of the input of plastics in a marine environment is limited by the following factors [6,16,24,25]:
- • The wide array of pathways by which plastics may enter the marine environment such as rivers, surface runoff, municipal and industrial wastewater treatment, etc.
- • The requirement of accurate timescales for which plastics remain in the marine bodies prior to degradation
- • The complexities arising due to the vastness of the oceans compared to the size of plastics being assessed
- • The spatial and temporal variability caused by oceanic currents and seasonal variations
- • The variation in sampling methods due to the absence of universally recognized protocols for collection or sampling
Despite the difficulties posed by the limitations described above, a variety of sampling techniques have been developed that allow the determination of spatial and temporal distribution of plastic debris. These include beach combing, sediment sampling, marine trawls, marine observational surveys and biological sampling .