Issues of scale

When attempting to assess the scale of the pollution existent within the oceans several major problems become apparent:

1. Lack of data

This problem arrises due to the scale of the investigation. The oceans cover 361 million km2 of the Earths surface, physically measuring and mapping plastic pollution within seems a difficult and costly venture. Globally there is an asymmetry in the location of data collection, with greater amounts of data collected in the northern hemisphere. Within the literature there is a call for increased data collection in the southern hemisphere and remote areas.

The scale of the oceans provide a fundamental issue concerning the methodology of estimating global pollution. The scaling up of direct measurements and modelling techniques are often used, though like any extrapolation issues ensue. Data collection consists of the measurement of plastic concentrations at various points along boat routes and extrapolated to provide global estimates.

One such attempt to estimate global plastic pollution is evident in Eriksen et al (2014), whereby they collected plastic pollution data via surface net tows and visual survey transects.

Field locations at 1571 sites

As can be seen in the image above field locations cover only a small fraction of the ocean surface and so modelling extrapolations from field data may be erroneous. Eriksen et al estimated used primary and secondary data to estimate that the ocean contains at a minimum 5.25 trillion particles of plastic, weighing 268,940 tons. This minimum predicted is just 0.1% of global plastic production (288 million tons of plastic produced globally in 2012) and so this figure seems an underestimate and possibly erroneous.


    2.   Diversity of methodologies in assessing plastic pollution

Currently within literature several methods are utilised when attempting to assess marine plastic pollution, which can lead to varying results and estimates. From collecting plastic in plankton nets to assessing plastic pollution via a by sight 'transect' to taking water samples.