Plastic

Scratching the surface: Microplastic distribution in the surface layer of the world’s ocean

Isobe, A., et al. (2021). A multilevel dataset of microplastic abundance in the world’s upper ocean and the Laurentian Great Lakes. Microplastics and Nanoplastics 1(1): 16.

Microplastics in our oceans

Microplastics (plastic particles < 5 mm) are found across the globe. While many surveys have been conducted over the past couple of decades to determine exactly how many plastic particles are floating in our oceans, it is difficult to say what the exact numbers are. Microplastic distribution can vary drastically across distances of only a couple of feet. Plastics come in many different shapes, sizes, and densities, which can influence where they end up in the water column. Less dense, smaller particles are more likely to float at the surface, while denser, larger particles can sink to the bottom of the ocean. Besides the particle’s physical properties, ocean mixing, currents, and biofouling (when organisms attach to the surface of the particle) can influence how microplastics disperse in the ocean. Because scientists use different methods to collect and identify these particles, it’s difficult to compare results. With all of this in mind, researchers are working to piece all these data together to form a more complete picture of microplastic distribution in the global oceans.

Putting the data together

The authors compiled data collected between 2000-2019 to create a publicly available dataset describing the global distribution of microplastics in the surface layer of the ocean and the Laurentian Great Lakes. The microplastics were either collected by towing a net along the surface of the water or by pumping water continuously through a filter system. While these methods collected microplastics down to 0.2-0.3 mm in size, the equivalent of a fine needle tip, they missed some of the smaller and potentially more concerning particles. The authors modified the data to account for the use of different methods. This was done by taking ocean conditions, such as wind speed at the time of sampling into account and adjusting for the potential overestimation of plastic particles if the survey in question did not confirm the particles to be plastic.

 

Figure 1. A map showing the number of microplastics found across our world’s oceans using the publicly available dataset Microplastics and Nanoplastics 1(1): 16

Major results

The dataset suggests there are 24.4 trillion microplastics spread across the surface of the world’s oceans, much higher than previously indicated. The highest concentrations occur where dominant ocean currents converge and along the coast because of human populations. The most common polymers in the surface waters are polyethylene and polypropylene because they are lighter and tend to float. Both of these polymers are widely used across a number of industries (medical, consumer products, automotive). Polyethylene is used in the production of common household objects like plastic bags and squeeze bottles, while polypropylene is used for packaging, upholstery, carpet fibers and much more. This work helps researchers understand how many microplastics are in surface waters, where they are concentrated and what kinds of polymers can be found, which is the first step towards tackling the issue of plastic debris. As it stands, many laboratory studies exploring the effects of microplastics on marine animals have been using unrealistically high microplastic concentrations. This data provides more reliable concentrations on which to base studies and will help determine the true effects of microplastics on marine life in the current state. Data collected by standard sampling methods that can account for smaller microplastics will help validate this work and provide a more accurate picture of global microplastic distribution. There is still a lot of work to be done looking into how microplastics are transported throughout the depths of the ocean and what polymers marine life interact with directly, but this is a good start!

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