Microplastics

What exactly are microplastics and how have they become such a critical aspect of marine pollution? Since its introduction into academic literature in a 2004 paper, the term microplastic has generally been used to describe pieces of plastic that are smaller than 5mm in diameter, as per the NOAA definition. Though this is not considered a definitive description, as certain studies have pointed out the differences in size that exist across papers due to varying methods of capture. Calls have been made from people within the scientific community for a more rigid definition of the term microplastic to allow for more reliable comparison of differently sourced data. Nonetheless, one thing that we are certain of is that they are incredibly small, and with 5mm being the most widely used boundary, their size, or lack of, is what makes them so hard to quantify in the environment.

Spectroscopic analysis has discovered pieces as small as 20 nanometers in diameter (0.00002mm) - how do we keep track of these in the vast expanse that is the ocean? Quite simply we can't really, or at least we struggle to do so. As a review of all things microplastic points out, there are various ways by which we can attempt to quantify microplastics in the environment, but as of yet there is no robust solution, and ultimately, the fate of microplastics in the ocean remains an elusive phenomenon. This is not to say that there is no hope, as they were once an extremely understudied aspect of marine pollution, and it wasn't even until the turn of the century that they were considered a pollutant within their own right. Whereas they are now receiving a rapidly growing amount of attention, which is certainly an encouraging sign of progress. Another sign of such progress? Look no further than the White House.

Ban microplastics? Obama thinks so

Yes - Barack Obama does think that a ban of microplastics would be a good idea and has in fact signed a bill to pass such a ban. The ban specifically refers to the manufacture and introduction of microbead plastics used in cosmetics, which are one of the primary sources of microplastics in our oceans. These microbeads exist in common facial scrubs that you are more than likely to have come across in your local supermarket or may have even used. Studies have shown that the number of microbeads to be washed down the drain, with one just one use of a facial scrub, ranges from 4,500 to as many as 94,000 individual beads! These may not carry the issues associated with entanglement and choking that come with larger pieces of plastic and debris, but they come with their own different type of problem.

The sorptive properties of microplastics are what cause a threat to marine life, as they can carry harmful chemicals such as PCBs and DDTs (there will be a more in-depth look at this in my next post). Facial scrubs do not provide the only primary source of microplastic in the oceans, as they also exist in certain toothpastes and come from clothes too. Studies estimated that an average 6kg clothes wash of acrylic fabric can release in excess of 700,000 fibres into the environment. The primary release of microplastics into the ocean should therefore warrant significant concern, and the video below shows the attempts being made to raise such concerns.

Whilst the primary release of microplastics into marine environments certainly seems to contribute a large volume of plastic debris, it is the secondary release that perhaps poses a more daunting reality. This secondary production involves the gradual breaking down of larger pieces of plastic, eventually into small microplastics. This fragmentation and degradation of plastics occurs over varying periods of time at sea, depending on the properties of the item, but exact processes by which this degradation occurs are speculative and limited to controlled laboratory work. Though an example of a known process by which this fragmentation occurs is photodegradation - where plastics at the sea surface are broken down into smaller pieces by sunlight.

Why are these secondary microplastics more daunting? Well, the primary source of microplastics is something we have a greater control on right now - petitions and bills are in the pipeline to ban them from production. However, as was mentioned in my first post, there is already a colossal volume of plastic in our oceans, the entire amount of which is vulnerable to degradation into microplastics. Whilst we can improve our management and disposal of plastic waste in the future, to stop it getting into the ocean, the plastics that are already in there are largely out of our control and thus represent a huge potential source of microplastics yet to be added to the great big blue. 

As has been discussed, the abundance of microplastics in the ocean is something that is of great difficulty to measure, but it is likely large number with a fair few zeros on the end of it, hence their growing significance. It was briefly touched upon that the sorptive properties of plastics facilitates the transportation of harmful chemicals, which is essentially what makes these plastics the threat that they are, and this is something that we will look at in my next post.