New measurement method: many more microplastics in sea than thought

Amsterdam, 2 December 2017 – British researchers have developed a cost-effective method of detecting and counting microplastics in water. They add a fluorescent dye that binds to plastic particles, making them easy to see with a microscope. The method clearly shows that there is much more microplastics in the top layer of sea water than previously thought. The research is published in Environmental Science & Technology.

It has been known for a while that there is more microplastics (< 5 mm) in the top layer of water than larger pieces. The current measurement methods however, were unable to determine the proportion of microplastics smaller than 1 mm. The new method can do this, and the results show that it is precisely the smallest plastics (20 to 1000 μm) that form the largest proportion of plastics in the sea. It has already been argued that much less plastic is found in sea than that enters the sea. The question is where all that plastic is, and up to now there has not been a satisfactory answer. The researchers say that their method helps explain that much of the ‘lost’ plastic has become so small that the measurement methods used to date simply overlooked them.

Plastics in the environment degrade into ever smaller pieces. As the pieces become smaller, the number of pieces increases exponentially. That proportionately there are many more tiny plastic particles in water is confirmed by this method. The researchers also point out that the smaller the plastic particles, the higher the number of organisms that ingest them.

The method detects lightweight plastics (polypropylene, polyethylene, polystyrene and nylon-6) best. These plastics are mostly used for packaging that is thrown away after use and nylon-6 comes from machine washed synthetic clothing.