At least once a week a news report will mention the occurrence of plastic waste in our oceans, such as the LEGO pieces washing up on Cornish beaches (BBC News). Beaches might be end-points for larger plastic waste, but what about those that are trapped by ocean currents and circulating the globe? What about the plastic we can’t see, or need the aid of microscope count?
Cutlass on a beach (C) Tracey Williams
A recent study conducted by research from the University of Cadiz, Spain, and the University of Western Australia published in the Proceedings of the National Academy of Sciences set out to describe the levels of plastic pollution around the globe. This study looks as 3,070 samples which have been collected worldwide, including previously published data as well data collected as part of the 2010 Malaspina Science Expedition.
Researchers detected plastics in 88% of samples of the ocean surface during the Malaspina Expedition in 2010 and it demonstrates that the five accumulation gyres in the oceanic surface circulation match with trends of plastics debris. The concentration of plastics ranged over 4 orders of magnitude in the open ocean, matching areas of convergence and divergence in the ocean. They estimated tat the amount of plastic in surfaces waters of the open ocean was between 7,000 and 35,000 tons.
What is interesting about the study is that, yes they identified plastics in the 5 gyres (check out the NGO with the same name), but since the 1980s we have seen plastic production quadruple, and we would think that with all of the wave and wind action, a lot more microplastics would be floating at the sea surface. In reality, a whole lot more particle were predicated than what were actually found.
There appear to be 5 distinct areas where plastic accumulates :
- Pacific Ocean: to the west of the United states (AKA the North Pacific Central Gyre-add link)
- Pacific Ocean: to the west of South America
- Atlantic Ocean: between USA and Africa
- Atlantic Ocean: to the East of southern Africa
- Indian Ocean: to the west of Southern Africa
Although these areas tend to receive the most research, there are other areas of the ocean are likely to have plastics as well. From my own research we are finding microplastics throughout the Irish marine and coastal environment (watch this space – publication coming soon).
Nearly 300 million tons of plastic is produced every year, worldwide we do our best to recycle and reuse a large quantity of this, but it has been estimated about 10% (by mass) will eventually find its way into the marine environment. Once there is can be transported on currents, slowly breaking down into smaller and smaller pieces (processes include wave action and UV degradation). Microplastics are also input directly through the use of cosmetics, air blasting and loss of pre-production pellets at sea.
It’s not just these floating garbage patches that accumulate plastics, they only appear to account for 1 percent of what is expected to be found. So where could this plastic have gone? Plastics could end up sinking to the sea floor, washing up on beaches, or interacting with marine biota (take a look at my previous posts about this). If ingestion is the case, and chemical effects are associated with microplastics, this could have wide-ranging environmental impact, because so many different species living on the earth live in or eat from the oceans. It might even find its way onto our plates.
I guess the step forward is to continue looking for the sources and sinks of microplastics in the marine environment, to begin to understand their pathways around the globe and their eventual fate in the marine environment, be it interacting with marine organisms of burying deep in sediment.
What is known is that microplastics are certainly ubiquitous in the marine environment, and they will be there for many decades and centuries to come.
Published by Amy Lusher
If you want to read the full articles from PNAS you can access it here. I have copied the abstract below:
There is a rising concern regarding the accumulation of floating plastic debris in the open ocean. However, the magnitude and the fate of this pollution are still open questions. Using data from the Malaspina 2010 circumnavigation, regional surveys, and previously published reports, we show a worldwide distribution of plastic on the surface of the open ocean, mostly accumulating in the convergence zones of each of the five subtropical gyres with comparable density. However, the global load of plastic on the open ocean surface was estimated to be on the order of tens of thousands of tons, far less than expected. Our observations of the size distribution of floating plastic debris point at important size-selective sinks removing millimeter-sized fragments of floating plastic on a large scale. This sink may involve a combination of fast nano-fragmentation of the microplastic into particles of microns or smaller, their transference to the ocean interior by food webs and ballasting processes, and processes yet to be discovered. Resolving the fate of the missing plastic debris is of fundamental importance to determine the nature and significance of the impacts of plastic pollution in the ocean.
Authors: Andrés Cózar, Fidel Echevarría, Juan I. González-Gordillo, Xabier Irigoien, Bárbara Úbeda, Santiago Hernández-León, Álvaro Palma, Sandra Navarro, Juan García-de-Lomas, Andrea Ruiz, María L. Fernández-de-Puelles, and Carlos M. Duarte. Plastic debris in the open ocean. PNAS, 2014; DOI: 10.1073/pnas.1314705111