In 2020 five different plastics were deployed in coastal waters around Aotearoa, at marine sites in Auckland, Nelson and Christchurch. Held in place by large steel frames, the researchers left the plastics in the sea for a year to see what started living on their surface and what chemicals were released or became associated with them.
Once in the marine environment plastics quickly become colonised by microbial communities, followed by a wide variety of invertebrates and seaweed, until a climax community forms. These communities can be home to invasive species or pathogens of concern, due to the negative effects they can have on the native species.
The researchers monitored the communities over time, using next-generation DNA sequencing methods. They also looked at how they affected the plastics themselves. For example, do the things that grow on them assist with their breakdown and the formation of microplastics?
Testing different types of plastic
The five plastics used in the experiment were a mixture of new and artificially aged and included two commonly-found in plastic bags (polyethylene and oxo-polyethylene, the latter now banned in New Zealand), one commonly found in drink bottles (polyethylene terephthalate), one increasingly being used in food and liquid containers as a “sustainable” substitute for traditional plastics due to its compostability (polylactic acid), and one used in materials such as fishing lines (nylon). Although polylactic acid (PLA) is an industrially compostable plastic, the conditions required cannot be found in the ocean.
By studying the changes to the plastics over time, and the chemicals and organisms that become associated with them, the researchers can better understand the risks they may pose the environment. And by using artificially aged plastics they can assess how the risks and/or impacts the plastics pose the environment can change as the plastics weather This is important as we know that there are plastics in the oceans just days old as well as five-six decades old. Only looking at the effects of new plastics won’t tell us the full story.
This nation-wide study was preceded by a pilot project in Christchurch. Lead researcher Dr Olga Pantos explains more about the experiment in this video:
Beached plastic debris
Researchers including ESR scientists, with help from the Sustainable Coastlines(external link) and Litter Intelligence(external link) projects, are also analysing beached plastic debris from 27 sites spanning the length of Aotearoa. The beached plastic debris is being analysed for chemicals that are inherent in the plastic or acquired from the environment. The researchers are investigating how much of these chemicals are released when they’re ingested by marine organisms.
The beached debris that has been analysed so far has shown elevated concentrations of many toxic trace elements. These high concentrations of trace elements (such as cadmium and lead) have been linked with the inorganic pigments used to give plastics their colour and therefore intentionally added (inherent). By simulating the conditions of marine organisms’ gastric fluid, the researchers have also shown that trace elements are released upon ingestion, which demonstrates the exposure of plastic-associated trace elements to organisms.