Basics Plastic Marine Litter Can bioplastics save the plankton? Pollution and climate change are two of the many environmental issues we face. These are mostly considered separately. Pollution, especially marine, is one we can see with our eyes and exerts emotive feelings in most people. However quite often it is the pollution we cannot see that has the potential to affect us the most. Since it is estimated that more than a half of the total atmospheric oxygen is produced (and corresponding carbon sequestered) in the oceans by phytoplankton [1], marine litter and climate change are likely interlinked if the connection is proven that phytoplankton are affected by significant concentrations of plastics in the ocean. Plastic of all sizes, from nano- to macro-, and of all different polymer types are found in oceans around the world. They are present in all habitats from nearshore coastal zones, to deep sea trenches, and from pole to pole. It is estimated that in 2010 between 4.8 to 12.7 million metric tons of plastic entered the oceans, and these levels are expected to increase by an order of magnitude by 2025 [2]; newer studies estimate these levels are even higher. Plastic marine litter Plastic represents 84% of total marine litter [3], with ca. 80% originating from land-based activities, and the remaining 20% from sea-based activities. From land, food packaging makes up the majority of macroplastic items entering the oceans via rivers and streams. Microplastics are introduced from wastewater treatment plant effluent and stormwater runoff from roads, in the form of the breakdown products resulting from the wear and tear of items such as synthetic clothing (during laundering) and tyres on roads. The strong and light nature of plastics make it an ideal material for sea-based activities and are commonly used for fishing gear (buoys, lines, nets), as well as for the storage and transportation (boxes, packaging, insulation). Consequently, shipping, wild fisheries and aquaculture contribute significantly to marine litter of both macroplastics through accidental or intentional deposition and to microand nanoplastics through fragmentation of larger items through general wear and tear. For example, dolly ropes used to protect the trawl nets against wear and tear by providing a buffer between the nets and hard substrate. Plastics at all sizes present a range of threats to the environment and they may enter the ecosystem at different trophic levels. Impacts from ingestion range from causing physical internal damage to causing a false sense of satiation, resulting in subsequent implications for animal health and fitness. Inherent or acquired chemicals associated with the plastics, including microplastics, may also pose a significant risk to the biota at different trophic levels both following direct consumption of the plastics and from bioaccumulation and biomagnification through the food chain. Although microplastics have been found in the guts and tissues of marine species around the world (including samples taken from commercial markets) that humans consume as food, it is currently unclear whether they present a threat to human health. In addition to potential toxicological effects, plastic litter provides a new substrate for the development of biofilms posing a threat to ecosystems through their role in the translocation of invasive species and pathogens in the oceans over greater distances than previously possible [4]. The resilient nature which has made plastic so versatile and successful also make it difficult or impossible to be assimilated by nature. Therefore, plastics do not only influence the oceans today but also for many decades to come. Although the term litter implies items intentionally discarded in the environment, it is important to acknowledge that marine plastic litter can enter the environment unintentionally during use through accidental loss and general wear and tear. While it is universally agreed that plastic should not be littered into the oceans, its presence there is inevitable. As a result, biodegradable and compostable plastics are increasingly being discussed to replace traditional plastics in terrestrial and marine applications to reduce future marine litter. Are biodegradable plastics the solution? Even though a material is described as ‘biodegradable’, this does not mean it will degrade in all receiving environments. Some will biodegrade only under industrial composting conditions, others biodegrade in both composting and soil but not aquatic environments [5]. A range of different standard tests are available to measure biodegradation under different conditions including the ISO 18830 and ISO 19679 standards focussed on determining the aerobic biodegradation of non-floating plastic materials in a seawater/sediment interface. Of the commonly available compostable and biodegradable polymers, polybutylene succinate (PBS), polylactic acid (PLA), polybutyrate adipate terephthalate (PBAT) and poly(butylene succinateco-butylene adipate) (PBSA) do not meet requirements of biodegradability in marine environments. A few materials - certain grades of cellulose acetate and the polyhydroxybutyrate (PHB) family of co-polymers - have displayed marine biodegradability. Currently, for land-based activities, we focus on materials that are home or industrial compostable and possibly soil biodegradable. If 80 % of marine plastic litter comes from terrestrial sources and most compostable plastics are not marine biodegradable, then biodegradable plastic litter is still litter – likely contributing to the same problems coming from traditional plastics [6]. One might then decide that only marine biodegradable materials should be used for everything. There are two main issues here: 1. Materials fit for purpose - functionality 62 bioplastics MAGAZINE [03/20] Vol. 15
Basics By: Olga Pantos The Institute of Environmental Science and Research (ESR) Porirua, New Zealand Kate G. Parker and Dawn A. Smith Scion Rotorua, New Zealand and lifetime of items; and 2. impacts of these biodegradable plastics as they break down. Firstly, marine biodegradable materials don’t provide all the functionality necessary for their primary use (e.g packaging or marine nets, dolly ropes, etc). A more complicated concern is what happens as these marine biodegradable materials break down; they still undergo the transition from macro to micro to nanoplastics, they are just biomineralized along the way. Quite a number of studies have looked at effects of nanoplastics on marine species. With the highest concentration reported in aquatic systems in the ng/L (nanogram per litre) concentration; all the published studies should be interpreted with caution since they generally use much higher than 0.5 mg/L of nanoplastics [7]. Taking that into account, a recent study indicated that despite being marine biodegradable, secondary PHB-nanoplastics generated via abiotic degradation of PHB-microplastics were harmful for the tested organisms [8]. This suggests that marine biodegradable plastic still does not mean safe for the environment in the short term. On a more positive note, these nanoplastics are still susceptible to biotic (enzymatic) degradation meaning they do not accumulate over the long term. The impacts of nano- and microplastics are not limited to animals, with studies increasingly identifying effects on primary producers, including plants, algae and photosynthetic bacteria. Studies are increasingly identifying their effect on phytoplankton at the very base of the food chain with the ability to harness the sun’s energy and sequester carbon dioxide, whilst at the same time providing 50% of the Earth’s oxygen. Biodegradable is not the full solution Marine biodegradable means that the materials will be biomineralized at some point – depending on microbes and temperatures. While marine biodegradable plastics may influence the oceans in the shorter term, they may not continue to have these impacts in decades to come. Other biodegradable polymers, on the other hand, will have longer term impact on marine life. Biodegradable plastics are not the complete solution to solving the marine litter problem. A challenge of this magnitude requires layered solutions. We need to stop plastics from entering aquatic systems by re-thinking plastics and how we use it – this ranges from applying circular design principals to our materials and products to optimizing their (chemical) structure for the desired purpose to ultimately phase out marine litter. References 1. McQuatters-Gollop, A., Reid, P. C., Edwards, M., Burkill, P. H., Castellani, C., Batten, S., ... & Johnson, R. (2011). Is there a decline in marine phytoplankton?. Nature, 472(7342), E6-E7. 2. Jambeck, J. R., Geyer, R., Wilcox, C., Siegler, T. R., Perryman, M., Andrady, A. and Law, K. L. (2015). Plastic waste inputs from land into the ocean. Science 347(6223), 768–771. 3. European Commission (2018) https://www.europarl.europa.eu/RegData/ etudes/BRIE/2018/625115/EPRS_BRI(2018)625115_EN.pdf 4. Avio, C. G., Gorbi, S. and Regoli, F. (2017) Plastics and microplastics in the oceans: From emerging pollutants to emerged threat. Marine Environmental Research. 128, 2-11. 5. nova-Institute (2020) http://bio-based.eu/graphics/#biodegPoster 6. Agarwal, S. (2020). Biodegradable Polymers: Present Opportunities and Challenges in Providing a Microplastic-Free Environment. Macromolecular Chemistry and Physics, 221(6), 2000017. 7. Koelmans, A. A., Besseling E, and Won J. Shim. (2015) Nanoplastics in the aquatic environment. Critical review. Marine anthropogenic litter. Springer, Cham, 325-340. 8. González-Pleiter M., Tamayo-Belda M., Pulido-Reyes G, Amariei G, Leganés F., Rosal R. and Fernández-Piñas F. (2019) Secondary nanoplastics released from a biodegradable microplastic severely impact freshwater environments. Environ. Sci.: Nano, 6, 1382. Fig. 1: A piece of braided synthetic rope amongst natural detritus washed up on a beach www.scionresearch.com Fig 2: Biodegradable plastic pots showing degradation over time bioplastics MAGAZINE [03/20] Vol. 15 63
