The Circle of Life
In the last post, it was highlighted briefly that derelict fishing gear acts as vectors for other pollutants. This is, however, not limited to derelict fishing gear but all types of marine plastic waste. Besides introducing invasive species, toxins, chemical pollutants, and the distribution of microalgae, plastics also act as a dispersal vector of heavy metals and pharmaceuticals (Stanton et al., 2020). Heavy metal ions, including lead and mercury, are highly toxic in waters, with a very long residence time, and are thus likely to cause harmful impacts on the marine ecosystem.
Relative to heavy metals and pharmaceuticals, plastic polymers are neither toxic nor harmful to the marine ecosystem. This is because plastic polymers are generally biochemically inert due to their large molecular size (The Blastic Project, n.d.). However, additives to these plastics are a different story; more often than not, plastics contain a variety of additives. Unlike the large plastic polymers, additives are connected by weak bonds, making them comparably much more reactive. As plastics degrade, the “cocktail of additives” is released, of which many are toxic and harmful to the marine ecosystem. Additives to plastics include “Bisphenol-A (BPA), monomers, flame retardants, oligomers, metal ions, and antibiotics” (Thushari & Senevirathna, 2020, p. 5), which are all toxic chemicals.
Furthermore, weathering—whether physical, chemical, or biological—of marine plastic waste results in the production of microplastics. Defined as plastic fragments less than 5mm in length, microplastics can easily be mistaken as food sources by marine organisms. Exposure to high microplastic concentrations led to the European perch larvae’s preference for microplastics as a food source, and microplastic consumption is associated with weaker awareness of predators, increasing risks of mortality (Lönnstedt & Eklöv, 2016). Other marine organisms, including mussels and oysters, also ingest microplastics (Van Cauwenberghe & Janssen, 2014). The accumulation of toxic chemicals in these marine organisms gradually snowballs in the food chain, resulting in health impacts on humans through the ingestion of seafood.
Microplastic pollution in the oceans can also affect the marine carbon pump. Suspended microplastic particles obstruct sunlight, preventing phytoplankton from carrying out photosynthesis, reducing carbon sequestration from the atmosphere (Macleod et al., 2021). Zooplanktons, which feed on phytoplankton, and aid in carrying carbon into deeper parts of the ocean face a reduced food supply and are less able to sequester carbon into the deep ocean. Microplastic pollution thus has implications in the atmospheric carbon concentrations and hence global warming.
Figure 1: Impacts of microplastic pollution on the marine carbon pump (Heinrich Böll Stiftung, 2019)
References
Heinrich Böll Stiftung. (2019). Plastic Atlas [Photograph]. https://www.boell.de/en/2019/10/23/plastic-atlas-graphics-and-licensing-terms
Lönnstedt, O. M., & Eklöv, P. (2016). Environmentally relevant concentrations of microplastic particles influence larval fish ecology. Science. https://doi.org/10.1126/science.aad8828
MacLeod, M., Arp, H. P. H., Tekman, M. B., & Jahnke, A. (2021). The global threat from plastic pollution. Science, 373(6550), 61–65. https://doi.org/10.1126/science.abg5433
Stanton, T., Kay, P., Johnson, M., Chan, F. K. S., Gomes, R. L., Hughes, J., Meredith, W., Orr, H. G., Snape, C. E., Taylor, M., Weeks, J., Wood, H., & Xu, Y. (2021). It’s the product not the polymer: Rethinking plastic pollution. WIREs Water, 8(1). https://doi.org/10.1002/wat2.1490
The Blastic Project. (n.d.). Toxicity of plastics. Blastic. Retrieved January 28, 2022, from https://www.blastic.eu/knowledge-bank/impacts/toxicity-plastics/
Thushari, G. G. N., & Senevirathna, J. D. M. (2020). Plastic pollution in the marine environment. Heliyon, 6(8), e04709. https://doi.org/10.1016/j.heliyon.2020.e04709
Van Cauwenberghe, L., & Janssen, C. R. (2014). Microplastics in bivalves cultured for human consumption. Environmental Pollution, 193, 65–70. https://doi.org/10.1016/j.envpol.2014.06.010