1.2 Microplastics
The term ‘microplastics’ and ‘microlitter’ has been defined differently by various researchers. Gregory and Andrady (2003) defined microlitters as the barely visible particles that pass through a 500 μm sieve but retained by a 67 μm sieve (∼0.06–0.5 mm in diameter) while particles larger than this were called mesolitter. Others(Fendall and Sewell, 2009, Betts, 2008, Moore, 2008), including a recent workshop on the topic (Arthur et al., 2009) defined the microparticles as being in the size range <5 mm (recognizing 333 μm as a practical lower limit when neuston nets are used for sampling.) Particles of plastics that have dimensions ranging from a few μm to 500 μm (5 mm) are commonly present in seawater (Ng and Obbard, 2006, Barnes et al., 2009). For clarity, this size range alone is referred to as ‘microplastics’ here; the larger particles such as virgin resin pellets are referred to as ‘mesoplastics’ after Gregory and Andrady (2003). Persistent organic pollutants (POPs) that occur universally in seawater at very low concentrations are picked up by meso-/microplastics via partitioning. It is the hydrophobicity of POPs that facilitates their concentration in the meso-/microplastic litter at a level that is several orders of magnitude higher than that in seawater. These contaminated plastics when ingested by marine species present a credible route by which the POPs can enter the marine food web. The extent of bioavailability of POPs dissolved in the microplastics to the biota (Moore, 2008) and their potential bio-magnification in the food web (Teuten et al., 2007) has not been studied in detail.
Microplastic (less than 5 mm was commonly defined) pollution, identified as an important emerging threat by a horizon scan of global conservation issues for 2010 (Sutherland et al., 2010), has been a particularly concern in recent years because of its prevalence in the ocean and potential ingestion by marine organisms (Andrady, 2011). The occurrence and distribution of microplastics to the global marine environment include both primary sources (derived from hand and facial cleansers, cosmetic preparations, scrubbers in air-blasting, and production waste from plastic processing plants) and secondary sources (derived from fragmentation of larger plastics as a result of physical and chemical effects) (Zitko and Hanlon, 1991, Gregory, 1996, Barnes et al., 2009).
Microplastics are compositional complex containing a wide range of additives such as
plasticizers, fillers and stabilizers. They also provide the surface area for adsorption of various chemicals in the environment including drugs and hydrocarbons, which complicate their ecotoxicological effects (
Tang, 2020,
2021). Together with nanoplastics which have the potential to enter cells and disrupt cellular functions, their removal from the environment has been a primary concern (
Tang, 2020). As long-term solutions to microplastics elimination from the environment have yet to be framed, water and
sludge treatment provides an immediate and feasible means of microplastics removal.
Microplastics can be transported by the hydrodynamic process, winds and ocean currents, and have been found abundant in almost every corner of our oceans over the past few years, ranging from coastline (
Claessens et al., 2011;
Martin et al., 2017), the Irish continental shelf (
Martin et al., 2017), the Atlantic Ocean (
Cózar et al., 2017;
Law et al., 2010), the Pacific Ocean (
Eriksen et al., 2013;
Law et al., 2014), European coastal areas (
Interwies et al., 2013) and the Indian Ocean (
Reddy et al., 2006), even to the polar regions (
Bergmann et al., 2016;
Waller et al., 2017) and the deep-sea (
Taylor et al., 2016;
Van Cauwenberghe et al., 2013;
Woodall et al., 2014). As pointed out by the G20 Action Plan on Marine Litter (2017), it is an arduous task to reverse the far-reaching impact of marine pollution, which will take 67 ships one year to clean up less than 1% of the garbage in the North Pacific Ocean. Tracks of microplastics even extend to terrestrial environments inland (
McCormick et al., 2016), threatening the access to clean water and the sustainable management of water in freshwater systems.
2 Management of microplastics in the marine environment
MPs in marine waters and their adverse effects have been reported since the early 1970s, giving rise to research based on MPs in aqueous environments (Carpenter and Smith, 1972).
To date, most research has addressed the distribution, transport, fate, and toxicity of MNPs in aquatic and terrestrial environments in the form of case studies (Kanhai et al., 2017; Nobre et al., 2015). Some data, such as quantity, quality, source identification, and estimates of plastics, are available for the sustainable management of MNPs. However, the problem of MNPs in the environment persists and is increasing gradually. This implies that unidentified gaps exist at the interface of research findings and practical actions, which may be due to global, regional, and local challenges, as well as the lack of infrastructure. Various studies have been conducted on sustainable plastic waste management techniques, such as source reduction, value addition, and beneficial utilization via regulatory and legislative changes.
Conclusion and future direction
References
Arthur, C., Baker, J., and Bamford, H., (Eds.), ( 2009 ). Proceedings of the International Research Workshop on the Occurrence, Effects and Fate of Micro-plastic Marine Debris, Sept 9-11, 2008. NOAA Technical Memorandum NOS-OR&R-30.
Carpenter EJ, Smith KL Jr. Plastics on the Sargasso sea surface. Science. 1972 Mar 17;175(4027):1240-1. doi: 10.1126/science.175.4027.1240. PMID: 5061243.
D.K.A. Barnes, F. Galgani, R.C. Thompson, M. Barlaz, (2009). Accumulation and fragmentation of plastic debris in global environments. Philos. Trans. R. Soc. B, 364, pp. 1985-1998
K. Betts. (2008). Why small plastic particles may pose a big problem in the oceans, Environ. Sci. Technol., 42 , p. 8995
Gregory, M.R., Andrady, A.L., 2003. Plastics in the marine environment. In: Andrady, Anthony.L. (Ed.), Plastics and the Environment. John Wiley and Sons, ISBN 0- 471-09520-6, (2003)
C.J. Moore, (2008). Synthetic polymers in the marine environment: a rapidly increasing, long-term threat, Environ. Res., 108 (2), pp. 131-139
K.L. Ng, J.P. Obbard, (2006). Prevalence of microplastics in Singapore’s coastal marine environment. Marine Pollution Bulletin, 52 (7), pp. 761-767
E.L. Teuten, S.J. Rowland, T.S. Galloway, R.C. Thompson, (2007). Potential for plastics to transport hydrophobic contaminants, Environ. Sci. Technol., 41 (22), pp. 7759-7764
Kanhai, LDK, (2017). Microplastic abundance, distribution and composition along a latitudinal gradient in the Atlantic Ocean, Marine Pollution Bulletin., 10.1016/j.marpolbul.2016.12.025
Wang, J., Tan, Z., Peng, J., Qiu, Q., & Li, M. (2016). The behaviors of microplastics in the marine environment.
Marine Environmental Research,
113, 7-17.
https://doi.org/10.1016/j.marenvres.2015.10.014 Zitko, M.; Hanlon, M. (1991) Another source of pollution by plastic skin cleaners with plastic scrubbers. Marine Pollution Bulletin 22(1): 41-42. ISSN/ISBN: 0025-326X. DOI: 10.1016/0025-326x(91)90444-w
Gregory, M.R. (1996) Plastic 'scrubbers' in hand cleansers: A further (and minor) source for marine pollution identified. Marine Pollution Bulletin 32(12): 867-871
Sarkar, B., Dissanayake, P. D., Bolan, N. S., Dar, J. Y., Kumar, M., Haque, M. N., Mukhopadhyay, R., Ramanayaka, S., Biswas, J. K., Tsang, D. C., Rinklebe, J., & Ok, Y. S. (2022). Challenges and opportunities in sustainable management of microplastics and nanoplastics in the environment.
Environmental Research,
207, 112179.
https://doi.org/10.1016/j.envres.2021.112179 Tang, K. H. D., & Hadibarata, T. (2021). Microplastics removal through water treatment plants: Its feasibility, efficiency, future prospects and enhancement by proper waste management.
Environmental Challenges,
5, 100264.
https://doi.org/10.1016/j.envc.2021.100264 K.H.D. Tang. (2020). Ecotoxicological impacts of micro and nanoplastics on marine fauna.
Examines in Marine Biology and Oceanography, 3, pp. 1-5,
10.31031/EIMBO.2020.03.000563 Waller CL, Griffiths HJ, Waluda CM, et al. (2017) Microplastics in the Antarctic marine system: An emerging area of research. Science of the Total Environment 598: 220–227.
Martin J, Lusher A, Thompson RC, et al. (2017) The deposition and accumulation of microplastics in marine sediments and bottom water from the Irish Continental Shelf.
Scientific Reports 7. Available at:
https://www.nature.com/articles/s41598-017-11079-2.
Claessens M, De Meester S, Van Landuyt L, et al. (2011) Occurrence and distribution of microplastics in marine sediments along the Belgian coast. Marine Pollution Bulletin 62: 2199–2204.
K.H.D. Tang. (2021) Interactions of microplastics with persistent organic pollutants and the ecotoxicological effects: a review. Trop. Aquat. Soil Pollut., 1, pp. 24-34
Law KL, Moret-Ferguson S, Maximenko NA, et al. (2010) Plastic accumulation in the North Atlantic Subtropical Gyre. Science 329: 1185–1188.
Reddy MS, Basha S, Adimurthy S, et al. (2006) Description of the small plastics fragments in marine sediments along the Alang-Sosiya ship-breaking yard, India. Estuarine, Coastal and Shelf Science 68: 656–660.
Wang, J., Zheng, L., & Li, J. (2018). A critical review on the sources and instruments of marine microplastics and prospects on the relevant management in China.
Waste Management & Research.
https://doi.org/10.1177/0734242X18793504 Bergmann M, Sandhop N, Schewe I, et al. (2016) Observations of floating anthropogenic litter in the Barents Sea and Fram Strait, Arctic. Polar Biology 39: 553–560.
Thompson RC, Moore CJ, vom Saal FS, et al. (2009) Plastics, the environment and human health: Current consensus and future trends. Philosophical Transactions of the Royal Society B – Biological Sciences 364: 2153–2166.
Andrady AL, Neal MA (2009) Applications and societal benefits of plastics. Philosophical Transactions of the Royal Society B – Biological Sciences 364: 1977–1984.
Van Cauwenberghe L, Vanreusel A, Mees J, et al. (2013) Microplastic pollution in deep-sea sediments. Environmental Pollution 182: 495–499.