Plastics in the Indian Ocean – sources, fate, distribution and impacts

Abstract

Abstract. Plastic debris are the most common and exponentially increasing human pollutant in the world's oceans. The distribution and impact of plastics in the Pacific and Atlantic Oceans have been the subject of many studies but not so for the Indian Ocean (IO). Some of the IO rim countries have the highest population densities in the world and mis-management of plastic waste is of concern in many of these IO rim states. Some of the highest plastic-polluted rivers end up in the IO with all this suggesting that the IO receives a tremendous amount of plastic debris each year. However, the concentration, distribution and impacts of plastics in the IO are poorly understood as the region is under-sampled compared to other oceans. In this review, we discuss sources and sinks, which are specific for the IO as well as unique atmospheric, oceanographic and topographic features of the IO such as reversing wind directions due to the monsoon, fronts and upwelling regions that control plastic distribution. We identified hotspots of possible plastic accumulation in the IO, which were different in the two hemispheres. In the northern Indian Ocean, the majority of the plastic material will most likely end up being beached due to the absence of a sub-tropical gyre, whereas in the southern Indian Ocean, the garbage patch is not well defined and there may be leakage of plastics into the southern Atlantic Ocean. Hotspots of predicted plastic accumulations are identified here as well as the vast knowledge gaps about the plastic issue of the IO and point to the most striking future investigation topics.

Plastic Pollution and Small Juvenile Marine Turtles: A Potential Evolutionary Trap

“…In contrast to other studies on this life stage, samples from the Indian Ocean were dominated by filamentous pieces that were green and blue in colour and were polyethylene, polypropylene and nylon in composition. One of the key sources of marine debris in this area, and indeed in similar studies of turtles in Northern Australia, is that of abandoned, lost or otherwise discarded fishing gear (ALDFG) often comprised of plastic fibres (Kiessling et al, 2003;Gunn et al, 2010;Wilcox et al, 2013;Van Der Mheen et al, 2020;Nelms et al, 2021;Pattiaratchi et al, 2021). Evidence from regionally relevant riverine inputs show polyethylene, polypropylene and nylon fishing gear can contribute to ALDFG in the environment (Nelms et al, 2021).This ghost gear has the capacity to breakdown into bioavailable pieces following long-term degradation (Cole et al, 2011;Jâms et al, 2020).…”

“…Fluid dynamic processes that aggregate organisms into these areas have also been found to concentrate buoyant, passively floating plastics (van Sebille et al, 2012(van Sebille et al, , 2015Critchell et al, 2015;Gove et al, 2019). Regionally, these include the East Australian Current (EAC), Indian Ocean South Equatorial Current (SEC) and the Leeuwen Current (Limpus and Nicholls, 1988;Whiting et al, 2008;Boyle et al, 2009;Feng et al, 2011;Robson et al, 2017;Wildermann et al, 2017;Pattiaratchi et al, 2021). Knowledge indicates that small juveniles are associated within these currents or sites of convergence (Ryan et al, 2016;Pham et al, 2017;Eastman et al, 2020;Rice et al, 2021).…”

The Abundance of Microplastics in the World’s Oceans: A Systematic Review

“…For instance, the Atlantic Ocean exhibited the highest mean concentration of microplastics (4.98 items/m 3 ), which could potentially be explained by the extensive subtropical gyres, maritime traffic, high coastal population density, and inappropriate plastic waste disposal practices in surrounding regions [42,114]. The Indian Ocean followed closely, with a mean concentration of 3.170 items/m 3 , likely influenced by shipping routes, coastal urbanization, and regional waste management practices [115]. The Pacific Ocean, with a mean concentration of 1.49 items/m 3 , may indicate the impact of ocean currents, especially the subtropical gyres as well as proximity to major plastic pollution sources, such as the Great Pacific Garbage Patch [64].…”

Garbage Patches and Their Environmental Implications in a Plastisphere

“…[24] Plastics in the Indian Ocean: Sources, fate, distribution and impacts Describes the outcomes for plastics in the Indian ocean, including feeding the gyre and leakage to other gyres. [25] There is a noticeable need for more literature on aspects related to microplastics, which make up for a substantial part of the garbage patches. The wide presence of plastics in the aquatic environment has led to the coining of the term "plastisphere", a term used to assess the influences of plastic and microplastics on microbes [26], also meaning that a novel type of substrate for river and marine micro-organisms is evolving [27].…”