Microplastic and charred microplastic in the Faafu Atoll, Maldives
Graphical abstract
Introduction
Plastic has undoubtedly extraordinary properties: is easy to process, durable, lightweight and it has low production costs. These properties are the reasons of its capillary use across the world and of its exponential production. It has been estimated that the cumulative value of worldwide plastic production has already exceed the 5 billion tons and it is expected to increase to 33 billion tons by 2050 (Plastics Europe, 2016).
A side effect of this mass production is that an enormous quantity of plastic waste ends up into the ocean due to improper disposal (from 4.8 to 12.7 million metric tons each year) and accordingly to anticipated trends, the number will continue to grow (Jambeck et al., 2015). Plastic is just now so abundant that it has been proposed as a new stratigraphic indicator of Anthropocene (Zalasiewicz et al., 2016).
Once introduced into the environment, plastic may persist for decades due to its chemical properties (Barnes et al., 2009; Ivar do Sul and Costa, 2014), and undergo over time to disintegration into smaller fragments under the combined effect mechanical breakdown caused by waves, UV induced photolysis, and biological degradation (Browne et al., 2007; Barnes et al., 2009; Ceccarini et al., 2018).
This process lead to the formation of very tiny particles – called microplastics (smaller than 5 mm) that represent the new challenge of the plastic contamination problem (Eriksen et al., 2013; Lusher et al., 2015): over 92% of all plastic items currently found at sea are microplastic (Moore, 2008). Open ocean water bodies (Cole et al., 2011; Desforges et al., 2014; Hidalgo-Ruz et al., 2012; Lusher et al., 2014), beaches and coastlines (Claessens et al., 2011; Hengstmann et al., 2018; Moore et al., 2002; Zhang et al., 2018), subtropical oceanic gyres (Brach et al., 2018; Ory et al., 2017), polar areas (Lusher et al., 2015; Obbard, 2018), deep ocean sediments (Van Cauwenberghe et al., 2015), and freshwater systems (Eriksen et al., 2013; Vaughan et al., 2017; Wagner and Lambert, 2018) have been already documented to accumulate microplastics.
Microplastic may severely affect marine wildlife. Main problems arise due to ingestion (Gall and Thompson, 2015): microplastic particles are mistaken by food because their size, shape and colour (Schuyler et al., 2014) by the marine fauna as zooplankton and larval fish (Desforges et al., 2015; Sun et al., 2017; Steer et al., 2017), sessile invertebrates (Wright et al., 2013) sea turtles (Camedda et al., 2014) marine birds (Van Franeker et al., 2011) and fish species (Boerger et al., 2010). In addition to direct mechanical effects, i.e. particles may entangle block or abrade feeding appendages and internal organs (Wright et al., 2013), a variety of indirect effects is also observed: harmful substances present as ingredient in the microplastic particles may leach into the digestive tract reducing survival, feeding, immunity or antioxidant capacity (Browne et al., 2007), organic and metal contaminants may be accumulated from surrounding water and found an easy enter inside the organism (Koelmans et al., 2016); a wide range of rafting alien species and microbial communities may found in microplastic a vector to colonize ecosystems (Barnes, 2002; Kirstein et al., 2016).
Although worldwide attention to the marine plastic litter has been grown in the last decades, together with the number of scientific publications devoted to the microplastic topic, knowledge about the abundance, composition and size distribution of plastic debris in areas remote to human civilization is still considered scarce (Thompson et al., 2004; Bergmann et al., 2015; van Sebille et al., 2015). This information is fundamental to support the management of the problem (GESAMP, 2015).
Maldivian coral reef is the seventh largest coral reef system on the globe, with a total surface of 8920 km2, accounting for 3.13% of the world's reef area (Spalding et al., 2001) and probably accounting for the highest coral cover values in the western Indian Ocean (Goreau et al., 2000). Unfortunately, several threats are contributing to its environmental decline. Some are natural such as coral bleaching, algal overgrowth, invertebrate outbreaks and coral diseases (Montano et al., 2012; Saponari et al., 2018), other are human-related, such as coral mining, pollution, fishing, tourism and land reclamation (Jaleel, 2013).
The microplastic contamination in the Maldivian area and the possible impact on the coral reef ecosystem has been still scarcely investigated (Barnes, 2004, Browne et al., 2011; van Sebille et al., 2015; Imhof et al., 2017). Considering that the Republic of Maldives is constituted by a human population of about 300 thousands located in an archipelago of about 1200 islands, and it is now facing a rapid economic growth, scientific investigation is needed in order to plan sustainable development policies and efficient waste management practice.
Under this light, in this study we surveyed the level of microplastic contamination along the Faafu Atoll, a complex of 23 inhabited and uninhabited islands with a total of about 3000 locals, that is far about 140 km from the capital city Malè and 720.000 km from India, the closest country. For the best of our knowledge, this is the first on field investigation regarding its microplastic contamination.
Section snippets
Sampling location
The study was conducted during May 2018 in Faafu Atoll, Republic of Maldives (Fig. 1). This atoll is approximately 31 km long and 24 km wide and is subjected to two main oceanic stream/current: one toward southwest-northeast from May to November, and another in opposite direction from December to April (Montano et al., 2012). Twelve different sampling sites (Table 1), among those accessible in two side of the atoll, and showing heterogeneous characteristics in terms of reef morphology and
Abundance of plastic particles in the beach sediments
A total of 824 visible plastic particles were identified across the six surveyed beaches, with an average abundance of 22.7 ± 10.5 plastic particles/m2 (mean ± standard deviation, Fig. 2).
The highest concentration of particles was found at beach BD1 (38.5 ± 15.6 particles/m2) whereas the lowest concentration was found at beach FY (4.2 ± 2.0 particles/m2).
Since plastics larger than >25 mm represented a small percentage of the total plastic debris (as number of items), mesoplastic (5–25 mm) and
Conclusion
This study aimed to examine the microplastic contamination in the Faafu Atoll, a coral Maldivian atoll placed far about 140 km away from the capital city of Malè, and characterized by a low touristic pressure in comparison to the northern Maldivian atolls.
Despite the remoteness of the atoll and limited number of inhabitants, a considerable amount of plastic particles was found in the beach sediments and in the seawater samples collected inside the atoll rim. This result strengthens the
Acknowledgments
This works was financially supported by University of Milano-Bicocca – Mahre center. We warmly thank the Captain and the crew of Rhantari research vessel for the support during the sampling operation and our students Chiara D'Alconzo, Andrea Ghezzi and Erika Colombo for the help in performing the experiments.
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