MICROPLASTIC IN THE DEEP-SEA SEDIMENT OF SOUTHWESTERN SUMATERA WATERS

Indonesia is recently ranked second as the world’s largest plastic wastes producer. Plastic is a very durable material that can be degraded by thermal oxidation with ultraviolet radiation and/or mechanically to smaller sizes. Degraded plastic with size less than 5mm is referred to as microplastic. Here, we investigate the pervasiveness of microplastic pollution by studying deep-sea sediments retrieved from western Sumatera in the eastern Indian Ocean during the Ekspedisi Widya Nusantara (EWIN) 2015 research cruise. The cruise, which took place between May 7-18, is part of Indonesia’s contribution to the ongoing International Indian Ocean Expedition-2 (IIOE-2) campaign. Deep-sea sediments were taken at depths ranging from 66.8 to 2182m and microplastic characterization of the sediments was carried out following a modified flotation method. Our finding reveals that microplastics are present in 8 out of 10 sampling locations. We find 41 particles of microplastic in the forms of the granule (35 particles) and fiber (6 particles). Most or 20 microplastic particles are found at depths less than 500 m. Furthermore, the presence of microplastics in the western Sumatera sediments at more than 2000m deep confirms that plastics have pervaded marine environments including pristine areas despite being a relatively recent material that started being produced in the early 19th century.


INTRODUCTION
The convenience of using plastics has resulted in its increased production throughout years with a negative consequence to marine environments.Being versatile, lightweight, strong, durable and inexpensive materials, plastics are used to make tools, clothing, transportation and building materials, and more.Global plastic production increased from about 0.5 million tons per year in 1950 to 288 million tons in 2012.This trend continued to increase at about 4% per year by 2016 (PlasticsEurope, 2010(PlasticsEurope, , 2013(PlasticsEurope, , 2015)).In Indonesia, the production of plastics reached 1.9 million tons in 2013 with an average production rate of 1.65 million tons per year (Kementerian Perindustrian dan Perdagangan, 2013).As such, it has been estimated that Indonesia is indeed the world's second largest plastic producer and consumer (Jambeck & Johnsen, 2015).With an assumption that about 10% of plastics would end up in seas (Van Cauwenberghe et al., 2015), we can estimate that about 165,000 tons of plastic waste pollute Indonesian seawaters every year.The increased plastic use unfortunately poses as one of the major environmental problems today.This phenomena would endanger marine organisms as have been observed elsewhere (Moore et al., 2001).
One concerning issue related to plastic pollution is the existence of microplastic in the environment.Plastic can be degraded by UV thermal oxidation and/or mechanical processes forming microscopic sizes (Andrady, 2011;Wagner et al., 2014).Plastic waste that is micrometer in size ahs been referred to as microplastic.Aside from being a mechanically degraded plastic, microplastic in the environment could also come from microbeads contained in cosmetics and fabrics (Browne et al., 2011;Fendall & Sewell, 2009).Many studies categorize microplastic as plastic waste with size no more than 5mm (Arthur et ald, 2009;Wright et aly, 2013), while some categorize microplastic as plastic waste with size below 1mm (Browne et al., 2011;Van Cauwenberghe et al., 2013).Regardless, previous works have detected microplastics in coastal and mangrove ecosystems, the water column and even in deep-sea sediments (Claessens, et al., 2011;Mohamed Nor & Obbard, 2014;Moore et al., 2002;Thompson et al., 2004;Van Cauwenberghe et al., 2013).The small size would increase plastic bioavailability for digestion by marine organisms.Some laboratory studies show that detritivores organisms (e.g.amphipods), deposit feeders (e.g.lugworm), filter feeders (e.g.barnacles and bivalves), and deposit and suspension feeders (e.g.sea cucumber and copepods) consume microplastics (Graham & Thompson, 2009;Thompson et al., 2004).Plastic consumption would irritate digestive system (Betts, 2008) and furthermore could cause other serious problems since the consumed plastics may also adsorb organic pollutant (Teuten et al., 2009).Microplastic consumption by marine organisms could happen as the organisms falsely identify the microplastic as an edible food (Van Cauwenberghe et al., 2012).
The eastern Indian Ocean especially southwestern Sumatera waters is of an interest for studying microplastic due to the fact that it is a busy domestic and international shipping route.This condition increases the possibility for receiving pollution.Furthermore, scientific data particularly on marine pollution and microplastic from this area is rare.Therefore, it is important to characterize microplastic pollution in this area by analyzing its pervasiveness in deep-sea sediments.

MATERIALS AND METHODS
Deep-sea sediment sampling was conducted during the Ekspedisi Widya Nusantara (E-WIN) research cruise between May 7-18, 2015.Samples were retrieved using a 60 x 40 x 50cm boxcore from 10 stations with depths ranging from 66.8 to 2182m (Figure 1).Sub-samples were taken using a stainless steel shovel (20ml) from sediment surface within a 10cm x 5cm x 2cm section.Then, the samples were stored in a freezer (4°C) prior to analysis at the Chemical Oceanography Laboratory of the Research Center for Oceanography (Indonesian Institute of Sciences).
Microplastic extraction was conducted using a modified flotation method by using a concentrated saline solution at 1.18 g/l (Claessens et al., 2011;Mohamed Nor & Obbard, 2014;Thompson et al., 2004) and double-distilled deionized water.The sediments were oven dried (60°C, 24h).To remove organic matters, the sediments were added with H 2 O 2 and heated (90ºC), and then the visible froth was removed.Dried sediment samples weighted 62.5g was put on erlenmeyer bottle with 250 ml concentrated saline solution, and then stirred using a mechanical shaker (200 rpm, 10 minutes).After 6 hours, the supernatant was extracted from the mixture and filtered into Whatman cellulose filter paper (diameter 47mm; pore size 0.45µm).Vacuum filtration unit was used to accelerate the filtration process.Samples from the filter paper were stored in petri-disk within a vacuum desiccator.
We conducted sample observation and quantitative analysis using a Nikon Eclipse E600 microscope.The criteria for identifying microplastic follows (Cole et al, (2013), namely (a) organic or cellular structure is absent, (b) homogenous in color, not shiny or sparkling, (c) plastic fibers are unbranched and not tapered at the ends, and (d) there is no segmented fiber.

RESULT General trend
A total of 41 microplastic particles were found from eight out of ten the sampling stations (Table 1 Our finding shows that microplastics found in southwestern Sumatera sediments are in the forms of granule and fiber (Figure 2).Most microplastics found in this study are granulates from depths of less than 500 m with a total of 16 particles.Fiber form is also most commonly found at the same depth range (<500m) with a total of 4 particles.
Based on the size classification of microplastic, most observed microplastic particles in the southwestern Sumatera sediments are those with the size range of 100-500µm with a total of 16 particles (Figure 3).This is followed by the size range of 60-100µm (13 particles) and less than 20µm (6 particles).While the least of all are the size range of 20-60µm and >500µm, each having 3 particles.

DISCUSSION
The suspected sources Relatively higher amount of microplastics found in areas close to terrestrial input and along a busy shipping route is consistent with anthropogenic influence.The microplastic particles are found mostly from sediment samples taken from depths less than 500 m.These particles were likely derived from anthropogenic activities on the west coast of Sumatera then carried by ocean currents (Mohamed Nor & Obbard, 2014).As for sampling station, most or 14 particles of microplastic are found in the Sunda Strait (Station 2) at a depth of 88.5 m.This is a busy ocean shipping route with more than 100,000 passengers and 2,200 ships passing by per year (Rusli, 2012).Therefore, our study supports other works suggesting that areas near port or along shipping traffic have high presence of microplastic (Claessens et al., 2011).Other sampling sites with higher amount of microplastic are Station 1 (at a depth of 970.4m) and Station 10 (66.8m), each with 6 plastic particles.We suspect that the high microplastic abundance came from the east coast of Sumatera specifically near Bengkulu.This area has large rivers namely Bengkulu River, Jenggalu River and Babat River.In all, microplastic particles found from these three locations represent 63.4% plastic particles found from all sampling sites in this study.Indeed, the proximity to human activity causes higher exposure of microplastic (Frias et al., 2016).We also found microplastic on the southwestern Sumatera deep-sea sediment sample taken at a depth of >2000m.This suggests that plastics which have been produced since 1910 (with its mass production since the 1950s), have pervaded marine environments even in pristine sites (Van Cauwenberghe et al., 2013).
Eventually, microplastics would fall into seabed via a process called "marine snow" (discussed more in the next section) and be ingested by bottom-dwelling marine organisms that accumulate microplastics in their bodies (Goldberg, 1997).Plastics could reach sea bottom at depths of >2000m within a few days or a year, depending on ocean currents (Van Cauwenberghe et al., 2013).Eventually, microplastic would reach the seabed and be covered with sand and mud (Ivar Do Sul & Costa, 2014).

The potential downward vector of microplastic
Marine snow is the downward export of organic matters that may also influence the transport of microplastic and other pollutant.Marine snow is a component in biogeochemical vector of biological pump (Turner, 2015).And as suggested by some studies, marine snow may also become a vector for microplastic downward transport (Goldberg, 1997;Van Cauwenberghe et al., 2013).Furthermore, it has been widely known that the formation of marine snow is not merely composed of organic materials (e.g.fecal pellets, phytodetritus, transparent exopolymer, but also inorganic materials and others Graham et al., 1999;Passow et al., 2014;Passow et al., 2012).
The downward transport of microplastic could occur in stages along the depth.Since plastic could adsorb organic pollutant (Teuten et al., 2009), it is possible that other non-pollutant organic materials may also attach to plastic.This process may occur during the formation of transparent exopolymer (TEP) by microorganisms  (Turner, 2015).TEP itself attracts other materials such as fecal pellets, phytodetritus from planktonic organisms, and even dead materials to aggregate into bigger sizes (M.Graham et al., 1999;Turner, 2015).This process would accelerate the downward export (Passow et al., 2014).However, the crucial downward export process may happen in the twilight zone up to the upper aphotic zone (300-1000m) when the microbial process enhances biogeochemical processes.Within this zone, marine snow may be degraded by microbes (Sanders et al., 2014), but the process may not affect the non-degradable microplastics.Then in the depth below 1000m, the microplastics would aggregate with freshly produced particulate matters (Liu et al., 2007), the process that is affected by partial pressure of CO2 and particle size (Passow et al., 2014).

The potential impacts of microplastic
Plastic pollution was initially seen as an aesthetic problem (Galgani, Hanke, Werner, & De Vrees, 2013;Gregory, 2009), but many researches in recent decades show how marine animals could be negatively affected by the presence of plastics (Boerger, Lattin, Moore, & Moore, 2010;Galgani et al., 2013).Marine organisms could be affected mainly through the winding of plastic, getting trapped by plastic and plastic consumption (Gregory, 2009;Thompson, Moore et al., 2009;Van Franeker et al., 2011).Worse, the microscopic size allows the bioavailability of plastic through ingestion tract (Betts, 2008).A number of marine organisms have been observed to accumulate microplastics in their bodies, including crabs (Farrell & Nelson, 2013), copepods (Cole et al., 2013), blue mussels (Browne et al., 2008;Van Cauwenberghe & Janssen, 2014) and mussels (Van Cauwenberghe & Janssen, 2014).Microplastic ingested by marine organisms could disrupt the functioning of digestive tract (Cole et al., 2013) and become a carrier for other organic contaminants adsorbed on microplastic such as brominated diphenyl ethers and polychlorinated biphenyls (Teuten et al., 2009).

CONCLUSION
Microplastics found on the southwestern Sumatera deep-sea sediments tend to increase towards the main island, consistent with increased anthropogenic activities.Our finding also shows that microplastic pollution has pervaded relatively pristine environments.We project that the continuing increase of plastic production and consumption in Indonesia would lead to increased microplastic pollution that subsequently affects marine organisms.

Figure 1 .
Figure 1.Study site and sampling stations.

Table 1 .
).The highest number of microplastics (14 particles) was observed at a station located in the Sunda Strait at a depth of 88.5m (Station 2).Microplastic particles were found only in two types of sediments (i.e.sandy mud and mud), where 26 particles were found in the sandy mud type of sediment and 15 particles in the mud sediment.Whereas the two stations where microplastic is absent are made of muddy sand Number of microplastic particles according to location, depth and sediment volume.