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Rendiconti Lincei. Scienze Fisiche e Naturali

, Volume 29, Issue 4, pp 805–809 | Cite as

Microplastics in marine sediments in the area of Pianosa Island (Central Adriatic Sea)

  • Michele Mistri
  • Vanessa Infantini
  • Marco Scoponi
  • Tommaso Granata
  • Letizia Moruzzi
  • Francesca Massara
  • Miriam De Donati
  • Cristina Munari
Marine litter: from environmental emergency to potential resource
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Part of the following topical collections:
  1. Marine litter: from environmental emergency to potential resource

Abstract

We investigated the occurrence of plastic contamination in sediments collected in the area of Pianosa Island (Adriatic Sea). In November 2015, 20 sediment samples were collected at depth varying between 119 and 142 m. At the laboratory, plastic debris in samples were weighted, measured and classified into dimensional groups, and categorized according to shape. Polymer types were identified using FT-IR analysis. All sediment samples contained plastics. In terms of numerical abundance, microplastics accounted for 64.4% of the total amount found. Filaments (66%) were the most common shape category. Identification through FT-IR spectroscopy evidenced the presence of 6 polymer types. Considering abundance, the majority of plastic debris were nylon (53.2%), followed by polyethylene (18%). By weight, polyethylene (61.4%) was the most represented polymer type, followed by polypropylene (19.6%). Because the distance from the coast, we hypothesize that plastics could be originated from marine-based sources including fishing vessels, merchant vessels and recreational boats.

Keywords

Microplastics Sediments Adriatic Sea 

1 Introduction

World production of plastics has strongly expanded, from 1.7 million tonnes in 1950 to 322 million tonnes in 2015 (Plastic Europe 2016). Discarded “end-of-life” plastic accumulates particularly in marine habitats (Derraik 2002). Marine plastic litter results from both land and sea-based sources and once at sea, larger items tend to either fragment or sink, and then accumulate on the coastline or on the seafloor, harming wild life and marine food chains (Avio et al. 2017). Due to its light weight nature it can travel far from its original source covering vast distances being carried by wind and ocean currents and its durability means it can take many years to fully breakdown (Singh and Sharma 2008). Small plastic debris, defined as microplastics in a size range of < 5 mm (Barnes et al. 2009), have emerged as an imminent source of plastic contamination in the marine environment, as a consequence of their eluding presence in sediments and seawater (Andrady 2011). Microplastics can be separated into two different types, primary and secondary microplastics. Primary microplastics include pre-production pellets as well as microbeads used in personal care products, while, secondary microplastics are formed through the degradation of larger plastic material by environmental stressors such as sunlight, wind, rain and wave action. The assessment of marine microplastic pollution is relatively recent, and extensive areas of seas remain yet poorly explored.

The EU Marine Strategy Framework Directive (MSFD, 2008/56/EC) was launched in 2008 with the main goal of achieving Good Environmental Status (GES) of European marine waters by 2020. Eleven qualitative descriptors were defined, including marine litter (Descriptor 10), which was recognized as one of the main causes of marine pollution. Microplastics are considered specifically in descriptor 10 of the MSFD (10.1.3 “Trends in the amount, distribution and, where possible, composition of micro-particles (in particular micro-plastics)”), and implicitly in the indicator related with impacts of litter on marine life. According to the MSDF, microplastics should be categorized according to their physical characteristics including size and shape. It is also important to obtain information on polymer type (Gago et al. 2016).

Located in the central Mediterranean, the Adriatic Sea is an elongated basin, with its major axis in the NW–SE direction, between Italy and the Balkans. It is characterized by one of the greatest floating plastic particles pollution among Mediterranean regions (Suaria and Alliani 2014). The distribution and accumulation of small plastic debris in Adriatic shorelines is relatively documented (Laglbauer et al. 2014; Munari et al. 2017), however, contributions to minimize the knowledge gap on seafloor benthic small plastic debris are still needed.

Taking into account the global distribution and implications of small plastic debris and the early stages of studies dealing with microplastics deposition in Mediterranean sediments, and that microplastics is one of the descriptors of the MSFD, with the present study we wanted to assess the quality and quantity of microplastics occurring in the seafloor in the vicinity of Pianosa Island, a 13 ha-wide plateau, 20 NM off the Italian coast in the southern Adriatic Sea.

2 Materials and methods

We investigated the occurrence and extent of plastic contamination in sediments collected in the area of Pianosa Island, outside the boundaries of the MPA, which is an area of intense ship traffic. The Pianosa Island is located about 11 NM north–northeast of the Tremiti archipelago main islands (San Nicola, San Domino and Caprara). Up at the depth of 70 m there is the integral reserve regime. In November 2015, 20 sediment samples (Van Veen grab, area 0.1 m2) at 10 sites were taken along a 25 km-long transect, at depth varying between 119 and 142 m. At each site, 2 samples were taken, at a distance of about 200 m from each other. Table 1 shows the geographic coordinates of the 10 survey sites.
Table 1

Sediment characteristics at the ten sites of investigation

Stn

Lat WGS 84

Long WGS 84

Depth (m)

Gravel (%)

Sand (%)

Silt (%)

Clay (%)

Biogenic (%)

DDMMSS.dd

DDMMSS.dd

23

422,226.881

153,521.267

142

< 0.1

1.4

22.3

76.3

< 0.1

24

422,223.749

153,520.037

142

< 0.1

2.6

24.2

73.2

< 0.1

25

422,158.976

153,856.617

138

< 0.1

1.5

35.5

63.0

< 0.1

26

422,155.845

153,855.384

138

< 0.1

2.0

38.8

59.2

1.0

27

422,130.959

154,231.914

132

0.2

3.5

45.7

50.6

2.0

28

422,127.828

154,230.678

132

< 0.1

6.0

25.7

68.3

2.3

29

422,101.763

154,606.915

130

0.2

4.1

27.6

68.1

2.1

30

422,058.645

154,605.681

130

0.2

7.8

34.0

58.0

2.1

31

421,909.911

154,924.795

119

0.7

8.8

38.9

51.6

3.7

32

421,907.522

154,921.843

119

0.8

15.8

32.8

50.6

2.8

At our laboratories, the plastic debris in sediment samples were removed under a dissection microscope (Nikon SMZ45T, magnification 3.35–300 ×), counted and weighted to the nearest 0.0001 g. The identified plastics were measured at their largest cross-section using calipers and classified into three groups: micro (1–5 mm), meso (> 5–20 mm), and macro (> 20 mm). Plastic debris were also categorized according to shape, i.e. filament, film, and fragment. An aliquot of sediments was used to analyze the sedimentary texture.

Fourier-transform infrared spectroscopy (FT-IR) analysis of plastic debris was carried out with a CARY 600 FT-IR (Agilent Technologies) instrument. Measurements were carried out in attenuated total reflectance (ATR) configuration, with a Pike Miracle diamond cell. Tests were carried out at 25 °C in dry air. Particles were identified by comparing FT-IR absorbance spectra of the microplastics to those in a polymer reference library.

3 Results

Sediment characteristics at the 10 sampling sites are shown in Table 1. Seafloor was characterized by particles ranging from gravels (diameter between 4 and 2 mm) to clay (diameter < 0.0039 mm), according to the Wentworth grain-size classification. The fraction of finer sediments (silt + clay) was always dominant.

All sediment samples contained plastics. Some examples of plastic debris collected during the study are shown in Fig. 1. Average abundance was 5.9 pcs 0.1 m2, average weight was 0.109 g 0.1 m2. The samples contained both filaments, film and fragments in a range of colors (mostly green and blue), implying that particles may have originated from multiple sources. In terms of numerical abundance, microplastics (< 5 mm) accounted for 64.4% of the total amount found, mesoplastics (> 5–20 mm) made up 33.1%, macroplastics (> 20 mm) accounted for 2.5%. Considering shape type, filaments (66%) were the most common shape category, followed by fragments and film (17% each). All plastics in our samples were secondary products derived from degradation and fragmentation of larger fragments, but it was not possible to attribute a specific source or a specific activity of origin if not for some fishing lines filaments. Because the distance from the coast, we suggest that plastics could be originated from marine-based sources including fishing vessels, merchant vessels and recreational boats.
Fig. 1

Examples of the collected plastic debris

Identification through FT-IR spectroscopy evidenced the presence of six polymer types: polyethylene (PE), polypropylene (PP), Nylon 6.6 (Nylon), linear low-density polyethylene-octene copolymer (LLDP/Oct), ethylene vinyl alcohol copolymer (EVOH), and thermoplastic polyurethane (TPU). The composition by abundance and by weight of polymer type is shown in Table 2: considering abundance, the majority of plastic debris were Nylon (53.2%), while, by weight, PE (61.4%) was the most represented polymer type.
Table 2

Composition by abundance and by weight of polymer type

 

EVOH

NYL

LLDPE/Oct

PE

PP

TPU

Abundance

12.9

53.2

2.2

18.0

3.0

10.6

Weight

3.8

5.9

9.0

61.4

19.6

0.2

4 Discussion

Plastic debris has become increasingly recognized as a global ocean-wide problem due to its ubiquity and recalcitrance, allowing particles to persist for estimated years to millennia. This study gives a first insight into microplastic concentration in the Pianosa area seafloor, and this data could be used as reference or baseline data to test the effectiveness of any reduction measures adopted to address the MSFD requirements. In the seafloor in vicinity of Pianosa Island, 20 NM off the Italian coast, plastics particles were found in 100% of the sediments collected. The collected plastics were categorized in three principal categories: filaments (66%), fragments (17%), and film (17%). Most of the filaments seemed to derive from the breakage of fishing lines and from the frying of ropes. Microplastics comprised the majority of the plastic debris (64%). All plastics in our samples were secondary products derived from degradation and fragmentation of larger fragments, but it was rarely possible to attribute a specific source or a specific activity of origin if not for some fishing lines filaments. This part of the Adriatic Sea is a busy shipping route with thousands ships passing by per year (Fig. 2; https://www.marinetraffic.com). We hypothesize that plastics found at our sampling sites are originated from marine-based sources including fishing vessels, merchant vessels and recreational boats, according to other studies which suggested that areas along shipping traffic have high presence of microplastics (Claessens et al. 2011). Results of a recent large-scale survey of neustonic micro and mesoplastics floating in Mediterranean waters seem to suggest an high influence of ship-based pollution in the Adriatic Sea (Suaria et al. 2016). As a matter of fact, in the northern Adriatic, Gajšt et al. (2016) found an average concentration of floating microplastics of 406 × 103 particles km−2, with over 80% of the particles identified as polyethylene. In a previous paper (Mistri et al. 2017), studying microplastic contamination along a 140 km-long transect from the town of Pescara to the open sea, we found filaments (69.3%) to be the most common plastic debris. Filaments represented 90% of all seafloor plastics in the Telascica Bay (Croatia; Blăsković et al. 2017).
Fig. 2

Shipping densities in the Adriatic (from: https://www.marinetraffic.com). The blue oval shows the study area

FT-IR spectroscopy evidenced the presence of six plastic types. The density of plastics can vary considerably depending upon the type of polymer and the manufacturing process. Although plastic particles of different polymer types could be heavier or lighter than water and might be able to sink or float over its surface, many of them become negatively buoyant and sink to the sea floor as a result of fouling by organisms or adherence of denser particles (Morét-Ferguson et al. 2010). The density of PE ranges from 0.92 to 0.96 g cm−3, LLDP/Oct from 0.91 to 0.94 g cm−3, PP from 0.90 to 1.00 g cm−3. These microplastics can be carried long distances because they are less dense than seawater (~ 1.025 g cm−3). Other plastics are denser than seawater (e.g. Nylon from 1.13 to 1.15 g cm−3, EVOH from 1.12 to 1.22 g cm−3, TPU from 1.14 to 1.20 g cm−3), and tend to settle on the sea bottom. Deposition of less dense microplastics in sediments is influenced by many biologically driven or physico-chemical transport mechanisms. Colonization by organisms, adherence to phytoplankton, the aggregation with organic debris and small particles in the form of marine snow will eventually enhance settling (Avio et al. 2017). Of all the plastic debris collected in this study, 61.4% by weight (18% by numbers) of microplastics were made of PE, and 19.7% by weight (3% by numbers) were made of PP, all polymers less dense than seawater. These polymers are principally used to make packaging that is used once and then discarded. Our findings agree with previous studies of plastic debris in which packaging for food were among the most abundant types of debris found in marine habitats (Claessens et al. 2011). The denser microplastics found in this study are unlikely to have drifted independently in the upper sea. Nylon, which forms the largest proportion of plastic filaments in this study, is a common polymer detected in some other microplastics studies (Claessens et al. 2011), and it is used for making ropes and fishing lines. Nylon is also among the most abundant polymers found in egagropiles, spherical balls generated by the progressive disintegration of fibrous material sourced from the foliage of Posidonia oceanica (Pietrelli et al. 2017).

Results from this study can be useful as baseline data to test the effectiveness of any reduction measures adopted to address the MSFD requirements. Further studies are needed to better elucidate factors influencing the occurrence of microplastics in the marine biota, and modulation of biological effects.

Notes

Acknowledgements

This study was supported by Terna SpA, Italy (submarine cable HVDC 500 kV cc Italy-Montenegro “MONITA” project). We are very grateful to Mr. Patrizio Fontana and Mr. Albino Moretti for their help with the sampling. Our sincere gratitude to all crew members of the vessel “Kiya” for their support at sea. An anonymous reviewer is acknowledged for constructive criticism.

Supplementary material

12210_2018_736_MOESM1_ESM.xlsx (10 kb)
Supplementary material 1 (XLSX 10 kb)

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Copyright information

© Accademia Nazionale dei Lincei 2018

Authors and Affiliations

  • Michele Mistri
    • 1
  • Vanessa Infantini
    • 1
  • Marco Scoponi
    • 2
    • 3
  • Tommaso Granata
    • 4
  • Letizia Moruzzi
    • 4
  • Francesca Massara
    • 5
  • Miriam De Donati
    • 5
  • Cristina Munari
    • 1
  1. 1.Dipartimento di Scienze Chimiche e FarmaceuticheUniversità di FerraraFerraraItaly
  2. 2.ISOF-CNR c/o Dipartimento di Scienze Chimiche e FarmaceuticheUniversità di FerraraFerraraItaly
  3. 3.Advanced Polymer MaterialsFerraraItaly
  4. 4.CESIPiacenzaItaly
  5. 5.TERNARomeItaly

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