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MICROPLASTICS ABUNDANCE IN THE WATER
Scientific research has mainly focused on the abundance of microplastics in the marine environment with oceans considered as the final sink for these pollutants (Horton and Dixon, 2018). Microplastics distribution in marine environment is affected by both temporal and spatial variability due to seasonal patterns in oceanic currents (Cole et al., 2011; Ryan et al., 2009). The majority of studies on microplastics occurrence were reported in the surface and subsurface water of several areas worldwide (reviewed by Akdogan and Guven, 2019). Most of them have taken into consideration the spatio-temporal variation of MPs abundance, including their shape, size, color and polymer type. Microplastics have been reported in the water of Pacific Ocean (Desforges et al., 2014; Díaz-Torres et al., 2017; Lebreton et al., 2018; Rios Mendoza and Jones, 2015), the North Sea (Liebezeit and Dubaish, 2012; Lorenz et al., 2019), the Atlantic ocean (Kanhai et al., 2017; Lusher et al., 2014; Reisser et al., 2015), Bohai and South China Seas (Cai et al., 2018; Zhang et al., 2017), Artic polar waters (Lusher et al., 2015), and the Mediterranean Sea (Baini et al., 2018; Cózar et al., 2015; Gündoğdu and Çevik, 2017; Lefebvre et al., 2019) (see Annex 1). Microplastics in coastal waters are affected by strong hydrodynamic factors (tides, wind, waves and salinity gradients), and undergo beaching, drifting and settling, with only a small faction being carried into the open ocean (Zhang, 2017). Various sampling methods were used along with several mesh sizes (Table 4). Different analyses protocols were used in various studies: for clean water samples, no digestion method was used and they were directly filtered. If this was not the case, organic material destruction was used (enzymatic or mechanical) and samples underwent density separation (various solution were used between studies) (Reviewed by Stock et al. (2019)). Recovered items in the coastal water samples, were made of all kind of shapes: fibers, fragments, films and microbeads. The dominant shape varied from one study to another and from one region to another (Lusher et al., 2015, 2014; Pedrotti et al., 2016; Suaria et al., 2016): Fibers were abundant in the Western Mediterranean surface water (Lefebvre et al., 2019), whereas fragments were dominant in the Eastern Mediterranean (Gündoğdu, 2017; van der Hal et al., 2017). The dominant polymer type differed with the dominant shape: PE, PP and PS were dominant in the areas with high abundance of fragments (Pedrotti et al., 2016; Zhang et al., 2017); Polyester (PET) and PA were highly dominant in samples with important fibers.
MICROPLASTICS IN SEDIMENTS
Microplastics in the surface water can be either washed up on the coast or sunk at the bottom. Deep sea sediments have been recognized to potentially accumulate microplastics and are considered as major sink of MPs (Martellini et al., 2018). Microplastics on the shore are affected by important anthropogenic pressure (tourism) whereas the offshore sediments are influenced by environmental conditions such as tides, wind speed and direction, resuspension, current and biofouling (Wang et al., 2018; Zhang, 2017). The abundance of microplastics in sediments vary worldwide. There is no standard sampling and extraction protocol: some digested their samples before using a density separation method, whereas others skipped digestion and went directly to density separation, and some even visualized their samples without treatment. Even different solutions were used as a density separation medium with sodium chloride (NaCl) the most used solution (see Figure 28). Microplastics observed after extraction from sediments are expressed in different units (items/kg; items/m2) complicating the comparison between various studies. Extreme high values were observed in sediments of Venice Lagoon reaching 2175 MPs/Kg d.w (Vianello et al., 2013) and in the Xiangshan Bay (China) 1739 ± 2153 items/Kg (Chen et al., 2018). Whereas other regions had lower number: 67 ± 76 items/Kg d.w in the French Atlantic Ocean (Phuong et al., 2018a); 85 ± 141 items/kg d.w in the North of Crete (Piperagkas et al., 2019), 45.9 ± 23.9 items/Kg in the Spanish Mediterranean coast (Filgueiras et al., 2019) and 60– 240 items/Kg in the Yellow Sea and East China Sea (Zhang et al., 2019). All kinds of shapes can be observed: fragments, films, fibers and pellets with abundant shapes and polymers different between studies (Reviewed by Yao et al., 2019). Several studies indicated the high significance of pellets in the sediment samples (Fanini and Bozzeda, 2018; Karkanorachaki et al., 2018; Turner and Holmes, 2011; Turra et al., 2014). A wide range of polymers were detected in sediments: PE, PP, PS, PES, PA, PVC and rayon, and their distribution varied with different studies.
MICROPLASTICS IN BIOTA
Due to the size of the MP items and characteristics, they can be mistaken as food for various animals and may, therefore, be ingested and integrated within the trophic chain. Once microplastics have reached the different environmental aquatic environment (water and sediments), they are more or less available to the aquatic biota depending on the items shape and size (Cole et al., 2011; Thompson et al., 2009). The ingestion of microplastics has been observed in invertebrates, mollusks, fish, seabirds and big predatory mammals. The MPs items characteristics lead to their uptake by aquatic species. Evidence of microplastics ingestion has been observed in several marine species: crustaceans (Desforges et al., 2014), pelagic fish (Lefebvre et al., 2019), demersal fish (Neves et al., 2015), sea turtles (Duncan et al., 2018; Tomás et al., 2002), seabirds (Rodríguez et al., 2012; Tanaka et al., 2013) and mammals (De Stephanis et al., 2013). Also, these MPs were observed in invertebrates, mollusks and fish existing in the freshwater systems (reviewed by O’Connor et al., 2019). The same as in the other matrices, no standard protocol exist and the comparison between studies would not be accurate even if the MPs concentration were expressed in the same units.
Mussels and oysters are fixed animals, they obtain their food through filter-feeding and are, therefore, prone to ingesting microplastics. As Annex 2 shows, more studies were conducted on mussels rather than on oysters. Microplastics ingestion by wild and caged blue mussels (Mytilus edulis) varied from one study to another ranging from 0.2 ± 0.3 items/g in wild mussels collected from the French, Belgian and Dutch North Sea (Van Cauwenberghe et al., 2015) and 1.43 ± 0.30 items/g in wild mussels collected from South West coast of U.K. (Scott et al., 2019). Most of the studies realized indicated that fibers were the most abundant shape found in Mytilus sp. (Hermabessiere et al., 2019; Van Cauwenberghe and Janssen, 2014), whereas a couple of studies indicated the abundance of fragments (Digka et al., 2018; Gomiero et al., 2019).
Other than mollusks, microplastics ingestion in fish from different seas and regions have been observed. This ingestion was observed in pelagic, meso-pelagic, demersal and benthic species (Bellas et al., 2016; Güven et al., 2017; Neves et al., 2015; Rios-Fuster et al., 2019). Among these fish, flatfish as well as forage fish have been analyzed for microplastics ingestion. For example, European flounder, Platichthys flesus, and European anchovies, Engraulis encrasicolus, are two different species occupying different habitats and regions. Both species showed different microplastics ingestion occurrence from one study to another.
MICROPLASTICS BIOMONITORING
Living organisms (plants, microbes and animals) that provide information on the quality of the environment (e.g marine environment) are called “Bioindicators” (Burger, 2016). Their usage relies on their ability to accumulate pollutants existing in their environment (Bartell, 2016; Zukal et al., 2015). Numerous species have been used as bioindicators for various marine pollutants: mollusks (Cunha et al., 2017; Dirrigl et al., 2018; Viñas et al., 2018), turtles (Santos et al., 2018), sponges (Orani et al., 2018) and fish (Caçador et al., 2012; Smalling et al., 2016). Suitable organisms that reflect the contamination of their environment should be chosen. For a species to be considered as sentinel species for chemical contaminants, it has to fulfill several criteria:
• A wide geographical abundance for it to be present throughout the study area (for inter-sites comparisons)
• Capacity to accumulate contaminants without being affected by the encountered concentrations nor by the environmental stress.
• Sufficient amount of tissue for laboratory analyses
• Be easy to samples in situ and easy to manipulate in laboratory
• Capacity to integrate temporal fluctuations of a specific environment that cannot be followed in the water column
Two types of biomonitoring exist: passive and active. The former consists of choosing indigenous organisms as representatives of the pollution of a specific area. Mussels and oysters are sedentary animals capable of accumulating pollutants and have been widely used as indicators of metals contamination in different biomonitoring programs (Beyer et al., 2017). The “Mussel Watch” program was first introduced in 1976 and it aimed to be a monitoring tool in marine waters (Goldberg, 1975). This approach has proven to be valid for monitoring metals and various organic contaminants by comparing them to a “reference” clean site. Also, fish have important structural and functional importance in aquatic trophic chain and have been considered as chemical pollutant indicators (Miramand et al., 1998). Passive monitoring is confronted to several factors such as species’ genetic differences, age, size, growth, nutrition status, gender, sexual maturity and spawning. In some cases, reference site is not present or is not under the same environmental conditions as the studied sites. Whereas active approaches consist of caging experiments. Selected individuals are acclimated for a period of time before putting inside cages and transplanted in the study sites (Beyer et al., 2017; Oikari, 2006). The advantage of caging technique is the feasibility of using organisms to monitor a surrounding environment, and can also be used in ecotoxicology and population biology studies (Henry and Jenkins, 1995). Other advantages transplantation experiments have (Oikari, 2006):
• Knowledge of the caging and the duration of exposure
• Similarity in species age, size and physiological characteristics
• Can be conducted at any desired time depending on the species
• Transplantation depth can be controlled
• Evaluation of a specific site by limiting species’ area
• Prone to various modification in order to be standardized
Some species cannot tolerate caging conditions (deterioration of nutritional status, solitary living, cannibalism, unknown stress) (Oikari, 2006) and an acclimation period is recommended (e.g. maintaining the organism up to 1 week in laboratory conditions). Till present, most biomonitoring techniques were used to evaluate chemical pollutants and their ecotoxicological effects on organisms (Kerambrun et al., 2013; Oikari, 2006). The recent emerge of microplastics as the pollutant of the decade has led to considering potential approaches for MPs monitoring. The importance and advantages of caging in pollutant monitoring allowed its consideration for microplastics studies. Biomonitoring for microplastics assessment has been recently tested. The first study used caging for microplastics monitoring was tested in 2017 (Avio et al., 2017) and, since then, it has not been very well investigated. To this day, four studies in total have been realized for microplastics biomonitoring: all of them using bivalves as sentinel species (three of them using blue mussels (marine) and one using Painter’s mussels (freshwater)).
The preference of using bivalves for microplastics biomonitoring is because they are easy to manipulate and maintain, filter-feeders that ingest the particles of their surrounding environment and are prone to take up microplastics. These studies transplanted their cages in areas affected by anthropogenic pressure and near important microplastics sources: wastewater discharge (Domogalla-Urbansky et al., 2019; Railo et al., 2018), wreck removal (Avio et al., 2017) and urban port (Catarino et al., 2018).
ESTUARIES: THE SEINE, THE CANCHE AND THE LIANE
These three estuaries are located along the Eastern English Channel differing mostly in size and degree of pollution.
The Seine river has a length of 780 km, a mean discharge of 400 m3/s forming a catchment area of 78 000 km2 serving 17.5 million inhabitants and strongly urbanized and industrialized. The Seine estuary forms a basin of important economic value leading to approximately 40% of the economic activity of France. It is divided into 3 parts from Poses to Le Havre and varying in their salinity gradient: the upstream zone (freshwater), the “in-between” (interaction of both fresh and seawater/ brackish water) and the funnel shaped downstream zone (seawater) (Figure 7). This macrotidal estuary exhibits semi-diurnal tides with a tidal range that varies from 3 m (neap tides) and 7.5 m (spring tides) (Avoine et al., 1986) with a sediment cover mostly composed of sild and clay (fine-grained material). The Seine estuary is subjected to both water currents and marine parameters. The river currents effects decrease downstream, whereas tidal forces decrease upstream. These two currents have the highest energy in an internal narrow segment of the estuary (further upstream). The Seine estuary is known for its ability to stock chemical contaminants due to its limited dilution factor. Until the 70’s, several sources had played an important role in the pollutants’ entry in this basin (Fisson, 2017)
1) The inputs coming from the upstream catchment area via the Seine river (Poses)
2) Groundwater bodies and affluent inflow
3) Direct discharges into the estuary via urban and industrial wastewater treatment plants
Table of contents :
Funding
List of Figures (excluding publications)
List of Tables (excluding publications)
Scientific Contributions
Abstract
Resume
CHAPTER 1: STATE OF THE ART
1. General overview: Plastics pollution
2. The new emerging pollutant ‘Microplastics’
2.1 History and definition
2.2 Origin of microplastics
2.3 Sources of microplastics in the aquatic environment
3. Occurrence of microplastics in the aquatic environment
3.1 Microplastics abundance in the water
3.2 Microplastics in sediments
3.3 Microplastics in biota
4. Microplastics biomonitoring
5. Objectives of the thesis
CHAPTER 2: STUDY SITES, METHODOLOGIES AND ANALYSIS PROTOCOLS
1. Study sites
1.1 Estuaries: the Seine, the Canche and the Liane
1.2 Coastal systems: Sainte-Adresse and the Lebanese coast
1.3 Wastewater treatment plant: Edelweiss
2. Sampling techniques of all three matrices (water, sediments and native biota)
2.1 Water surface
2.2 Sediment samples
2.3 Native biota
3. Caging experiment
3.1 Juvenile flounder caging experiment
3.2 Farmed blue mussels caging experiments
3.2 Caging model comparaison
4. Laboratory analyses and samples preparation
4.1 Contamination prevention
4.2 Water samples
4.3 Sediment samples
4.4 Biota samples
5. Microplastics analyses
5.1 Visual observation
5.2 Micro-Raman spectroscopy analysis and polymer identification
CHAPTER 3: SOURCES OF MICROPLASTICS AND PASSIVE BIOMONITORING
A. Synthesis of Article 1:
I. Article 1: Sources of microplastics pollution in the marine environment: importance of wastewater treatment plant and coastal landfill
Abstract
1. Introduction
2. Material and methods
3. Results
4. Discussion
5. Conclusion
Supplementary files
B. Synthesis of Article
II. Article 2: Microplastics pollution along the Lebanese coast (Eastern Mediterranean Basin): Occurrence in surface water, sediments and biota sampl
Graphical abstract
Abstract
1. Introduction
2. Materials and methods
3. Results and discussion
4. Conclusion
Supplementary files
CHAPTER 4: ACTIVE BIOMONITORING AS A TOOL FOR MICROPLASTICS ASSESSMENT
A. Synthesis of Article
III. Article 3: Juvenile fish caging as a tool for assessing microplastics contamination in estuarine fish nursery grounds
Abstract
1. Introduction
2. Material and methods
3. Results
4. Discussion
5. Conclusion
Supplementary files
B. Synthesis of Article 4:
IV. Article 4: Effect of exposure period on caged blue mussels (Mytilus edulis) microplastics bioaccumulation
Abstract
1. Introduction
2. Material and Methods
3. Results
4. Discussion
5. Conclusion
Supplementary files
C. Synthesis of Article 5
V. Article 5: Is blue mussel caging an efficient method for monitoring environmental microplastics pollution?
Graphical abstract
Abstract
1. Introduction
2. Material and methods
3. Results
4. Discussion
5. Conclusion
Supplementary files
CHAPTER 5: GENERAL DISCUSSION AND PERSPECTIVES
1. Is achieving a standard sampling and preparation protocol far from reality?
2. Microplastics sources in the aquatic environment
3. Microplastics occurrence in biota and the potential use of Biomonitoring as a tool for MPs monitoring
Perspectives
References
