# Plastic leachates: Bridging the gap between a conspicuous pollution and its pernicious effects on marine life

Camille Delaeter, Nicolas Spilmont, Vincent M.P. Bouchet, Laurent Seuront

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Camille Delaeter, Nicolas Spilmont, Vincent M.P. Bouchet, Laurent Seuront. Plastic leachates: Bridging the gap between a conspicuous pollution and its pernicious effects on marine life. Science of the Total Environment, 2022, 826, pp.154091. 10.1016/j.scitotenv.2022.154091. hal-03860626

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# 1 Plastic leachates: bridging the gap between a conspicuous pollution and its pernicious effects on marine life

Camille Delaeter¹, Nicolas Spilmont¹, Vincent M.P. Bouchet¹, Laurent Seuront¹,²,³

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(1) Univ. Lille, CNRS, Univ. Littoral Côte d'Opale, UMR 8187 - LOG - Laboratoire d'Océanologie et de Géosciences, F-59000 Lille, France

(2) Department of Marine Resources and Energy, Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato-ku, Tokyo, 108-8477 Japan

(3) Department of Zoology and Entomology, Rhodes University, Grahamstown, 6140 South Africa

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## 11 Abstract:

With 4 to 12 million tons of plastic entering the marine environment each year, plastic pollution has become one of the most ubiquitous sources of pollution of the Anthropocene threatening the marine environment. Beyond the conspicuous physical damages, plastics may release a cocktail of harmful chemicals, i.e. monomers, additives and persistent organic pollutants. Although known to be highly toxic, plastic leachates seemingly appear, however, as the “somewhat sickly child” of the plastic pollution literature. We reviewed the only 26 studies investigating the impact of plastic leachates on marine microbes and invertebrates, and concluded that the observed effects essentially depend on the species, polymer type, plastic composition, accumulated contaminants and weathering processes. We identified several gaps that we believe may hamper progress in this emerging area of research and discussed how they could be bridged to further our understanding of the effects of the compounds released by plastic items on marine organisms. We first stress the lack of a consensus on the use of the term ‘leachate’, and subsequently introduce the concepts of primary and secondary leachates, based on the intrinsic or extrinsic origin of the products released in bulk seawater. We discuss how
methodological inconsistencies and the discrepancy between the polymers used in experiments and their abundance in the environment respectively limit comparison between studies and a comprehensive assessment of the effects leachate may actually have in the ocean. We also discuss how the imbalanced in the variety of both organisms and polymers considered, the mostly unrealistic concentrations used in laboratory experiments, and the lack of investigation on key ecosystem engineers may considerably narrow the spectrum of our understanding of the plastic leachates' effects. We finally discuss how increasing multi-disciplinarity through collaborations between different research fields may benefit to an area of research which is still in its early infancy.

**Keywords:** plastic leachate, plastic pollution, marine invertebrates, marine microbes, marine algae

**Abbreviations**

BBP: Butyl benzyl phthalate

CTR: Car tire rubber

DBP: Dibutyl phtalate

DDT: Dichlorodiphenyltrichloroethane

DEHA: Bis(2-ethylhexyl) adipate

DEHP: Bis(2-ethylhexyl) phthalate

DEP: Diethyl phtalate

DMP: Dimethyl phtalate

HDPE: High density polyethylene

LDPE: Low density polyethylene

PAH: Polycyclic aromatic hydrocarbon

PAM: Polyacrylamide

PAN: Polyacrylonitrile

PBDE: Polybrominated diphenyl ethers

PC: Polycarbonate

PCB: Polychlorinated biphenyls

PE: Polyethylene

PES: Polyester

PET: Polyethylene terephthalate

PFA: Phenol-formaldehyde

PIR: Polyisopropene rubber

PLA: Polyamide
PMMA: Polymethyl methacrylate

POP: Persistent organic pollutant

PP: Polypropylene

PS: Polystyrene

PUR: Polyurethane

PVC: Polyvinyl chloride

SBR: Styrene-butadiene rubber

TWP: Tire wear particles
## 1. Introduction

Following the early visionary description of the potentially infinite applications of plastics and the predicted advent of the so-called 'plastic era' (Yarsley and Couzens, 1942), yearly plastic pollution skyrocketed from 1.5 million tons in 1950 to 368 million tons in 2019 (PlasticEurope, 2020) and the staggering 9 billion tons (9 × 10⁹ t) produced so far are expected to increase sixfold by the mid-21st century (Zalasiewicz et al., 2016). Plastics are also increasingly discarded (6.3 × 10⁹ tons of total plastic waste in 2015; Geyer et al., 2017), resulting in alarming accumulation of debris in landfills or environments (ca. 5 × 10⁹ tons between 2015 and 2017; Geyer et al., 2017). As low-density, decay-proof and commonly robust materials, easily transported by wind and water, plastics have become one of the most ubiquitous and conspicuous sources of pollution of the Anthropocene, threatening the environment, the economy and human well-being on a global scale (Amelia et al., 2021; Galloway, 2015; Nelms et al., 2017), and the potential threats presented by plastic debris have been identified as a major global conservation issue and a key priority for research (GESAMP, 2010; Harrison and Hester, 2019; Végter et al., 2014).

Beyond the growing awareness of anthropogenic litter as a critical environmental problem, plastics are now widely reported within the marine environment (Browne et al., 2010; De-la-Torre et al., 2020; Nelms et al., 2017). Noticeably, plastics represent 50 to 90% of the total litter found on shorelines and seafloors (Agamuthu et al., 2019), and up to 100% of floating debris (Galgani et al. 2015). The situation may even get worse as every year 4 to 12 million tons of plastics enter the marine environment, a figure expected to increase by an order of magnitude by 2050 (Jambeck et al., 2015). The majority of these plastic litter originates from land via inland waterways and wastewater outflows, but fisheries and aquaculture are also generators of plastic wastes. Once released into the marine environment plastic debris have the potential to
disperse via wind and currents (Jambeck et al., 2015) and accumulate in coastal environments (Lebreton et al., 2019).

Macroplastics (i.e. plastic items larger than 5mm) are perceived as one of the most concerning form of plastic pollution due to their ubiquitous presence in the environment, such as the deposition of beached debris (Barnes et al., 2009). Macroplastics cause conspicuous physical damages, as the injuries causes by ingestion of plastic debris (Andrady, 2011) or the entanglement of marine fauna (Andrady, 2011; Gall and Thompson, 2015) through lost fishing nets or traps (Browne et al., 2015). These debris can also lead to the alteration, and even the destruction, of habitats, e.g. lost lobster traps on seabed cause a 14 – 20% reduction in the corals’ cover (Uhrin et al., 2014).

Plastic pollution is, however, also related to microplastics (i.e. plastic smaller than 5 mm; Law and Thompson, 2014) and nanoplastics (i.e. smaller than 1 µm; Cole and Galloway, 2015). Macroplastics are a major contributor to microplastics due to their fragmentation through natural weathering process, i.e. mechanical abrasion and photochemical oxidation (Andrady, 2011), hence called secondary microplastics. On the other hand, primary microplastics may also directly enter the marine environment, especially originating from plastic industry, i.e. plastic pellets, microfibers from clothing or microbeads used in cosmetics (Hermabessiere et al., 2017). Altogether, microplastics are now considered as the most numerically abundant form of solid waste on Earth (Eriksen et al., 2014) and represent a potential threat to marine ecosystems globally (Galloway et al., 2017). Noticeably, they constitute a far more pernicious source of pollution than macroplastics with a large range of detrimental effects on marine life. Their ingestion prompts the desorption of the chemical pollutants adsorbed onto their surface which causes adverse effects (Avio et al., 2015). Furthermore, the subsequent accumulation into tissues and organs leads to cascade through the food chain (Desforges et al., 2015); see also Galloway et al. (2017) and de Sá et al. (2018) for recent reviews.
In addition to physical damages, it is noticeable that plastic polymers can be intrinsically harmful. For instance, a study assessing the toxicity of 55 plastic polymers based on their chemical composition (Lithner et al., 2011) found that 31 of them are made of monomers that belong to the two worst of the ranking model's five hazard levels, i.e. levels IV–V that are classified either as carcinogenic, mutagenic or toxic for reproduction. Beyond the toxicity of the polymers themselves, two main categories of harmful chemicals may typically originate from plastics: (i) the ever growing number of additives (i.e. over 400 so far as listed under the mapping exercise of the European Chemical Agency plastic additives initiative; www.echa.europa.eu) that enter the composition of plastics when manufactured such as light and heat stabilizers, antioxidants, nucleating and antistatic agents, flame retardants, plasticizers and colorants (Hahladakis et al., 2018; Hermabessiere et al., 2017), and (ii) the wide range of anthropogenic contaminants that accumulate onto plastic surface (Fries and Zarfl, 2012) at concentrations reaching up to 6 orders of magnitude higher than those found in the surrounding water (Hermabessiere et al., 2017). These latter chemicals include a variety of persistent organic pollutants (POP) such as polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB), polybrominated diphenyl ethers (PBDE), pesticides or dichlorodiphenyl-trichloroethane (DDT) (Kedzierski et al., 2018; Ogata et al., 2009).

Both the accumulation of these chemicals onto, and their release from, plastic surface are a function of salinity, UV exposure, and environments enriched in organic matter (Delle Site, 2001). In addition, studies conducted on both non-weathered and weathered plastic products of various polymer types (e.g. Bejgarn et al., 2015; Gandara e Silva et al., 2016; Li et al., 2016; Lithner et al., 2009, 2012; Seuront, 2018; Seuront et al., 2021), suggest that plastics release significant amounts of hazardous chemicals over their lifetime. As an example, a recent study (Gardon et al., 2020) identified 7 additives—including 6 phthalates (DMP, DEP, DBP, BBP, DEHA and DEHP) and an antioxidant (Irgafos 168®)—and 20 PAHs released by new and aged
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plastic gear used in the pearl-farming industry. Specifically, though both additives and POPs are known to be either toxic, carcinogenic, mutagenic or endocrine disruptors (Weis, 2019), the sub-lethal effects of these hazardous chemicals have still, however, been relatively overlooked in the plastic pollution literature, despite the very active nature of this research field.

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To illustrate this aspect further, we used the Web of Science (accessed February 7, 2022) which returned 42,506 papers included the words 'plastic' and 'pollution' (i.e. '*plastic*' and 'pollut*' ) in their topic since 1950 (i.e. the beginning of industrialization of plastic production), and this figure has since been growing exponentially (Fig. 1a). Noticeably, however, only 526 papers include the term 'leachate' (i.e. '*plastic*' and 'pollut*' and 'leachate*' ) in their topic (Fig. 1b), a word often used in a generic way to refer to the release of hazardous chemicals from plastics into the environment in the absence of ingestion. More specifically, when considering the research areas “Environmental Sciences and Ecology” and “Freshwater and Marine Ecology”, figures drastically dropped by ca. 99% when looking for leachate (i.e., 35,646 to 501 and 7,064 to 107 papers, respectively for each field; Web of Science, accessed February 7, 2022; Fig. 1). Even more noteworthy is the number of papers assessing the impact of plastic leachates i.e., free from particles, on marine microbes and invertebrates that only reaches 26 papers (Table S1). Considering that plastic leachates are likely to be ubiquitous in marine environments as they are likely to be produced over the plastic lifetime, especially during the continuous process of fragmentation, we stress that addressing the origin, nature and impact of plastic leachates is of upmost importance for the future of plastic pollution research.

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In this context, the present work aims at critically reviewing the blossoming research area devoted to plastic leachates. Specifically, we first identify and discuss the terminological ambiguity in the use of the word *leachate* in the literature, and subsequently suggest a tentatively universal definition of leachates in the context of plastic pollution. Next, we critically review the literature assessing the biological effects of leachates on marine microbes

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and invertebrates through the identification of clear discrepancies between the organisms and polymers considered in the literature and plea for more unified approaches. Finally, we discuss future directions that the research on plastic leachates impacts on marine life may need to follow to reach a better understanding of the potential effects of the hidden side of a pernicious component of the ever-increasing plastic pollution.

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## 2. What does ‘leachate’ actually mean: towards a process-based terminological consensus

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In the area of research devoted to marine biology, the impact of plastic leachates on fauna was first investigated in the early nineties (Weis et al., 1992). Although plastic accumulation in the oceans is now conspicuous and ubiquitous, and widely debated in areas ranging from molecular biology to sociology and politics, the number of publications related to plastic leachates remained rather anecdotal until 2021, as more than 65% of the plastic leachate literature (i.e., 17 out of 26 papers) have been published since 2020. Even more noticeably and unexpectedly, a clear and non-ambiguous definition of plastic leachate is still critically lacking.

To the best of our knowledge, only three papers actually explicitly defined the word ‘leachate’, i.e. “*the capacity of [chemical compounds] to be desorbed (leached)*” (Nobre et al., 2015), the “*desorption of chemicals into the surrounding environment in the absence of plastic ingestion*” (Gardon et al., 2020) and “*the ability of plastic to transfer POPs to biota via desorption and subsequent dermal absorption (i.e. leaching)*” (Coffin et al., 2018). These definitions noticeably appear to be context-dependent, which worsen the actual lack of consensus. Fundamentally, the subsequent terminological ambiguities may potentially ultimately be detrimental to the development of this research field, by analogy to what has been shown for scientific progress in general (Popper, 2002).

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Noticeably, the 26 papers that assessed the impact of plastic leachates on marine microbes and invertebrates indistinctly used the words ‘leachate’, ‘release’ and ‘desorption’ to refer to
the transfer of chemicals from plastic to the surrounding seawater and sediment. *Sensu stricto*,
the term ‘release’ is by far the most generic in the sense that it does not refer to any chemical
nor physical process, but describes “*a substance that is allowed to flow out from something*”
(Cambridge Dictionary). In contrast, ‘desorption’ and ‘leaching’ have much more specific
meanings. Desorption is the process by which molecules (essentially POPs) adsorbed onto a
surface or molecules (specifically here additives) or absorbed (i.e. incorporated) into a solid are
released (Schaschke, 2014). In turn, leaching is a separation process by which a soluble
component is removed from a solid by the action of a percolating solvent (Backhurst, 2002)
i.e., a fluid passing through the substance. As a consequence, the term ‘leachate’ does not cover
all the chemical and physical processes leading to the transfer of contaminant from plastics to
the environment.

In this context, the definition of leachate provided by Gardon et al. (2020) i.e., “desorption
of chemicals into the surrounding environment in the absence of plastic ingestion”, is relevant
given that they investigated the release of both additives and POPs that are respectively
absorbed i.e., intrinsically bounded to the polymer during the manufacturing process, and
adsorbed to plastic polymers. To overcome the intrinsic limitation related to the term
‘desorption’ which indistinctively refers to the desorption of absorbed and adsorbed molecules,
and given the fact that the word ‘leachate’ has now been extensively used and acknowledged
in the plastic literature, we suggest to refine the use of the term ‘leachate’ as primary and
secondary leachates to describe the release of molecules that are respectively absorbed and
adsorbed to plastic polymers (Fig. 2).

This terminological distinction is particularly relevant in the context of the research
conducted on the effects of the molecules released by non-weathered plastics and weathered
plastics (e.g. Cormier et al. 2021; Gardon et al. 2020; Gewert et al. 2021; Koski et al. 2021;
Lithner et al. 2009, 2012; Nobre et al. 2015; Sarker et al. 2020; Seuront 2018). Non-weathered
190 (i.e. virgin) plastics include plastic consumer products (e.g. DVD-case, bags, food packaging,
191 cups and bottles) and plastic pellets (i.e. raw resin pellets used in the manufacture of plastic
192 products; Hidalgo-Ruz et al., 2012) that have not been exposed to any weathering process such
193 as biodegradation, heat and UV irradiations, physical abrasion or oxidation (Liu et al., 2020).
194 Once discarded in the ocean, these items are a source of primary leachates (Fig. 2). In contrast,
195 weathered plastics include both naturally and experimentally weathered plastic items. Naturally
196 weathered plastics are discarded plastic consumer products of various origins that are found
197 stranded on beaches, floating at the surface of the ocean or sank on the ocean seafloor; they
198 range from macroplastic items such as tires, fishing nets and down to primary microplastics
199 such as pellets accidentally lost during the process of production, transport and manufacturing
200 and secondary microplastics resulting from the continuous fragmentation of larger plastic items.
201 These items, during their stay in the ocean accumulate (i.e. adsorb), either through hydrophobic
202 and electrostatic interactions, and non-covalent bounding such as van der Walls forces (see Fu
203 et al. (2021) and Joo et al. (2021) for reviews), anthropogenic pollutants on their surface, e.g.
204 heavy metals, PCBs, PAHs, DDT, PBDE (Kedzierski et al., 2018; Ogata et al., 2009), that are
205 potentially released as secondary leachates (Fig. 2). Note, however, that these plastic items are
206 also intrinsically a source of primary leachate (Fig. 2).

207 The release of additives from plastic particles is facilitated by both their lack of covalent
208 bound to the plastic molecules and their low molecular weight. The amount of released
209 additives further depends on a range of factors including (i) the proportion of additives used in
210 the manufacture of the polymer (e.g. PVC typically contain more than 40 % by weight of
211 plasticizers, mostly phthalates; Andrade et al., 2021), (ii) the permeability of the polymer
212 structure, which is driven by its physical state (e.g. the size of the gaps in rubbery polymers are
213 much larger than in glassy and crystalline ones, hence rubbery polymers are characterized by
214 higher release rates), and (iii) the molecular weight, shape and polarity of additives, i.e. lighter
and linear additive molecules will be release at faster rates than heavier and branched ones (Brydson, 1999; Gilbert, 2017). Alternatively, virgin plastics can be experimentally aged (Bejgarn et al., 2015; Martínez-Gómez et al., 2017), which prevent the accumulation of environmental pollutants in order to understand the impact of weathering process on the desorption of additives.

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## 3. Methodological issues

### 3.1. Keeping (or not?) plastic particles in the leachate solution to assess their effect?

The effects of leachates on marine organisms have typically been evaluated from both virgin and weathered plastics by putting a given number of plastic items in seawater where they were left for a given incubation time. The subsequent biological assays were conducted on leachate solutions separated from plastic items by filtration (e.g. Gardon et al. 2020; Ke et al. 2019; Piccardo et al. 2020; Tetu et al. 2019), but also on leachate solutions where plastic items were then kept in suspension (e.g. Avio et al. 2015; Gandara e Silva et al. 2016; Silva et al. 2020; Song et al. 2020; Tang et al. 2018). Though the former is appropriate to assess the effects of primary and secondary leachates on marine organisms, the latter may be misleading as it might be challenging to decipher the physical effects due to the presence (and eventually the ingestion) of plastic particles from the chemical effects that can be exclusively related to the leachate. To the best of our knowledge, only 26 papers investigated the impact of leachate sensu stricto, i.e. without particles (Aminot et al., 2020; Bejgarn et al., 2015; Capolupo et al., 2021, 2020; Chae et al., 2020; Cormier et al., 2021; Gardon et al., 2020; Gewert et al., 2021; Ke et al., 2019; Koski et al., 2021; Langlet et al., 2020; Lehtiniemi et al., 2021; Li et al., 2016; Martínez-Gómez et al., 2017; Nobre et al., 2015; Oliviero et al., 2019; Piccardo et al., 2020; Rendell-Bhatti et al., 2021; Sarker et al., 2020; Schiavo et al., 2021; Seuront, 2018; Seuront et al., 2021; Tetu et al., 2019; Thomas et al., 2020; Trestrail et al., 2020; Weis et al., 1992). Among
these papers, 4 investigated the physical impacts alongside the chemical impacts, by exposing their organisms to both leachate *per se* and solution still containing particles (Martínez-Gómez et al., 2017; Nobre et al., 2015; Oliviero et al., 2019; Piccardo et al., 2020). Noticeably, the difficulty in deciphering the physical and chemical effects of plastics in the leachate-oriented literature also exists in the literature investigating the physical effects of plastic particles on marine organisms. For instance, to the best of our knowledge, among the 8 papers (Bhattacharya et al., 2010; Davarpanah and Guilhermino, 2015; Long et al., 2015; Prata et al., 2018; Sjollema et al., 2016; Su et al., 2020; Zhang et al., 2017; Zhu et al., 2019) assessing the impact of microplastic particles on marine phytoplankton, only 2 papers mentioned that toxic substances may be released by microplastics in their discussion (Su et al. 2020; Zhang et al. 2017).

In this context, the next section specifically focuses on papers investigating the impact of plastic-free leachate solutions on microbes and invertebrates.

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## 3.2. Imbalance in organisms and polymers considered

To examine in further details the research effort devoted to assess the impact of plastic leachates on marine organisms, from the 26 papers listed above, we estimated the number of organisms and polymers assessed, identified the overall number of experiment conducted (e.g. a paper investigating the impact of the leachate from 3 type of PVC particles from different origins on a single species, i.e. blue PVC, green PVC and orange PVC originating from different toys on *Paracentrotus lividus* (Oliviero et al., 2019), would be considered as 3 separate experiments), and subsequently estimated the research effort devoted to each a species, a phylum or a polymer type. The plastic particles without any chemical indication or only partial indications on the polymer type were considered as unknown polymers, i.e. beached plastics, plastic products without manufacturer indication, particles for which polymer is supposed because of its color or texture but without chemical proof.
Eighty-seven percent (87%) of the research effort is focused on pluricellular organisms (i.e. crustaceans, mollusks, echinoderms and cnidarians), versus 13% on unicellular organisms (i.e. foraminifera, microalgae and bacteria; Fig. 3). One of the most striking piece of evidence coming out of our literature review, is that crustaceans appear to be a highly considered taxon, as it accounts for ca. 61% of the research effort (Fig. 3), especially *Nitocra spinipes* which accounts for more than 50% of the research effort including the vast majority of the less-tested polymers (i.e. less than 1.3% of the research effort, e.g. bio-polymers, PLA, PUR). Molluscs, echinoderms and microalgae account for respectively ca. 12, 12 and 8%, whereas cyanobacteria, cnidarians, foraminifera and proteobacteria represent less than 4% of the research effort (Fig. 3). In addition, the impact of plastic leachates on foraminifera and proteobacteria was investigated for only one type of polymer, i.e. PP and PET respectively (Fig. 3). PE, PP, PVC, PS and PET are the most studied and account respectively for ca. 16 to 9% of the research effort (Fig. 3). The impact of rubber and mixtures of polymers leachates are respectively ca. 7 and 6% of the research effort (Fig. 3). In contrast, the remaining studied polymers account for less than 1.3% each (Fig. 3). It is also noticeable that the over-representation of crustaceans also manifests itself in terms of the polymer-species combination found in the literature. The first 7 polymer-species couples considered, are crustaceans exposed to leachates, respectively, from unknown polymer (12% of the research effort), PE (ca. 10%), PP (ca. 9%), PVC (ca. 7%), PS (ca. 6%), PET (ca. 6%) and rubber (ca. 6%; Fig. 3). The remaining polymer-species couples account for less than 4% of the research effort.

## 4. Effect of plastic leachate on marine microbes and invertebrates: state-of-the-art.

The experimental conditions, i.e. polymer concentration, leaching time, exposure time, observed biological parameters and observed effects, of each experiment investigating the impacts of plastic leachates on coastal microbes and invertebrates are gathered in Table S1.
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**4.1. Unicellular organisms**

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Though unicellular organisms still have barely been considered in a plastic leachate context (Fig. 1), contradictory results were found in the very few organisms exposed to plastic leachates. Specifically, bacteria and microalgae were impacted at various levels (see below), in sharp contrast to benthic foraminifera which were not affected either behaviorally nor physiologically (Langlet et al., 2020). Noticeably, the exposure of the proteobacteria *Vibrio fischeri* to PET leachates induced an increase in its natural bioluminescence which was hypothesized as a potential early sign of chronic stress (Piccardo et al., 2020). In addition, the cyanobacteria *Plochlorococcus* sp. showed a decrease in photosynthetic activity, membrane integrity and population growth when exposed to virgin (Sarker et al., 2020; Tetu et al., 2019) and aged (Sarker et al., 2020) PE and PVC leachates. Similarly in microalgae, the exposition to PS leachates induced an increase in chlorophytes photosynthesis activity (*Dunaliella salina*, *Scenedesmus rubescens*, *Chlorella saccharophila* and *Stichococcus bacillaris*; Chae et al., 2020) and PS, PE, and PP leachates inhibited growth and increased ROS production and DNA damages in *Dunaliella tertiolecta* (Schiavo et al., 2021). In addition, diatoms population growth changes depend on polymer types; population growth decreased when *Skeletonema costatum* was exposed to PP, PS, PVC and CTR leachates, whereas PET leachate did not affect *S. costatum* (Capolupo et al., 2020) and induced an increase in the population growth *Phaeodactylum tricornutum* exposed to lower concentration (Piccardo et al., 2020). Though still in its early age, the research devoted to assess the impact of plastic leachate on unicellular organisms nevertheless suggests that leachate toxicity may be phylum-dependent.

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**4.2. Pluricellular organisms: leachate effects at different levels of biological organization**

**4.2.1. Oxidative stress**
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The research related to the assessment of the molecular impacts of plastic leachate is based on modifications in biomarkers, i.e. the first signals of biological effects that are induced by toxicants (Capolupo et al., 2021). To the best of our knowledge, these biomarkers were only investigated in the mussel *Mytilus galloprovincialis* and oxidative stress was reported, inducing detoxification processes depending on the polymer type. The strongest effect was observed after an exposition to leachate from PS, then PET and finally PS, PVC and CTR (Capolupo et al., 2021). In contrast, PFA leachate did not induce any damage (Trestrail et al., 2020), despite the use of experimental concentrations more than one order of magnitude higher than those considered for the other polymers. Additionally, whereas PVC leachate was shown to be neurotoxic (Capolupo et al., 2021), this was not the case for other polymers such as PET, PS, PP, CTR (Capolupo et al., 2021) and PFA (Trestrail et al., 2020). Finally, metal (used as additives in some polymers to confer specific properties) exposure was investigated and the exposition to PET, PS, PVC, PP and CTR leachates did not reveal any change in *M. galloprovincialis* (Capolupo et al., 2021). These results suggest that toxicity of plastic leachates is likely to depend on polymer type.

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### 4.2.2. Cellular integrity and embryonic development

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The impacts of leachates on the embryonic development and the cellular integrity have been investigated only in echinoderms and mollusks. Specifically, PE leachate induces abnormal embryonic developments in the sea urchins *Lytechinus variegatus* (Nobre et al., 2015) and *Paracentrotus lividus* (Cormier et al., 2021; Martínez-Gómez et al., 2017). These results contrast with the effects of leachates from virgin PE free from additives on *P. lividus* (Rendell-Bhatti et al., 2021). Similarly, the embryonic development of *P. lividus* was impaired by an exposition to leachates from PET (Piccardo et al., 2020), both colored (Oliviero et al., 2019) and common white PVC (Rendell-Bhatti et al., 2021), PMMA (Thomas et al., 2020) and
beached pellets mainly composed of PE (Rendell-Bhatti et al., 2021) and of a mixture of PE and PP (Cormier et al., 2021). In turn, beached pellet leachates have no effect on the development of *L. variegatus* embryos (Nobre et al., 2015). As the tested concentration was similar to the previously mentioned PE leachate (Nobre et al., 2015), these results suggest that leachate toxicity is likely to depend on the cocktail of additives and pollutants that are released during the leaching process. No conclusions can be drawn on the impact of PS leachate on the embryonic development of *P. lividus* as contradictory outcomes have been reported, i.e. significant decrease (Martínez-Gómez et al., 2017) vs. no significant changes (Thomas et al., 2020). In addition, the leachate solution's concentrations are reported in different units (i.e. number of microspheres per liter vs. mg mL⁻¹; Table S1), preventing any comparisons. Furthermore, development abnormalities were observed in the mussels *Meretrix meretrix* exposed to PE leachate (Ke et al., 2019) and *Mytilus galloprovincialis* exposed to PET, PS, PVC, PP and CTR leachates (Capolupo et al., 2020), and in the oyster *Pinctada margaritifera* exposed to the leachate of virgin and weathered plastic gears made of a mixture of PE and PP originated from pearl-farms (Gardon et al., 2020). The cellular integrity of bivalve is also affected by plastic leachate, with PP, PVC and CTR leachates were the most damaging on *M. galloprovincialis*, followed by PS leachate and PET leachate (Capolupo et al., 2021, 2020).

### 4.2.3. Mortality

Mortality is by far the most studied biological parameter in the investigation of plastic leachates' impacts, both on larvae and adults. Mortality increased for each polymer type tested in barnacle larvae (*Amphibalanus amphitrite* exposed to PC, HDPE, LDPE, PET, PP, PS and PVC leachates; Li et al., 2016) and crustacean larvae (*Artemia* sp. exposed to PFA and bio-PFA leachates; Trestrail et al., 2020). Noticeably, jellyfish larvae were, however, not sensitive (*Aurelia* sp. exposed to PE and beached pellets leachates; Cormier et al., 2021). Nonetheless,
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*Aurelia* sp. larvae were exposed to lower concentration of leachates than *Artemia* sp. larvae, and the concentration tested on *A. amphitrite* larvae was in a different unit; conclusions cannot thus be drawn easily.

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The mortality of adult mussels exposed to PP, PVC, CTR (*Mytilus galloprovincialis*; Capolupo et al., 2020), virgin and aged mixture of PE+PP (*Pinctada margaritifera*; Gardon et al., 2020) and PE (*Meretrix meretrix*; Ke et al., 2019) leachates increased, whereas it did not with PET and PS leachates (*M. galloprovincialis*; Capolupo et al., 2020). The mortality of the adult copepod *Nitocra spinipes* also increased following an exposure to the leachates of PUR, aged PIR and bio-PES particles (Bejgarn et al., 2015). In contrast, no significant change was observed with PE, PET, PP (Bejgarn et al., 2015; Gewert et al., 2021), PLA and bio-PET leachates (Bejgarn et al., 2015). Similarly, the mortality of the adult copepod *Limnocalanus macrurus* was not impacted by the exposition to LDPE (from virgin granules and vegetable package; and SBR leachates (Lehtiniemi et al., 2021). Taken together, these results suggest that the survival of adult copepods to plastic leachate typically depends on the polymer type and the species; see Bejgarn et al. (2015), Capolupo et al. (2020), Gewert et al. (2021) and Lehtiniemi et al. (2021).

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Noticeably, the toxicity of plastic leachates may also depend on weathering processes, e.g. mechanical abrasion and photochemical oxidation (Andrady, 2011). For instance, artificial UV exposure triggered a toxicity in every polymer tested (i.e. PE, PET, PP, PS pellet, PS, PVC) on the *Nitocra spinipes* adult survival, although the great majority (i.e. PE, PET, PP, PS pellet) were not toxic before the weathering process (Gewert et al., 2021). The impact of the weathering process on toxicity is dependent on the polymer origin, i.e. composition, as PP leachate became toxic after irradiation for *N. spinipes* whereas PUR leachate lost its toxicity (Bejgarn et al., 2015).

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Moreover, additives composition is likely to have a great role in toxicity of leachates as the *Nitocra spinipes* adult survival was different depending on the origin of plastic particles. Among PVC leachates originated from 3 different objects, 2 leachates induced an increase in *N. spinipes* mortality whereas the last one did not (Bejgarn et al., 2015). Similarly, leachates from PS food packaging induced mortality whereas leachate from PS pellet did not (Gewert et al., 2021). Even weathering processes have different impact on toxicity depending on plastic origin, i.e. PVC packaging became toxic after irradiance whereas PVC from garden hose lost its toxicity (Bejgarn et al., 2015). Consequently, for a same polymer, toxicity can be different, which emphasize the importance of additives in the toxicity of plastic leachates and on the impact of weathering processes.

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### 4.2.4. Behavior and cognition

Organisms' behaviors have been investigated in mussels, gastropods, in which significant changes have been described, and copepods. Specifically, the aggregation behavior of different mussel species was studied. The percentage of aggregated mussels, the time to aggregate and the crawling distance increased, whereas the byssal thread production was not impacted by the exposition to PP leachate, for *Choromytilus meridionalis* and *Mytilus edulis* (Seuront et al., 2021). The opposite was observed for *Mytilus galloprovincialis* and *Perna perna* (Seuront et al., 2021). Consequently, the strategy adopted when mussels are exposed to plastic leachate seems to be species-dependent, and driven by their intrinsic dominant trait (Seuront et al., 2021). In the gastropod *Littorina littorea* a decrease in vigilance and antipredator behaviors was shown when exposed to PP and beached pellets showed (the beached pellet being the more toxic; Seuront 2018), which might have an impact on its survival. In contrast, the swimming behavior of the copepod *Limnocalanus macrurus* was not impaired by an exposition to any
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plastic leachate (i.e. LDPE from virgin granules, vegetable package, and SBR from artificial turf or recycling factory; Lehtiniemi et al., 2021).

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### 4.2.5. Reproduction

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The impact of plastic leachates on the reproduction has been studied on crustaceans (copepods and barnacles), mollusks (mussels), and echinoderms (urchins), through the measurement of egg production, fertilization, hatching or settlement. The nauplii's settlement of the barnacle *Amphibalanus amphitrite* decreased irrespective of the polymer type (Li et al., 2016). Noticeably, the impacts of rubber leachate on copepods depend on its origin. The exposition to virgin and aged CTR leachates had no effect on the egg production and hatching of the copepods *Acartia tonsa* and *Temora longicornis*, whereas an exposure to TWP leachate caused an increase in *A. tonsa* egg production but not on hatching (Koski et al., 2021). In addition, no changes in fertilization were observed neither in the sea urchin *Paracentrotus lividus* exposed to PMMA and PS leachate (Thomas et al., 2020), nor in the mussel *Meretrix meretrix* exposed to PE leachate (Ke et al., 2019). On the contrary, the exposition to PET, PS, PVC, PP and CTR leachate induced a decrease in the gamete fertilization of the mussel *Mytilus galloprovincialis* (Capolupo et al., 2020). Consequently, results revealed that the impacts of plastic leachates on reproduction may depends on polymer type and species. Note however that leachate concentrations and units are not homogenous between studies preventing any inter-study comparisons.

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## 5. The future of plastic leachate research: perspectives toward an environmental and unified approach

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In the present work we showed that the area of research devoted to plastic leachates is still at its very early beginning and, as detailed above, is suffering from both relatively serious

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conceptual and methodological gaps, and a critical lack of consensus on what the term 'leachate' actually means. These gaps are likely to hamper our ability to understand the actual ecological effect of this new and pernicious type of pollution. In this context, we claim that plastic leachates-related research would largely benefit from the adoption of conceptual, terminological and methodological consensuses within the scientific community. As for now, comparisons between studies are hardly possible since the units used are often different; see Table S1). Similarly, the range of both concentrations (i.e. from 0.0003 to 100 mg/mL) and size (i.e. 1 µm to 10 cm³) of plastic particles used to prepare leachate solutions as well as leaching times (i.e. 24 hours to 28 days) and exposure times (i.e. 15 min to 7 days) used in the leachate-related biological assays consistently vary dramatically between studies (Table S1), which then become barely comparable. We also identified a remarkable disequilibrium in both organisms and polymers that have been considered in studies so far (Fig. 3).

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## 5.1. On the need to use realistic concentration of plastic particles

Typical environmental plastic concentrations range between ng to µg/L (Lenz et al. 2016) or 1-500 particles/m³ (Koski et al., 2021), and can even reach up to ca. 17 mg/L in the intertidal zone (Paul-Pont et al. 2018). Although this issue has previously been pointed out (Lenz et al. 2016; Haegerbaeumer et al. 2019), experimental concentrations of plastic-related studies are still orders of magnitude higher, i.e. up to 100 g/L or 100,000 particles/L for plastic leachate studies (Table S1), than what is usually found in the field. Though ecotoxicological investigations are relevant to identify general hazards and establish toxicity threshold for a given contaminant-organism pair (Paul-Pont et al., 2018), environmentally realistic concentrations should be systematically investigated in plastic leachate literature to understand the current impact and ecological consequences of plastic contamination on marine organisms.

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**5.2. Research effort should be fine tuned to the polymer type found in the environment**

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The polymers considered are not in complete accordance with what is found in natural environments. Noticeably, PE is the most abundant polymer type in natural aquatic environments (i.e. 23% of the abundance of polymers), followed by the group PP&A (i.e. PES, PLA and acrylics including PAM, PMMA and PVA; 20%), PP (i.e. 13%) and PS (i.e. 4%; Erni-Cassola et al., 2019). Specifically, in intertidal environments, PE and the group PP&A plastics are dominant (Pannetier et al., 2019), i.e. respectively 18% and 23% at a global scale, whereas PS, PP, PET and PVC particles only account for 6%, 5%, 3% and 3% respectively (Doyen et al., 2019; Erni-Cassola et al., 2019). Consequently, if PVC, PE, PET, PP and PS are over-investigated, polymers from the PP&A group (i.e. accounting for 3% of the research effort; Fig. 3) are greatly under-investigated and may probably deserve more attention. The disequilibrium between the polymers studied and their abundance in the environment may be explained by their toxicity or their high industrial demand. PUR, PAN and PVC are considered as the most hazardous polymer types according to their monomer composition, whereas PP, PLA, PET, PE and PS are evaluated to be among the least hazardous (Lithner et al., 2011). In this context, the over-investigation of PVC may be justified by its toxicity. In addition, the appeal for PET and PP may be explained by their high use in packaging industry (PlasticsEurope, 2020, 2018), and the ones for PE and PP by their general industrial demand (i.e. respectively 29,8 and 19,4 % of the 2019 plastics demand distribution by resin type; PlasticsEurope, 2020). Although investigating the hazardousness of each polymer type is important, it is now critical to explore the actual risks run by marine organisms in their natural habitat by focusing on polymers that are abundantly found in the environment.

**5.3. Leachate solutions should be particle-free to avoid confounding effects**
In section 3.1, we stressed that leachate solutions still containing plastic particles do not allow to decipher the relative contribution of the physical and chemical effects of plastics. It is hence of major importance to be specific about what type of leachate solution a study deals with, i.e. particle-free leachate solution vs. particle-loaded leachate solution, for the reader to be able to assess the relevance of the so-called leachate effects. As a consequence, it is critical to conduct experiments assessing the physical effects of plastics using additive-free polymers, and further run in-parallel experiments with particle-free leachate solution vs. particle-loaded leachate solution in order to unambiguously unravel the chemical and physical impacts of plastics.

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## 5.4. From simple to chemically complex leachate soups

In the environment, organisms are exposed to a complex mixture of polymers which have undergone weathering processes constraining their toxicity and their size (Paul-Pont et al., 2018). Consequently, using only similar-sized virgin manufactured particles from a single polymer type is an unrealistic scenario considering the variety of plastic particles encountered in the environment. As previously stressed, plastic exposure involves organisms being potentially exposed to several sources of contaminants: (i) monomers, (ii) additives and (iii) POPs. Though known to be highly toxic (e.g. styrene monomers impaired the embryonic development of *Mytilus galloprovincialis*; Wathsala et al., 2018), the impact of monomers on marine organisms is barely investigated and should be considered in future investigations.

Furthermore, only 11/26 papers investigated the impact of naturally weathered plastics. Knowing that more than 5 × 10⁹ tons of plastic are already accumulating in the environment (Geyer et al., 2017) against 4 – 12 × 10⁶ tons entering marine environment each year (Jambeck et al., 2015), organisms are likely to be more exposed to secondary (i.e. sorbed contaminants) than primary leachates (i.e. manufactured additives). The former should hence deserve more
512 attention. Consequently, in order to match experimental conditions with what is encountered
513 by organisms in their environment, authors should rather mix beached and virgin particles, of
514 different size, to assess a more realistic potential impact of plastic leachates on organisms. It
515 would further allow to draw conclusions at an ecosystemic scale.

516

517 **5.5. What organisms should be considered next?**

518 As for polymer types, the diversity of studied organisms is not representative of the *in situ*
519 diversity. As already stressed (Haegerbaeumer et al., 2019), meiofauna are still widely
520 neglected and there is an urge to consider them in future investigations given their role in key
521 processes such as bioturbation and related water-sediment fluxes. Noticeably, in contrast to
522 crustaceans that are over-represented, some major ecosystem engineers are missing (Fig. 3,
523 Table S1). To the best of our knowledge, no studies have investigated the impact of plastic-free
524 leachate on annelids or crabs (the impact of plastic-free leachate was investigated on the crab
525 *Uca pugilator* to compare two materials and no negative control was performed; Weis et al.,
526 1992), whereas they are considered as key organisms in bioturbation and bio-irrigation
527 processes (Kristensen et al., 2012). Nonetheless, plastic-loaded leachate experiments revealed
528 an impact of plastic exposition on the annelids *Hediste diversicolor* (i.e. PS nanoplastics
529 impaired biomarkers expression and burrowing time; Silva et al., 2020), *Perinereis aibuhitensis*
530 (i.e. PS microplastics increased mortality and reduced the rate of posterior segment
531 regeneration; Leung and Chan, 2017) and *Arenicola marina* (i.e. polylactic acid, PE and PVC
532 affected metabolic rates and sediment nutrient cycling; Green et al. 2016). These results suggest
533 that plastic leachates would limit the contribution of these two ecosystem engineers to sediment
534 reworking and bio-irrigation, which is likely to hamper the benthic ecosystem functioning. It
535 further shows the importance of considering plastic leachates effects on species having different
536 roles in the ecosystem functioning in order to understand their harmful effects at the ecosystem
scale. Similarly, studies on macroalgae are missing, though they are structuring rocky-shore
habitats. Adopting an ecosystemic point of view, hence considering the previously cited
organisms in future investigations, is critical to conclude on the impact of plastic leachates on
the ecosystem functioning.

541

542 **5.6. Towards interdisciplinarity**

Plastic has been a prolific research area (Fig. 1a) in numerous fields, from oceanography to
ecology, by way of e.g., physics, economy and politics. Although complementary (e.g. chemists
analyse the composition of plastic leachates, biologists explain their impacts on organism's
biology and ecologists investigate the effects on the interactions between organisms and their
environment), there is still a remarkable lack of collaboration between research fields. For
instance, ecologists do not often analyze leachates composition (e.g. 13 % of the leachate
experiments are driven with particles of unknown polymers; Fig. 3), though polymer
composition varies greatly from one type to another, even for one manufacturer to another for
a same polymer type. In addition, plastic particles following different path once discarded in
the environment, they must accumulate, and then release, a unique mixture, leading to
potentially very different effects. Hence, characterizing the type of polymers, and their
composition in terms of primary and secondary leachates, to which a species would be exposed
in its environment and/or experimentally appears of high importance to draw sound conclusions
on the effect of plastic leachates.

Multidisciplinary research requires specific skills and tools (e.g. assessing the composition
of plastic particles and leachates is particularly difficult as it is time-consuming, expensive and
technical), and collaborations is the way forward. It is a matter of necessity to consider inter-
disciplinarity for future investigations in order to further understand the source, the pathway
561 and to predict the impact of plastic leachate at cellular, individual, community and ecosystemic scales.
562

563
564 Acknowledgement
565 C. Delaeter is funded by a PhD fellowship from the Région Hauts de France and the University of Lille.
566

567
568 Competing interests
569 The authors declare no competing interests.
570

571 Reference
572 Agamuthu, P., Mehran, S.B., Norkhairiyah, A., 2019. Marine debris: a review of impacts and global initiatives. Waste Manag. Res. 37, 987–1002.
573
574 Amelia, T.S.M., Khalik, W.M.A.W.M., Ong, M.C., Shao, Y.T., Pan, H.J., Bhubalan, K., 2021. Marine microplastics as vectors of major ocean pollutants and its hazards to the marine ecosystem and humans. Prog. Earth Planet. Sci. 8, 1–26.
575
576
577 https://doi.org/10.1186/s40645-020-00405-4
578 Aminot, Y., Lanctôt, C., Bednarz, V., Robson, W.J., Taylor, A., Ferrier-Pagès, C., Metian, M., Tolosa, I., 2020. Leaching of flame-retardants from polystyrene debris: Bioaccumulation and potential effects on coral. Mar. Pollut. Bull. 151, 1–7.
579
580
581 https://doi.org/10.1016/j.marpolbul.2019.110862
582 Andrade, H., Glüge, J., Herzke, D., Ashta, N.M., Nayagar, S.M., Scheringer, M., 2021. Oceanic long-range transport of organic additives present in plastic products: an overview. Environ. Sci. Eur. 33. https://doi.org/10.1186/s12302-021-00522-x
583
584
585 Andrady, A.L., 2011. Microplastics in the marine environment. Mar. Pollut. Bull. 62, 1596–1605. https://doi.org/10.1016/j.marpolbul.2011.05.030
586
587 Avio, C.G., Gorbi, S., Milan, M., Benedetti, M., Fattorini, D., D’Errico, G., Pauletto, M., Bargelloni, L., Regoli, F., 2015. Pollutants bioavailability and toxicological risk from microplastics to marine mussels. Environ. Pollut. 198, 211–222.
588
589
590 https://doi.org/10.1016/j.envpol.2014.12.021
591 Backhurst, J.R., 2002. Leaching. In: Richardson, J.F., Harker, J.H. & Backhurst, J.R. (eds.) Chemical Engineering. Chemical Engineering Series, Butterworth-Heinemann, 502–541.
592
593
594 Barnes, D.K.A., Galgani, F., Thompson, R.C., Barlaz, M., 2009. Accumulation and fragmentation of plastic debris in global environments. Philos. Trans. R. Soc. B Biol. Sci. 364, 1985–1998. https://doi.org/10.1098/rstb.2008.0205
595
596
597 Bejgarn, S., MacLeod, M., Bogdal, C., Breitholtz, M., 2015. Toxicity of leachate from weathering plastics: An exploratory screening study with Nitocra spinipes.
598
599 Chemosphere 132, 114–119. https://doi.org/10.1016/j.chemosphere.2015.03.010
600 Bhattacharya, P., Lin, S., Turner, J.P., Ke, P.C., 2010. Physical adsorption of charged plastic
601 nanoparticles affects algal photosynthesis. J. Phys. Chem. C 114, 16556-16561.

602 https://doi.org/10.1021/jp1054759

603 Browne, M.A., Galloway, T.S., Thompson, R.C., 2010. Spatial patterns of plastic debris along
604 estuarine shorelines. Environ. Sci. Technol. 44, 3404-3409.

605 https://doi.org/10.1021/es903784e

606 Browne, M.A., Underwood, A.J., Chapman, M.G., Williams, R., Thompson, R.C., Van
607 Franeker, J.A., 2015. Linking effects of anthropogenic debris to ecological impacts.

608 Proc. R. Soc. B Biol. Sci. 282, 1-10. https://doi.org/10.1098/rspb.2014.2929

609 Brydson, J.A., 1999. Plastics Materials, Butterworth-Heinemann.

610 Cambridge Dictionary, https://dictionary.cambridge.org/fr/dictionnaire/anglais/release.

611 Accessed 8 August 2021

612 Capolupo, M., Gunaalan, K., Booth, A.M., Sørensen, L., Valbonesi, P., Fabbri, E., 2021. The
613 sub-lethal impact of plastic and tire rubber leachates on the Mediterranean mussel
614 Mytilus galloprovincialis. Environ. Pollut. 283, 117081.

615 https://doi.org/10.1016/j.envpol.2021.117081

616 Capolupo, M., Sørensen, L., Jayasena, K.D.R., Booth, A.M., Fabbri, E., 2020. Chemical
617 composition and ecotoxicity of plastic and car tire rubber leachates to aquatic
618 organisms. Water Res. 169, 115270. https://doi.org/10.1016/j.watres.2019.115270

619 Chae, Y., Hong, S.H., An, Y.J., 2020. Photosynthesis enhancement in four marine microalgal
620 species exposed to expanded polystyrene leachate. Ecotoxicol. Environ. Saf. 189,
621 109936. https://doi.org/10.1016/j.ecoenv.2019.109936

622 Coffin, S., Dudley, S., Taylor, A., Wolf, D., Wang, J., Lee, I., Schlenk, D., 2018.
623 Comparisons of analytical chemistry and biological activities of extracts from North
624 Pacific gyre plastics with UV-treated and untreated plastics using in vitro and in vivo
625 models. Environ. Int. 121, 942-954. https://doi.org/10.1016/j.envint.2018.10.012

626 Cole, M., Galloway, T.S., 2015. Ingestion of Nanoplastics and Microplastics by Pacific
627 Oyster Larvae. Environ. Sci. Technol. 49, 14625-14632.
628 https://doi.org/10.1021/acs.est.5b04099

629 Cormier, B., Gambardella, C., Tato, T., Perdriat, Q., Costa, E., Veclin, C., Le Bihanic, F.,
630 Grassl, B., Dubocq, F., Kärrman, A., Van Arkel, K., Lemoine, S., Lagarde, F., Morin,
631 B., Garaventa, F., Faimali, M., Cousin, X., Bégout, M.L., Beiras, R., Cachot, J., 2021.
632 Chemicals sorbed to environmental microplastics are toxic to early life stages of aquatic
633 organisms. Ecotoxicol. Environ. Saf. 208, 111665.

634 https://doi.org/10.1016/j.ecoenv.2020.111665

635 Davarpanah, E., Guilhermino, L., 2015. Single and combined effects of microplastics and
copper on the population growth of the marine microalgae Tetraselmis chuii. Estuar.
636 Coast. Shelf Sci. 167, 269-275. https://doi.org/10.1016/j.ecss.2015.07.023

638 De-la-Torre, G.E., Dioses-Salinas, D.C., Pizarro-Ortega, C.I., Saldaña-Serrano, M., 2020.
639 Global distribution of two polystyrene-derived contaminants in the marine environment:
640 A review. Mar. Pollut. Bull. 161, 111729.

641 https://doi.org/10.1016/j.marpolbul.2020.111729

642 de Sá, L.C., Oliveira, M., Ribeiro, F., Rocha, T.L., Futter, M.N., 2018. Studies of the effects
643 of microplastics on aquatic organisms: What do we know and where should we focus
644 our efforts in the future? Sci. Total Environ. 645, 1029-1039.

645 https://doi.org/10.1016/j.scitotenv.2018.07.207

646 Delle Site, A., 2001. Factors affecting sorption of organic compounds in natural sorbent/water
647 systems and sorption coefficients for selected pollutants. A review. J. Phys. Chem. Ref.
648 Data 30, 187-439. https://doi.org/10.1063/1.1347984
649 Desforges, J.P.W., Galbraith, M., Ross, P.S., 2015. Ingestion of Microplastics by
650 Zooplankton in the Northeast Pacific Ocean. Arch. Environ. Contam. Toxicol. 69, 320-
651 330. https://doi.org/10.1007/s00244-015-0172-5

652 Doyen, P., Hermabessiere, L., Dehaut, A., Himber, C., Decodts, M., Degraeve, T., Delord, L.,
653 Gaboriaud, M., Moné, P., Sacco, J., Tavernier, E., Grard, T., Duflos, G., 2019.

654 Occurrence and identification of microplastics in beach sediments from the Hauts-de-
655 France region. Environ. Sci. Pollut. Res. 26, 28010-28021.

656 https://doi.org/10.1007/s11356-019-06027-8

657 European Chemical Agency, 2021. Mapping exercise – Plastic additives initiative,
658 https://echa.europa.eu/fr/mapping-exercise-plastic-additives-initiative#table. Accessed 8
659 August 2021

660 Eriksen, M., Lebreton, L.C.M., Carson, H.S., Thiel, M., Moore, C.J., Borerro, J.C., Galgani,
661 F., Ryan, P.G., Reisser, J., 2014. Plastic Pollution in the World's Oceans: More than 5
662 Trillion Plastic Pieces Weighing over 250,000 Tons Afloat at Sea. PLoS One 9, 1-15.
663 https://doi.org/10.1371/journal.pone.0111913

664 Erni-Cassola, G., Zadjelovic, V., Gibson, M.I., Christie-Oleza, J.A., 2019. Distribution of
665 plastic polymer types in the marine environment; A meta-analysis. J. Hazard. Mater.
666 369, 691-698. https://doi.org/10.1016/j.jhazmat.2019.02.067

667 Fries, E., Zarfl, C., 2012. Sorption of polycyclic aromatic hydrocarbons (PAHs) to low and
668 high density polyethylene (PE). Environ. Sci. Pollut. Res. 19, 1296-1304.
669 https://doi.org/10.1007/s11356-011-0655-5

670 Fu, L., Li, J., Wang, G., Luan, Y., Dai, W., 2021. Adsorption behavior of organic pollutants
671 on microplastics. Ecotoxicol. Environ. Saf. 217, 112207.
672 https://doi.org/10.1016/j.ecoenv.2021.112207

673 Galgani, F., Hanke, G., Maes, T., 2015. Global distribution, composition and abundance of
674 marine litter, in: Bergmann, M., Gutow, L., Klages, M. (Eds.), Marine Anthropogenic
675 Litter. Springer, Cham, pp. 29-56. https://doi.org/10.1007/978-3-319-16510-3

676 Gall, S.C., Thompson, R.C., 2015. The impact of debris on marine life. Mar. Pollut. Bull. 92,
677 170-179. https://doi.org/10.1016/j.marpolbul.2014.12.041

678 Galloway, T.S., 2015. Micro- and nano-plastics and human health, in: Bergmann, M., Gutow,
679 L., Klages, M. (Eds.), Marine Anthropogenic Litter. Springer, Cham, pp. 343-366.
680 https://doi.org/10.1007/978-3-319-16510-3

681 Galloway, T.S., Cole, M., Lewis, C., 2017. Interactions of microplastic debris throughout the
682 marine ecosystem. Nat. Ecol. Evol. 1, 1-16.

683 Gandara e Silva, P.P., Nobre, C.R., Resaffe, P., Pereira, C.D.S., Gusmão, F., 2016. Leachate
684 from microplastics impairs larval development in brown mussels. Water Res. 106, 364-
685 370. https://doi.org/10.1016/j.watres.2016.10.016

686 Gardon, T., Huvet, A., Paul-Pont, I., Cassone, A.L., Sham Koua, M., Soyez, C., Jezequel, R.,
687 Receveur, J., Le Moullac, G., 2020. Toxic effects of leachates from plastic pearl-
688 farming gear on embryo-larval development in the pearl oyster Pinctada margaritifera.
689 Water Res. 179, 115890. https://doi.org/10.1016/j.watres.2020.115890

690 GESAMP, 2010. Microplastic particles as a vector in transporting persistent, bio-
691 accumulating and toxic substances in the ocean, Proceedings of the GESAMP
692 International Workshop on microplastic particles as a vector in transporting persistent,
693 bioaccumulating and toxic substances in the ocean.

694 Gewert, B., MacLeod, M., Breitholtz, M., 2021. Variability in Toxicity of Plastic Leachates
695 as a Function of Weathering and Polymer Type: A Screening Study with the Copepod
696 Nitocra spinipes. Biol. Bull. 240, 191-199.

697 Geyer, R., Jambeck, J.R., Law, K.L., 2017. Production, use, and fate of all plastics ever made.
698 Sci. Adv. 3, 1-5. https://doi.org/10.1126/sciadv.1700782
699 Gilbert, M., 2017. Brydson's Plastics Materials, Butterworth-Heinemann.

700 Green, D.S., Boots, B., Sigwart, J., Jiang, S., Rocha, C., 2016. Effects of conventional and
701 biodegradable microplastics on a marine ecosystem engineer (Arenicola marina) and
702 sediment nutrient cycling. Environ. Pollut. 208, 426-434.

703 https://doi.org/10.1016/j.envpol.2015.10.010

704 Haegerbaeumer, A., Mueller, M.T., Fueser, H., Traunspurger, W., 2019. Impacts of micro-
705 and nano-sized plastic particles on benthic invertebrates: A literature review and gap
706 analysis. Front. Environ. Sci. 7. https://doi.org/10.3389/fenvs.2019.00017

707 Hahladakis, J.N., Velis, C.A., Weber, R., Iacovidou, E., Purnell, P., 2018. An overview of
708 chemical additives present in plastics: Migration, release, fate and environmental impact
709 during their use, disposal and recycling. J. Hazard. Mater. 344, 179-199.

710 https://doi.org/10.1016/j.jhazmat.2017.10.014

711 Harrison, R.M., Hester, R.E., 2019. Plastics and the environment, Royal Soci. ed, Degradable
712 Polymers. https://doi.org/10.1007/978-94-011-0571-2_12

713 Hermabessiere, L., Dehaut, A., Paul-Pont, I., Lacroix, C., Jezequel, R., Soudant, P., Duflos,
714 G., 2017. Occurrence and effects of plastic additives on marine environments and
715 organisms: A review. Chemosphere 182, 781-793.

716 https://doi.org/10.1016/j.chemosphere.2017.05.096

717 Hidalgo-Ruz, V., Gutow, L., Thompson, R.C., Thiel, M., 2012. Microplastics in the marine
718 environment: A review of the methods used for identification and quantification.

719 Environ. Sci. Technol. 46, 3060-3075. https://doi.org/10.1021/es2031505

720 Jambeck, J., Geyer, R., Wilcox, C., Siegler, T.R., Perryman, M., Andrady, A., Narayan, R.,
721 Law, K.L., 2015. the Ocean: the Ocean: Mar. Pollut. 347, 768-771.

722 Joo, S.H., Liang, Y., Kim, M., Byun, J., Choi, H., 2021. Microplastics with adsorbed
723 contaminants: Mechanisms and Treatment. Environ. Challenges 3, 100042.

724 https://doi.org/10.1016/j.envc.2021.100042

725 Ke, A.Y., Chen, J., Zhu, J., Wang, Y.H., Hu, Y., Fan, Z.L., Chen, M., Peng, P., Jiang, S.W.,
726 Xu, X.R., Li, H.X., 2019. Impacts of leachates from single-use polyethylene plastic
727 bags on the early development of clam Meretrix meretrix (Bivalvia: Veneridae). Mar.

728 Pollut. Bull. 142, 54-57. https://doi.org/10.1016/j.marpolbul.2019.03.029

729 Kedzierski, M., D'Almeida, M., Magueresse, A., Le Grand, A., Duval, H., César, G., Sire, O.,
730 Bruzaud, S., Le Tilly, V., 2018. Threat of plastic ageing in marine environment.

731 Adsorption/desorption of micropollutants. Mar. Pollut. Bull. 127, 684-694.

732 https://doi.org/10.1016/j.marpolbul.2017.12.059

733 Koski, M., Søndergaard, J., Christensen, A.M., Nielsen, T.G., 2021. Effect of
734 environmentally relevant concentrations of potentially toxic microplastic on coastal
735 copepods. Aquat. Toxicol. 230, 105713. https://doi.org/10.1016/j.aquatox.2020.105713

736 Kristensen, E., Penha-Lopes, G., Delefosse, M., Valdemarsen, T., Quintana, C.O., Banta,
737 G.T., 2012. What is bioturbation? The need for a precise definition for fauna in aquatic
738 sciences. Mar. Ecol. Prog. Ser. 446, 285-302. https://doi.org/10.3354/meps09506

739 Langlet, D., Bouchet, V.M.P., Delaeter, C., Seuront, L., 2020. Motion behavior and metabolic
740 response to microplastic leachates in the benthic foraminifera Haynesina germanica. J.
741 Exp. Mar. Bio. Ecol. 529, 1-6. https://doi.org/10.1016/j.jembe.2020.151395

742 Law, K.L., Thompson, R.C., 2014. Microplastics in the seas. Science (80-. ). 345, 144-145.
743 https://doi.org/10.1126/science.1254065

744 Lebreton, L., Egger, M., Slat, B., 2019. A global mass budget for positively buoyant
745 macroplastic debris in the ocean. Sci. Rep. 9, 1-10. https://doi.org/10.1038/s41598-019-49413-5

747 Lehtiniemi, M., Hartikainen, S., Turja, R., Lehtonen, K.K., Vepsäläinen, J., Peräniemi, S.,
748 Leskinen, J., Setälä, O., 2021. Exposure to leachates from post-consumer plastic and
749 recycled rubber causes stress responses and mortality in a copepod Limnocalanus
750 macrurus. Mar. Pollut. Bull. 173. https://doi.org/10.1016/j.marpolbul.2021.113103

751 Lenz, R., Enders, K., Nielsen, T.G., 2016. Microplastic exposure studies should be
752 environmentally realistic. Proc. Natl. Acad. Sci. U. S. A. 113, E4121-E4122.
753 https://doi.org/10.1073/pnas.1606615113

754 Leung, J., Chan, K.Y.K., 2018. Microplastics reduced posterior segment regeneration rate of
755 the polychaete Perinereis aibuhitensis. Mar. Pollut. Bull. 129, 782-786.
756 https://doi.org/10.1016/j.marpolbul.2017.10.072

757 Li, H.X., Getzinger, G.J., Ferguson, P.L., Orihuela, B., Zhu, M., Rittschof, D., 2016. Effects
758 of Toxic Leachate from Commercial Plastics on Larval Survival and Settlement of the
759 Barnacle Amphibalanus amphitrite. Environ. Sci. Technol. 50, 924-931.
760 https://doi.org/10.1021/acs.est.5b02781

761 Lithner, D., Damberg, J., Dave, G., Larsson, Å., 2009. Leachates from plastic consumer
762 products - Screening for toxicity with Daphnia magna. Chemosphere 74, 1195-1200.
763 https://doi.org/10.1016/j.chemosphere.2008.11.022

764 Lithner, D., Larsson, A., Dave, G., 2011. Environmental and health hazard ranking and
765 assessment of plastic polymers based on chemical composition. Sci. Total Environ. 409,
766 3309-3324. https://doi.org/10.1016/j.scitotenv.2011.04.038

767 Lithner, D., Nordensvan, I., Dave, G., 2012. Comparative acute toxicity of leachates from
768 plastic products made of polypropylene, polyethylene, PVC, acrylonitrile-butadiene-
769 styrene, and epoxy to Daphnia magna. Environ. Sci. Pollut. Res. 19, 1763-1772.
770 https://doi.org/10.1007/s11356-011-0663-5

771 Liu, P., Zhan, X., Wu, X., Li, J., Wang, H., Gao, S., 2020. Effect of weathering on
772 environmental behavior of microplastics: Properties, sorption and potential risks.
773 Chemosphere 242, 125193. https://doi.org/10.1016/j.chemosphere.2019.125193

774 Long, M., Moriceau, B., Gallinari, M., Lambert, C., Huvet, A., Raffray, J., Soudant, P., 2015.
775 Interactions between microplastics and phytoplankton aggregates: Impact on their
776 respective fates. Mar. Chem. 175, 39-46.
777 https://doi.org/10.1016/j.marchem.2015.04.003

778 Martínez-Gómez, C., León, V.M., Calles, S., Gomáriz-Olcina, M., Vethaak, A.D., 2017. The
779 adverse effects of virgin microplastics on the fertilization and larval development of sea
780 urchins. Mar. Environ. Res. 130, 69-76.
781 https://doi.org/10.1016/j.marenvres.2017.06.016

782 Nelms, S.E., Coombes, C., Foster, L.C., Galloway, T.S., Godley, B.J., Lindeque, P.K., Witt,
783 M.J., 2017. Marine anthropogenic litter on British beaches: A 10-year nationwide
784 assessment using citizen science data. Sci. Total Environ. 579, 1399-1409.
785 https://doi.org/10.1007/978-3-319-16510-3_14

786 Nobre, C.R., Santana, M.F.M., Maluf, A., Cortez, F.S., Cesar, A., Pereira, C.D.S., Turra, A.,
787 2015. Assessment of microplastic toxicity to embryonic development of the sea urchin
788 Lytechinus variegatus (Echinodermata: Echinoidea). Mar. Pollut. Bull. 92, 99-104.
789 https://doi.org/10.1016/j.marpolbul.2014.12.050

790 Ogata, Y., Takada, H., Mizukawa, K., Hirai, H., Iwasa, S., Endo, S., Mato, Y., Saha, M.,
791 Okuda, K., Nakashima, A., Murakami, M., Zurcher, N., Booyatumanondo, R., Zakaria,
792 M.P., Dung, L.Q., Gordon, M., Miguez, C., Suzuki, S., Moore, C., Karapanagioti, H.K.,
793 Weerts, S., McClurg, T., Burres, E., Smith, W., Velkenburg, M. Van, Lang, J.S., Lang,
794 R.C., Laursen, D., Danner, B., Stewardson, N., Thompson, R.C., 2009. International
795 Pellet Watch: Global monitoring of persistent organic pollutants (POPs) in coastal
796 waters. 1. Initial phase data on PCBs, DDTs, and HCHs. Mar. Pollut. Bull. 58, 1437-
797 1446. https://doi.org/10.1016/j.marpolbul.2009.06.014
798 Oliviero, M., Tato, T., Schiavo, S., Fernández, V., Manzo, S., Beiras, R., 2019. Leachates of
799 micronized plastic toys provoke embryotoxic effects upon sea urchin Paracentrotus
800 lividus. Environ. Pollut. 247, 706–715. https://doi.org/10.1016/j.envpol.2019.01.098

801 Pannetier, P., Morin, B., Clérandeau, C., Laurent, J., Chapelle, C., Cachot, J., 2019. Toxicity
802 assessment of pollutants sorbed on environmental microplastics collected on beaches:
803 Part II-adverse effects on Japanese medaka early life stages. Environ. Pollut. 248, 1098–
804 1107. https://doi.org/10.1016/j.envpol.2018.10.129

805 Paul-Pont, I., Tallec, K., Gonzalez-Fernandez, C., Lambert, C., Vincent, D., Mazurais, D.,
806 Zambonino-Infante, J.L., Brotons, G., Lagarde, F., Fabioux, C., Soudant, P., Huvet, A.,
807 2018. Constraints and priorities for conducting experimental exposures of marine
808 organisms to microplastics. Front. Mar. Sci. 5, 1–22.
809 https://doi.org/10.3389/fmars.2018.00252

810 Piccardo, M., Provenza, F., Grazioli, E., Cavallo, A., Terlizzi, A., Renzi, M., 2020. PET
811 microplastics toxicity on marine key species is influenced by pH, particle size and food
812 variations. Sci. Total Environ. 715, 136947.
813 https://doi.org/10.1016/j.scitotenv.2020.136947

814 PlasticsEurope, 2018. Plastics – the Facts 2017: An analysis of European plastics production,
815 demand and waste data, PlasticsEurope.

816 PlasticsEurope, 2020. Plastics – the Facts 2020: An analysis of European plastics production,
817 demand and waste data, PlasticsEurope.

818 Popper, K., 2002. The Logic of Scientific Discovery. Routledge, London.

819 Prata, J.C., Lavorante, B.R.B.O., Maria da, M. da C., Guilhermino, L., 2018. Influence of
820 microplastics on the toxicity of the pharmaceuticals procainamide and doxycycline on
821 the marine microalgae Tetraselmis chuii. Aquat. Toxicol. 197, 143–152.
822 https://doi.org/10.1016/j.aquatox.2018.02.015

823 Rendell-Bhatti, F., Paganos, P., Pouch, A., Mitchell, C., D'Aniello, S., Godley, B.J., Pazdro,
824 K., Arnone, M.I., Jimenez-Guri, E., 2021. Developmental toxicity of plastic leachates
825 on the sea urchin Paracentrotus lividus. Environ. Pollut. 269, 115744.
826 https://doi.org/10.1016/j.envpol.2020.115744

827 Sarker, I., Moore, L.R., Paulsen, I.T., Tetu, S.G., 2020. Assessing the Toxicity of Leachates
828 From Weathered Plastics on Photosynthetic Marine Bacteria Prochlorococcus. Front.
829 Mar. Sci. 7, 1–14. https://doi.org/10.3389/fmars.2020.571929

830 Schaschke, C., 2014. A dictionary of chemical engineering, Oxford University Press.
831 https://doi.org/10.5860/choice.52-0031

832 Schiavo, S., Oliviero, M., Chiavarini, S., Dumontet, S., Manzo, S., 2021. Polyethylene,
833 Polystyrene, and Polypropylene leachate impact upon marine microalgae Dunaliella
834 tertiolecta. J. Toxicol. Environ. Health. Part A 84, 249–260.
835 https://doi.org/10.1080/15287394.2020.1860173

836 Seuront, L., 2018. Microplastic leachates impair behavioural vigilance and predator avoidance
837 in a temperate intertidal gastropod. Biol. Lett. 14, 1–5.
838 https://doi.org/http://dx.doi.org/10.1098/rsbl.2018.0453

839 Seuront, L., Nicastro, K.R., McQuaid, C.D., Zardi, G.I., 2021. Microplastic leachates induce
840 species-specific trait strengthening in intertidal mussels. Ecol. Appl. 31, 1–10.
841 https://doi.org/10.1002/eap.2222

842 Silva, M.S.S., Oliveira, M., Valente, P., Figueira, E., Martins, M., Pires, A., 2020. Behavior
843 and biochemical responses of the polychaeta Hediste diversicolor to polystyrene
844 nanoplastics. Sci. Total Environ. 707, 1–9.
845 https://doi.org/10.1016/j.scitotenv.2019.134434
846 Sjollema, S.B., Redondo-Hasselerharm, P., Leslie, H.A., Kraak, M.H.S., Vethaak, A.D., 2016. Do plastic particles affect microalgal photosynthesis and growth? Aquat. Toxicol.
847 170, 259-261. https://doi.org/10.1016/j.aquatox.2015.12.002
848

849 Song, C., Liu, Z., Wang, C., Li, S., Kitamura, Y., 2020. Different interaction performance between microplastics and microalgae: The bio-elimination potential of Chlorella sp.
850 L38 and Phaeodactylum tricornutum MASCC-0025. Sci. Total Environ. 723, 1-10.
851
852 https://doi.org/10.1016/j.scitotenv.2020.138146

853 Su, Y., Zhang, K., Zhou, Z., Wang, J., Yang, X., Tang, J., Li, H., Lin, S., 2020. Microplastic exposure represses the growth of endosymbiotic dinoflagellate Cladocopium goreaui in culture through affecting its apoptosis and metabolism. Chemosphere 244, 1-8.
854
855
856 https://doi.org/10.1016/j.chemosphere.2019.125485

857 Tang, J., Ni, X., Zhou, Z., Wang, L., Lin, S., 2018. Acute microplastic exposure raises stress response and suppresses detoxification and immune capacities in the scleractinian coral
858 Pocillopora damicornis. Environ. Pollut. 243, 66-74.
859
860 https://doi.org/10.1016/j.envpol.2018.08.045

861 Tetu, S.G., Sarker, I., Schrameyer, V., Pickford, R., Elbourne, L.D.H., Moore, L.R., Paulsen, I.T., 2019. Plastic leachates impair growth and oxygen production in Prochlorococcus, the ocean's most abundant photosynthetic bacteria. Commun. Biol. 2, 1-9.
862
863
864 https://doi.org/10.1038/s42003-019-0410-x

865 Thomas, P.J., Oral, R., Pagano, G., Tez, S., Toscanesi, M., Ranieri, P., Trifuoggi, M., Lyons, D.M., 2020. Mild toxicity of polystyrene and polymethylmethacrylate microplastics in Paracentrotus lividus early life stages. Mar. Environ. Res. 161, 105132.
866
867
868 https://doi.org/10.1016/j.marenvres.2020.105132

869 Trestrail, C., Walpitagama, M., Hedges, C., Truskewycz, A., Miranda, A., Wlodkowic, D., Shimeta, J., Nugegoda, D., 2020. Foaming at the mouth: Ingestion of floral foam microplastics by aquatic animals. Sci. Total Environ. 705, 135826.
870
871
872 https://doi.org/10.1016/j.scitotenv.2019.135826

873 Uhrin, A. V., Matthews, T.R., Lewis, C., 2014. Lobster Trap Debris in the Florida Keys
874 National Marine Sanctuary: Distribution, Abundance, Density, and Patterns of
875 Accumulation. Mar. Coast. Fish. 6, 20-32.
876 https://doi.org/10.1080/19425120.2013.852638

877 Vegter, A.C., Barletta, M., Beck, C., Borrero, J., Burton, H., Campbell, M.L., Costa, M.F., Eriksen, M., Eriksson, C., Estrades, A., Gilardi, K.V.K., Hardesty, B.D., Ivar do Sul, J.A., Lavers, J.L., Lazar, B., Lebreton, L., Nichols, W.J., Ribic, C.A., Ryan, P.G., Schuyler, Q.A., Smith, S.D.A., Takada, H., Townsend, K.A., Wabnitz, C.C.C., Wilcox, C., Young, L.C., Hamann, M., 2014. Global research priorities to mitigate plastic pollution impacts on marine wildlife. Endanger. Species Res. 25, 225-247.
878
879
880
881
882 https://doi.org/10.3354/esr00623

883 Wathsala, R.H.G.R., Franzellitti, S., Scaglione, M., Fabbri, E., 2018. Styrene impairs normal embryo development in the Mediterranean mussel (Mytilus galloprovincialis). Aquat. Toxicol. 201, 58-65. https://doi.org/10.1016/j.aquatox.2018.05.026

884
885
886 Weis, J.S., 2019. Improving microplastic research. AIMS Environ. Sci. 6, 326-340.
https://doi.org/10.3934/environsci.2019.5.326

889 Weis, P., Weis, J.S., Greenberg, A., Nosker, T.J., 1992. Toxicity of construction materials in the marine environment: A comparison of chromated-copper-arsenate-treated wood and recycled plastic. Arch. Environ. Contam. Toxicol. 22, 99-106.
890
891
892 https://doi.org/10.1007/BF00213307

893 Yarsley, V.E., Couzens, E.G., 1942. Plastics, Pelican Bo. ed. Allen Lane: Penguin Books, Harmondsworth.
894
895 Zalasiewicz, J., Waters, C.N., Ivar do Sul, J.A., Corcoran, P.L., Barnosky, A.D., Cearreta, A.,
896 Edgeworth, M., Gałuszka, A., Jeandel, C., Leinfelder, R., McNeill, J.R., Steffen, W.,
897 Summerhayes, C., Wagreich, M., Williams, M., Wolfe, A.P., Yonan, Y., 2016. The
898 geological cycle of plastics and their use as a stratigraphic indicator of the
899 Anthropocene. Anthropocene 13, 4–17. https://doi.org/10.1016/j.ancene.2016.01.002
900 Zhang, C., Chen, X., Wang, J., Tan, L., 2017. Toxic effects of microplastic on marine
901 microalgae Skeletonema costatum : Interactions between microplastic and algae.
902 Environ. Pollut. 220, 1282–1288. https://doi.org/10.1016/j.envpol.2016.11.005
903 Zhu, Z. lin, Wang, Su chun, Zhao, F. fei, Wang, Shu guang, Liu, F. fei, Liu, G. zhou, 2019.
904 Joint toxicity of microplastics with triclosan to marine microalgae Skeletonema
905 costatum. Environ. Pollut. 246, 509–517. https://doi.org/10.1016/j.envpol.2018.12.044
906
907
908
909
**Figures Captions**

**Figure 1.** Temporal evolution of the number of papers published between 1950 (i.e. beginning of the industrialization of plastic production) and 2021 that include (a) plastic and pollution (i.e. *plastic* and *pollut*) or (b) plastic and pollution and leachate (i.e. *plastic* and *pollut* and *leachate*). The total bar represents the number of papers in the global field. The part of papers in Environmental Sciences and Ecology is in black among which the part of papers in Marine and Freshwater Biology is in grey.

**Figure 2.** Composition of plastic leachate of virgin and aged, i.e. that have stayed in the environment, polymers. add: plastic additives, pop: persistent organic pollutants.

**Figure 3.** Heatmap analysis of the research effort in the area of research devoted to the impact of plastic leachates on coastal invertebrates, microorganisms and plants. The more intense the red is, the more experiments have been made on the polymer-phylum couple considered. The percentage of research effort devoted to a polymer-phylum couple is written in the crossing box. Barplots represent the percentage of research effort devoted to a specific polymer or phylum.
a.

7000

b.

<figure><img src="image_2.png" /></figure>
## Virgin polymers

<figure><img src="image_3.png" /></figure>

Primary leachate

## Weathered polymers

<figure><img src="image_4.png" /></figure>

Primary leachate

Secondary leachate
<figure><img src="image_5.png" /></figure>
## Plastic leachate definition

<figure><img src="image_6.png" /><figcaption>Weathered pellet</figcaption></figure>

## Future directions for plastic leachate research

### Consensus on protocols

Investigations on key ecosystem engineers

Need of environmental relevance

Multidisciplinary studies