Abstract
The ubiquitous occurrence of microplastics (MPs) in the marine environment is raising concern for interactions with marine organisms. These particles efficiently adsorb persistent organic pollutants from surrounding environment and, due to the small size, they are easily available for ingestion at all trophic levels. Once ingested, MPs can induce mechanical damage, sub- lethal effects and various cellular responses, further modulated by possible release of adsorbed chemicals or additives. In this study, ecotoxicological effects of MPs and their interactions with benzo(a)pyrene (BaP), chosen as a model compound for polycyclic aromatic hydrocarbons (PAHs) were investigated in Mediterranean mussels, Mytilus galloprovincialis. Organisms were exposed for four weeks to 10 mg/L of low-density polyethylene (LD-PE) microparticles (2.34x107 particles/L, size range 20-25 µm), both virgin and pre-contaminated with BaP (15µg/g). Organisms were also exposed for comparison to BaP dosed alone at 150 ng/L, corresponding to the amount adsorbed on microplastics. Tissue localization of microplastics was histologically evaluated; chemical analyses and a wide battery of biomarkers covering molecular, biochemical and cellular levels allowed to evaluate BaP bioaccumulation, alterations of immune system, antioxidant defenses, onset of oxidative stress, peroxisomal proliferation, genotoxicity and neurotoxicity. Obtained data were elaborated within a quantitative weight of evidence (WOE) model which, using weighted criteria, provided synthetic hazard indices, for both chemical and cellular results, before their integration in a combined index. Microplastics were localized in haemolymph, gills and especially digestive tissues where a potential transfer of BaP from MPs was also observed. Significant alterations were measured on the immune system, while more limited effects occurred on the oxidative status, neurotoxicity and genotoxicity, with a different susceptibility of analyzed pathways, depending on tissue, time and typology of exposure. Molecular analyses confirmed the general lack of significant variations on transcriptional activity of antioxidant and stress genes. The overall results suggest that microplastics induce a slight cellular toxicity under short-term (28 days) exposure conditions. However, modulation of immune responses, along with bioaccumulation of BaP, pose the still unexplored risk that these particles, under conditions of more chronic exposure (months to years) or interacting with other stressors, may provoke long-term, subtle effects on organisms’ health status.
Highlights
Microplastics are particles smaller than 5 mm in diameter (NOAA, 2015), identified as the predominant component of plastic debris in the marine environment (Goldstein et al, 2013; Eriksen et al, 2014)
In gills of mussels treated with contaminated microplastics, BaP levels significantly increased until the end of exposure at 28 days when values were similar to those of BaP treatment (Figure 1B, Table 2)
The present study was aimed to provide new insights on the capability of microplastics to transfer adsorbed pollutant to organisms after ingestion and to evaluate potential ecotoxicological effects of virgin and contaminated microplastics, using the Mediterranean mussel M. galloprovincialis as model marine organism
Summary
Microplastics are particles smaller than 5 mm in diameter (NOAA, 2015), identified as the predominant component of plastic debris in the marine environment (Goldstein et al, 2013; Eriksen et al, 2014). Several laboratory experiments have been performed, in recent years, to understand dynamics of particles uptake, bioaccumulation and toxicological mechanisms possibly leading to detrimental effects in a variety of bioindicators organisms (Lusher, 2015; Phuong et al, 2016). Such studies demonstrated that ingested microplastics can be taken up into the cells by endocytosis, retained and even traslocated to different tissues (Browne et al, 2008; Von Moos et al, 2012; Avio et al, 2015). Several effects have been described in terms of histological alterations, inflammatory reactions, and ecotoxicological responses at cellular, biochemical, and molecular levels, and in terms of modulations of physiological functions such as respiration, nutrition, reproduction and growth (Avio et al, 2015; Paul-Pont et al, 2016; Pedà et al, 2016; Détrée and Gallardo-Escárate, 2017; Karami et al, 2017)
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