Abstract
The impact of a microplastic (MP) mixture composed of polyethylene (PE) andpolypropylene (PP) plastic particles, prepared from commercially available products,was evaluated in blue mussels Mytilus spp. exposed to three environmentally relevantconcentrations: 0.008 μg L−1 (low), 10 μg L−1 (medium), and 100 μg L−1 (high).Organisms were exposed for 10 days followed by 10 days of depuration in clean seawaterunder controlled laboratory conditions. The evaluation of MP effects on mussel clearancerate, tissue structure, antioxidant defenses, immune and digestive parameters, and DNAintegrity were investigated while the identification of plastic particles in mussel tissues(gills, digestive gland, and remaining tissues), and biodeposits (feces and pseudofaeces)was performed using infrared microscopy (μFT-IR). Results showed the presence of MPsonly in the digestive gland of mussels exposed to the highest tested concentration ofMPs with a mean of 0.75 particle/mussel (after the 10 days of exposure). In biodeposits,PE and PP particles were detected following exposure to all tested concentrationsconfirming the ingestion of MPs by the organisms. A differential response of antioxidantenzyme activities between digestive gland and gills was observed. Significant increasesin superoxide dismutase (SOD) and catalase (CAT) activities were measured in thedigestive gland of mussels exposed to the low (0.008 μg L−1) and medium (10 μg L−1)concentrations ofMPs and in the gills frommussels exposed to the highest concentration(100 μg L−1) of MPs that could be indicative of a change in the redox balance. Moreover,an increase in acid phosphatase activity was measured in hemolymph of musselsexposed to 0.008 and 10 μg L−1concentrations. No significant difference was observedin the clearance rate, and histopathological parameters between control and exposedmussels. This study brings new insights on the potential sublethal impacts of MPs atenvironmentally relevant concentrations in marine bivalves.
Highlights
In the last decades, global production of plastic has increased by 500% and almost 10% of the annual production is estimated to end up into the oceans (Plastics Europe, 2016)
In order to confirm our method of dispersion, an aliquot of the stock and diluted suspensions, which corresponds to the volume added to aquariums to obtain 100, 10, and 0.008 μg L−1, was observed under the microscope to confirm the presence of PE and PP particles
The impact of a mixture of PE and PP plastic particles in mussels Mytilus spp. exposed at environmentally relevant concentrations were investigated by identifying their presence using infrared spectroscopy, and assessing their effects on organism physiology, tissue structure, and several biomarker responses
Summary
Global production of plastic has increased by 500% (over 322 million tons in 2016) and almost 10% of the annual production is estimated to end up into the oceans (Plastics Europe, 2016). Effects of MPs have been previously studied in phytoplancton (Cole et al, 2013), lugworms (Wright et al, 2013), and bivalves (Paul-Pont et al, 2016; Sussarellu et al, 2016; Ribeiro et al, 2017) As they are filter-feeding organisms, bivalves are well-known bioindicators for environmental pollution and are closely studied to investigate the presence and toxicity of MPs toward aquatic organisms. Several effects have been shown such as reproduction alterations (Sussarellu et al, 2016), inflammatory responses (von Moos et al, 2012), oxidative and DNA damages (Ribeiro et al, 2017), or translocation of particles into the circulatory system (Browne et al, 2008) In these studies, bivalves were exposed to mono-dispersed plastic microbeads at concentrations ranging from 23 μg L−1 to 2.5 g L−1 and exposures conducted at environmentally relevant concentrations are scarce. Few authors started to test MPs made from fragmented plastics which can be considered as more representative of MPs found in aquatic ecosystems (Rainieri et al, 2018; Weber et al, 2018)
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