Abstract
The study of the contamination of plastic mixtures sampled in natural environments is currently focused on their qualitative and quantitative assessment, while the evaluation of their effects on organisms is normally performed by experiments carried out at exposure conditions (size, shape, polymers) often far from the environmental ones. To improve the ecological realism, the aim of this study was to collect different plastic mixtures in 9 sampling stations located in 7 watercourses within the metropolitan city of Milan, one of the most anthropized and industrialized European areas, to evaluate both their qualitative and quantitative characteristics and, at the same time, to assess their ecotoxicological effects by exposing for 7 days some specimens of the freshwater bivalve Dreissena polymorpha to the mixtures collected in the sampling sites. The plastic characterization was performed by a Fourier-Transform Infrared spectrometer coupled with an optical microscope (μFT-IR), after several stages aimed to sample cleaning, separation of plastics and visual sorting. The possible effects caused by the plastic mixtures were carried out by the measurements of a biomarker suite to evaluate many cellular and molecular endpoints in mussel tissues. The main results showed a widespread and heterogeneous contamination of plastics in the entire metropolitan area, with contamination peaks found above all in the only two rivers of natural origin (Olona River and Lambro River) where comparable or higher values were reached than plastic concentrations measured in several European rivers. Despite this worrying contamination, the ecotoxicological data obtained after the exposures to the plastic mixtures collected in the selected water bodies showed only a mild effect on oxidative stress and on the variation of some antioxidant enzymes.
Highlights
Plastic pollution represents one of the major environmental problems of the 21st century due to the constant increase in its world production, but above all to the incorrect disposal of plastic products that end up in any aquatic and terrestrial ecosystems worldwide
There is no correlation (r = 0.04; p = 0.889) between the volumes of water filtered in each sampling station and the number of detected plastics, as well shown in Table 1 in which the two sites (OLO and Lambro River Downstream” (LAD)) where we collected the smallest volume of water were those where we sampled the highest number of floating plastics
Concerning the effects, superoxide dismutase (SOD), GST, protein carbonylation content (PCC) and P-gp showed levels in the bivalves exposed to the different mixtures similar to the controls and no differences were detected between the sampling sites of the same water system (Fig. 6)
Summary
Plastic pollution represents one of the major environmental problems of the 21st century due to the constant increase in its world production, but above all to the incorrect disposal of plastic products that end up in any aquatic and terrestrial ecosystems worldwide. This could be due to bans on the use of microplastics in cosmetic products in many European countries and to recent restrictions on the single-use plastic products as stated by the EU Directive 2019/904 Despite this encouraging decrease, the presence of plastics in natural ecosystems is ubiquitous, as synthetic polymeric materials can be dispersed by wind and carried by rivers and ocean currents across the globe, even thousands of kilometers away from the place of release into the environment (Oliveira et al, 2019). These smaller debris can be directly present in many personal care products, such as scrubs, toothpastes and cosmetics, increasing their presence especially in aquatic environments (Germanov et al, 2018)
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