Abstract
The large-scale production of plastic and the resulting release of waste is leading to a huge accumulation of micro-sized particles in the environment that could have an impact on not only aquatic organisms but also on humans. Despite the extensive literature on the subject, there is still an insufficient harmonization of methodologies for the collection and analysis of microplastics (MPs) in complex matrices; especially for high density polymers; such as polyvinyl chloride (PVC), which tend to sink and accumulate in sediments, becoming available to benthonic organisms. In this article, mussels have been chosen as model for microplastic accumulation due to their extensive filtering activity and their wide distribution in both fresh and salt water basins. To facilitate the identification and quantification of microplastics taken up by mussels, novel fluorescent and metal-doped PVC microplastics (PVC-Platinum octaethylporphyrin (PtOEP) MPs in the size range of 100 µm) have been synthesized and characterized. For the analysis of the mussels following exposure, an enzymatic protocol using amylase, lipase, papain, and SDS for organic material digestion and a sucrose-ZnCl2 density gradient for the selective separation of ingested microplastics has been developed. The final identification of MPs was performed by fluorescence microscopy. This work can greatly benefit the scientific community by providing a means to study the behavior of PVC MPs, which represent an example of a very relevant yet poorly studied high density polymeric contaminant commonly found in complex environmental matrices.
Highlights
The historical use of synthetic polymers dates back to the early 19th century, in recent decades companies have been producing ever increasing amounts of new synthetic polymers of different chemical compositions, density, sizes and shapes for a wide range of applications, especially in the packaging, construction and automotive industries [1]
About 25% of the collected plastic waste ends up in landfills without being recycled or destined for energy recovery [2]. This has created an enormous growing reservoir of plastic lost to the environment, which will age and slowly degrade, resulting in a release of smaller plastic fragments, known as microplastics (MPs,
The evidence of a positive and quantitative correlation of microplastics in mussels and their surrounding waters [23] qualifies it as a suitable tool to detect MPs environmental levels, while laboratory exposure studies demonstrate that mussels can be good model organisms when investigating uptake, accumulation and toxicity of microplastics [26]
Summary
The historical use of synthetic polymers dates back to the early 19th century, in recent decades companies have been producing ever increasing amounts of new synthetic polymers of different chemical compositions, density, sizes and shapes for a wide range of applications, especially in the packaging, construction and automotive industries [1]. They are classified as primary microplastics produced intentionally as additives (microspheres or plastic pellets) [4,5,6] or secondary microplastics generated by fragmentation of larger plastic waste in the environment through natural ageing processes [7,8] Due to their surface hydrophobicity and large surface area to volume ratio [9], MPs have the potential to adsorb, concentrate, transport and eventually re-release in living organisms and in the soil matrix environmental hydrophobic organic contaminants [10,11,12] and heavy metals such as Cd, Ni, Zn and Pb [13,14]. To assess the degree of micro- and nano-plastic contamination in freshwater ecosystems, freshwater mussel species are being increasingly used [25,28]
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