Microplastic Occurence in North Sea Surface Waters - Analyzed using Fourier Transform Infrared Spectroscopy

The global plastic production is increasing steadily, and so the amount of synthetic material reaching our marine environment does. In recent years, more and more studies focused on the occurrence of microplastics, i.e. synthetic organic polymers with a size < 5 mm. These pollutants are omnipresent and hardly degradable, leading to an accumulation in the environment. They are easily ingested by a wide range of animals throughout the food web, and may act as a vector for persistent organic pollutants (POPs). For a valid evaluation of microplastic pollution in marine ecosystems appropriate assessment strategies are crucial. By now, no standardized sampling and analysis techniques are available, which would be urgently needed in order to generate solid and comparable data bases. In many studies, microplastics are identified and quantified solely through visual examination, although this approach is highly subjective and may lead to misidentification. In this work, state-of-the-art methods were used for the identification and quantification of microplastics in seven North Sea neuston samples. The samples were split into two size fractions, on which two different methodological approaches were applied. Microplastics > 500 μm were extracted using a stereomicroscope, followed by polymer identification via Attenuated Total Reflection based Fourier Transform Infrared spectroscopy (FTIR-ATR). For the size fraction < 500 μm, more complex methodologies were employed: a recently developed enzymatic purification protocol was used in order to extract microplastics from the sample matrix. This was conducted in a novel semi-closed filtration system (Microplastic-Reactor), followed by spectroscopic analysis via focal plane array based μ-Fourier-Transform Infrared spectroscopy (μFTIR-FPA). A subsequent automated analysis pipeline provided detailed information on particle number, chemical composition and size classes. Microplastic concentrations ranged from 0 – 2.5 m−3 (0 – 2.7 × 105 km−2) in the size fraction > 500 μm and from 16.1 – 393.1 m−3 (1.3 × 106 – 4.3 × 107 km−2) in the size fraction < 500 μm. With regard to the size distribution small-sized particles clearly dominated in both fractions. In total, 17 different synthetic polymers were detected in the studied neuston samples with comparably high abundances of polyethylene, polypropylene, varnish and rubber, possibly stemming from land-based sources or shipping activities.