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Microplastics in the water cycle

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Microplastics in the water cycle – sampling, sample preparation, analytics, occurrence, removal, and assessment

Microplastics in the water cycle – sampling, sample preparation, analytics, occurrence, removal, and assessment

Plastics and the products made thereof mark a substantial component of our life and environment, and they have manifold applications in the domestic, commercial, and industrial sectors. In Germany, 10 million tons of new plastics enter the market every year in various products. About 5 million tons of these plastics are disposed of per year, leaving 5 million tons annually in continuing existence. Despite a comprehensive legislation, the direct or indirect discharge of plastics into the environment currently cannot be fully prevented. The degradation of these materials is very slow and, depending on the respective material characteristics, they will potentially remain in the ecosystems for several hundred years.

To date, most data on plastics occurrence are available for marine environments. The occurrence of plastics in coastal waters can be traced back to the 1960s. The information on the associated sources is variable. Plastics from land-based sources reach the sea via limnic waterbodies. Therefore, the entry of plastics into the environment is not only of national but also of European and international concern.

Oceans play a major role in the comprehensive consideration of the problem, because they are at the end of transport pathways and, thus, are a final sink for plastics in the environment. Nonetheless, in streams and lakes, similar processes occur. There and on the way to the oceans, large pieces of plastic can be fragmented, generating secondary microplastics (MP). Moreover, many products consisting of or containing primary MP reach the environment directly or indirectly. Due to the small size of MP particles (by definition smaller than 5 mm), organisms at the base of the food webs can ingest them. To date, it is not sufficiently clarified if and to which extent MP can accumulate in organisms over several trophic levels. In addition, effects of MP on limnic and marine organisms are under discussion. Besides insufficient data on MP ingestion, retention, and impacts on the environment and on biota, no scientific ecologic assessment has been conducted. Even more, there are currently no approaches available for environmental and risk assessments.

The majority of plastics is composed of synthetically manufactured macro molecules or polymers which themselves consist of repeating monomer units. Depending on the kind and linkage of the monomers, polymers of different properties can be produced. Technical polymers typically have molar masses of 50,000 to 200,000 g/mol. They can be assembled in a non-ordered fashion or ordered as loosely or tightly linked networks. For everyday usage, plastics do not only consist of the respective polymer itself but are also equipped with additives for the optimization or manipulation of material properties. Such additives can be antioxidants, thermal or optical stabilizers, processing agents, bulking agents, pigments, and flame retardants. The degradation of plastic products into fragments or MP proceeds differently for different polymers, and the contained additives can influence this degradation substantially.

The joint project aims at elucidating the existence and extent of potential impacts, associated with the usage of plastics, on humans and the environment. Currently the aim is to identify and assess possible adverse effects or threats arising from plastics. If such effects or threats can be detected, means for their reduction or minimization are to be established. To this end, it is necessary to promote a reduction of discharges in the environment by now. These aims require adjusted and harmonized analysis methods as well as an environmental risk assessment of MP in fresh water systems.

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