Contamination of the environment with plastic debris :“Development, improvement, and evaluation of monitoring methods”

Abstract

Improper disposal of plastics, coupled with their durability and low weight, has led to the widespread environmental pollution of plastic debris. For larger plastic debris negative ecological, cultural, economic, safety, and health impacts are reported and well known. For microplastics (particle size ≤5 mm), harmful effects are still a matter of debate. Nevertheless, microplastics are the distinct subject of national and international marine monitoring directives (i.e. MSFD, NOAA), due to their bioavailability to a wide range of organisms, their omnipresence in the marine environment, and the lack of removal techniques once introduced. Microplastic contamination levels have been intensively examined within marine habitats. And even though the relationship of human activities and plastic debris inputs are known, significant knowledge gaps exist on the sources, transport, and accumulation areas in terrestrial environments. Thus, the first objective of this thesis was the identification of potential sources, pathways, and accumulation areas of plastic debris in terrestrial environments. Three case studies on overlooked, yet potentially plastic debris containing sources and accumulation areas, were carried out. As plastics frequently enter biowastes through misthrows, we exemplarily investigated organic fertilizer from biowaste fermentation and composting as input source of microplastic debris to farmlands. Our results indicate that, depending on receiving wastes, pretreatment of the substrate, and the technical state of the plant, organic fertilizers can contain high concentrations of microplastics. When applied to farmlands, a potential input of 35 billion to 2.2 trillion microplastic particles per year was calculated for German arable land. As around 50% of land use in Germany is agricultural, we further investigated plastic debris contamination of a farmland neither subjected to known plastic-containing fertilizer or to plastic applications. We detected 206 large plastic pieces, and 158,100 to 292,400 microplastic pieces per hectare. Additionally, we were the first to investigate the hyporheic zone of streambed sediments, a transition zone between fresh- and groundwater. Our exemplary study at the Rote Main river indicated that especially small microplastics (<50 μm) are infiltrated into sediments of the hyporheic zone of streambeds. Even though, results from this study are based on one sample, it points towards another temporal sink and relevant transportation pathway for microplastics. The lack of sufficient sample replication is a common issue in microplastic studies, mainly due to the high costs of sampling, sample processing, and analytics. Consequently, the second objective was to improve existing sampling and sample processing methods for microplastics. Concerning sample processing, environmental samples often contain a high number of natural particles that impair spectroscopic identification of microplastics if not removed. Thus, I contributed to the development of a gentle sample purification…