Since the 1970s it has been known that plastic waste in the form of microplastics (MP <5 mm) is increasingly found in our aquatic environment. Sampling and processing causes many problems, especially in water with a high biomass content. In this work due to these methodological difficulties successfully two methods have been developed a) to enable the sampling in the entire water column, without limitation in regard to the particle size or density, and b) modifying a device from the recycling management to simplify the separation of MP (<5 mm) from environmental samples. Furthermore, the sediment contact test for determining the effects of MP on the organism L. variegatus was adapted with the question, which effect a direct contact with plastics (PVC, PET, PMMA, PLA and PS) or an indirect contact (via leaching of additives such as phthalates) on the organism. It could be confirmed that, especially from PVC products, toxic additives dissolve in the water. Direct contact with PVC causes an increased mortality with a lethal concentration (LC 50) of 1.7 mg / g TG from an MP concentration of 0.1 mg / g dry weight (TG). Plastic types such as PET, PS, PMMA and the bioplastic PLA, have no effects on the organism. It was also investigated whether the different plastic concentrations exert a negative influence on the fitness (based on the glycogen content) of the organisms. The results show that only at high concentrations of PVC does the glycogen content in the organism decrease.