In the environment, the representative detection of microplastics is a major challenge. Especially in the aquatic area, the measuring method is essential for a comparable result. To develop efficient, reliable, and reproducible sampling and detecting methods it is indispensable to use realistic and defined reference material during the development procedure. To understand how microplastics behave in the environment, it is first to be known how it ends up in the environment. The majority of environmental microplastics is the secondary microplastics. This is mostly produced by aging of plastics and therefore disintegrating into small particles known as microplastics. In this paper the aging process is reviewed with focus on ultraviolet damaging of PE film. It will show that the physical and chemical characteristics change with exposure time.