Microplastics are degraded continuously in the aquatic environment by abiotic and biotic factors such as UV-irradiation, temperature, mechanical abrasion, hydrolysis and bacteria. For this reason, chemicals that are typically incorporated into the polymer matrix can leach into the surrounding medium more readily. Although chemical effects of plastics have been examined recently with in-vitro bioassays, only a few studies have studied the impact of weathering on plastic leaching. Therefore, we investigated in-vitro effects of 12 different UV-weathered microplastic (pellets