Plastic pollution in the environment has increasingly become the focus of science, politics, and the public. Nowadays, almost 80% of the plastic waste ever produced lies in landfills and rubbish dumps or is littered in the environment. The economic impacts of plastic waste include not only the lost economic value of the material, but also the cost of disposal and losses to tourism, fisheries and shipping. For this reason, single-use plastics, like straws and food containers, have been banned since 2021 by the European Union. Manufacturers and researchers are looking for alternatives to conventional plastic. Therefore, the use and production of biodegradable plastics is increasing. Registration by REACH is not obligated for polymers as the monomers and additives must be registered. Therefore, toxicological studies of new polymers are not regulated by law before being launched onto the market. Although the individual components of the polymers are classified as non-toxic, the introduction of bioplastics into the environment can cause them to become toxic for organisms. For example, degradation and leaching of toxic by-products and transformation products can occur in the environment (e.g., many bioplastics contain plasticizers (phthalates)). In addition, bioplastic can absorb pollutants such as polycyclic aromatic hydrocarbons from the environment, thereby increasing the plastic’s toxicity. Such persistent—and in particular hydrophobic—organic compounds (HOCs) can have significant changes on ecological diversity, leading to ecosystem function losses. As many studies on conventional plastics have been performed, it is known that polymers can have toxic effects on organisms. Compared with that body of research, the data on the environmental hazard potential of bioplastics is small. For plastics manufacturers knowledge of toxicity alone is not enough to produce non-toxic polymers. A holistic approach including both ecotoxicology and chemical analysis is required to understand how and why (bio)polymers provoke effects towards organisms. In our studies on bioplastics, we developed an innovative approach that combines bioassay and chemical analysis. With this holistic concept we are able to identify toxic compounds and/or toxic mixtures in polymers. In studies on biopolymers within the project BIO-PLASTICS Europe, one bioplastic material showed toxic effects on Daphnia magna. Chemical analysis of the biopolymer identified the toxic chemical 2-methylnaphthalene. With this information, the manufacturer was able to identify the source of the contamination and adjust the production process.