Particles of microplastic are now the most abundant form of solid-waste pollution on our planet. Many plastics contain chemical additives, such as plasticizers, dyes, and antimicrobials, which can reach out into sediments and seawater. Microplastics also concentrate water-borne chemicals on their surfaces, such as pesticides and detergents. In other words, the problem with microplastics isn't just the plastic itself, but the complex mix of chemicals the plastics carry with them.