The chapter "The ecotoxicology and chemistry of manufactured nanoparticles" by Handy et al. provides an overview of the emerging literature on the ecotoxicity of nanoparticles and nanomaterials. It explains the fundamental physico-chemical properties that govern particle behavior in an ecotoxicological context and outlines techniques for measuring nanoparticles in various biological and chemical matrices. The literature indicates that manufactured nanoparticles can have toxic effects on fish and invertebrates at low concentrations, but data on bacteria, plants, and terrestrial species are limited. Initial findings suggest that some manufactured nanoparticles may interact with other contaminants, influencing their ecotoxicity. Particle behavior is influenced by size, shape, surface charge, and the presence of other materials in the environment. Nanoparticles tend to aggregate in hard water and seawater and are affected by specific types of organic matter or colloids in freshwater. The state of dispersion can alter ecotoxicity, but many abiotic factors remain to be systematically investigated. The chapter concludes with a discussion on the implications for environmental risk assessment of manufactured nanoparticles.The chapter "The ecotoxicology and chemistry of manufactured nanoparticles" by Handy et al. provides an overview of the emerging literature on the ecotoxicity of nanoparticles and nanomaterials. It explains the fundamental physico-chemical properties that govern particle behavior in an ecotoxicological context and outlines techniques for measuring nanoparticles in various biological and chemical matrices. The literature indicates that manufactured nanoparticles can have toxic effects on fish and invertebrates at low concentrations, but data on bacteria, plants, and terrestrial species are limited. Initial findings suggest that some manufactured nanoparticles may interact with other contaminants, influencing their ecotoxicity. Particle behavior is influenced by size, shape, surface charge, and the presence of other materials in the environment. Nanoparticles tend to aggregate in hard water and seawater and are affected by specific types of organic matter or colloids in freshwater. The state of dispersion can alter ecotoxicity, but many abiotic factors remain to be systematically investigated. The chapter concludes with a discussion on the implications for environmental risk assessment of manufactured nanoparticles.