Environmental Fate and Exposure Modeling of Nanomaterials

Different types of engineered nanomaterials (ENMs) are used in a wide range of applications, such as (coated) titanium dioxide (TiO ₂) nanoparticles (NPs) in sunscreens, silver nanoparticles as biocide in textiles, water disinfection, or wound dressings, and gold nanoparticles as carriers or sensors in medical applications. Because many ENM applications are open, ENMs are released from the systems or devices where they are used. In many cases, ENM releases are to water, either to the sewer system via wastewater from households, hospitals, and industry, or directly to freshwater bodies that receive NPs from, e.g., application of TiO ₂ NPs in sunscreens. ENMs may also be released to soil, be it with biosolids from wastewater treatment plants, or as components of new types of plant protection products. However, it is currently not well known in what amounts and in what chemical and physical forms ENMs actually reach the environment. This calls for emission estimates and environmental fate assessments of ENMs. We describe the processes that govern the environmental fate of ENMs and how these processes can be represented in environmental fate models for ENMs. Environmental fate models are well-established tools in the risk assessment of organic chemicals, but the process descriptions used for organic chemicals are not suitable for ENMs. We show how new process descriptions can be set up for ENMs, with a particular focus on heteroaggregation of ENMs and natural particulate matter, and present results from several environmental fate models for ENMs, along with a summary of currently available ENM emission data required as input to the models. We also review models used to describe vertical transport of ENMs in soil column experiments and highlight areas for further model development.