The existence of nanomaterials (materials containing nanoparticles) itself is not a hazard. Only some aspects of it are harmful, especially their mobility and enhanced reactivity. Only when certain aspects of certain nanoparticles are harmful to biology or the environment, we face a real hazard.
To discuss the impact of nanomaterials on health and the environment, we must distinguish two types of nanostructures:
Nano-sized particles are assembled on a substrate, material or device on a nanocomposite, nanosurface structure or nanocomponent (electronics, optical sensors, etc.), also known as fixed nanoparticles.
"Free" nanoparticles, regardless of whether they are stored in certain steps of production or used as individual nanoparticles.
These free nanoparticles may be nano-sized single elements, compounds, or complex mixtures, such as "coated" nanoparticles or "core-shell" nanoparticles in which one element is coated with another substance.
In modern times, the accepted view is that although we need to focus on materials with fixed nanoparticles, free nanoparticles are the most urgent concern.
Because nanoparticles are so different from their daily counterparts that their harmful effects cannot be derived from known toxicity. This discussion of the health and environmental impact of free nanoparticles is of great significance.
What’s more complicated is that when we discuss nanoparticles, we must know that the powder or liquid containing nanoparticles is almost never monodispersed, but has many different sizes within a certain range. This makes the experimental analysis more complicated, because large nanoparticles may have different properties from small ones. Moreover, nanoparticles have a tendency to polymerize, and polymerized nanoparticles have different behaviors from individual nanoparticles.