Table 5.

Environmental risks of nanomaterials.

Environment Type	Environmental Risks	Ref.
Air	Nanoparticles can be formed in urban areas, several combustion sources (engines, biomass burning, power generation plants) are directly emitting carbonous nanoparticles to the atmosphere. They classify as nanosized pollutants in industrialized areas.	[277]
Soil	Metal nanoparticles from the utilized biomass can be transferred to soil by nanoparticles sorption. Therefore, the high Ag concentration in the resulting biomass might restrict its agricultural use; the concentration would act as an inhibitor of bacterial growth (including the beneficial microorganisms present in the soil, such as nitrogen-fixing bacteria).	[278,279]
Water	Antimicrobial metal and metal oxide nanoparticles have a toxic effect in model organisms (e.g., nematodes, zebrafish embryos) suggesting that cumulative exposure to silver nanoparticles might significantly affect the ecological balance of aquatic environments. It is crucial to carefully assess the possible eco-toxicity when large amounts of manufactured oxide nanoparticles are released in natural waters.	[280,281,282,283,284,285]
Humans	Exposure to carbon nanomaterials and silica nanoparticles can cause lung inflammation, granuloma, and fibrosis. Carbon, Ag, and Au nanomaterials can reach also other organs (e.g., central nervous system). Quantum dots, carbon, and TiO2 NPs can go through the skin barrier. MnO2, TiO2, and carbon nanoparticles may enter the brain via olfactory neurons in the nasal epithelium. TiO2, Al2O3, carbon black, Co, and Ni NPs might be more toxic than micro-particles.	[286,287,288]
Microorganisms	Toxicities associated with nanoparticles in microorganisms are mainly related to their nanosize effect that causes membrane disorganization, generation of reactive oxygen species (ROS), and in some cases, oxidative DNA damage.	[289,290]
Plants	Nanoparticles may also adhere to the roots of the plants and cause physical or chemical toxicity to plants. Some nanoparticles were observed to be nontoxic to plant (SiO2 NPs), but some studies observed the toxic effect due to decrees in pH of the media after addition of these nanoparticles. The Zn- and Al-containing nanoparticles negatively affect germination and root growth of agriculturally relevant plant species.	[291,292]