Apart from the natural sources of the nanomaterials present in the environment like colloids in soil and water, the manufacture of synthetic nanomaterials has also contributed to the increase in the amount of the nanoparticles present in the environment. The unique properties of the nanomaterials such as mechanical, optical, electrical conductivity, catalytic, etc due to their size in nanoscale has resulted in an exponential growth in the development of various engineered and manufactured nanomaterials for their exploitation in different fields. The development of a wide range of nanomaterials including carbon nanotubes, nanopolymers, quantum dots, dendrimers, nanofibers, nanowires, etc are constantly expanding the synthetic preparation of the NPs. Due to the tremendous increase in the production of NMs, their release into the environment affects the ecosystem health, which is an increasing concern for the regulatory authorities. It necessitates the setting of different guidelines that will give adequate environmental protection as well as help in the growth and development of nanotechnology.
The effect of the accumulation of NMs after uptake is not clearly known, as much research has not been conducted in this area. However, it is assumed that the different organisms living in the environments loaded with NPs would incorporate the NPs within their bodies mainly through the gut, which then gives rise to the possibility of their translocation within the body. Various ecotoxicological studies have been conducted on the different animal models e.g. daphnids. Uptake of the NPs and their translocation from the gut to the reserve fat droplets has been demonstrated successfully. However, the exact mechanism of the whole process is still under investigation. It has been suggested that the entry of NPs is also possible by diffusion through the plasma membranes as well as by endocytosis or adhesion processes.
The release of the NPs into the environment could be intentional or unintentional. The intentional release includes the release of iron NPs into the groundwater for remediation and is controlled in nature. However, the unintentional release of the NPs includes the emissions in atmosphere as well as the solid or liquid waste streams from the production facilities and is uncontrolled. The NPs present in fabric, health care products, cosmetics, etc also enter the environment proportional to the use of the products. Although, the toxicity mechanisms related to the NMs have not been completely elucidated, the different cellular mechanisms in the human body in which the NMs may have adverse effect include
a) the disruption of cell membranes leading to loss of membrane integrity;
b) protein oxidation and loss of structure and function of proteins;
c) genotoxicity due to damage in nucleic acids;
d) energy transduction interruption and disruption in intracellular communication;
e) reactive oxygen species (ROS) formation leading to cell damage; and
f) release of toxic components
Ecotoxicological studies on other aquatic organisms and microorganisms have shown the toxic effects of NPs. In case of microorganisms, they have been found to inhibit their growth acting as antibacterial agents and are toxic to other microorganisms due to the formation of ROS species. In case of other aquatic animals, they have been found to accelerate the lipid peroxidation in the brain acting as neurotoxins and causing changes in the gene expression as well as affecting the developmental stages of the animals post fertilization. The toxicity studies of NPs on soil faces a number of issues due to the presence of manufactured as well as natural NPs that limit the knowledge regarding the effect of different NPs on soil and terrestrial plants. Hence, in-depth study related to the interaction of the NPs with the soil components is essential. The repercussions of the interactions between the NPs and natural organic matter on the fate of ecosystem can be known by the study of the behaviour, bioavailability and characterization of the NPs.