Many of these nanoparticles have a fairly short lifespan because they tend to agglomerate or dissolve in water. In addition, the human body has developed various mechanisms for filtering out or removing some of these particles. may The effects of exposure to engineered nanoparticles be different from the effects caused by naturally occurring nanoparticles. Engineered nanoparticles may be better able to evade the body's defenses because of their size or pro tective coatings. Moreover, the health and environmental risks raised due to the exposure to engineered nanoparticles need further study. At present, research efforts in nanotox cology are just beginning, and less than 4 of all current U.S. governmental research expenditures on nanotechnolo gy are targeted at studying effects on human health and the environment. Again the potential environmental impacts of exposure to nanomaterials are even less well understood than the human health effects. Therefore, extensive studies are required to understand the mechanism for nano- materials toxicity and their impacts on natural environment.