Whilst ENPs may be emitted during the manufacturing process, the route of input to the environment will primarily depend on the end use of the ENP (Boxall et al. 2007). For example, pharmaceuticals, cosmetics and sunscreens may be emitted to the sewage system following excretion from the patient or during washing and showering. Once they have passed through the sewer system, they may be released to surface waters. Sunscreens and other cosmetics applied on skin may also enter surface waters directly during swimming or bathing. Waste cosmetics are most likely to be disposed of in household waste that may be landfilled or incinerated. Paints containing ENPs can have both industrial and domestic uses. It is possible that runoff from painted surfaces and domestic use of paints could result in discharges to sewers. In instances where paint is applied to underwater structures or ships, ENPs may be released directly to surface waters. The use of ENPs in fuel and catalysts in vehicles will result in direct aerial emission ofparticles through vehicle exhaust or emissions to the surface waters and sewers through leakage and spills. Waste lubricants are most likely to be disposed of as special waste that may be landfilled or incinerated. The use of nanoparticles in treatment of polluted water is likely to result in direct emissions to surface and groundwaters or soil. ENPs used to deliver agrochemicals will be released directly to soils and surface waters.
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