Nanomaterials can be both incidental and engineered. Engineered nanomaterials (ENMs) are nanoparticles that are made for use, are defined as materials with dimensions between 1 and 100 nm, for example in cosmetics or pharmaceuticals like zinc oxide and TiO2 as well as microplastics. Incidental nanomaterials are found from sources such as cigarette smoke and building demolition. Engineered nanoparticles have become increasingly important for many applications in consumer and industrial products, which has resulted in an increased presence in the environment. This proliferation has instigated a growing body of research into the effects of nanoparticles on the environment. Natural nanoparticles include particles from natural processes like dust storms, volcanic eruptions, forest fires, and ocean water evaporation.
Sources Products containing nanoparticles such as cosmetics, coatings, paints, and catalytic additives can release nanoparticles into the environment in different ways. There are three main ways that nanoparticles enter the environment. The first is emission during the production of raw materials such as mining and refining operations. The second is emission during use, like cosmetics or sunblock getting washed into the environment. The third is emission after disposal of nanoparticle products or use during waste treatment, like nanoparticles in sewage and wastewater streams. The first emission scenario, causing 2% of emissions, results from the production of materials. Studies of a precious metals refinery found that the mining and refining of metals releases a significant amount of nanoparticles into the air. Further analysis showed concentration levels of silver nanoparticles far higher than OSHA standards in the air despite operational ventilation. Wind speed can also cause nanoparticles generated in mining or related activities to spread further and have increased penetration power. A high wind speed can cause aerosolized particles to penetrate enclosures at a much higher rate than particles not exposed to wind. Construction also generates nanoparticles during the manufacture and use of materials. The release of nanoscale materials can occur during the evacuation of waste from cleanout operations, losses during spray drying, filter residuals, and emissions from filters. Pump sprays and propellants on average can emit 1.1 x 10^8 and 8.6 x 10^9 particles/g. A significant amount of nanoparticles are also released during the handling of dry powders, even when contained in fume hoods. Particles on construction sites can have prolonged exposure to the atmosphere and thus are more likely to enter the environment. Nanoparticles in concrete construction and recycling introduce a new hazard during the demolition process, which can pose even higher environmental exposure risks. Concrete modified with nanoparticles is almost impossible to separate from conventional concrete, so the release may be uncontrollable if demolished using conventional means. Even normal abrasion and deterioration of buildings can release nanoparticles into the environment on a long-term basis. Normal weathering can release 10 to 10^5 mg/m^2 fragments containing nanomaterials. Another emission scenario is release during use. Sunscreens can release a significant amount of Titanium dioxide (TiO2) nanoparticles into surface waters. Testing of the Old Danube Lake indicated that there were significant concentrations of nanoparticles from cosmetics in the water. Conservative estimates calculate that there were approximately 27.2 micrograms/L of TiO2, if TiO2 was distributed throughout the entire 3.5*10^6 M^3 volume of the lake. Although TiO2 is generally considered weakly soluble, these nanoparticles undergo weathering and transformation under conditions in acidic soils with high proportions of organic and inorganic acids. There are observable differences in particle morphology between manufactured and natural TIO2 nanoparticles, though differences may attenuate over time due to weathering. However, these processes are likely to take decades. Copper and zinc oxide nanoparticles that get into the water can additionally act as chemosensitizers in sea urchin embryos. It is predicted that for animals in aquatic systems sunscreen is probably the most important exposure route to harmful metal particles. ZnOs from sunblock and other applications like paints, optoelectronics, and pharmaceuticals are entering the environment at an increasing rate. Their effects can be genotoxic, mutagenic, and cytotoxic. Nanoparticles can be transported through different mediums depending on their type. Emissions patterns have found that TiO2 NPs accumulate in sludge-treated soils. This means that the dominating emission pathway is through wastewater. ZnO generally collects in natural and urban soil as well as landfills. Silver nanoparticles from production and mining operations generally enter landfills and wastewater. Comparing different reservoirs by how readily nanoparticles pollute them, ~63-91% of NPs accumulate in landfills, 8-28% in soils, aquatic environments receive ~7%, and air around 1.5%.
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