Persistence of engineered nanoparticles in a municipal solid-waste incineration plant

Abstract

More than 100 million tonnes of municipal solid waste are incinerated worldwide every year 1 . However, little is known about the fate of nanomaterials during incineration, even though the presence of engineered nanoparticles in waste is expected to grow 2 . Here, we show that cerium oxide nanoparticles introduced into a full-scale waste incineration plant bind loosely to solid residues from the combustion process and can be efficiently removed from flue gas using current filter technology. The nanoparticles were introduced either directly onto the waste before incineration or into the gas stream exiting the furnace of an incinerator that processes 200,000 tonnes of waste per year. Nanoparticles that attached to the surface of the solid residues did not become a fixed part of the residues and did not demonstrate any physical or chemical changes. Our observations show that although it is possible to incinerate waste without releasing nanoparticles into the atmosphere, the residues to which they bind eventually end up in landfills or recovered raw materials, confirming that there is a clear environmental need to develop degradable nanoparticles.The amount of consumer goods containing engineered nanomaterials is expected to grow 2 , and the disposal of these products represents an increasing proportion of the over one billion metric tonnes of municipal solid waste disposed globally 1 . Although landfilling is still common practice in many countries, thermal waste treatment is becoming an important alternative. For example, China plans to expand its capacity for waste incineration from 3% in 2011 to 30% by 2020 (refs 3,4), and the European Commission has been phasing out the landfill of biodegradable waste through legislation 5 . These efforts aim to minimize the amount of untreated landfill waste.Engineered nanoparticles are often designed to be evenly distributed, insoluble and stable when incorporated into consumer goods. However, these characteristics can pose problems when the nanoparticles enter the natural environment 6 . For example, the use of persistent chemicals such as fluoro-chloro-hydrocarbons in fridges has depleted the stratospheric ozone layer 7 , and the use of fibrous solids such as asbestos in building materials has resulted in high incidences of mesothelioma 8 . Furthermore, the widespread use of insecticides has seen various fluorinated compounds, dioxins and halogenated biphenyl compounds accumulate in the food web 9 . It is expected that exposure of the biosphere to persistent nanoparticles may also result in similar undesirable outcomes, so the best precautionary measure is to limit their presence and residence time in the environment. This means that there is a need for proper disposal of persistent nanoparticles.With the growing interest in using persistent nanomaterials in products, we need information on the extent to which they are modified and later made bioavailable through incineration. Nanowaste is treated directly or indirectly. For instance, wastewater treatment plants efficiently...

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