New products containing nanomaterials are constantly being released to the market and used for diverse purposes. As a result, growing amounts of products containing nanomaterials enter the end-of-life phase of the lifecycle and are disposed. Nanowaste in solid or liquid form is currently treated as normal waste and is hence disposed via the existing waste management systems. Also, nanowaste may enter the environment directly through littering. Prevention of littering and illegal dumping of waste is generally achieved through good practices in waste management and education. However, to date there is little knowledge on the environmental release of nanomaterials from waste.
Nanowaste: collective term for many different types of waste
Most products containing nanomaterials will ultimately end as waste. Due to the diverse applications of nanomaterials, however, nanowaste is not a uniform type of waste. Nano waste can enter the waste system through various sources such as household waste, industrial waste as well as waste from hospitals or research institutes. Currently, there is no official definition of the term “nanowaste”. One proposed definition is, “separately collected or collectable waste materials which are or contain engineered nanomaterials”. The incorporation of the nanomaterials in the waste depends on the initial product it was used in. For example, nanomaterials may be tightly embedded in a solid matrix (e.g. carbon nanotubes in displays) or are present as free particles or agglomerates thereof, in liquids (such as titanium dioxide in some sunscreens) .
To estimate the amounts of nanowaste, information is needed on:
- number of products on the market containing engineered nanomaterials
- the expected lifespan of these products
- characteristics of the waste matrix
It has been estimated that plastic is the waste fraction most frequently containing engineered nanomaterials in Europe in general.
Nanowaste during waste management
The waste management systems are organised differently in the European countries, and include different technologies e.g. recycling, incineration and landfilling. The latter comprising of different processing steps such as shredding. Hence, solid nanowaste will be handled using different waste treatment technologies depending on the local waste management systems [2-4].
Outside Europe, landfilling may be the predominant solution . Partly, the nanomaterials will also be discharged into the water and further processed under controlled conditions in waste water treatment plants. Examples for this are titanium dioxide nanoparticles contained in sunscreen which are removed by showering or the nanoparticle-containing leachate from solid waste.
Currently, the European Waste Legislation does not foresee any specific regulation for the treatment of nanowaste. Hence, solid waste containing nanomaterials enter the waste management systems as part of the waste material. However, the regular solid waste management systems were not originally designed for handling nanomaterials. Hence the presence of nanowaste raises concerns for humans and the environment as possible emissions caused by incineration, leakage of landfills or during recycling processing may lead to increased environmental concentrations of nanomaterials.
In the course of the different treatment steps, nanomaterials may be released from the raw waste. During recycling, the size of the waste is reduced mechanically by crushing, shredding or grinding, which may lead to the release of nanomaterial from the waste. During incineration, the waste matrix is almost completely burned at very high temperatures and hence the nanomaterials may be volatilized. In landfilling of nanowaste, the waste matrix is likewise disintegrated and particles may be released. Hence, the transformation of the waste matrix and the velocity of nanomaterial release during the waste phase will strongly depend on the type of process used for waste handling.
Release into the environment?
Nanomaterials contained in nanowaste may be released to the environment via common waste treatment processes thereby also entering the different environmental compartments air, water and soil. For example, nanomaterials may become airborne due to mechanical treatments during recycling or due to the combustion processes during incineration. Release into water may occur also during recycling operations or during the long-term disposal in landfills where rainwater is not collected or fully retained. Further, the released nanomaterials may leach into the soil.
In general, the waste treatment processes include systems to retain any material emitted from the waste, e.g. by filtering systems, gas cleaning systems or closed landfills. However, the effectiveness of such systems to prevent release of nanomaterials into the environment is not fully clear for all pathways.
Hence, the specific environmental exposure will depend not only on the specific waste treatment processes and release behaviour but also on the properties of the nanowaste (solid / liquid) and the used nanomaterials respectively. The results of few case studies have indicated that the potential for environmental exposure is low to medium, while it is highlighted that generalisation of such findings is not possible [1, 6-11].
The current data situation does not allow for any generalised statements on the environmental exposure and risks posed by nanomaterials in the waste. Overall, current knowledge gaps include different parts and aspects of the waste management system, including quantification and characterisation of waste flows containing nanomaterials, estimation of nanomaterials release in landfill conditions, fate of nanomaterials during waste incineration, and working exposure during recycling operations.
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