Nanotechnology is developing rapidly and, in the future, it is expected that increasingly more products will contain some sort of nanomaterial and that more and more applications will be discovered and implemented. Despite increasing research efforts, to date, still little is known about the occurrence, fate and toxicity of engineered nanomaterials (ENMs) when released into the environment. Our knowledge gaps are partly due to the lack of methodology for the detection and characterisation of engineered nanomaterials in complex matrices, i.e. water, soil or air as well as a lack of understanding nanomaterial behaviour and properties. Although more and more data is being published in regard to the fate and ecotoxicity of ENMs in the environment, which shed some light on the possible effects, an important aspect of the environmental risk assessment of ENMs is still completely unknown: the exposure. To be able to quantify exposure to engineered nanomaterials, their detection in environmental matrices, which are highly complex and therefore challenging, is essential. So far, environmental scientists have not been able to solve this problem due to a number of reasons including (1) the fact that nanomaterials are a highly diverse class of substances (e.g. different coatings, core elements, and sizes) with many unique properties, (2) exposure concentrations are anticipated to be very low, (3) a high background of naturally occurring particulate materials and (4) limited information from manufacturers e.g. on application and production of ENMs.
To be able to provide a full environmental risk assessment of nanotechnology, analytical methods have to be (further) developed to be able to detect and quantify ENMs of all types (inorganic and organic particles, wide range of sizes and coatings, different chemical composition, differentiation from natural nanoparticles) in natural waters, soil and air. A first step to achieve this goal is the identification of techniques possibly suitable for nanomaterial detection or techniques that have potential to be suitable after further development. A range of analytical techniques is available including microscopy-based approaches (e.g. transmission and scanning electron microscopy), dynamic light scattering, and size separation approaches (e.g. field flow fractionation and hydrodynamic chromatography) coupled to detection methods such as inductively coupled plasma mass spectrometry. All of these have their disadvantages: some are unable to distinguish between ENPs and natural interferences; some techniques require sample preparation approaches that can introduce artefacts; and others are expensive, time-consuming and complex. A careful selection and possible combination of techniques is therefore needed. The knowledge in this area is still limited, and advancement requires a co-ordinated research to gain a better understanding of the factors and processes affecting ENP fate and effects in the environment as well as the development of more usable, robust and sensitive methods for the characterisation and detection of ENPs in environmental systems.
This study will provide an overview of available analytical techniques to detect nanoparticles in the environment. An account will be presented of the methods that have been developed for natural or engineered nanomaterials in simple & complex matrices, and which could be optimized to provide the necessary tools for the detection of nanomaterials. These include methods based on microscopy, chromatography, spectroscopy, centrifugation, as well as filtration and related techniques. A combination of these is often required and therefore such possible combinations will also be discussed.
The study will also look into other fields of nanotechnology namely nanomedicine and nanotoxicology where staining, tagging and labelling approaches are used to visualise and track nanomaterials. This approaches in combination with suitable detectors could then be applied to distinguish and detect nanomaterials in the environment.
The study will provide valuable insights and comparisons of the most suitable techniques for the detection of different ENMs in environmental matrices discussing advantages, disadvantages and potenital for further developments. The most promising analytical approaches to track ENMs in the environment, but also key limitations that still have to be overcome will be identified. Based on the outcomes of this study recommendations for future work will be given.