As previously described, emerging contaminants are those of historical use but whose negative effects have only recently begun to be studied or synthetic contaminants of recent production or newer use/emerging use. Due to their emerging state, the information available on their production and global distribution in the environment, as well as the damage they cause to the environment and human health, is still limited and practically non-existent in many regions of the world, especially in developing countries.
These contaminants are found in relatively small concentrations, and the technologies for their accurate detection in different environmental media are still under development. However, the upward trend in use means that the release of this class of contaminants and their accumulation in the environment is increasing. Their constant use and their release into the environment pose a medium- and long-term risk, so it is essential to improve knowledge about their emissions, fate in the environment, and impacts on human and ecosystem health.
Micro- and nanoplastics are a clear example of the potential global risk posed by emerging contaminants. Plastics have gained great popularity in recent decades and their use has become widespread throughout the world and in all sectors due to their resistance (da Costa et al., 2016). Micro- and nanoplastics, whether derived from the weathering and fragmentation of larger pieces or from the release of small particles and fibres of various materials, have been found in virtually all ecosystems (Figure 14), including soils, riverbeds, deep ocean and in ice cores from the Antarctic and Artic (Bancone et al., 2020; Kanhai et al., 2020; Kelly et al., 2020). Micro- and nanoplastics are capable of crossing biological barriers and are therefore also widely found in living organisms (da Costa et al., 2016). Due to their small size, micro- and nanoplastics can be transported by runoff to neighbouring areas and water bodies, and they can also be transferred to the atmosphere, where they are subjected to LRT and dry and wet atmospheric fallout at distance (Akanyange et al., 2021; Chen, Feng and Wang, 2020). Around 80 percent of land-based plastics end up in the oceans mainly from rivers and coastal areas, although atmospheric deposition can also contribute significantly (Chen, Feng and Wang, 2020). Marine currents redistribute the waste, which can travel long distances and be deposited again in coastal areas far away from the source (da Costa et al., 2016). Snow at high latitudes and altitudes represents an important stock of micro- and nanoplastics and provides a good record of their emissions (Bancone et al., 2020).
Although there are some studies that have analysed the content of micro- and nanoplastics in different environmental matrices (Kanhai et al., 2020; Koutnik et al., 2021; Okoffo et al., 2021), technical limitations still make it difficult to have a clear global picture of the scope of the problem.
Other emerging contaminants, such as pharmaceuticals and personal care products or nanoparticles, are in a similar situation as micro- and nanoplastics, for which the available information is still limited, and the technology for their detection is still in its early stages or there is no harmonized analysis methodology. However, given the widespread use of these contaminants worldwide, the expected growth in their production, use and disposal, and their relevance to human and environmental health, it is imperative to better understand point sources as well as large-scale diffuse distribution.