LAUSR

Plastic pollution remains a global anthropogenic threat due to its universal use in our daily life and ubiquitous presence in all environmental compartments (Geyer et al. 2017). Despite large and increased research efforts within this field (Sorensen and Jovanović 2021), clear guidelines on safe concentrations, thresholds and ultimately adverse effects for environmental health are lacking (Toussaint B et al 2019.). This can be largely attributed to the fact that micro- and nanoplastics are, unlike other groups of contaminants, an extremely heterogeneous group. They vary in shape, size and chemical composition and each of these parameters may influence the behaviour, fate, transport and effects. In the past, most studies have focussed on homogenous pristine micro- or nanoplastics in a defined shape and size class (Paul-Pont et al. 2018). While these studies certainly have value in unravelling modes of action and mechanisms of toxicity, the gap between laboratory and natural exposure is large and these studies remain far from environmental reality. Micro- and nanoplastics can actually be seen as a mixture of different types of particles that can further interact with the environment. These interactions include environmental weathering, absorption/desorption of chemicals and additives (Lusher et al. 2017; Koelmans et al. 2016) and biofilm formation which may lead to pathogen transfer (Huang et al. 2021). At present, more and more studies are addressing these issues and the current knowledge gaps are primarily related to small micro- and nanoplastics and their fate, transport and ultimately environmental risk. This is can be partly attributed to analytical challenges in terms of extraction, quantification and characterization in complex environmental matrices where only recently significant progress was made (Silva et al 2018). This special issues integrates publications that will contribute scientific knowledge to (1) improved analytical methodologies for complex environmental matrices, (2) effect assessments of micro- and nanoplastics accounting for physico-chemical properties as well as environmental interactions and (3) integrated perspectives and analyses on risk assessment. This article is protected by copyright. All rights reserved.