On March 3, 2022, collaborators of the five CUSP research projects gathered for a first-of-its-kind CUSP Thematic Workshop focused on exposure assessment. The workshop titled “Micro/nanoplastic exposure metrics: Priorities for research to inform human health risk assessment” was organized as online event for members of the CUSP research cluster, including the projects AURORA, IMPTOX, Plasticheal, PlasticsFatE, and POLYRISK. It was organized by the cluster’s working group 4 (WG4) on exposure, together with AURORA. Roel Vermeulen of the University Medical Center Utrecht and Utrecht University, and coordinator of the AURORA project, explained the dual purposes of the workshop, namely, on the one hand, sharing inspiration and hands-on experience from experts already working on engineered nanoparticles and microplastics, and on the other hand, for identifying gaps and refining the research priorities of the five cluster projects as they move towards assessing exposure to micro- and nanoplastics (MNPs) in humans.
Two guest speakers introduced exposure assessment: Araceli Sánchez Jimenez of the Spanish Institute for Health and Safety, spoke about “Exposure metrics for future human health risk assessment of micro/nanoplastics: what can be learned from risk assessment of nanomaterials in occupational settings.” Araceli shared her wealth of knowledge from working on this issue, and she stressed that for nanoparticles a linear approach to risk assessment, where exposure and hazard assessments are first carried out, does not work. Instead, in her opinion, both steps (hazard and exposure assessment) need to be performed iteratively and should be focused on real-world mixtures. She concluded that possibly biomarkers of effect are the best exposure metric, as analyzing nanoparticles in complex biological matrices may not be readily feasible due to the very low prevalence of particles.
The second guest speaker, Stephanie Wright of Imperial College London, shared her experience on “Exposure assessment of MNPs, with a focus on approaches for detection in air.” Stephanie stressed that there is a size data gap since most studies look at particles larger than 10 µm, but for central and lower airway exposure, smaller particles are more relevant for exposure. Different analytical methods for assessing different parameters of MNPs are available, and Stephanie compared the benefits and disadvantages of commonly available approaches, showing that a combination of tools likely is most effective. She also stressed the importance of robust statistical tools for evaluating data.
Exposure work in the five CUSP projects was presented by Douglas Walker (AURORA), Mirjana Andjelkovic (IMPTOX), Alba Hernández Bonilla (Plasticheal), Raquel Portela (PlasticsFatE), and Berit Brunstad Granum (POLYRISK). Next, a panel discussion with representatives of the five projects with different disciplinary backgrounds related to exposure assessment revealed that there are different views on how to best approach the issue. Hubert Dirven (POLYRISK) stressed the importance of first clarifying that internal exposure in humans is a reality, by developing methods to analyze MNPs for example in blood. Meike van der Zande (PlasticsFatE) reminded the audience that effect assessment could input into exposure analysis by defining relevant detection limits based on the lowest observed effect concentrations. Mirjana Andjelkovic (IMPTOX) explained that the communication between exposure and hazard assessment specialists is ridden with challenges and needs to be managed carefully. Florian Meirer (AURORA) pointed out the importance of careful sampling to avoid contamination leading to false positive findings. And Thorsten Reemtsma (Plasticheal) questioned whether the focus on detailed exposure assessment should be placed on the notable differences between natural particles and MNPs – albeit, in the absence of a clear understanding to date, of what exactly constitutes these differences.
Matthew Boyles of the Institute of Occupational Medicine, and member of the AURORA consortium, presented the findings of a CUSP-internal survey on exposure. He concluded that currently exposure assessment can be summarized in a “chicken and egg” problem: How to measure? And what to measure? Both need to be defined, but defining one will affect definition of the other – and at present, it seems unclear how to move forward. In this spirit, Roel Vermeulen closed the workshop by saying “if you don’t know where to go, just take one step forward” and then evaluate findings and re-iterate.