Table 4 Open-ended answers selected to illustrate responses to “If you have indicated that you are worried for any of the above, please briefly state what impacts you are specifically worried about.”

Uncertainty

“[…] the unknown worries me most.” (Female, Early Career, UK)

“Microplastics are still not fully investigated and understood, that's the creepy part of it. […]” (Male, Early Career, Germany)

“the uncertainty – there might be a lot more microplastic e.g. on the seafloor than we know […]” (Female, Early Career, Portugal)

“The unknown effects of plastics on humans, the prevalence of plastics in the natural environment and the harms of plastics to marine life” (Female, Early Career, Netherlands)

Effects/ Impact of (micro)plastics

“physical (consumption/entanglement) and chemical (physiological) effects of materials and additives on organisms. [The] incorporation of plastics and their components into natural compartments (e.g. changes in sand composition) [and I am] mostly concerned about endocrine disruption in humans” (Female, Early Career, Canada)

“chemical leaching impacts” (Female, Early Career, Australia)

“[…] Especially the additives come into account again, as they leach out more easily and/or deeper in the body as microplastics can into the blood circle and accumulate in the body. Same issue with the natural environment.” (Male, Early Career, Germany)

“[…] there are bigger concerns for the natural environment. But reduced energy uptake, additives or chemical adsorption making plastics more harmful to flora and fauna. […]” (Female, Early Career, UK)