How can we test plastic pollution perceptions and behavior? A feasibility study with Danish children participating in "the Mass Experiment".

Research suggests that behavior change programs can be fast and cost-effective solutions to plastic pollution alongside traditional environmental policy-making. Furthermore, encouraging change in perception and behavior can be a tool to change consumption and waste handling towards increased circularity, which is of high concern in the EU. Beyond knowledge, predictors of pro-environmental behavior include concern, social norms, nature-connectedness, identity and self-efficacy. Citizen Science (CS) as a way to raise awareness and potentially change behavior show promise within plastic litter monitoring. We tested the feasibility of evaluating a nation-wide citizen science intervention, 'the Mass Experiment' (ME), with school students (age 7-16) in Denmark. With more than 57,000 students signed up for ME, this is to our knowledge one of the largest CS activity on plastic debris targeting young people. As an addition to the core CS activity we developed a voluntary and anonymous questionnaire to study the perceptions and behaviors of the students. We hypothesized that the intervention would increase risk perception, self-efficacy and empowerment as well as self-reported actions. Through 931 pre-surveys and 838 post-surveys aggregated at the team level (n = 48), we found that the intervention had no significant overall effect on team, risk-perception, pro-environmental behaviors, nor self-efficacy or empowerment. However, unexpected patterns emerged for age effects, potentially advising some caution over the design of such CS activities particularly for younger children. We discuss methodological limitations, the high baseline for nearly all variables, the Danish context and the intervention itself and make recommendations for studying future CS interventions.