Microplastic particles (MPs) less than 5 mm in size swirl and bob in freshwaters and seas around the world. To familiarize college biology students with the pressing issue of microplastic pollution and designing their own experiments, I assigned investigatation into whether marine copepods (Tigriopus californicus) or freshwater cladocerans (Daphnia magna) ingest MPs in the laboratory.

Groups of students produced a title, hypothesis, and annotated bibliography. They developed their experiments in a project planning table. They carried out three weeks of experiments. Students wrote papers or gave poster presentations. They wrote reflections that revealed expected gains, such as recognition of the importance of sample size, and more nuanced gains, such as developing personal views on working with live organisms.

The students found that 20 µm of blue MPs could be seen within the digestive tract and released fecal pellets of Tigriopus californicus within 24 hours. And, 20 µm of red MPs accumulated in the digestive tract of Daphnia magna within two days. The ingestion did not increase death rates over controls (in keeping with much published research on this topic). Students had the opportunity to see and reflect on the direct interaction of organisms with plastic pollution.