Investigating the Impact of Polyethylene Microplastic Concentrations on the pH Trajectory and Acidification Rate of Artificial Seawater

This investigation explores how varying concentrations of polyethylene microplastics (0, 20, 50, and 100 mg L⁻¹) affect the pH trajectory and acidification rate of artificial seawater exposed to carbon dioxide.

Using a digital pH meter and a controlled CO₂ injection method, the student measured pH changes over 15 minutes across five trials per concentration. The results demonstrate a negative correlation between microplastic concentration and the rate of pH decline, suggesting that hydrophobic surface layers inhibit CO₂ dissolution and slow the acidification process.

The exemplar is characterized by its rigorous uncertainty propagation, detailed qualitative observations, and a comprehensive evaluation of experimental limitations, such as manual injection variability and the use of a single polymer type.