Microplastics are tiny fragments of plastic that can be difficult to see and have become a growing concern in coastal environments. This project focused on Pacific Beach in San Diego, a popular destination for recreation. The presence of microplastics is important because these particles may accumulate in beach sediments, get ingested by small marine organisms, and potentially end up in seafood humans eat.

The primary hypothesis was that microplastic concentrations would increase as the sampling sites approached the ocean. This study could inform where on the beach and what tide level people experience greater exposure. Understanding these patterns can guide more effective environmental management to encourage policies to reduce pollution at its source while helping individuals reduce their own health risks.

To test this hypothesis, ten sand samples were collected along a straight line from the sidewalk toward the waterline, covering roughly 200 feet. Chemical treatments involving hydrogen peroxide (H₂O₂) and sodium chloride (NaCl) were used to isolate microplastics from other materials in the sand. After filtration, the filters were examined using a microscope to identify and count the microplastic particles.

The data showed that samples taken closer to the ocean contained more microplastic particles than those collected farther inland. Some samples near the shoreline had over one thousand microplastics, while locations near the sidewalk had fewer. Despite these findings in the sediment, no microplastics were detected in the single water sample collected at the ocean’s edge during this particular time.

These observations supported the initial hypothesis: microplastics accumulated in greater numbers as the sampling sites approached the ocean. However, the absence of detectable microplastics in the water sample raises questions about how the microplastics got there. Future research could focus on understanding when microplastics accumulate, how long they remain in the sediment, and the extent of their impacts on small marine organisms and human health.

Figure 1 Graph representing microplastic counts at each sampling site for Set A (Blue), Set B (Red), and the Average (Yellow). The sidewalk, hide tide line, and the ocean are visually represented to indicate where these are in relation to the sampling locations. We can observe the spike right after the hide tide line and then an increase as we get closer to the ocean.