Assessment of microplastics pollution in Biscayne Bay: Spatial distribution, tidal variability, and polymer hazard analysis

Microplastics (MPs) are pervasive and ubiquitous emerging contaminants potentially affecting both the environment and human health. This study investigates the occurrence and spatial distribution of MPs in Biscayne Bay, evaluating the influence of tidal cycles on MP abundance and assessing their potential hazard based on polymer type. Surface water samples were collected using a plankton net trawl method. This study found an average MP abundance of 7.16 ± 1.57 particles/m, mainly low-density polymers such as Polypropylene (40%) and Polyethylene (24%). Detected MPs were mainly fragments (63.4%) and fibers (21.3%), within a size range of 300-1000 μm. As expected, tidal cycles influence the abundance and distribution of MPs, with the low tide grab samples exhibiting a significantly higher (38.8 ± 10.50 particles/L) MP abundance than the high tide samples (17.2 ± 4.02 particles/L). MP polymer hazard assessment reveals that PVC hazard level is of critical concern, and Miami River (MR) exhibited the highest level (level IV) due to the accumulation of hazardous MPs. Polymer hazard index (H) is negatively correlated with MP abundance (ρ = -0.37, p > 0.05). This study provides baseline data for understanding the occurrence, and distribution of MPs in Biscayne Bay, and the findings underscores the need for targeted and integrated management intervention to address MP pollution.