The plastic size spectra: Assessing the size structure of plastic particles across the land-water ecotone

Plastics of different types and sizes pollute most of Earth's environmental systems. Here, we used size spectra analysis (SSA) to evaluate and characterize size-frequency patterns of plastic pollution across the land-water ecotone of 20 urban lakes. We first tested the general hypothesis that plastic particles in the environment reflect a detectable and inverse size-frequency pattern as large plastics regularly breakdown in increasingly smaller pieces. To further evaluate the utility of SSA, we tested whether slope (λ) and intercept (Γ) coefficients from lake-specific models were sensitive to distinguish trends among lake zones. Overall, our findings detected an overall inverse relationship between particle counts (#/m²) and binned particle length, confirming the presence of a plastic size spectra for all aggregated data. We further improved the explanatory power of SSA models by (1) separating thin films from thicker plastic fragments and by (2) assessing sampling environments (i.e., upland vegetation, shoreline sediments, offshore sediments) separately. Doing so revealed statistically distinct size-frequency gradients that tracked the shift from land to water for both films and fragments. Analysis and comparison of SSA models also confirmed that coefficients were sensitive enough to detect differences among lake zones. All told, the SSA framework was successfully used to detect and describe several patterns of plastic pollution in the environment. This analytic framework holds promise for developing hypothesis-driven studies to all plastics rather than focusing on small or large particles.