Lightweight expanded clay aggregates in a coastal ecosystem: a spatial snapshot of an overlooked marine litter component.

Marine litter research has largely focused on plastic debris, while other persistent anthropogenic materials remain poorly documented. Lightweight expanded clay aggregates (LECA) are inorganic, porous materials widely used in construction, environmental engineering, and horticulture, and have recently been identified as an abundant litter item on the Portuguese coast. This study presents the first spatial assessment of the occurrence and distribution of LECA in a coastal environment. Shoreline surveys were conducted at eight sites along the coast of Aveiro (Portugal), encompassing oceanic and lagoon-facing beaches, and a channel adjacent to port infrastructure. Particles were collected along 50 m transects and subsequently characterised for selected physical properties. LECA was detected at all sampled sites, with abundances ranging from 4 to 2006 per 50 m. Higher counts were observed near the central lagoon and close to its inlet, suggesting a possible link to port-related cargo handling activities, while tidal hydrodynamic processes may contribute to transport to adjacent areas. Particle densities (0.53-0.67 g/cm) and morphometric properties were consistent with commercially available LECA. However, the study cannot determine whether detected particle fragmentation reflects environmental processes or pre-existing material properties. Overall, these results confirm the presence of LECA in the study area and highlight the need for further research to better understand its sources, environmental behavior, and potential ecological implications.