In situ plastic fragmentation between two contrasting ecosystems in the Atlantic

The mechanical fragmentation of a conventional (low-density polyethylene, LDPE) and a biodegradable plastic polymer (polybutylene sebacate-co-terephthalate, PBSeT) was investigated in two contrasting coastal environments in the Atlantic: The Equatorial Brazilian Amazon coast and the Spanish temperate coast of Galicia. The experiment consisted of in situ exposition of the two polymers to natural conditions in the marine environment and in two distinct depths, near the bottom and at the subsurface. Cellulose strips were used as positive control. Our results showed that PBSeT and cellulose degraded faster than LDPE, with complete fragmentation of PBSeT occurring in 90 days in the Amazon coast and 120 days in the Spanish coast, with complete cellulose disintegration before 60 days for both the locations. LDPE showed minimal fragmentation in both environments. Higher water temperatures, turbulence, hydrodynamic features such as the macrotidal regime and accelerated colonization in the Amazon likely accelerated fragmentation. These findings highlight the variability in plastic fragmentation in different environments and the need of future research to understand the main environmental variables responsible for such variation.