Are polylactic acid (PLA) microplastics a risk to marine organisms? Acute and chronic effects on the amphipods Gammarus aequicauda

Conventional plastics have become a major environmental concern due to their persistence and accumulation in marine ecosystems. Recently, the development of bio-based polymers, such as polylactic acid (PLA), has gained particular attention as an alternative to limit plastic pollution, as these materials can be degraded under certain conditions. This study investigated the ecotoxicity of polylactic acid (PLA) microplastics (38–220 μm) in the marine amphipod Gammarus aequicauda. To achieve this, juvenile amphipods (2–4 mm) were exposed to PLA in acute toxicity tests to assess mortality after 96 hours. In addition, the effects of chronic exposure (60 days) to PLA microplastics were assessed on the growth and fertility (reproduction, embryonic development and aborted eggs). The results showed a low acute effect with a LC₅₀ of 91.57 mgPLA/L, but exposure to sublethal concentrations (5 and 10 mgPLA/L) of MPs resulted in lower growth and reproduction success compared to control ones. The mean time spent by males and females of G. aequicauda in the precopulation and the time of appearance of the first ovigerous females were not affected by PLA exposure. However, the total number of ovigerous females and the total number of neonates per female were significantly reduced at sublethal concentrations of MP-PLA. Finally, reproductive failures (aborted eggs) were higher at 5 and 10 mgPLA/L. The results provide interesting food for thought and underline that although PLA is known as an innovative biodegradable polymer, its impact on marine biota should not be minimized and the use of biodegradable plastics should be strongly cautioned.