# The Harmful Footprint of Aged Biomicroplastics on Algal Development: A Comparative Study of Polylactic Acid, Polyhydroxybutyrate, and Cellulose Acetate

## TL;DR

This study shows that aged bioplastics like PLA, PHB, and CA can harm seaweed growth in lab conditions, raising concerns about their environmental impact.

## Contribution

The study reveals polymer-specific toxicity from aged bioplastics and their degradation products in marine environments.

## Key findings

- Aged PLA and PHB showed significantly increased toxicity to Ulva mutabilis compared to their virgin forms.
- Cellulose acetate (CA) was the most toxic, with an LC50-value of <0.5 mg/mL in aged samples.
- Toxic effects were linked to substances released during photodegradation and hydrolysis of the biopolymers.

## Abstract

Biopolymers are increasingly produced as sustainable
alternatives
to plastics, but their degradation in aquatic ecosystems raises ecological
concerns. This study demonstrates that the photodegradation of polylactic
acid (PLA), polyhydroxybutyrate (PHB), and cellulose acetate (CA)
in artificial seawater substantially increased toxicity under the
elevated laboratory conditions used, compared with virgin counterparts,
adversely affecting the development and growth of seaweeds. Those
aged biopolymers and their leached substances impaired the growth
and development of the green macroalgae Ulva (Chlorophyta)
under standardized conditions, but the ecological relevance at natural
seawater concentrations is likely lower. Chlorophyll a fluorescence, median lethal concentration (LC50-values),
and HR-MS analysis corroborated these findings, emphasizing detrimental
impacts on the fitness and development of Ulva mutabilis. Toxic effects were linked to substances released during photodegradation
and hydrolysis, especially for PLA and PHB. PLA exhibited a 6.7-fold
increase in toxicity following UV exposure; LC50-values
indicate increased toxicity from direct polymer exposure and from
leached compounds at the applied concentration. PHB exhibited the
strongest degradation-related toxicity, with over a 10-fold increase.
CA was the most toxic overall, with an LC50-value of <0.5
mg/mL in aged samples under laboratory conditions. Even nonaged CA
showed effects at these elevated concentrations, but environmental
relevance remains uncertain. Although this is an explorative model
study in lab scale using elevated concentrations, the observed persistence
and (post-)­degradation effects of biomicroplastics highlight potential
polymer-specific toxicity and emphasize the need for further research
on the degradation of biopolymers in the marine environment.