Growth and chlorophyll-a responses of marine microalgae to biodegradable polypropylene microplastic leachates: an initial toxicity assessment

Biodegradable plastics are increasingly promoted as alternatives to conventional plastics; however, their degradation may release leachates containing potentially harmful compounds. Complementary field observations on microplastic occurrence along Indonesian coasts underscore the environmental relevance of this study. In marine environments, such leachates may affect algal communities. This study evaluated the toxicity of leachates derived from biodegradable polypropylene (PP) microplastics on three marine microalgal species (Chlorella sp., Tetraselmis sp., and Navicula sp.). Fourier Transform Infrared (FTIR) analysis confirmed the polymer identity of the biodegradable PP material used in the experiments. Toxicity assays were conducted under controlled laboratory conditions following 96 h exposure. Growth was assessed based on changes in cell density, and chlorophyll-a content was measured for species exhibiting significant inhibition. Preliminary range finder tests revealed species-specific responses. Navicula sp. did not exhibit clear concentration-dependent inhibition and was therefore excluded from the definitive test. Definitive testing was conducted on Chlorella sp. and Tetraselmis sp., both of which showed concentration-dependent growth inhibition. Chlorella sp. exhibited the highest sensitivity (IC₅₀-96 h = 0.49 mg L⁻¹), followed by Tetraselmis sp. (IC₅₀-96 h = 37.84 mg L⁻¹). These findings indicate that biodegradable polypropylene microplastic leachates can induce measurable sublethal effects in marine microalgae, supporting the need for further long term ecotoxicological evaluation.