Chemistry and Biochemistry: Research Progress Vol. 10

Background: Phthalate esters are representative plasticisers. Understanding how plastic additives are involved in the biodegradation behaviour of polyhydroxybutyrate (PHB) is an indispensable issue for considering future biodegradable material design and additive selection.

Aim: The study aims to evaluate the effects of phthalate ester plasticisers and glycol-based additives on PHB biodegradation by Ralstonia sp. strain C1.

Study Design:  A controlled laboratory experiment was conducted using liquid minimal salt medium (MSM) with PHB as the sole carbon source and individual additives at defined concentrations.

Place and Duration of Study: Muroran Institute of Technology, Muroran, Hokkaido, Japan, 2024–2025.

Methodology: Ralstonia sp. strain C1, isolated from Kurodake in Daisetsuzan National Park, Hokkaido, was cultivated in PHB-supplemented MSM. Phthalate esters (DEHP, DAP, DBP, BBP, DIBP, MBP, DEP) were tested at 200, 500, and 1000 µg/L; glycol-based additives (PEG, DPDM, DBG, TEG) at 2500 mg/L. Residual PHB was quantified every 24 hours over 96 hours by HPLC following acid depolymerisation to 3-hydroxybutyric acid. All experiments were conducted in triplicate.

Results: No significant inhibition of PHB degradation was observed for any phthalate ester additive at 200–500 µg/L. Among glycol-based additives at 2500 mg/L, DPDM and TEG showed minimal effect, whereas PEG exhibited transient inhibition at 24 and 48 hours. DBG showed strong inhibition at 48 hours. Further investigation is warranted to fully characterise the inhibitory effect of DBG.

Conclusion: Phthalate ester plasticisers do not substantially impede PHB biodegradation by Ralstonia sp. C1 at environmentally relevant concentrations. PEG may transiently suppress degradation at high concentrations, possibly through preferential microbial metabolism. These findings provide baseline data for designing PHB-based biodegradable products with environmentally compatible additives.