Effects of High-Concentration Phthalate Esters on the Biodegradation of Poly(3-hydroxybutyrate)

In recent years, biodegradable plastics have attracted attention as a solution to plastic waste pollution, increasing the demand for improved biodegradability. Poly(3-hydroxybutyrate) (PHB) is one of the most widely studied polyhydroxyalkanoates (PHAs). Phthalate esters are commonly used as plasticizers, often exceeding 20 wt.% in many conventional plastic products, but some exhibit reproductive toxicity and endocrine-disrupting effects. These additives may also influence the microbial degradation of PHB. Since the plasticizing effect of phthalate esters decreases above 20 wt.% in PHB, this study investigates the biodegradation of PHB in the presence of various additives at concentrations up to 20 wt.%. Biodegradation experiments were conducted using Ralstonia sp. strain C1 in mineral salts (MS) medium containing PHB. Dibutyl phthalate (DBP) and diethyl phthalate (DEP) were added at 10 and 20 wt.% and biodegradation was monitored every 24 h for 96 h in comparison with an additive-free control. After 96 h, the addition of DBP inhibited PHB biodegradation. Compared with the control, 18% and 40% more PHB remained in the presence of 10 wt.% and 20 wt.% DBP, respectively. In contrast, DEP enhanced PHB biodegradation. Compared with the control, PHB degradation increased by 34% and 12% in the presence of 10 wt.% and 20 wt.% DEP, respectively. In our previous study, no significant effects on PHB degradation were observed at lower additive concentrations. The results of this study showed that dibutyl phthalate inhibited biodegradation, while diethyl phthalate promoted it. These findings suggest that dibutyl phthalate may be microbially toxic at high concentrations, and that diethyl phthalate may be usable as a carbon source. Further investigation into these possibilities is necessary.