Polyhydroxybutyrate (PHB) is a biodegradable polyester that has drawn increasing attention as a sustainable alternative to conventional plastics. Although PHB is widely recognized for its biodegradability, its persistence in certain environments has raised concerns about its actual environmental impact. In particular, the role of plasticizers commonly added to bioplastic formulations remains poorly understood regarding biodegradation.

In this study, we examined the effect of phthalate esters and glycols on PHB degradation using Ralstonia sp. C1. The bacterium was cultivated in LB medium at 30°C for 18 hours, washed to remove residual nutrients, and transferred to a defined medium containing 0.5% (w/v) PHB. Plasticizers were applied at concentrations ranging from 50 to 2000 μg/L.

Cultures were incubated aerobically at 30°C for 96 hours with shaking, and samples were collected every 24 hours. Residual PHB was measured using HPLC.

Under all tested conditions, over 50 percent of the PHB was degraded within the first 24 hours, and more than 98 percent degradation was observed by the end of the incubation period. The degradation rates were comparable regardless of the presence or absence of additives.

Additionally, no evidence was found that Ralstonia sp. C1 metabolized the additives. These results suggest that phthalate and glycol plasticizers do not inhibit the microbial degradation of PHB or alter its availability to degrading bacteria.

This study provides the first clear evidence that environmental isolates can effectively degrade PHB containing such additives. The findings offer valuable insights into the environmental behavior of bioplastics and support the continued development of additive-containing biodegradable materials for commercial use.