Ultrasonic-assisted biodegradation of endocrine disrupting compounds by Pseudomonas putida the importance of rhamnolipid for intermediate product degradation

Abstract

The present study aimed to completely remove estrogens, including oestrone(E1), oestradiol(E2), oes-triol(E3), 17α-ethinylestradiol(EE2) and bisphenol-A(BPA), from soil using Pseudomonas putida(P. putida). A central composite design was developed to determine the optimal conditions of three variables(ultrasonication time, quantity of P. putida, and concentration of added rhamnolipid) for the removal of the estrogens, and the biodegradation rates of the estrogens were investigated under the optimum conditions. Moreover, a quantitative structure-biodegradation relationship(QSBR) was used to analyze the effect of the estrogenic physicochemical properties on the enhancement of the biological degradation. The optimal conditions were an ultrasonication time of 3 min, a P. putida quantity of 8 mL, and a rhamnolipid concentration of 100 mg/L. These conditions resulted in removal of 100%, 94.86%, 94.90%, 96.56% and 94.56% of E1, E2, EE2, BPA and E3, respectively after 7 d. The degradations were more rapid and com-plete than those reported in previous studies, indicating the suitability of the adaptation of P. putida to estrogen de-gradation under conditions of ultrasonic-assistance and adding rhamnolipid; improvement was particularly apparent from the complete degradation of E3. Based on a Pearson correlation analysis, the estrogen molecule polar surface area(PSA) and surface tension were significantly related to the biodegradation effect. An analysis of the QSBR model with the estrogen biodegradation rates as a dependent variable and the PSA and surface tension as independent va-riables indicated that larger PSA caused decreased estrogen biodegradation, while the biodegradation progress was dominated by the surface tension of the estrogens. The interaction of PSA and surface tension had an antagonistic ef-fect on the biodegradation of estrogens. Therefore, rhamnolipid/ultrasonication can significantly improve the biode-gradation rates of oestrogens in soil, while simultaneously adjusting other environmental conditions would influence and control the biodegradation processes of estrogens.