The promotion of phthalate esters bioaccessibility by heavy metals during biodegradation: Insight from compound-specific stable isotope analysis

In this study, we investigated the inhibition extent, pattern, and mechanism of four heavy metals ion (Cd 2 + , Cu 2+ , Ni 2+ , Zn 2+ ) on di-n-butyl phthalate (DBP) biodegradation by Bacillus megaterium . The inhibitory extent of DBP biodegradation depends on a variety of factors, including the metals’ nature, metals concentration, and initial DBP concentration. The presence of Cd 2+ , Cu 2+ , or Ni 2+ has been found to exert strong and comparable inhibitory effects on the 2 mg/L DBP biodegradation, while Zn 2+ has a slightly inhibitory effect. In addition, the inhibitory effects of heavy metals on DBP biodegradation rate diminished as the initial DBP concentration increased from 2 to 10 mg/L. The inhibitory effects of individual metals on DBP biodegradation by Bacillus megaterium were found to be dose-dependent. The inhibitory effects of metal ion mixtures could be greater, similar, or less than the greatest inhibition of individual metals. Positive δ 13 C (+2.54 ‰) and nonsignificant δ 2 H (< ± 5 ‰) isotopic fractionation occurred during DBP biodegradation by Bacillus megaterium with or without the addition of heavy metal ions. The ε C were −1 . 45 ± 0.36 ‰, −1.54 ± 0.31 ‰, −1.77 ± 0.55 ‰, and −1.72 ± 0.28 ‰ when 1, 3, 5, and 10 mg/L Ni 2+ was added, respectively, which showed a decreasing trend of ε C with increased heavy metal concentrations. This could be attributed to the promotion of DBP bioaccessibility by heavy metals. • Inhibition of mixtures on biodegradation was more complex than single metal ions. • The inhibition of heavy metals diminished as the pollutants concentration increased. • Heavy metals have effects on isotopic fractionation during pollutant biodegradation.