Effects of sodium benzoate and heavy metals on biodegradation of 2,2',4,4'-tetrabromodiphenyl ether by Rhodococcus jostii RHA1

We investigated the effects of co-metabolic substrate, sodium benzoate, and heavy metal ions (i.e., Cd(II), Cr(III), Cu(II), Ni(II), Pb(II)) on the biotransformation of 2,2',4,4'-tetrabrominated diphenyl ether (BDE-47), which is a PBDE congener commonly found in the e-waste contaminated sites, by Rhodococcus jostii RHA1 (RHA1). In the co-metabolic degradation reactors, 1000 ppb and 1200 ppb of BDE-47 were degraded 54.58% and 60.98%, respectively; however, 100 ppb, 250 ppb and 500 ppb of BDE-47 were hardly transformed. With heavy metals co-existing, 1000 ppb of BDE-47 was converted from 6.56% (with 50 ppm of Cu(II) added) to 86.32% (with 1 ppm of Cr(III) added). Meanwhile, 88.40%~100% of heavy metal ions (50ppm) were removed in the extracted aqueous solutions. The co-contaminants of Cd(II)+BDE-47 and Cu(II)+BDE-47 were predicted to threaten the growth of RHA1, while Cr(III)+BDE-47 provided amenable conditions for RHA1 to thrive. As the concentration of heavy metal ions increasing (from 1 ppm to 50 ppm), the critical role of RHA1 transferred from BDE-47 co-metabolism to heavy metal removal (i.e., via absorption, mineralization, and/or uptake). RHA1 can produce extracellular polymeric substances (EPS) matrix under the exposure to BDE-47, which in turn, influenced the bioavailability of BDE-47 and the removal of heavy metal ions in the aqueous environments. These results demonstrated that the presence of dissolved heavy metals is predicted to affect the performance of RHA1 to transform BDE-47 in the contaminated sites.