Conductive black carbon promoted biotransformation of undissolved 2, 2'-dinitrobiphenyl by mediating electron transfer.

With low bioaccessbility, persistence of the undissolved organic pollutants in soil and sediments poses threat to health of the resident. Although ubiquitous black carbon catalyzes a wide range of biogeochemical reactions in nature, its role in biotransformation of the compounds in non-aqueous phase like 2, 2'-nitrobiphenyl remains unclear. Reduction rate constants of 2, 2'-dinitrobiphenyl by Shewanella oneidensis MR-1 increased from 0.0044 h-1 by 7-fold to 0.035 h-1 in the presence of black carbons produced at pyrolysis temperature of 250-900 °C. Accordingly, electrical conductivity of black carbon was enhanced from 0 to 5.56 S∙cm-1. The reactivity of black carbon for catalyzing the biotransformation positively correlated with its electrical conductivity (R2 > 0.89), which was strongly associated with conductive graphitic clusters in it. The surface oxygenated groups in black carbon were likely not involved in the bioreduction. This work attaches importance to role of the ubiquitous black carbon in natural biotransformation of the undissolved pollutants, and elucidates new mechanism for the biotransformation.