The oxidation of organic micro-pollutants by biogenic manganese oxide nanoparticles (BioMnOx) has been studied with respect to possible implementation of BioMnOx in wastewater treatment. For this it would be prerequisite that microbial Mn2+ oxidation and BioMnOx-driven pollutant removal can occur in situ, i.e. in the same reactor as the removal. Here we present the in situ reactivity of BioMnOx produced by Pseudomonas putida towards a range of micro-pollutants at environmentally relevant concentrations (10 mu g L-1). We found that in situ formed BioMnOx completely removed the steroid hormones estrone and 17-alpha ethinylestradiol, while only 26% removal of diclofenac was achieved. Ibuprofen, tebuconazole, carbamazepine, carbendazim, and terbutryn were not removed under in situ conditions. (C) 2014 Elsevier Ltd. All rights reserved.