Identifying redox transition zones in the subsurface of a site with historical contamination Xin Yin a, ⁎, Han Hua a , Frank Burns b , Donna Fennell c , James Dyer d , Richard Landis e , Lisa Axe f, ⁎ a Department of Civil and Environmental Engineering, New Jersey Institute of Technology, Newark, NJ 07032, USA b BioPrimate, Newark, DE, USA c Rutgers University, Department of Environmental Sciences, 14 College Farm Rd., New Brunswick, NJ 08901, USA d Savannah River National Laboratory, Aiken, SC 29808, USA e RichLand Consulting, LLC, USA f Otto H. York Department of Chemical and Materials Engineering, New Jersey Institute of Technology, Newark, NJ 07032, USA HIGHLIGHTS • The study focused on characterizing sed- iment core samples where the redox con- dition was preserved. • Redox transition zones were identified based on gradients observed in screening analyses. • Fe and S concentrations correlated with bacteria supporting delineation of redox transition zones. GRAPHICAL ABSTRACT abstract article info Article history: Received 24 August 2020 Received in revised form 11 October 2020 Accepted 13 October 2020 Available online xxxx Editor: Filip M.G.Tack Keywords: Reactive iron mineral coatings Iron cycling Screening analyses Redox transition zone Reactive iron mineral coatings found throughout reduction-oxidation (redox) transition zones play an important role in contaminant transformation processes. This research focuses on demonstrating a process for effectively de- lineating redox transition zones at a site with historical contamination. An 18.3 meter core was collected, subsam- pled, and preserved under anoxic conditions to maintain its original redox status. To ensure a high vertical resolution, sampling increments of 5.08 cm in length were analyzed for elemental concentrations with X-ray fluo- rescence (XRF), sediment pH, sediment oxidation-reduction potential (ORP), total volatile organic carbon (TVOC) concentration in the sample headspace, and abundant bacteria (16S rRNA sequencing). Over the core's length, gra- dients observed ranged from 3.74 to 8.03 for sediment pH, -141.4 mV to +651.0 mV for sediment ORP, and from below detection to a maximum of 9.6 ppm TVOC concentration (as chlorobenzene) in the headspace. The Fe and S gradients correlated with the presence of Fe and S reducing bacteria. S concentrations peaked in the Upper Zone and Zone 1 where Desulfosporosinus was abundant, suggesting precipitation of iron sulfide minerals. In Zone 2, Fe con- centrations decreased where Geobacter was abundant, potentially resulting in Fe reduction, dissolution, and precip- itation of minerals with increased solubility compared to the Fe(III) minerals. Using complementary geochemical and microbial data, five redox transition zones were delineated in the core collected. This research demonstrates a systematic approach to characterizing redox transition zones in a contaminated environment. © 2020 Elsevier B.V. All rights reserved. Science of the Total Environment xxx (xxxx) xxx ⁎ Corresponding authors. E-mail addresses: xy239@njit.edu (X. Yin), axe@njit.edu (L. Axe). STOTEN-143105; No of Pages 10 https://doi.org/10.1016/j.scitotenv.2020.143105 0048-9697/© 2020 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv Please cite this article as: X. Yin, H. Hua, F. Burns, et al., Identifying redox transition zones in the subsurface of a site with historical contamination, Science of the Total Environment, https://doi.org/10.1016/j.scitotenv.2020.143105