Transport, retention, and release of Escherichia coli and Rhodococcus erythropolis through dry natural soils as affected by water repellency

authored by

Nasrollah Sepehrnia, Jörg Bachmann, Mohammad Ali Hajabbasi, Fereidoun Rezanezhad, Lubomir Lichner, Paul D. Hallett, Mark Coyne

Abstract

Microbial transport in soil affects pathogen retention, colonization, and innoculant delivery in bioremediating agricultural soils. Various bacteria strains residing in the fluid phases of soils are potential contaminants affecting human health. We measured the transport of hydrophilic Escherichia coli (E. coli) and hydrophobic Rhodococcus erythropolis (R. erythropolis) bacteria through initially air-dried wettable or water-repellent soil columns to understand the effect of water repellency and the hydrophobicity of the organism on its retention, release, and transport properties. Bacteria suspensions infiltrated the top of the columns under saturated (0 cm) and unsaturated (−5 cm) flows in the air-dried (pulse 1) and rewetting (pulse 2) conditions. Cells were recovered from the leachates and the soil extracts by the viable counts. Wettable soil efficiently retained both hydrophobic and hydrophilic bacteria (>80%) in initial air-dried conditions (pulse 1). Even after rewetting, and the formation and expansion of water films and corresponding reduction of the air-water interfacial area (pulse 2), few bacteria were released (maximum 31.5% and 10.1% for saturated and unsaturated flows, respectively), whereas more cells were released from the water-repellent counterpart (more that 72%). The smaller size of hydrophobic R. erythropolis made cell transport possible within the thinner water films of both soils compared to hydrophilic E. coli through pulses 1 and 2. The shape of each strain's retention profiles was uniform and exponential as influenced by soil, strain, and water flow conditions. The results suggest that hydrophobic bacteria will disperse readily when leached into initially dry soil, while hydrophilic bacteria are more susceptible to leaching, posing a risk of pathogen contamination. Clearly the wettability of soil and organisms affects fate and transport.

Organisation(s)

Institute of Soil Science
Section Soil Physics

External Organisation(s)

Isfahan University of Technology
University of Waterloo
Slovak Academy of Sciences
University of Bristol
University of Kentucky

Type

Article

Journal

Science of the Total Environment

Volume

694

ISSN

0048-9697

Publication date

01.12.2019

Publication status

Published

Peer reviewed

Yes

ASJC Scopus subject areas

Environmental Engineering, Environmental Chemistry, Waste Management and Disposal, Pollution

Sustainable Development Goals

SDG 3 - Good Health and Well-being

Electronic version(s)

https://doi.org/10.1016/j.scitotenv.2019.133666 (Access: Closed)