Zero-Valent Iron Filtration Reduces Microbial Contaminants in Irrigation Water and Transfer to Raw Agricultural Commodities

Abstract

Groundwater depletion is a critical agricultural irrigation issue, which can be mitigated by supplementation with water of higher microbiological risk, including surface and reclaimed waters, to support irrigation needs in the United States. Zero-valent iron (ZVI) filtration may be an affordable and effective treatment for reducing pathogen contamination during crop irrigation. This study was performed to determine the effects of ZVI filtration on the removal and persistence of Escherichia coli, and pepper mild mottle virus (PMMoV) in irrigation water. Water was inoculated with E. coli TVS 353, filtered through a ZVI filtration unit, and used to irrigate cucurbit and cruciferous crops. Water (n = 168), leaf (n = 40), and soil (n = 24) samples were collected, the E. coli were enumerated, and die-off intervals were calculated for bacteria in irrigation water. Variable reduction of PMMoV was observed, however E. coli levels were consistently and significantly (p < 0.05) reduced in the filtered (9.59 lnMPN/mL), compared to unfiltered (13.13 lnMPN/mL) water. The die-off intervals of the remaining bacteria were significantly shorter in the filtered (−1.50 lnMPN/day), as compared to the unfiltered (−0.48 lnMPN/day) water. E. coli transfer to crop leaves and soils was significantly reduced (p < 0.05), as expected. The reduction of E. coli in irrigation water and its transfer to crops, by ZVI filtration is indicative of its potential to reduce pathogens in produce pre-harvest environments.

Development and evaluation of a modified most probable number (MPN) method for enumerating rifampicin‐resistant Escherichia coli in agricultural, food, and environmental samples

“…Rifampicin in LPBR may create a low selection pressure to those cells that may have lost their rifampicin resistance, but this potential limiting factor occurs in all traditional MPN methods that utilize TSBR followed by plate confirmation. In addition, inclusion of rifampicin in TSB for MPN assays has been widely accepted in agricultural research (Anderson‐Coughlin et al, 2021; Limoges et al, 2022; Moyne et al, 2022; Weller, Kovac, Kent, et al, 2017; Weller, Kovac, Roof, et al, 2017), and the results in the current study revealed no statistical significance between the broths with and without the inclusion of rifampicin. Therefore, the LPBR MPN assays verified in this study generated comparable results as of the traditional MPN methods using TSB or TSBR followed by MACR plating.…”

“…Therefore, scientists routinely use a generic surrogate adapted for specific antibiotic resistance to facilitate selective plate enumeration. For example, E. coli TVS353 with rifampicin resistance has been widely used in agricultural studies in the United States (Anderson‐Coughlin et al, 2021; Limoges et al, 2022; Moyne et al, 2022; Sharma et al, 2016; Sharma et al, 2019; Weller et al, 2019; Weller, Kovac, Kent, et al, 2017; Weller, Kovac, Roof, et al, 2017; Wright et al, 2018).…”

“…It is based on a presence/absence of determination of microorganisms from several consecutive dilutions of the test sample conducted in three or more replications. Over the years, MPN methods have been well‐established for E. coli TVS353 from agricultural and environmental samples (Anderson‐Coughlin et al, 2021; Limoges et al, 2022; Moyne et al, 2022; Sharma et al, 2016; Sharma et al, 2019; Weller et al, 2019; Weller, Kovac, Kent, et al, 2017; Weller, Kovac, Roof, et al, 2017; Wright et al, 2018). Traditionally, samples are inoculated in the MPN assays using tryptic soy broth (TSB) with or without supplementation of an appropriate antibiotic, such as rifampicin (TSBR).…”

“…Traditionally, samples are inoculated in the MPN assays using tryptic soy broth (TSB) with or without supplementation of an appropriate antibiotic, such as rifampicin (TSBR). After overnight incubation, the presence of the target bacteria such as E. coli in each dilution and replicate of the broth is confirmed by plating on selective or differential agar plates such as MacConkey, sorbitol MacConkey, or ChromAgar (Anderson‐Coughlin et al, 2021; Limoges et al, 2022; Moyne et al, 2022; Sharma et al, 2016; Sharma et al, 2019; Weller et al, 2019; Weller, Kovac, Kent, et al, 2017; Weller, Kovac, Roof, et al, 2017; Wright et al, 2018). The entire process requires at least two overnight incubation periods and is highly labor‐ and resource‐intensive, possibly limiting the scope or replication of environmental studies.…”

The Suitability of Hybrid Fe0/Aggregate Filtration Systems for Water Treatment

“…Despite their promise, Fe 0 filters have so far failed to attain the expected widespread adoption within low-income communities [29,[143][144][145][146][147]. To be commercially viable, the costs of producing, marketing, and distributing Fe 0 filters should be covered by the purchase price paid for the product by the consumer.…”