Zero-valent Iron filtration reduces microbial contaminants in irrigation water and transfer to raw agricultural commodities

Authors: ANDERSON-COUGHLIN, BRIENNA - University Of Delaware; LITT, PUSHPINDER - University Of Delaware; KIM, SEONGYUN - University Of Maryland; CRAIGHEAD, SHANI - University Of Delaware; KELLY, ALYSSA - University Of Delaware; CHIU, PEL - University Of Delaware; Sharma, Manan; KNIEL, KALMIA - University Of Delaware

Submitted to: Microorganisms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/16/2021
Publication Date: 9/23/2021
Citation: Anderson-Coughlin, B.L., Litt, P.K., Kim, S., Craighead, S., Kelly, A.J., Chiu, P., Sharma, M., Kniel, K.E. 2021. Zero-valent Iron filtration reduces microbial contaminants in irrigation water and transfer to raw agricultural commodities. Microorganisms. 9(2009):1-14. https://doi.org/10.3390/microorganisms9102009.
DOI: https://doi.org/10.3390/microorganisms9102009

Interpretive Summary: Ground water is a finite resource in agriculture. The use of surface water (rivers, creeks) can help preserve groundwater levels by providing an additional source of irrigation water, but can introduce bacterial contamination to fruits and vegetables, increasing the risk of foodborne contamination. Zero-valent iron (ZVI) filtration can reduce bacterial contamination in a cost-effective manner to provide confidence to growers to use surface irrigation water. Research presented in this study showed that ZVI filtration reduced levels of E. coli significantly compared to unfiltered water. Furthermore, E. coli levels from ZVI-filtered water declined more quickly than in non-filtered water. Lower levels of E. coli in ZVI-filtered water were transferred to soils and leaves compared to unfiltered water. ZVI filtration has the potential to reduce bacterial pathogens in pre-harvest agricultural environments. Our work benefits small scale farmers by providing data on ZVI filtration to provide a more sustainable approach to fruit and vegetable production.

Technical Abstract: Groundwater depletion is a critical agricultural irrigation issue and 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 irrigation of crops. This study was performed to determine the effects of ZVI filtration on removal and persistence of E. coli in irrigation water and transfer to crops leaves. 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, E. coli enumerated by MPN assay, and die-off intervals were calculated for bacteria in irrigation water. Filtration significantly (p<0.05) reduced E. coli levels in filtered water (9.59 lnMPN/mL), compared to unfiltered water (13.13 lnMPN/mL). Die-off intervals of remaining bacteria were significantly shorter in filtered water (-1.50 lnMPN/day) than unfiltered water (-0.48 lnMPN/day). E. coli transfer to both crop leaves and soils was significantly reduced (p<0.05), as expected. The reduction of E. coli in irrigation water, as well as on crops, by ZVI filtration is indicative of its potential to remove pathogens in produce pre-harvest environments.