Filters comprised of sand and Zero Valent Iron hold promise as tools to mitigate risk posed by Cyclospora cayetanensis oocysts

Authors: Yeager, Christina; Tucker, Matthew; GUTIERREZ, ALAN - Orise Fellow; O'BRIEN, CELIA - Former ARS Employee; Sharma, Manan; Fournet, Valsin; Dubey, Jitender; Jenkins, Mark; KNIEL, KALMIA - University Of Delaware; Rosenthal, Benjamin

Submitted to: Food and Waterborne Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/29/2024
Publication Date: 8/31/2024
Citation: Yeager, C.L., Tucker, M.S., Gutierrez, A., O'Brien, C., Sharma, M., Fournet, V.M., Dubey, J.P., Jenkins, M.C., Kniel, K., Rosenthal, B.M. 2024. Filters comprised of sand and Zero Valent Iron hold promise as tools to mitigate risk posed by Cyclospora cayetanensis oocysts. Food and Waterborne Parasitology. 37. Article e00243. https://doi.org/10.1016/j.fawpar.2024.e00243.
DOI: https://doi.org/10.1016/j.fawpar.2024.e00243

Interpretive Summary: Simple, low-cost filters deserve evaluation as tools to mitigate risks posed by parasites that can contaminate irrigation water, compromising the safety of produce. Here, we sought to determine if sand filters remove coccidian parasites such as Eimeria and Cyclospora, and if adding zero valent iron renders such filters more effective. Here, ARS researchers and their collaborators evaluated the effects of filter composition, water composition, and parasite size, maturity, bleaching, and viability, finding filters perform especially well when partially comprised of zero valent iron filings. Dozens of experiments with Eimeria surrogates (of chickens) yielded highly reproducible results and accurately predicted filter performance against Cyclospora cayetanensis, a parasite that burdens human health and harms the reputation of the fresh produce industry. These data offer encouragement that filters can mitigate parasite risk, which will be of interest to growers, food safety professionals, and food safety regulators.

Technical Abstract: Irrigation water contaminated by human fecal material may elevate the risk of produce contamination with the enteric parasite Cyclospora cayetanensis. Oocysts of C. cayetanensis are resistant to commonly used disinfectants and a method of removing C. cayetanensis from irrigation water would mitigate this risk. We evaluated zero valent iron (ZVI) sand filtration as one such method. We sought to determine if sand filters containing ZVI outperformed those without ZVI. We first evaluated the abundant poultry parasites Eimeria maxima, E. tenella and E. acervulina as surrogates for C. cayetanensis. We determined if a miniaturized gravity fed ZVI-sand filter, scaled to evaluate scarce supplies of C. cayetanensis oocysts, provided useful information about the performance of larger filtration systems. Filters were inoculated with oocysts, rinsed, and the resulting filtrate examined microscopically for oocysts. We performed experiments to measure the effect of varying ZVI concentrations, repeated filter use, simulated agricultural water, and oocyst size and condition. We then compared the performance of mini filters to that of larger, gravity-fed pool filters and found that ZVI-sand filtration was far more effective at removing Eimeria spp. from water when compared to sand filtration, at both scales. Sand mini filters retained 13–54 % of E. acervulina oocysts, and pool filters retained 82 %, but when combined with 50 % (mini filter) or 35 % (pool filter) v/v ZVI, mini filters retained 89–99 % of oocysts and pool filters retained >99 %. The effectiveness of the mini filters increased with increasing ZVI concentration, and the addition of ZVI far outweighed the influence of any other measured variable. We then performed experiments including C. cayetanensis, which provided similar results to those utilizing Eimeria; 59 % of inoculated C. cayetanensis oocysts were retained in sand mini filters, and 97 % in mini filters composed of 35 % v/v ZVI. In sum, ZVI is highly effective in removing oocysts from water and Eimeria is a useful surrogate for C. cayetanensis to assess filtration. ZVI-sand filtration shows promise as a tool to mitigate the risk of C. cayetanensis contamination of irrigation water. Further studies should evaluate the performance of ZVI-sand in pressurized fast filtration systems under a range of field conditions.