Elimination of Tobacco mosaic virus from irrigation runoff using slow sand filtration

- This is the first report that SSFs remove Tobacco mosaic virus (TMV) from runoff.
- TMV removal mechanisms were biological as evidenced by an adaptation period.
- Virus assessments were conducted using bioassays and ELISA.
- Complete and continued removal of TMV occurred after 6-9 weeks of exposure.

Slow sand filters (SSF) are effective in removing pythiacious organisms from captured runoff to prepare the water for reuse in irrigation. Plant viruses can also be present in this runoff, but until this study, it hadn't been clearly shown that SSFs can remove these pathogens. In this study, purified preparations of Tobacco mosaic virus (TMV) were regularly added to captured irrigation runoff water that was provided to the SSFs. Water samples were collected weekly from sampling ports above and below the sand bed and tested for the presence of TMV by ELISA and inoculation to indicator plants. Biologically viable TMV passed through the sand filters for approximately 5 weeks, followed by a gradual reduction and then elimination of detectable amounts of the virus by week 6-9. Testing of water samples continued for several more weeks after the initial loss of virus titer to confirm complete elimination. This is the first controlled study showing elimination of a plant virus from captured irrigation runoff using SSFs. Since TMV is a highly robust organism, it is likely that other plant pathogenic viruses can also be removed using SSF systems.

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