Can pesticides dissolved in runoff and exposed to maturing rice (Oryza sativa) plants be transferred to seeds?

Authors: Moore, Matthew; Locke, Martin

Submitted to: Bulletin of Environmental Contamination and Toxicology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/23/2021
Publication Date: 1/8/2022
Citation: Moore, M.T., Locke, M.A. 2022. Can pesticides dissolved in runoff and exposed to maturing rice (Oryza sativa) plants be transferred to seeds. Bulletin of Environmental Contamination and Toxicology. 108:1013-1018. https://doi.org/10.1007/s00128-021-03423-0.
DOI: https://doi.org/10.1007/s00128-021-03423-0

Interpretive Summary: Research has demonstrated that aquatic plants have the ability to act as filters to clean contaminants from the water. The success of these plants differs among various plants and contaminants. One plant in particular which has shown promise in cleaning up the water is rice. However, rice is primarily used as a food source for the global population. Our research examined whether or not rice could be used to clean contaminants, particularly pesticides, from the water without affected the seed that is used for food. For the three pesticides studied, concentrations in seeds were below any human health concern. Therefore, rice has the potential to serve not only to clean up contaminated water, but it may also be used simultaneously as a food source.

Technical Abstract: Agriculture’s global challenge to feed an estimated 7.7 billion people is further exacerbated by less available cropland for production and rapidly changing climate patterns. Pesticides are often utilized to minimize crop losses due to pest infestations; however, problems arise when these chemicals are transported off production acreage, either by storm or irrigation events, and into nearby water bodies. Innovative management practices are needed to not only reduce the volume of runoff, but also to mitigate various pollutants, such as pesticides, within the runoff. One such practice being evaluated involves using rice (Oryza sativa) as a pesticide mitigation tool. While rice plants may serve as a mechanism for phytoremediation, whether the seeds harvested from exposed plants could then be utilized as a human food source is an unanswered question. Thirty round mesocosms (55 L volume; 56 cm diameter; six replicates per treatment) were established with rice and exposed to aqueous concentrations of the pesticides clomazone, propanil, or cyfluthrin, as well as a mixture of the three pesticides. Six replicates with rice and no pesticide exposure served as controls. Initial pesticide exposure took place eight weeks post-planting and continued once a week for five weeks. Rice plants, unmilled seeds, and mesocosm sediment were collected from each mesocosm two weeks after seed formation began and analyzed for pesticide concentrations using gas chromatography. Concentrations of pesticides in unmilled seed were below detection for individual exposures of clomazone, propanil, and cyfluthrin. When rice was exposed to the pesticide mixture, the mean ± SE unmilled seed cyfluthrin concentration was 14.8±1.25 µg kg-1. These small-scale, preliminary studies offer insight into the possibility of using immature rice plants as a phytoremediation tool, while harvesting its grain after plant maturation for human consumption. Further research is needed to address this question on a larger scale and with multiple pesticide mixtures.