Can Pesticides Dissolved in Runoff and Exposed to Maturing Rice (Oryza sativa) Plants be Transferred to Seeds?

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 8 weeks post-planting and continued once a week for 5 weeks. Rice plants, unmilled seeds, and mesocosm sediment were collected from each mesocosm 2 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.