Environmental fate and impact assessment of thiobencarb application in California rice fields using RICEWQ

Authors: WANG, RUOYU - University Of California, Davis; LUO, YUZHOU - University Of California, Davis; CHEN, HUAJIN - University Of California, Davis; YUAN, YONGPING - Environmental Protection Agency (EPA); Bingner, Ronald - Ron; DENTON, DEBRA - Environmental Protection Agency (EPA); Locke, Martin; ZHANG, MINGHUA - University Of California, Davis

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2019
Publication Date: 2/21/2019
Citation: Wang, R., Luo, Y., Chen, H., Yuan, Y., Bingner, R.L., Denton, D., Locke, M.A., Zhang, M. 2019. Environmental fate and impact assessment of thiobencarb application in California rice fields using RICEWQ. Science of the Total Environment. https://doi.org/10.1016/j.scitotenv.2019.02.003.
DOI: https://doi.org/10.1016/j.scitotenv.2019.02.003

Interpretive Summary: Pesticide application in cropland has the potential to be harmful to ecological health, such as through toxicity to non-target organisms. Thiobencarb is a commonly used herbicide in Northern California rice fields that may pose ecological risks to non-targeted organisms. An ecohydrological model was applied to the study watershed to evaluate the fate and transport of pesticides rice fields. The study found that a thirty-day water holding time in the rice fields can reduce thiobencarb concentration by 64%, when compared to a 6-day water holding practice. The geo-spatial pattern of exposure in the study domain indicates the differing extents of pollutant level and its distribution over space. “Risk zones” for different species could be identified based on the geospatial pattern of thiobencarb exposure. The same exposure of thiobencarb may impose different levels of risk to various non-target species due to their susceptibility differences. The ecohydrological modeling assessment approach presented in this study is not only suitable for evaluating pesticide impacts in rice fields, but also for assessment of ecological impacts on various non-target organisms.

Technical Abstract: Thiobencarb is a commonly used herbicide in Northern California rice fields. Released paddy water containing thiobencarb may pose ecological risks to non-targeted organisms. In this research, RICEWQ model is employed to assess the environmental fate and impacts of thiobencarb in the Colusa Basin. Different water/pesticide management practices on water use and thiobencarb exposures are compared using RICEWQ. The model can predict the thiobencarb concentrations from rice fields for multiple years in the entire Colusa Basin, using input information from California Pesticide Use Reporting (PUR) database. The temporal/spatial distribution of thiobencarb exposure was evaluated, followed by assessment of ecological impacts on various non-target organisms. Our study indicated that RICEWQ is able to correctly reflect the initial partitioning of thiobencarb in both paddy water and soil phases. The dynamics of thiobencarb are also well captured by the model at field level after calibration. Mandatory water holding plays a critical role in reducing thiobencarb exposure in released paddy water. A thirty-day holding time can reduce thiobencarb concentration by 64%, when compared to a 6-day holding practice. The geo-spatial pattern of exposure in the study domain indicates the differing extents of pollutant level and its distribution over space. “Risk zones” for different species could be identified based on the geospatial pattern of thiobencarb exposure. The same exposure of thiobencarb may impose different levels of risk to various non-target species due to their susceptibility differences.