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 was employed to assess the environmental fate and impacts of thiobencarb in the Colusa Basin. RICEWQ was first equilibrium tested and then calibrated at the field level. Different water/pesticide management practices for water use and thiobencarb use were compared. The model predicted the thiobencarb concentrations from rice fields for multiple years in the entire Colusa Basin, using input information from California Pesticide Use Reporting database. The temporal/spatial distribution of thiobencarb was evaluated, followed by assessment of ecological impacts on various non-target organisms.  Our research indicated that RICEWQ was able to correctly reflect the initial partitioning of thiobencarb in both paddy water and soil phases. The dynamics of thiobencarb were also well captured by the model at field level after calibration. Mandatory water holding plays a critical role in reducing thiobencarb in released paddy water. A thirty-day holding time can reduce thiobencarb concentration by 64%, when compared to a 6-day holding time. The geospatial 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 concentration of thiobencarb may impose different levels of risk to various non-target species due to their susceptibility differences.

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

256th National Meeting (2018)

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