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

• Published in: The Science of the total environment Vol. 664; pp. 669 - 682
• Main Authors: Wang, Ruoyu, Luo, Yuzhou, Chen, Huajin, Yuan, Yongping, Bingner, Ronald L., Denton, Debra, Locke, Martin, Zhang, Minghua
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 10-05-2019
• Subjects: Environmental impacts; Pesticide fate; RICEWQ; Thiobencarb; Environmental impacts; Pesticide fate; Thiobencarb; RICEWQ
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2019.02.003

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, the Rice Water Quality Model (RICEWQ) is equilibrium tested and then calibrated using monitoring data at field level. Then it is employed to assess the environmental fate and impacts of thiobencarb in the Colusa Basin, and the effects of different management practices on water use and thiobencarb exposures. The model predicted thiobencarb concentrations from rice fields for multiple years throughout the Basin, using input from California Pesticide Use Reporting (PUR) database, and assessed both the temporal/spatial distribution of thiobencarb exposure and potential acute toxicity on non-target organisms.
Our study indicated that RICEWQ can accurately reflect the initial partitioning of thiobencarb in both paddy water and soil phases and capture the dynamics of thiobencarb at field level after calibration. Mandatory water holding is critical for reducing thiobencarb exposure in released paddy water. A thirty-day holding time reduces thiobencarb concentrations by 64% relative to a 6-day holding practice. The geo-spatial pattern of exposure in the study domain indicates the differing extents of pollutant levels and their distribution over space. “Risk zones” for different species were identified based on the geospatial patterns of thiobencarb exposure and the species-specific susceptibilities of various non-target species to thiobencarb.
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•RICEWQ correctly reflects thiobencarb initial partitioning in water/soil phases.•The time series of thiobencarb exposure are well captured after field calibration.•Mandatory water holding practice reduces thiobencarb concentration by 64%.•Geo-spatial pattern of exposure reveals pollutant level and ecological risks.•“Risk zones” with higher exposure could be identified for further studies.