Fate of Thiobencarb and Molinate in Rice Fields

Abstract

AbstractThe fate of thiobencarb (S‐[4‐chlorobenzyl] N,N‐diethylthiolcarbamate) and molinate (S‐ethyl hexahydro‐1 H‐azepine‐1‐carbothioate) in air, water, soil, and vegetation of rice (Oriza sativa L.) fields was documented for 32 d following application. Analysis of variance was used to determine if holding periods facilitated herbicide dissipation in water prior to release to drainage canals. Maximum thiobencarb concentrations in air, water, soil, and vegetation were 1.4 µg/m3, 576 µg/L, 3860 µg/kg, and 1750 µg/kg, respectively. During the 6‐d holding period, thiobencarb concentrations in water did not decline significantly, indicating that this period was not sufficient to facilitate dissipation. The mass balance budget indicated that thiobencarb was predominantly distributed between water (34%) and soil (43%) and <1% was located in air and vegetation. Maximum molinate concentrations in air, water, soil, and vegetation were 48 µg/m3, 3430 µg/L, 2210 µg/kg, and 918 µg/kg, respectively. Molinate concentrations in water declined significantly during the holding period, indicating that this water‐management practice facilitated dissipation of molinate. The mass balance budget indicated that as much as 81% of the molinate applied was dissolved in water followed by soil (10%), air (9%), and vegetation (<1%). Partitioning of these herbicides in the field was closely related to their physico‐chemical properties.