Sorption and degradation of fipronil in flooded anaerobic rice soils.

The fate of fipronil in flooded, reductive rice soils was modeled using a conceptual model. Rate constants for the various sorption and degradation processes were calculated from experimental studies involving intact soil cores, and the reductive degradation constant was used to calculate half-lives for fipronil on each soil. The data predicted that fipronil was subject to rapid, reductive degradation or immediate sorption to the soil and any sorbed fipronil desorbed was reductively degraded.

The mobility of thiobencarb and fipronil in two flooded rice-growing soils.

The mobility of the rice pesticides thiobencarb (S-[(4-chlorophenyl) methyl] diethylcarbamothioate) and fipronil ([5-amino-3-cyano-1-[2,6-dichloro-4-(trifluoromethyl)phenyl]-4-[(trifluoromethyl)sulfinyl]pyrazole) were investigated in the glasshouse under flooded conditions using two Australian rice-growing soils. When using leakage rates of 10 mm day(-1), less than 20% of applied thiobencarb and fipronil remained in the water column after 10 days due to rapid transfer to the soil phase. Up to 70% and 65% of the applied thiobencarb and fipronil, respectively, were recovered from the 0-1 cm layer of soils.

Influence of imidacloprid seed treatments on rice germination and early seedling growth.

Background: Seed treatments with the chloronicotinyl insecticide imidacloprid (Gaucho 600 FS) were evaluated to determine whether differences in concentration and exposure regime influence the germination and early growth of rice.

Results: Continuous exposure to imidacloprid (4 days at 2000 mg AI L(-1)) significantly (P < 0.001) reduced normal germination by an average of 18% across the 15 cultivars examined.

The impact of rice plant roots on the reducing conditions in flooded rice soils.

The impact of oxygen diffusion from plant roots on the soil redox in the root zone in flooded rice bays was investigated using two Australian rice growing soils. The rates of production of Fe(II) and Mn(II) in pore water resulting from the reduction of soil minerals was used to gauge the extent of development of anaerobic conditions and the time taken for equilibrium to establish. Soil concentrations of readily reducible Fe were 13-28 times greater than Mn, making Fe a more reliable indicator of redox conditions than Mn.

Extraction of fipronil and thiobencarb from anaerobic water samples using solid-phase extraction.

Anaerobic water samples containing levels of soluble Fe(II) may form insoluble Fe(III) particulates that could hinder subsequent extraction and analysis. Solid-phase extraction (SPE) cartridges could become blocked by this material, reducing the volume that can be processed. The ability of ascorbic acid to reduce these Fe(III) colloids and/or to prevent further oxidation of Fe(II) by dissolved oxygen during sampling was investigated and compared to sample stabilization with hydrochloric acid.