Metabolism of uniconazole‐P in water‐sediment systems under illumination

Abstract

Aerobic soil metabolism of uniconazole-P ([S]-E-1-[4-chlorophenyl]-4,4-dimethyl-2-[1,2,4-triazole-1-yl]-penten-3-ol) and the effect of illumination on metabolic profiles were studied in the water-sediment system when spiked to water. Uniconazole-P was gradually partitioned to the sediment with an aquatic half-life of 6.9 d in darkness with formation of bound residues. Illumination of the system from a xenon lamp (>290 nm) greatly accelerated the degradation of uniconazole-P via photoinduced isomerization between E- and Z-isomers with a subsequent intramolecular cyclization, and its aquatic half-life was greatly reduced to 0.6 d. Kinetic analysis based on compartment models suggested the possible contribution of photodegradation at the water-sediment interface, leading to more formation of the cyclized derivative in the sediment.

Effect of illumination on degradation of pyriproxyfen in water-sediment system

“…The determination of 14 CO 2 as well as other analytical details was similar to those previously reported. 6,7) …”

“…The base of the vessels was enclosed inside a cooling block, cooled by flowing water, and used to maintain the temperature in the units at 20Ϯ3°C, similarly to reported previously. 6) The spectral distribution of the incident light (Ͼ290 nm) simulated that of natural sunlight and irradiance at 300-800 nm was measured by a LI-1800 spectroradiometer (Li-Cor Inc) to be 343 watts/m 2 . Irradiation for 12 hr per day was mostly equal to exposure to summer sunlight.…”

“…For this purpose, a laboratory-scale water-sediment study under illumination in addition to the usual study in darkness is required for the European registration of pesticides, 3) as reported for imidacloprid 4) and pyraclostrobin. 5) We have recently investigated the partition and degradation profiles in the illuminated watersediment system for uniconazole-P 6) and esfenvalerate 7) and demonstrated that the balance between the hydrophobicity controlling the partition to sediment and degradation rate controlling the behavior of these photo-labile pesticides and the contribution of photolysis is greatly reduced. A similar extent of photodegradation was found even in the presence of sediment for chlorothalonil 8) , which is less sorptive to soils than our pesticides tested, supporting the above concept.…”

Degradation of esfenvalerate in illuminated water-sediment system

“…In the case of illuminated water-sediment systems, each glass vessel was irradiated only from the top side using a 2 kW Xenon arc lamp (UXL-25SC Xenon lamp, Usio, Tokyo, Japan) through a Pyrex glass plate (4 mm thickness) to remove UV light with wavelengths below 290 nm, as previously reported. 4) Light intensity was kept almost constant throughout the experiment with irradiance at 300 to 400 nm of 0.672 MJ/m 2 /day on average. Illumination was continued for 8 hr/ day during the experiment, which was equivalent to the daily irradiance of natural sunlight in Tokyo (35°N, April-June).…”

“…2) Therefore, we have recently developed methodology for a water-sediment study under illumination with artificial sunlight using the plant growth regulator uniconazole-P [(S)-E-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazole-1-yl)-penten-3-ol] as a model compound. 4) Pyrethroids are one of the most important and popular insecticides for agricultural use and many higher-tier outdoor microcosm and field mesocosm studies have been conducted to investigate their aquatic ecotoxicological impacts. 5) Their high hydrophobicity resulted in very rapid partition from water overlaid on bottom sediment.…”