| Umweltverhalten | A steep hill country area (1.66 ha) of gorse and pasture was sprayed with 2,4,5-T, N-butyl ester (0.72 kg/l solution at an application rate of 300 l/ha) by air. Soil and vegetation samples were collected at regular intervals and a stream at the bottom of the trial area was monitored continuously over 6 mo. Only 0.6% of the applied herbicide entered the stream during the trial, with 0.4% being washed out in the first storm. Measurable traces of the original ester formulation, 2,4,5-T (acid), and the principal breakdown product 2,4,5-trichlorophenol (2,4,5-TCP), with a combined avg of about 0.4 mg/kg, were found in pasture vegetation 6 mo after initial application. The persistence of these residues may be a cause of dietary intake by grazing livestock. Soil residues (expressed as butyl ester) persisted throughout the study, principally as 2,4,5-TCP (12-100 ng/g after 185 days), and were also detected from a treatment 1 yr before the trial began (20-90 ng/g). An estimate of the masses of residues and losses 6 days after spraying accounted for about 20% of the applied mass. A significant part of the balance (80%) is thought to have been lost in spray drift.TERRESTRIAL FATE: Under field conditions, the n-butyl ester of 2,4,5-T should be hydrolyzed in soil to the parent acid in approximately 1 day or less at moisture levels in excess of the wilting point(1). Massive quantities of the n-butyl ester of 2,4,5-T (up to 4,480 kg/ha, the recommended application rates are 0.56 to 17.9 kg/ha(3)) were applied to field plots in three climatically different areas of the US, namely Northwestern Florida, Western Kansas, and Northwestern Utah(2). The soil type and rainfall in the three areas were: sandy loam (0.5% organic matter (OM), pH 5.6), 150 cmsilt loam (1.7% OM, pH 7), 40 cmand clay loam (1.4% OM, pH 7.8), 15 cm, respectively. After 2 yrs, the acid of 2,4,5-T compromised most of the total residue at all sites, and 90% of that was confined to the top 15 cm of the soil profile. The application of lime, organic matter, or fertilizer did not increase the rate of disappearance. However the incorporation of activated charcoal impeded degradation, probably by binding the herbicide(2).TERRESTRIAL FATE: In another experiment involving the fate of massive quantities of 2,4,5-T, n-butyl ester, the herbicide was applied at 560 and 1800 kg/ha to Washington Silt loam (5.0% OM, pH 5.5), Wyoming Clay loam (3.8% OM, pH 7.6) and Mississippi Sandy loam (2.2% OM, pH 4.7) in lysimiters in Pullman, WA(1,2). The analysis did not distinguish between the acid or the ester. Little or no degradation occurred over the first four cool winter months. At the lower application rate, the Washington and Wyoming soils respectively contained 2.4 and 0.5% of the applied ester after 28 months(2). In experiments the following year, residues in Mississippi and Washington soils were reduced to 47.9 and 7.9% after 20 months(2). Most of the residue was found in the top 10 cm3.74%, 0.33%, and 2.08% were found in the 10-30 cm depth in the Washington, Wyoming, and Mississippi soils, respectively(2). The experiments indicate that the pesticide is primarily lost by degradation, rather than by leaching or volatilization(SRC). Little or no degradation occurred at the higher level of application(2).AQUATIC FATE: The 2,4,5-T, n-butyl ester can pollute water from runoff or deposition after spraying operations. It's hydrolysis half-life is 7.5 days at pH 7.5 and 20 °C and considerably longer at lower temperatures(1). The half-life is 1.4 and 12.8 days at pH 8.4 and 5.4, respectively. Hydrolysis is catalyzed by acid or base. The ester will adsorb to humic material in the water column. Humic material not only adsorbs the ester but exerts a pH dependent catalytic effect on the hydrolysis, the result of which would be to retard hydrolysis in basic waters and accelerate it in acid waters. Therefore, the rate of disappearence of the n-butyl ester of 2,4,5-T from natural waters will be dependent on pH and on the amount of humic materials in the water. The half-life is speculative but would probably vary from days to weeks(SRC).For more Environmental Fate (Complete) data for 2,4,5-T, N-BUTYL ESTER (6 total), please visit the HSDB record page. |
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