Insecticide Dissipation after Repeated Field Application to a Northern Thailand Ultisol

Abstract

Nontarget effects of pesticides may occur when the active ingredients have a long persistence in the environment. The half-lives of six insecticides commonly used in Thai fruit orchards under tropical field conditions were determined. A mixture of endosulfan-alpha and -beta, chlorpyrifos, malathion, dimethoate, and mevinphos was applied five times in 10-day intervals onto an Ultisol (lychee plantation ground-covered with grass vegetation, northwestern Thailand). On days 1, 3, 5, 7, and 10 after each application, composite samples of the topsoil (0-10 cm) were collected and exhaustively extracted. Fitting a first-order model to the datasets revealed rapid initial dissipation [half-lives from 2.2 +/- 0.4 (malathion) to 5.4 +/- 1.3 days (chlorpyrifos)]. Volatilization appeared to be a major process of pesticide dissipation, especially for malathion and mevinphos. Because 8% of the applied endosulfan-alpha and -beta had been converted to the sulfate metabolite within 1 day after the first application, also microbial degradation contributed significantly to pesticide dissipation. Nevertheless, no trend in half-lives over the five application cycles could be observed, indicating that accelerated microbial degradation did not occur for these insecticides following the five applications. Precipitation and soil moisture were key parameters of dissipation, but dissipation processes were too complex to be generalized for all substances studied. Despite their short half-lives, all pesticides except mevinphos accumulated in soil (up to 656%; endosulfan-alpha), and this accumulation correlated significantly with the hydrophobicity of the substances (r = 0.88). This was interpreted as an aging process, and it was concluded that pesticide aging must be considered relevant also in tropical environments, where it has received very limited attention so far.

Micro‐Trench Experiments on Interflow and Lateral Pesticide Transport in a Sloped Soil in Northern Thailand

“…Under lab conditions (30°C and a water content of 32% by weight), the average half‐life of methomyl in the topsoil was 15.5 d, which is in the range of published values (Extoxnet, 1996). Under field conditions, however, at the same research site Ciglasch et al (2006) found significantly decreased field half‐lives of several pesticides compared with published values. Therefore, we might expect a faster decay of methomyl and chlorothalonil.…”

Environmental Consequences of the Demise in Swidden Cultivation in Montane Mainland Southeast Asia: Hydrology and Geomorphology

“…Agrochemicals are increasingly contributing to water quality degradation in upland agriculture areas where swiddening was once prevalent, for example in the Mae Sa catchment in northern Thailand (Ciglasch et al 2005(Ciglasch et al , 2006Kahl et al 2008), Inle lake in Myanmar (Sidle et al 2007), and potentially, the Cameron Highlands of Malaysia (cf. Ismail et al 2004;Mazlan and Mumford 2005).…”

Effect of Irrigation Levels on Dissolved Organic Carbon Soil Distribution and the Depth Mobility of Chlorpyrifos

“…Konda and Pásztor (2001) obtained a 33% decrease for the level of 0-5 cm at the end of 14 days, in a field study for soils from the Luvisol order in Hungary, in the context of precipitation (approximately 25 mm on average for the period of the study), a situation that would be in agreement with what was obtained in the treatment with greater irrigation in the present study. On the other hand, other authors have found that in tropical soils (Ultisol) CHP recovery at a depth of 0-10 cm was 23.6% (Ciglasch et al, 2006); a situation that shows a high decrease of initially applied AI, associated with moisture and precipitation during the assay. At the depth of 20-30 cm, the values of the decrease in AI were 5.6, 9.3 and 13.1% of the concentration found at the surface of the column, from the control to the treatment with the greatest flow, respectively, which shows some influence of excess water on the vertical movement of CHP.…”