Dissipation and Leaching of Acephate, Chlorpyrifos, and Their Main Metabolites in Field Soils of Malaysia

Abstract

Preventive treatment with insecticides at high dosing rates before planting of a new crop- soil drenching- is a common practice in some tropical intensive cropping systems, which may increase the risk of leaching, soil functioning, and pesticide uptake in the next crop. The degradation rates and migration of acephate and chlorpyrifos and their primary metabolites, methamidophos and 3,5,6-trichloropyridinol (TCP), have been studied in clayey red yellow podzolic (Typic Paleudults), alluvial (Typic Udorthents), and red yellow podzolic soils (Typic Kandiudults) of Malaysia under field conditions. The initial concentrations of acephate and chlorpyrifos in topsoils were found to strongly depend on solar radiation. Both pesticides and their metabolites were detected in subsoils at the deepest sampling depth monitored (50 cm) and with maximum concentrations up to 2.3 mg kg(-1) at soil depths of 10 to 20 cm. Extraordinary high dissipation rates for weakly sorbed acephate was in part attributed to preferential flow which was activated due to the high moisture content of the soils, high precipitation and the presence of conducting macropores running from below the A horizons to at least 1 m, as seen from a dye tracer experiment. Transport of chlorpyrifos and TCP which both sorb strongly to soil organic matter was attributed to macropore transport with soil particles. The half-lives for acephate in topsoils were 0.4 to 2.6 d while substantially longer half-lives of between 12.6 and 19.8 d were observed for chlorpyrifos. The transport through preferential flow of strongly sorbed pesticides is of concern in the tropics.

Environmental Behavior of the Chiral Organophosphorus Insecticide Acephate and Its Chiral Metabolite Methamidophos: Enantioselective Transformation and Degradation in Soils

“…It is well-known that both AC and ME are readily biodegraded and nonpersistent in native soils, with half-lives ranging from 0.5 to 4.0 days in most of the cases, depending on the varied conditions of soils, ,− whereas ME has been found to be degraded faster than AC under the same conditions . Also, AC and ME are hydrophilic; with a high water solubility and correspondingly low adsorption to soils resulting in their high mobility in soils and consequent potential water contamination. ,, It has been found that AC may lead to the contamination of groundwater much more readily than ME under normal conditions and that wet soils are the conditions most conducive for contamination of the aquatic environment with AC and its metabolites . Moreover, the enantioselective bioactivity of enantiomers of AC and ME has been observed during past years.…”

Comparative study on the dissipation of thiram in two type of soils at oil palm (Elaeis guineensis Jacq.) nursery

“…Macrospores are large voids, often distinct in some manner in the soil matrix, and they can permit the preferential flow of water and contaminants through the soil profile (Cey and Rudolph, 2009). The preferential flow through the porous soils has been identified in previous field studies (Flury et al, 1994;Chai et al, 2009a;Maznah et al, 2015). The preferential pathways in structured soils may provide a short circuit from the soil surface not only to the surface waters via tiled drains but also to the groundwater (Tang et al, 2012).…”

Evaluating Hexaconazole Leaching in Laboratory and Field Experiments: Effects of Application Rate, Soil Type, and Simulated Rainfall

“…We also believe that these findings might have resulted from the soil drenching method used during the experiment, which is known to use a large amount of water, which in turn can act as a medium for hexaconazole residue dissipated through the soil profile. Chai et al [27] agreed that high dissipation rates for acephate and methamidophos in the soil profile were observed due to high moisture content of the soils from the soil drenching method applied, and attributed to the preferential flow in soil profile. Previous studies indicated that the main transport modes of pesticide particles under field conditions via surface runoff (of splash-eroded particles) and through preferential flow (macropores) [28][29].…”