Metolachlor persistence in laboratory and field soils under Indian tropical conditions

Abstract

Metolachlor [2-chloro-N-(2-methoxy-1-methylethyl)-2'-ethyl-6'- methyl acetanilide] dissipation under both field and laboratory conditions were studied during summer season in an Indian soil. Metolachlor was found to have moderate persistence with a half-life of 27 days in field. The herbicide got leached down to 15-30 cm soil layer and residues were found up to harvest day of the sunflower crop in both 0-15 cm and 15-30 cm soil layers. Metolachlor was found to be more persistent in laboratory studies conducted for 190 days. The rate of degradation was faster in soil under flooded partial anaerobic conditions as compared to aerobic soil with a half-life of 44.3 days. In aerobic soil, metolachlor was very stable with only 49% dissipation in 130 days. Residues remained in both the soils up to the end of the experimental period of 190 days.

Biomonitoring of exposure to pesticides

“…The currentuse or contemporary pesticides include OP, carbamates, and pyrethroid insecticides, and triazine, chloroacetanilides and phenoxy herbicides and are considered nonpersistent. These pesticides have much shorter environmental half-lives [22][23][24][25][26][27][28][29][30] and tend not to bioaccumulate. In fact, most of these pesticides are excreted from humans within 24 hr as the parent pesticide, a mercapturic acid detoxification product, oxidative or dealkylation metabolites, and/or glucuronide-or sulfate-bound metabolites.…”

Effect of Light on the Degradation of Two Neonicotinoids viz Acetamiprid and Thiacloprid in Soil

“…It has been reported in literature that among various biotic and abiotic transformation processes, photodegradation is an important factor influencing the fate of pesticides in the field (Konstantinou et al 2001). In practice also it has been observed that pesticides persist longer under laboratory studies as compared to field studies (Sanyal et al 2000;Ganier et al 1996;Fernandez et al 2001). Also surface residues following foliar spray degrade faster than the translocated residues inside plant matrix even though physiological activity is more inside the plant matrix.…”

Environmental Fate Considerations for Pesticides in Tropical Ecosystems

“…When endosulfan was applied to field soil columns in a Philippine rice field, the dissipation rate was slower as it passed down the columns [21]. The same behavior has been reported for metalochlor and in both cases it was attributed to reduced microbial degradation in the subsurface soil layers [22] The dissipation of the herbicides, hexazinona, tebuthiuron, imazapir and glyphosate was studied under tropical conditions in Hawaii, Peru, and Panama [23]. Dissipation occurred much faster under these tropical than temperate conditions.…”

“…New growth was observed a few months after treatment in Peru and Panama. Under field conditions, metalochlor had a half-life of 27 days though residues remained in the soil after the growing season [22]. In laboratory studies, the half-life of metalochlor under flooded conditions was 44.3 days as opposed to aerobic conditions when it was considerable longer being more than 130 days.…”