Fate of the insecticide lambda‐cyhalothrin in ditch enclosures differing in vegetation density

Abstract

Use of the insecticide lambda-cyhalothrin in agriculture may result in the contamination of water bodies, for example by spray drift. Therefore, the possible exposure of aquatic organisms to this insecticide needs to be evaluated. The exposure of the organisms may be reduced by the strong sorption of the insecticide to organic materials and its susceptibility to hydrolysis at the high pH values in the natural range. In experiments done in May and August, formulated lambda-cyhalothrin was mixed with the water body of enclosures in experimental ditches containing a bottom layer and macrophytes (at different densities) or phytoplankton. Concentrations of lambda-cyhalothrin in the water body and in the sediment layer, and contents in the plant compartment, were measured by gas-liquid chromatography at various times up to 1 week after application. Various water quality parameters were also measured. Concentrations of lambda-cyhalothrin decreased rapidly in the water column: 1 day after application, 24-40% of the dose remained in the water, and by 3 days it had declined to 1.8-6.5%. At the highest plant density, lambda-cyhalothrin residue in the plant compartment reached a maximum of 50% of the dose after 1 day; at intermediate and low plant densities, this maximum was only 3-11% of the dose (after 1-2 days). The percentage of the insecticide in the ditch sediment was 12% or less of the dose and tended to be lower at higher plant densities. Alkaline hydrolysis in the water near the surface of macrophytes and phytoplankton is considered to be the main dissipation process for lambda-cyhalothrin.

Effects of the pyrethroid insecticide gamma-cyhalothrin on aquatic invertebrates in laboratory and outdoor microcosm tests

“…Thus, it appears that the aquatic risk profile of LCH, in terms of relative species sensitivity, population effects and community response in a complex exposure system can largely be attributed to the single active enantiomer GCH. This indicates that the fate and behavior of the active enantiomer in LCH is not dissimilar to that of the inactive enantiomer, as indicated by the rapid dissipation of GCH from the water column in our study (with 40% of dose remaining in the water column after 1 day) which was similar to that reported for LCH (Leistra et al 2003;Roessink et al 2005). Therefore, the microcosm data illustrate that the two enantiomers making up LCH have similar fate profiles, with the single enantiomer GCH demonstrating up to twice the level of toxicity to aquatic invertebrates as the racemate LCH.…”

Ecological Effects of Spring and Late Summer Applications of Lambda-Cyhalothrin on Freshwater Microcosms

“…Treatments were made by pouring a carefully measured volume of treatment solution into the enclosures, after which the water column was gently stirred to mix the compound throughout the water column without disturbing the sediment. Methods of application and chemical analysis are further described in Leistra et al (2003).…”

“…Brock et al (1992), for example, showed for chlorpyrifos that the mixing of the compound through the water column was strongly influenced by the vegetation structure in microcosms. For lambda-cyhalothrin, it has been demonstrated that different densities of macrophytes can have considerable influence on the fate and bioavailability of this compound (Hand et al 2001;Leistra et al 2003). Experiments with chlorpyrifos simulating different environmental conditions indicated that at higher water temperatures, and in combination with higher light intensities, dissipation rates increased (Van Wijngaarden et al 2005).…”

“…The pyrethroid insecticide lambda-cyhalothrin was used as the test compound. Lambda-cyhalothrin was chosen because it is highly lipophilic and tends to bind rapidly and strongly to organic materials (Maund et al 1998;Leistra et al 2003). Consequently, seasonal changes in biomass of plants and algae in aquatic ecosystems may affect exposure to this compound.…”

“…Leistra et al (2003) studied the fate of the compound. Separate enclosures were installed to follow the dynamics of lambda-cyhalothrin in detail.…”