Blooming of insecticides from polyethylene mesh and film

Malaria remains a public health concern with vector control still the vital component of disease prevention, control, and elimination strategies. Recent years has seen a “stalling” in the progress made towards the reduction in the global malaria burden, highlighting the need to develop new, innovative, and safe alternative tools and delivery systems to achieve global malaria elimination. Interventions based on the use of indoor residual spraying (IRS) and long-life insecticidal bed nets (LLINs), i.e. insecticide-containing wall linings (IWLs), can contribute towards the reduction of malaria. Both LLINs and IWLs rely on the presence of insecticides on the fibre or filament surfaces. However, materials directly incorporating the insecticides into the polymer melt during extrusion, allows for effective killing of the mosquitoes when they come into contact with the surface of the material, only if there is insecticide present there. This means that the insecticide must migrate to the surface and precipitate there (bloom). Over time the internal concentration of insecticide will decay. This investigation was done using Fourier transform infrared spectroscopy (FTIR) in both the transmission and attenuated total reflection (ATR) modes to better understand the blooming of three World Health Organization-approved contact insecticides, i.e. alphacypermethrin, fipronil and chlorfenapyr, from mesh or film to better understand the likeliness of insecticides within the materials to migrate to the surface. Film-based samples were prepared in addition to wall lining mesh, because of their easier characterisation than the irregular shaped mesh filaments. FTIR, in ATR and in transmission modes, enabled the tracking of the migration of the three insecticides, over time to the surface of polyethylene mesh or film. This made it possible to estimate the apparent solubility of the insecticides in the polymer matrix. However, scanning electron microscopy (SEM) revealed that a portion of the insecticide is trapped, in a crystalline state, inside the polymer matrix. These results suggest the possibility of developing products-based insecticides for protection against infective mosquito bites in malaria-endemic regions.