Abstract
Pyrethroids are among the insecticidal compounds indicated by the World Health Organization for mitigation of vector-borne diseases. Active deltamethrin (with chiral configuration α-S,1-R-cis) is one of the most effective pyrethroids characterized by low toxicity to humans, and it is currently tested as active ingredient for insecticidal paints. Nevertheless, several degradation processes can occur and affect the insecticidal efficacy in the complex paint matrix. In the present study, a detailed NMR analysis of deltamethrin stability has been carried out under stress conditions, mimicking a water-based insecticidal paint environment. Two novel by-products, having a diastereomeric relationship, were identified and their structure was elucidated by combining NMR, HPLC, GC-MS, and ESI-MS analyses. These compounds are the result from a nucleophilic addition involving deltamethrin and one of its major degradation products, 3-phenoxybenzaldehyde. Given the known toxicity of the aldehyde, this reaction could represent a way to reduce its concentration into the matrix. On the other hand, the toxicology of these compounds towards humans should be addressed, as their presence may adversely affect the performance of deltamethrin-containing products.
Highlights
Pyrethroids are among the insecticidal compounds indicated by the World Health Organization for mitigation of vector-borne diseases
Formulations commonly termed as insecticidal paints (IPs) have been developed; the active ingredient is added to the paint to provide a “ready-to-use” product in which the insecticide is released in a controlled way once the paint is dried [5,6,7]
A-DLM converts to its inactive stereoisomer inactive deltamethrin (i-DLM) quite slowly compared to other water miscible organic solvents
Summary
Pyrethroids are among the insecticidal compounds indicated by the World Health Organization for mitigation of vector-borne diseases. Two novel by-products, having a diastereomeric relationship, were identified and their structure was elucidated by combining NMR, HPLC, GC-MS, and ESI-MS analyses These compounds are the result from a nucleophilic addition involving deltamethrin and one of its major degradation products, 3-phenoxybenzaldehyde. Spraying (IRS) method, which consists in spraying residual insecticide on the interior walls of houses [2] Both solutions have a limited effect though, and the need to find more effective vector control strategies is still compelling [3]; a recent approach promotes the use of Insecticide-Treated durable Wall Linings (ITWL) for protecting interior house walls [4]. Water-based paints are generally preferred because their use helps in reducing volatile organic compounds (VOCs) emissions, albeit temperature and humidity can constitute an issue for the stability of the formulation [8,9]
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