The manganese-containing pesticide known by its trade name Maneb has been extensively used in agriculture on a global scale since the 1950s. Maneb is a broad-spectrum, surface-acting fungicide which can be applied to a wide range of crops including potatoes, tomatoes, soy beans and bananas. Since Maneb has only a preventative effect, the fungicide needs to be applied repeatedly, resulting in large quantities of the substance being released into the environment. Despite its long history of usage, very little is in fact known about the substance. For example, neither its molecular structure nor coordination environment and oxidation state of the manganese centre were known with certainty until our first detailed studies from 2023.1 We developed a synthetic procedure which reproducibly affords good yields of high-purity Maneb. Since Maneb is insoluble in almost all solvents (except DMSO and DMF), any physicochemical analysis of Maneb in solution is challenging. However, with the help of XAFS, X-ray powder diffraction and electron diffraction we could elucidate the structure of the solid bulk material and thus also determine the coordination number and oxidation state of the manganese atom.
It has been observed that chronic exposure to Maneb affects the nervous system, resulting in development of symptoms similar to those of Parkinson’s disease. Indeed, reports of chronic neurotoxicity of manganese compounds go back as far as the late 19th century. At that time the resulting disease affecting the motor-system was referred to as manganese madness and later renamed manganism. Very little is however known on how Maneb exerts these neurotoxic effects. We therefore embarked on a detailed investigation of both in vivo toxicity and neurotoxicity of Maneb using the nematode Caenorhabditis elegans as model organism.2 In this presentation we will detail our approach to elucidating the structure of Maneb and we will discuss its toxicity and pathways leading to neurodegeneration.