Q. What evidence is there that paraquat doesn’t cause Parkinson’s disease, as associations and correlations have been found?

The view that paraquat does not cause Parkinson’s disease is prompted by the absence of evidence that paraquat is causally related with this disease in humans. This absence of evidence comes after more than 40 years of product usage around the world. An analysis by independent senior medical and epidemiological scientists under the guidance of Professor Sir Colin Berry (Emeritus Professor at Queen Mary, University of London, and former member of the UK Medical Research Council) and Professor Pierluigi Nicotera (Founding Director of the German Center for Neurodegenerative Diseases, Bonn) has found no causal link between exposure to paraquat and Parkinson’s disease (Berry, C., La Vecchia, C. & Nicotera, P., (2010). Paraquat and Parkinson’s Disease. Cell Death and Differentiation ,17, 1115–1125). You can find more information here