There is growing evidence that paraquat has chronic effects on the brain. Numerous studies – many based on animal experiments, but also epidemiological studies – have showed the possible role of pesticide exposure, in particular paraquat, in the risk of developing Parkinson’s disease (PD). Parkinsonism has been linked to insufficient levels of dopamine in the brain. In tests on animals it has been found that paraquat is toxic to dopamine-producing nerve cells.

References:

Hertzmann C, Wiens M, Bowering D, Snow B, Calne D, Parkinson's disease: a case-control study of occupa-tional and environmental risk factors, American Journal of Industrial Medicine 17(3), 349-355, 1990