An association with two specific biocides is reported and given the size and design of the study, the effects could be real. A plausible cumulative mechanism is supported. However, some data also suggest a lack of support for a cumulative mechanism. Previous reports from the same study failed to find a specific risk from rotenone or paraquat.
CM Tanner et al. Environmental Health Perspectives. (2011) doi: 10.1289/ehp.1002839
Statistically significant adjusted odds ratios for individual agents and when grouped by mechanism type, combined with a plausible mechanism suggest a causal role for the two pesticides.