She believes scientists must do more research on the effects of exposure to multiple chemicals. She also says more work must be done to see how much of these chemicals people are exposed to. It is often not clear exactly how much of a pesticide remains on crops by the time they reach the dinner table, she said. Without the use of herbicides like paraquat, crops can be choked by weeds. Maneb frequently shows up as a slight residue, while paraquat usually shows up just in trace amounts, said Cory-Slechta.
Exposures can also occur via other routes.
Often the two pesticides are used at different stages of the growing cycle. The real issue is what happens when they hit humans in the food chain. The University of Rochester team is currently pursuing several new avenues of research, with funding from the National Institutes of Environmental Health and Safety. Preliminary findings indicate that the Parkinson's like effects on mice may be permanent, and that older mice may be more sensitive to the combination than younger mice. The team is also studying the effects of exposure to the mixture early in life, and they have shown that mice with the same genetic abnormality that causes some people to develop Parkinson's are particularly vulnerable to the mixture.