The pesticides and herbicides used today are SO much safer than in the days of DDT and Agent Orange it isn't even funny. They are required to break down in a matter of weeks rather than in years. The soil organisms and fungi will probably break down the small amount left that they will be such small traces left that they would be rendered undetectible. I wouldn't worry about it, really.

You can assume that any grain meal you buy has been treated with pesticides. You have to balance those residual concerns against putting chemicals directly on your lawn. For my own part I think its always better to support the slow-small changes in the market rather than wait for the perfect ones.

The corn kernels themselves are protected from direct spray by a sheath and tassels. Then to make CGM the kernels undergo the wet milling process to remove some of the carbohydrates leaving the higher protein powder we know as CGM as a byproduct. I would think the farther away from raw corn you get, but less and less amount of any pesticide residue would remain.