duckluck,
I remember working in eastern Ohio, where a certain type of fescue was planted. This fescue would become infected with a fungus - an endophyte - and eating infected fescue caused fertility and birthing problems with horses. What a world!
Thanks for the links, fellow duck lovers . ...
Not to complicate your life, but I make a soil I learned from the Square Foot Gardening system. It's called Mel's Mix. You can make a variation on it. It is one part peat moss, one part coarse vermiculite, one part compost. For grass, you may not need the vermiculite. Can you find peat...
Many grass seeds are treated.
One option is getting wheat berries - wheat is a kind of grass. Also, rye is a nice, high-protein grass that grows pretty nicely. Both can be bought untreated as bulk grains in a health food store or similar store. You might be able to get untreated grass seed...