I recently had something similar happen, I had made a bucket of 4 pints glyphosate from powder to eradicate some bindweed, unfortunatly I spilt it on the lawn. As I expected a large patch turned brown and died, but there was a suprise, it was a perfect shape with razor sharp edges all the way around. I hadn't thought about the way it would look, but I must have expected something else such as a totally dead patch with sick grass around it.

The soil must have been saturated wtih glyphosate, but I managed to get grass seed germinating there within two months. Also, the edge was so sharp and visible I'm convinced it only killed the grass it touched and did not leach in to the ground killing plants via their roots. However, in comparison I have a few dead patches in the lawn over a year old where my 'helpful' step dad sprinkled a little salt on the slugs to kill them. No ammount of grass seed or watering to wash the salt down below the root level will revive these patchs. I'm going to have to dig them out with a trowl and discard the soil as it's useless and toxic to plants. In summary, four pints of glyphosate proved less toxic to my lawn than a teaspoon (perhaps desert spoon if you want to be generous with the estimate) of table salt.

I suspect the adversion to these products is more psychological than scientific because people assume something sold to kill plants/bugs/rodents must be really toxic and full of bad chemicals. Bizarely, those fear inspiring lables with skull and cross-bone symbols and warnings in huge red lettering have to be on weed killers regardless of what's in then, in fact if I was to mix vinegar and salt from my kitchen cupboard with water and sell it as weed killer I would have to by law put one of those lables on it, even though you could safely eat it on chips!