Hi, 

We are not medical professionals but think that it should be ok to use still. You wouldn't want any pets roaming on the area your are spreading seed anyways and anything should breakdown and start decomposing when exposed to the sun. If the seed is too old or hasn't been temperature controlled it may not be viable anyways. 

Wildlife is exposed to all kinds of animal droppings anyways so there shouldn't be an issue with that. 

You can make sure to wear gloves or a face mask when using it if you are concerned and just wash hands afterwards. 

If you are still wanting to dispose if it, you can just put in your trash collection or a yard waste pick up. The composting process at county level is hot enough to kill any disease and the grass seed. 

Emily