The question does not have a sure answer, but we can say that unless this material has been soaked in something other than water, or unless something (bacteria, mold) is growing in it, it does not pose any risk - not toxic. In fact the best way to dispose of any agricultural/horticultural product is according to the label instructions.

It's likely less beneficial than it would have been if it had been properly stored. In your shoes, I'd apply this at the label rate.