Technically, it is not zero tolerance, but it is very low. If the concentration is less than 1.0% Fertilizer pellets, they are considered as stone. Anything over 1.0% is held suspect contaminated grain.
The tricky part is anything over 0.05% in all grades becomes up to the buyer to call it rejected account stones, or sample account stones.
And anything over 2.5% fert pellets becomes sample salvage (pretty much landfill).
I would suggest if your numbers are not really high, call around, tell them what you have. You are going to take a kick in the pants on price, but it is better than paying a landfill to dump it for you. If you have an elevator that handles enough canola and they have the time they may special bin it for you and blend or IP ship it to the coast and blend it there.