In 2008 vegetable crops were damaged through residues of this weed killer chemical in livestock manure. Despite campaigns by numerous organisations the Advisory Committee on Pesticides agreed aminopyralid by Dow Chemicals could go back on the market. See eBay! 

To Test for Contamination

Take samples from various parts of the manure heap, chop it up and mix with equal parts of the same volume of multipurpose compost. Sow tomato seeds (these germinate quickly). If the seedlings are distorted, don’t apply to your plot as the manure may be contaminated. If your manure is contaminated you’ll need to break down the chemical. Spread a few inches over an area of ground. Soak it well and break down any lumps. Rotovate or dig into the ground, then dig over every month.

After few months try the tomato test again. Is it safe to eat plants grown in contaminated compost?

Back in 2008 Dow was advising NOT TO EAT plants from contaminated soil.