Howdy. I'm not an expert like the other guys, but this forum lead me to read the Humanure Handbook by Joe Jenkins. But not for humanure as much as the miracle of composting built right. This book really laid to rest many questions about toxins and chemicals in the compost and what is best for them.

It's as if composting can cure the entire world, but only if they're built. If you build it, they will heal it. Hmmm.. kinda catchy

When in doubt, build a segregated compost pile.

Call the county ans ask them what they are using and how to spell it.

Then look it up and see what the characteristics are, or post the proper name here and we can look it up for you.

Because right now there's not enough info to give you an answer.

I talked to the county extension agent. He said the herbicide likely used was 2,4-D. He also told me that it only stays in the environment for a few weeks before it gets broken down. I figure, any byproducts from decomposition have likely been washed down stream after a year has passed.
The water hyacinth is coming back with a vengeance so I know there is little to no intact herbicide left. I'm going to start gathering and composting again before they spray again.

If this is new growth that has not been sprayed, absolutely it will be fine.

2,4-D is a very common herbicide used in lawn weed & feed. It will break down in a reasonable time, so I wouldn't worry about composting that material even if it had been recently sprayed. I would not use it (or treated grass clippings, etc.) directly in the garden as mulch, but in the compost, no problem.