Nancy, I would also try to find as much as possible on the weedkiller. For example, a while ago, my evil neighbors were spraying weedkillers on my plants. I called the Ministry of Environment, Conservation and Parks and asked about the active substances in weedkillers. When you figure out which active substances have been used, you can do some research to find out how to get rid of the substance. There are probably other organizations that can provide the information.
In the meantime, I agree with Alex, flush as much as you can.