The answer to your questions lies in the half-life. While these chemicals are insecticidal/fungicidal, they do break down. Thiram has too many sulfurs in it to be a very stable molecule; any bacterium hungry for sulfur will be able to bite into it. The whole thiophosphate part of the chlorpyrifos molecule is just waiting to fall apart when hit by bacterial or fungal digestive enzymes. If you plant your seeds into healthy soil, the bacteria and fungi present in the soil will go to work on these two and eventually (i.e., by harvest time) there will be very little of these left to detect, even if you scour through the soil.
Like any compounds, these could be transferred into the plant, then into the goat that eats the plant, then into the milk the goat gives, but only with severe attenuation every step of the way. If you have healthy soil, maybe only 1/10 of 1% of the chemicals would be picked up intact by the plant. If it doesn't have a pathway to degrade it, the chemical stays in some walled off cell body until the animal eats it and starts digesting it. If the animal has a healthy rumen, maybe only 1% of that will not be metabolized and excreted by the animal. If the animal has a few parts per billion (ppb) in its system, then yes, the animal's milk will have a similar number of ppbs. You can see that it wouldn't take too many steps before the amount of chemical reaches the parts per trillion level, a level that even the best equipped chemical laboratory has difficulty detecting.
And to go Ken one better, the solution to pollution is to remove the pollution before you even plant the seed. You may have done some pre-soaking techniques to speed germination; you can use these same techniques to wash off the chemicals on your pre-treated seeds before you plant them. Take your sorghum seed, agitate it with some
water for 5 minutes, let it drain; then repeat. Maybe even add some bleach or alcohol to the water. Bleach can oxidize chlorpyrifos, breaking the molecule apart. Alcohol is a better solvent for these organic molecules and will enable the rinse water to hold more of the stuff you are trying to wash off. After you have washed your seed, plant as you normally would.
Now what to do with that rinse water that contains thiram/chlorpyrifos/alcohol/bleach? I would throw it into a
bucket of
wood chips and let it dry. The alcohol and the water go away. Then you are left with wood chips with thiram/chlorpyrifos/bleach residue. Put those chips into a
biochar burn. Once those chips turn into little black bits of char, it's going to be impossible to find any remaining residue of the chemicals.