I am not experienced but does he need to know the halflife or the
breakdown rate of the herbicide you recommended?

There is probably a low risk of him ingesting the chemicals through the
vegetables he plans grow there; one reason being that only the strong
ones would survive the weed killer in the soil.

In other countries, like France, the soil is very polluted as they used
plenty of chemicals to have the best looking, best growing, etc. plants
and now, especially in the vine growing areas, tap water is not
potable. Good luck!