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

Well Tridopyr is ether and the soil association accept it's use to a
certain extent. I don't know too much about the stuff, I'm a totally
organic gardener, but if there's one thing someone would propose, then
triclopyr is the safest as it degrades the fast. However I would not
use Roundup.

For my brambles, I cut low then i dig .... and dig.... and dig till I
get all root out.

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.

This stuff is selective - some organic growers uses it for

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.

Mmmmm.... a bit of a large generalisation here I think ;o)

Good luck!

Definitely if the OP decides to go for the digging method indeed!!