There is not, insofar as lead tends to be either inspired or ingested in contaminated water. For most people, it's the former. The "oral chelators" just bind lead that is mixed in with them, stopping you from absorbing as much of it. That is, Senapati 2001 (the garlic-rat study) didn't give lead acetate in the morning and garlic in the afternoon; they intentionally mixed the two together.

That is, oral intake of lead with oral intake of garlic, means maybe you shit out more lead with the garlic chelation agent. But lots of garlic will do nothing for water you drink later in the day, or the air passing into your lungs.

There may be some additional anti-oxidant activity. Anti-oxidants are good for you across the board. Have at them.

As to a safe blood lead level: depending on your local public health department, 5 mcg/dL will or should prompt public health action. <5mcg will usually prompt a doctor to start trying to figure out where you're exposed, and cut that exposure out. >5mcg turns into a little bit of a grey area depending on where you are, and by 10mcg your kid is getting chelation therapy. These numbers are built around children, not adults, because they're far more susceptible to the adverse effects of lead exposure.

That said, we have not identified any safe lead level - every level that has been tested has been shown to be associated with some sort of negative cognitive developmental impact (Lanphear 2000). I feel comfortable saying the safe level is "0", but that's not medical consensus, that's just my opinion.