It's a false equivalency to compare an amount of a substance eaten vs injected. Injected substances can get to places in the body and in different quantities than substances eaten.
There are different forms of aluminum, with different absorption rates, and different potential behaviors in the body.
Here's a study of aluminum accumulation in rodents after injection: https://bmcmedicine.biomedcentral.com/articles/10.1186/1741-...
I don't think there are any studies showing that aluminum doesn't accumulate or remain in the body long after injection - while I've found ~5 studies indicating that it does.
Doesn't mean it's dangerous, just that some amount of it does stick around long term and it is not clear to me that it's a drop in the bucket compared to the aluminum we eat. We also eat a lot more aluminum than people used to before the industrial revolution. The amounts of aluminum we eat now could be mildly harmful too - I don't know about that.
Below is the math on amount of aluminum that a normal baby ingests vs gets injected. I got a result that a baby's first year they get between 2x to 65x as much aluminum in their blood from injections vs from feeding.
A baby drinking breast milk (250L in the first year) would get 250 * 40µg = 10mg of aluminum in their first year from breast milk. A baby eats around 300000 calories in their first year, which leaves 120000 not from breast milk. At a rate of 8mg of aluminum per 2300 calories this would be another 416mg of aluminum from food for a total of 426mg.
The absorption rate into the bloodstream of that aluminum would vary between ~0.01% (for aluminum hydroxide) to ~0.3% (for aluminum citrate), so they would get 0.04mg to 1.3mg of aluminum in their blood across the first year from ingestion. Compared to 0.125mg to 0.85mg per dose of vaccine. They get around 10 doses of vaccines containing aluminum in the first year, for around ~2.6mg of aluminum total, but 100% of that is absorbed since it's injected. So the amount that gets into the blood during the first year from vaccination is somewhere from 2 to 65 times the amount a baby would get in their blood from eating/drinking.
I could be wrong on this logic or math somewhere, and welcome being corrected.
Another aspect of this is that the injected aluminum adjuvant comes in big (relative to ingestion) sudden doses with the intent to trigger a significant immune response to the antigen. That could affect the body differently than a gradual very small daily dose.
Again, not claiming that injecting aluminum is dangerous, but it seems to me babies could be getting far more persistent aluminum in their bodies from injections than from food, and as far as I know this has not undergone a long term study showing that it's safe. Almost all vaccine studies have aluminum injected in both arms of the study, and I haven't found a single aluminum vs placebo study - please share if you have one.