Are there any studies on safety of aluminum ingestion but that really distinguish between peroral and intramuscular bioavailability of the aluminum inside the body?

Directly? No. What surfaced here is a model paper that does compare dietary (oral) and injected (vaccine) aluminum in infants by route, plus critique letters saying the injected-route toxicokinetics are still untested to a rigorous standard.

The closest match is the 2011 Vaccine paper by the pediatric aluminum pharmacokinetics team, which modeled infant aluminum exposure separately through diet (oral) and vaccination (intramuscular), with dose timing and a retention function for each route, concluding vaccine-plus-diet exposures stay below established minimal risk levels [4]. Two honest caveats. It is a compartment model, not a direct measurement study, so it answers bioavailability by assumption and math, not by serial sampling in babies. And the assumptions it uses for how much injected aluminum leaves the muscle are exactly what the independent researchers dispute; their 2020 letter says aluminum hydroxide particles are nearly insoluble at body pH, can persist inside cells, and may travel to lymph tissue and possibly the brain, and that this demands proper toxicokinetic studies rather than model reassurance [1]. The adjuvant review [2] confirms the injected particles are engineered to stay put and release slowly, which is the whole reason oral and injected kinetics cannot be assumed equivalent. Neonatal IV nutrition data exist for parenteral aluminum [3], but IV is not IM, so it does not answer your route question either.

What this retrieval cannot see: the broader toxicokinetic literature, including any head-to-head oral-versus-IM aluminum PK experiment in the same animals. Such work exists outside this sample (mitigating against the "never studied" read); none surfaced here. Note the modeling paper's safety framing is the version regulators rely on, and its key muscle-retention assumption is the contested variable, though nothing here shows who funded it.

My call: one route-distinguishing study was retrieved, and it is a model, while the independent critique explicitly says the question of where injected aluminum actually goes remains untested. Confidence: moderate that retrieval captured the main modeling work, low on the overall literature.