Detection and dissolution of needle-like hydroxyapatite nanomaterials in infant formula

The unknowns surrounding presence, composition and transformations during the use phase of engineered nanoparticles (ENPs) in consumer products raises potential human and environmental health concerns and public discourse. This research developed evidence and confirmatory analytical methods to determine the presence and composition of ENPs in a consumer product with a complex organic matrix (six different infant formula samples). Nano-scale crystalline needle-shaped hydroxyapatite (HA; appx. 25 nm × 150 nm) primary particles, present as aggregates (0.3–2 μm), were detected in half the samples. This is the first report of these ENPs in infant formula. Dissolution experiments with needle-shaped HA were conducted to assess potential transformations of nano-HA particles. Rapid dissolution of needle-shaped HA occurred only under lower pH conditions present in simulated biological fluids (acidic gastric fluids), but not in simulated drinking water (near-neutral pH). Other non-nanosized HA minerals exhibited less dissolution under the same low pH conditions. This work demonstrates the occurrence of engineered nanomaterials in the food supply of a sensitive population (infants) and the need to consider transformations in nanomaterials that occur during use, which result in different exposures between pristine/as-produced ENPs and nanomaterials after passing through the human gut.