Changes in oral bioaccessibility of heavy metals in non-digestive sucking habits due to the formation of complexes between digestive fluid components and metals/metalloids

Abstract

Humans, especially infants, are exposed to harmful substances through various means, including non-nutritive sucking behaviors. Here, we compared the “one-compartment model” and the “three-compartment model” within the “suck model” to assess the oral bioaccessibility of heavy metals in various products and evaluated whether these models can be employed to assess 12 heavy metals present in consumer products. Several certified reference materials, including plastic, paint, glass, and metals, were employed to ensure sample homogeneity. By comparing the two models, we validated that a considerable amount of complexes were formed between saliva components and the extracted heavy metals and that some of these complexes dissociated during reactions with the gastric/intestinal fluids. Furthermore, we observed that in the cases of Cu and Pb, additional complexes were formed as a result of reactions with gastric/intestinal fluids. We measured the total concentrations of the extracted heavy metals using artificial saliva through acid digestion and found that up to 99.7% of the heavy metals participated in the formation of complexes, depending on the characteristics of the sample (e.g., composition) and the target element. This result indicates that the current suck model may notably underestimate the oral bioaccessibility of heavy metals in products associated with sucking behaviors. Therefore, we propose a more conservative and simpler test method for assessing oral bioaccessibility of heavy metals that involves measuring the total concentrations of heavy metals extracted from consumer products using artificial saliva. By doing so, we can account for potential variations in the digestive milieu (e.g., due to ingested food) and the inconsistency in complex formation-dissociation characteristics.