Solubility of Indium-Tin Oxide in simulated lung and gastric fluids: Pathways for human intake
Science of the Total Environment
From being a metal with very limited natural distribution, indium (In) has recently become disseminated throughout the human society. Little is know of how In compounds behave in the natural environment, but recent medical studies link exposure to In compounds to elevated risk of respiratory disorders. Animal tests suggest that exposure may lead to more widespread damage in the body, notably the liver, kidneys and spleen. In this paper, we investigate the solubility of the most widely used In compound, indium-tin oxide (ITO) in simulated lung and gastric fluids in order to better understand the potential pathways for metals to be introduced into the bloodstream. Our results show significant potential for release of In and tin (Sn) in the deep parts of the lungs (artificial lysosomal fluid) and digestive tract, while the solubility in the upper parts of the lungs (the respiratory tract or tracheobronchial tree) is very low. Our study confirms that ITO is likely to remain as solid particles in the upper parts of the lungs, but that particles are likely to slowly dissolve in the deep lungs. Considering the prolonged residence time of inhaled particles in the deep lung, this environment is likely to provide the major route for uptake of In and Sn from inhaled ITO nano- and microparticles. Although dissolution through digestion may also lead to some uptake, the much shorter residence time is likely to lead to much lower risk of uptake.
This paper was in part supported by the Natural Environment Research Council (NERC, NE/L001896/1). The authors benefited from advice from and discussions with Dr Adam Feldman, sample preparation and X-ray diffraction by Dr Gavyn Rollinson, and ICP- MS analysis by Sharon Uren.
This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.
Available online 16 November 2016