"There is evidence that indium has a low order of toxicity; however, care should be taken until further information is available" [ Los Alamos National Laboratory's Chemistry Division ].
"Indium is considered a non-toxic element, never being reported any serious accident with this element. Even in welding or semiconductor industry, where the exposition to indium is relatively high, there is no report of any kind of toxicity." [ Nautilus ].
"Tests on animals show it would have to be 1,000 times stronger to sicken mice."
Fundam Appl Toxicol. 1995 Aug;27(1):140-8.
PMID: 7589924 [PubMed - indexed for MEDLINE]
Indium [sulfate] is very safe to use. Most other trace elements are not that safe. It is highly toxic, however, when injected into blood. Avoid contact with eyes, wounds, and cuts.