Variable Valence State of Trace Elements Regulating Toxic Potencies of Inorganic Particulate Matter

Trace element is known to be one major component in determining particulate matter (PM) toxicities. However, there is still no accurate assessment of the toxic potency of the mixed valences. Here, we reported the oxidative stress and cytotoxicity potencies of 14 trace elements in their various valence states and estimated the toxic gaps of inorganic PM resulting from variations in element valences. Substantial discrepancies of up to 3 orders of magnitude in toxic potencies were observed among their different valences. When considering their abundance in PM, the toxicity gaps are estimated to range from 5 to 6 times between the greatest and weakest toxic valence states in the inorganic PM emitted from industrial sources, with iron contributing to 65.5%–91.0% of the overall gaps. Furthermore, the relative toxic variation of inorganic PM shows a significant correlation with the additive toxicities of Fe(II) and Fe(III) ions during aging process. The finding highlights that the multiple coexisting valence states of trace elements in PM need to be taken into account when estimating their toxic potencies.