Aerosol trace element solubility determined using ultrapure water batch leaching: An intercomparison study of four different leaching protocols

Abstract

Solubility of aerosol trace elements, which determines their bioavailability and reactivity, is operationally defined and strongly depends on the leaching protocol used. Ultrapure water batch leaching is one of the most widely used leaching protocols, while the specific leaching protocols used in different labs can still differ in agitation methods, contact time, and filter pore size. It is yet unclear to which extent the difference in these experimental parameters would affect the aerosol trace element solubility reported. This work examined the effects of agitation methods, filter pore size, and contact time on the solubility of nine aerosol trace elements and found that the difference in agitation methods (shaking vs. sonication), filter pore size (0.22 vs. 0.45 �m), and contact time (1 vs. 2 h) only led to small and sometimes insignificant difference in the reported solubility. We further compared aerosol trace element solubility determined using four ultrapure water leaching protocols, which are adopted by four different labs and vary in agitation methods, filter pore size, and/or contact time, and observed good agreement in the reported solubility. Therefore, our work suggests that although ultrapure water batch leaching protocols used by different labs vary in specific experimental parameters, the determined aerosol trace element solubility is comparable. We recommend that ultrapure water batch leaching be one of the reference leaching schemes and emphasize that additional consensus in the community on agitation methods, contact time, and filter pore size is needed to formulate a standard operating procedure for ultrapure water batch leaching.