Seawater solubility of natural and anthropogenic metals within ambient aerosols collected from Taiwan coastal sites

To evaluate the bioavailability and environmental mobility of aerosol metals to the seas, ambient aerosol samples collected from two coastal sites, i.e., Hsiyu located at the southwestern tip of the Penghu Islands in Taiwan Strait and Santiaolun on the west coast of Taiwan were determined for the seawater solubility of Al, Fe, Mn, Zn, Ni, Cu, Pb and Cd. The experiment of dissolution kinetics suggested that almost all soluble fractions of studied aerosol metals could be released within I h. Thereafter, dissolved particle-reactive metals like Al, Fe and Pb exhibited a slight decrease, suggestive of re-adsorption to residual particles. Seawater solubility of selected metals from Hsiyu aerosols showed the following order: Al (1.3%) = Fe (1.1%) < Pb(20%) <= Cu (27%) < Mn (43%) <= Zn (45%) <= Ni (50%) < Cd (69%). However, solubility data from Santiaolun were larger than those from Hsiyu for all aerosol metals analyzed, attributable to different degrees of anthropogenic contributions to the two sites. Moreover, Pb and Ni showed a positive correlation between solubility and log crustal enrichment factor (EFcrust), indicating that the dissolvable percentage is, to some extent, dependent on the anthropogenic contribution for specific aerosol metals and likely due to the presence of considerable contaminants such as organic, acidic and carbonaceous substances for anthropogenic aerosols. In addition, for Al, Fe, Zn and Pb, inverse power-law (log-log) correlations between solubilities and dust loadings have been observed, suggesting that particle scavenging may follow dissolution for certain metals in the marine environment. In conclusion, the dissolution of aerosol metals in seawater is predominantly controlled by which origins dominate their contributions (such as crustal or anthropogenic derivatives) and the behavior of a specific metal in seawater (such as dissolution/adsorption). Aerosol metals have substantial impacts on diverse eco-environments and accurate assessments of environmental impacts of eolian metal depositions must be based on such informative data. Thus more simulation experiments relevant to dissolution of aerosol metals in various natural waters are merited. (c) 2005 Elsevier Ltd. All rights reserved.