Characterisation of atmospheric deposition as a source of contaminants in urban rainwater tanks

Abstract

To characterise atmospheric input of chemical contaminants to urban rainwater tanks, bulk deposition (wet + dry deposition) was collected at sixteen sites in Brisbane, Queensland, Australia on a monthly basis during April 2007-March 2008 (N = 175). Water from rainwater tanks (22 sites, 26 tanks) was also sampled concurrently. The deposition / tank water was analysed for metals, soluble anions and selected samples were additionally analysed for PAHs, pesticides, phenols, organic & inorganic carbon. Flux (mg/m2/d) of total solids mass was found to correlate with average daily rainfall (R2 = 0.49) indicating the dominance of the wet deposition contribution to total solids mass. On average 97% of the total mass of analysed components was accounted for by Cl- (25.0%), Na (22.6%), organic carbon (20.5%), NO3- (10.5%), SO42- (9.8%), inorganic carbon (5.7%), PO43- (1.6%) and NO2- (1.5%). For other minor elements the average flux from highest to lowest was in the order of Fe > Al > Zn > Mn > Sr > Pb > Ba > Cu > Se. There was a significant effect of location on flux of K, Sb, Sn, Li, Mn, Fe, Cu, Zn, Ba, Pb and SO42- but not other metals or anions. Overall the water quality resulting from the deposition (wet + dry) was good but 10.3%, 1.7% and 17.7% of samples had concentrations of Pb, Cd and Fe respectively greater than the Australian Drinking Water Guidelines (ADWG). This generally occurred in the drier months. In comparison 14.2% and 6.1% of tank samples had total Pb and Zn concentrations exceeding the guidelines. The cumulative mean concentration of lead in deposition was on average only 1/4 of that in tank water over the year at a site with high concentrations of Pb in tank water. This is an indication that deposition from the atmosphere is not the major contributor to high lead concentrations in urban rainwater tanks in a city with reasonable air quality, though it is still a significant portion.