Development of Hybrid Methods for Source Apportionment by Coupling Lead Isotope Ratios, Multi-Element Concentrations, and Meteorology on Archived Precipitation Samples

Can hybrid techniques that couple geochemical analysis of archived precipitation samples and meteorology be used to assess past environmental impacts from a source apportionment perspective? To assess this possibility, we measured lead isotope ratios and multi-element concentrations using High Resolution – ICPMS on archived precipitation samples that were collected over a 15 month sampling period (July 1995- November 1996) at Bondville, Illinois. Unique attributes of this sample site in central Illinois included proximity to Pb smelters (providing a fingerprint for Pb and other metals from point sources in southeast Missouri) which could be contrasted to urban emissions (Chicago and Indianapolis areas) and regional emissions from coal fired power plants. Methods development work for the HR-ICPMS analysis indicated that high precision lead isotope ratios from the precipitation samples could be achieved “as is”, with no need for column chemistry or other clean up steps, on samples with lead concentrations as low as 200 ppt, and with total sample consumption of less than one ml. Cluster analysis on Hy-split based meteorological data allowed the precipitation samples to be parsed into six distinct groupings. Major differences in lead isotope and elemental ratios were found to correspond with the meteorological cluster analysis results. We used the coupled meteorology and geochemical techniques to then calculate a precipitation based mass balance for lead and other elements, to apportion smelter derived lead from other natural and anthropogenic sources. Although impacts from smelter derived lead were substantial, impacts from urban areas were the predominant lead source in central Illinois in the mid 1990s. This example of the use of hybrid methods for source apportionment, suggests future studies contrasting past versus present metal emission, transport, and deposition processes using archived precipitation samples are feasible.