2:30 PM - 2:45 PM
[HTT18-15] Investigation on the possibility of the identification of air pollutant sources using stable isotope ratios of lead and strontium
Keywords:stable isotope ratio, air pollution, heavy metal, lead, strontium, rainwater
In our study, rainwater was collected in a polyethylene bottle, on the top of which a polypropylene funnel was set, separately in every rainfall event from June 2016 to August 2018 at the campus of Osaka Prefecture University in Sakai, Osaka, Japan. The isotope ratios of Pb and Sr (207Pb/206Pb, 208Pb/206Pb, and 87Sr/86Sr) in the rainwater samples were measured using a multi-collector inductively coupled plasma mass spectrometer. Concentrations of heavy metals (Fe, Mn, Cd, Cu, Ni, and Pb), inorganic ions, pH, EC, TOC, COD, T-N, and T-P were measured as water quality parameters. Rainfall amount was measured with a rain gauge set near the rainwater sampling point. Other meteorological data needed to investigate and estimate the pollutant sources, such as air temperature, wind direction, and duration of drought, were obtained from the Japan Meteorological Agency.
There was no obvious trend either chronologically or seasonally for 207Pb/206Pb or 87Sr/86Sr. The values of the 207Pb/206Pb ratio declined slightly during the observation period, but the 87Sr/86Sr ratio did not show this chronological variation.
There was no obvious correspondence between most of water quality parameters and each isotope ratio. The 207Pb/206Pb varied widely during events in which Cr and Fe concentrations were low, but was close to 0.871 as the concentrations of these metals were getting higher. There is similar tendency in 87Sr/86Sr for Fe and Cr. It was suggested that these metals might be derived from the same source.
For correspondence with meteorological factors, the monthly rainfall amount weighted average of 207Pb/206Pb fluctuated when the wind from the west or the west-southwest was dominant, while it took almost a unique value for the south-southwest. It was suggested that Pb was originated from various sources with the west wind.
Plots of the obtained data on the 207Pb/206Pb vs. 208Pb/206Pb were distributed upside and parallel to the lead isotope growth curve. When comparing our plots with the previous global studies, we found that ours were distributed in a manner similar to those from China and Russia. It was indicated that it is difficult to identify pollutant sources from these countries, which are thought to cause transboundary pollution in Japan.
Further research, including the collection of data on isotope ratios as environmental tracers, is necessary to identify pollutant sources using isotope ratio of Pb and/or Sr.