Tracing lead pollution sources in abandoned mine areas using stable Pb isotope ratios

This study focused on Pb isotope ratios of sediments in areas around an abandoned mine to determine if the ratios can be used as a source tracer. For pretreatment, sediment samples were dissolved with mixed acids, and a multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS, Nu plasma II) was used to investigate the Pb isotopic composition of the samples. The measured isotope ratios were then corrected for instrumental mass fractionation by measuring the Tl-203/Tl-205 ratio. Repeated measurements with the NIST SRM 981 reference material showed that the precision of all ratios was below 104 ppm (+/- 2 sigma) for 50 ng/g. The isotope ratios (Pb-207/Pb-206) found were 0.85073 +/- 0.0004 similar to 0.85373 +/- 0.0003 for the main stream, while they were 0.83736 +/- 0.0010 for the tributary and 0.84393 +/- 0.0002 for the confluence. A binary mixing equation for isotope ratios showed that the contributions of mine lead to neighboring areas were up to 60 %. Therefore, Pb isotope ratios can be a good source tracer for areas around abandoned mines.