Figure 5

Scatter plots between lead (Pb) and thorium (Th) concentrations in (A) the suspended solids in the main stem of the Athabasca River (AR) and (B) the dust particles in snow samples collected from five peat bogs in the study area. The slopes of the regression lines (1.6) between Pb and Th in both graphs are similar to the ratio in the Upper Continental Crust^57,58. ^aThe Pb/Th ratio in the water samples studied here is also compared with the Pb/Th ratio in groundwaters collected from the HDPE well of the Elmvale Groundwater Observatory. The HDPE tubes and screen used to construct this well (known as EGO-2) are from Rotek (Denmark); they had been shipped to the University of Heidelberg, Germany, for cleaning in HNO₃. After rinsing, drying in metal-free, laminar flow clean air cabinets, and packing in sealed PE bags, the well materials were shipped from Germany to Canada and installed near (3 m) but hydrologically upgradient of EGO-1, a flowing, artesian groundwater sampling well constructed entirely of stainless steel. Water samples are collected from the EGO-2 (HDPE) well via a purpose-built, acid-cleaned Teflon valve, within a metal-free, laminar flow clean air cabinet. Both of these flowing, artesian wells near the Village of Elmvale, Ontario, emanate from an aquifer at a depth of 13 m: together they are known as the Elmvale Groundwater Observatory and are dedicated to the study of trace metals in water. The water samples were collected in March of 2011 and all measurements performed at the University of Heidelberg, Germany using an Element 2 ICP-SMS (Shotyk and Krachler, unpublished data). The data presented here from EGO-2 represents water samples (n = 10) that were collected using acid-cleaned HDPE bottles provided by Dr. Jiancheng (James) Zheng of the Geological Survey of Canada, Natural Resources Canada, Ottawa. In fact, these are the same types of bottles, prepared in the same manner, used in the study of Pb in the ice core from Devon Island, Nunavut, in the Canadian Arctic^4,44. The Pb/Th ratio in the particulate and dissolved fractions of the AR is remarkably similar to the Pb/Th ratio found in this groundwater. ^bPb/Th ratio in the Upper Continental Crust/10.