Scandium as a reference element for quantifying the natural and anthropogenic concentrations of lead in surface water and groundwater

Scandium has been used to distinguish between natural and anthropogenic sources of lead to the atmosphere. Here, scandium is used to estimate the natural abundance of lead in surface and groundwater. In pristine groundwater sampled at the Elmvale Groundwater Observatory in southern Ontario, the lead/scandium mass ratio (Pb/Sc) ranges from 1.1 to 1.2, similar to the ratio (1.2) most recently proposed for the Upper Continental Crust. In the Athabasca River of northern Alberta, where dissolved lead is well below the global average for uncontaminated river water, the average Pb/Sc ratio was 2.2 in 2014 and in 2015, consistent with the Pb/Sc ratio recently compiled for soil (2.3). In contrast, the average Pb/Sc ratio in the rivers and lakes of central Ontario was 6.0, reflecting the far larger cumulative inputs of anthropogenic, atmospheric lead in eastern Canada compared to western Canada. Support for this interpretation comes from contemporary snow from southern Ontario with an average Pb/Sc ratio of 400. Despite the profound differences in the geology of the study regions, and ignoring the geochemical processes affecting both elements in the watersheds, scandium appears to be a helpful, simple tool for estimating the natural abundance of lead in surface and groundwater. However, the use of the Pb/Sc ratio in this way depends critically on accurate, precise and sensitive measurements of both elements. While the problems of low level lead determinations are well known, those of scandium may have been underestimated.