Proposal to Evaluate Bioaccesibility and Mobility for Elements of Environmental Concern In Collected Samples from the North American Soil Geochemical Landscapes Project

The Mexican Geological Survey, U. S. Geological Survey, and the Geological Survey of Canada are collaborating on the North American Soil Geochemical Landscapes Project, which has as its long-term goal to establish the geochemical cartography of soils in North America. Our knowledge about the variability in chemical composition of soils in North America is very limited, thus inhibiting our ability to recognize and quantify changes in soil composition caused by urbanization, industrialization, agriculture, mining, waste disposal and other human activities. The resulting data set will also enable us to provide better estimates of background values (i.e., natural geochemical concentrations) of elements in soils.

Sampling for the Mexican portion of the Project is based on the grid of the Global Geochemical Reference Network, integrated by 100 cells of 160x160 km, covering the Mexican territory. Each cell is then divided into 16 subcells of 40x40 km, for a total of 1600 potential sampling points (plus field duplicates). Results of total recoverable content for 48 chemical elements in a pilot transect composed by 19 cells of 40x40 km are available (plus field duplicates, a total of 24 samples). However, the evaluation of total recoverable content of these 48 elements using ICP-mass spectrometery (prior digestion), is only enough to determine background values, but is not designed to evaluate mobility and/or bioaccesibility for elements of environmental concern such as As, Hg, Cd, Cu, Zn y Pb, in the same background soil samples.

For assessing bioaccesibility and mobility, the use of established methods in the Norma Oficial Mexicana NOM-147-SEMARNAT/SSA1-2004, are proposed. This regulation is used to determine remediation levels in impacted soils with As, Ba, Be, Cd, Cr, Hg, Ni, Ag, Pb, Se, Tl and V.

Achieving these evaluations will provide a better view about environmental quality and potential use of soils in México.