The North American Soil Geochemical Landscapes Project: Overview, Goals, Progress

Documenting the natural variability of potentially toxic elements such as mercury, arsenic, and lead in soil is one of the great challenges to the environmental regulatory, risk assessment, and earth science communities. At present, agencies involved with human health and environmental risk assessment and management have no common understanding of soil geochemical background variation for the continent of North America and the processes that control this variation. The North American Soil Geochemical Landscapes Project, a tri-national initiative among the United States, Canada, and Mexico, was designed to (1) develop a continental-scale framework for generating soil geochemical data and (2) provide soil geochemical data that are useful for a wide range of applications and disciplines.

The Project is based on low-density sample collection over a spatially balanced array of 13,215 sites for the North American continent (1 sample site per approximately 1,600 km²). There is a core set of samples to be taken at each site, and each country may add additional sample types to meet the needs of users. The core sampling protocols represent both depth-based and horizon-based samples. One depth-based sample is taken from 0 to 5 cm regardless of what soil horizon this represents. A composite of the A horizon and a composite of the C horizon are also collected at each site. The 0-5-cm and A-horizon samples are more likely to represent anthropogenic influence on soil composition, and the C-horizon sample will be more representative of geologic influence. Each sample is sieved to <2 mm and then ground to <150 µm prior to chemical analysis for over 40 major and trace elements. In addition, a separate sample of 0-5-cm soil will be collected for the determination of Bacillus anthracis (anthrax).

Sampling was initiated in 2007 and is expected to be completed in approximately ten years.