World’s Soil Resources

Figure 14.2 Map of Superfund sites in the contiguous United States Yellow indicates final EPA National Priorities List sites and red
indicates proposed sites. Source: EPA, 2014a.
In Canada, because it has a huge expanse of soil and a relatively small population, soil contamination in
a spatial context is a relatively minor issue. However, the most agriculturally productive soils and greatest
density of population and industry occur concomitantly along the narrow region close to the southern border.
This is also the region where there is the greatest potential for soil contamination. In addition, the hinterland
has widely dispersed petroleum and mineral resource industries that form hot spots of soil contamination
(Doyle et al., 2003).
More insidious is non‐ point‐ source, dispersed contamination (Chan et al., 1986). For example, field crop
soils surveyed throughout the Mixed Wood Plains ecoregions of southern Ontario in Canada showed elevated
levels of Ba, Cd, Mo, Pb, Sb, Se, Nb, U and Zn, which were speculatively attributed to non‐ specific urban sources
such as road dust (Sheppard et al., 2009). Watmough and Hutchinson (2004) came to a similar conclusion
about Pb in forest soils of Southern Ontario. Toxicity in soil from such sources, however, is a relatively remote
possibility.
There is concern about soil contamination by agricultural activities, especially as farms increase in size
and effectively become industrial point sources. For example, soils in areas of livestock facilities have been
found to have metal levels that exceed Canadian soil quality guidelines (Sheppard and Sanipelli, 2012). Some of
these metals came from livestock pharmaceuticals (e.g. Bi in teat dips). The contribution of livestock manures
containing antibiotic residues to the development of antibiotic-resistant genes in the environment is a growing
public concern. In a few cases, the naturally occurring, trace element bioavailability of some Canadian soils
has resulted in food crops with amount of elements that exceed guideline concentrations. The most notable
are spatially isolated cases of Cd in durum wheat and sunflowers (Grant et al., 1998).
As industrialization and urbanization increase, concomitant with increased agricultural activities in
decreasing land areas, the potential for soil contamination remains an important issue. Although soil
contaminants in the United States and Canada are ubiquitous in areas close to human populations, the
Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes
449
in North America