SPATIAL VARIABILITY AND ASSOCIATIONS AMONG TRACE METALS IN URBAN AGRICULTURAL GARDEN SOILS

The recent expansion of urban agriculture raises issues of human health and safety concerning the presence and distribution of metals in soils used for growing food, particularly in post-industrial cities such as Detroit, Michigan. Gardening in urban environments poses risks associated with exposure to metals of anthropogenic origin primarily through inhalation of garden dust or ingestion of soils adhering to vegetable roots and leaves. Although health risks associated with metals such as lead, zinc, cadmium, and arsenic have been recognized, the small scale distribution of these metals within garden plots is not well documented.

This study examined the presence, distribution, and associations among metals sampled in three community gardens in the Detroit metropolitan area. 65 soil samples and 10 replicates were collected using a nested grid pattern in each garden. Samples were air dried, sieved to 250 µm, and analyzed using x-ray fluorescence (XRF). Concentrations of arsenic, cadmium, chromium, copper, lead, manganese, nickel, titanium, uranium, and zinc were measured. Garden-scale spatial variability was characterized using variography, and ordinary kriging was used to generate conditioned soil concentration maps for each garden plot. Preliminary results demonstrate meter-scale variability for most metals as well as statistically significant correlations among the distributions for several metals investigated. These results have important ramifications for soil sampling strategies and will aid in the second phase of the study, which seeks to relate metals to the distribution of pesticides, PAHs, and bacteria in the garden soils.