Distribution of trace elements in soil from repeated sewage sludge applications

We studied the horizontal and vertical distribution in a soil profile (Metea sandy loam; loamy, mixed, mesic Typic Hapludalf) of trace elements as a result of their loading at phytotoxic levels to cropland. Municipal sludges containing high concentrations of Cd, Cr, Cu, Pb, Ni, and Zn were applied to cropland from 1977 to 1986 at three rates plus an untreated control. Total elemental analysis of soils collected in 1989 and 1990 indicated that lateral distribution of trace elements had occurred. This lateral distribution was most likely a result of the physical movement of soil particles with agronomic operations. The elements, however, were not distributed below the sampling depth of from 15 to 30 cm. Mass balance calculations resulted in average trace element recoveries that ranged from 45 to 155% of the total applied. These calculations were highly variable, indicative of the highly variable nature of sludge composition, lack of total uniform sludge applications, soil movement due to tillage operations, and sampling methods. Because of the potential errors associated in mass balance calculations, recoveries that have been calculated in this and other studies that deviate substantially from 100% should reasonably be expected. Direct examination of the relatively few ways in which trace elements are lost from a soil (i.e., plant uptake, soil movement via tillage, water and wind erosion, and deep leaching) may be more meaningful than mass balance calculations to determine the fate of trace elements applied to soil.