The Relationship Between Soil Particle Size And Lead Concentration

Many studies regarding heavy metal concentration in contaminated soils have observed increased concentrations in the smaller-sized particles. This phenomenon has been attributed to differences in organic matter, contaminant source, and particle surface area. The relationship between particle size and lead concentration in soils was explored. Data from four published studies were considered; the sources of lead contamination were lead smelting, metal manufacturing, and combustion of leaded automotive fuels. These four studies reported lead concentrations in different soil fractions, separated by particle size, or diameter. A total of 14 soil samples were evaluated, with each having 3 to 6 different particle-size fractions. The particle sizes ranged from less than 63 microns to between 850 to 2000 microns. Lead concentrations were plotted versus mid-range diameters. Data for each of the 14 soil samples were approximately linear on a log-log plot. Trend lines for each soil sample revealed strikingly similar slopes for all 14. The slopes ranged from -0.59 to -0.25, with a mean of -0.37. Correlation coefficients ranged from 0.75 to 0.999. This relationship suggests that soil lead concentrations are nearly proportional to the diameter raised to the power -0.37. Stated differently, soil lead concentrations within a given soil sample can be approximated as being inversely proportional to the cube-root of the particle diameter.