TRACE METAL SOURCES IN URBAN SOUTHERN CALIFORNIA SOILS

Human activities have altered the nature trace metals in soils through the combustion of fuels and manufacturing. However, distinguishing human derived added trace metals from rock derived elements can be difficult in geologically complex terrains. We studied trace metals in residual soils across the foothills of Southern California, focusing on the effect of lithology degree of urbanization, and precipitation. We collected soil, rock, and plant samples from over 50 sample sites in the Los Angeles Basin and along the Transverse and Peninsular Mountain ranges of Southern California. They were analyzed for pseudo-total element concentrations and physicochemical properties pH, % organic matter, and soil texture. Analysis of the samples showed that residual soil samples derived from granitic alluvium had the greatest accumulation of lead (Pb) (25.9 ± 4.9ppm) and arsenic (As) (4.4 ± 2ppm), while soils derived from volcanic rock had the highest concentration of nickel (Ni) (25.5±5ppm). The highest average Pb concentrations were found in the surface soils of the Los Angeles Basin (34.2± 7.2ppm) compared to (14.5± 2.3ppm) and (9.3± 1.4ppm) that were measured in the surface soils of the Peninsular and Transverse Mountain ranges respectively. Soil samples were found to be enriched with Pb in the upper 0-5cm with an average enrichment factor for Pb of (5.1±2.5) in the upper 0-5cm compared to (1.1±0.3) enrichment factor found from 15-20 cm. These findings signify that a portion of trace metals in Southern California soils are added into the upper horizons from anthropogenic sources, in addition to the trace metals from the underlying bedrock.