QUANTITATIVE COMPARISON OF AS, CR, CU, NI, PB, AND ZN IN ARABLE AND FOREST SOILS NEAR PEMBERVILLE, OHIO

Quantitative comparisons of As, Cr, Cu, Ni, Pb, and Zn contents in arable and forest soils near Pemberville, Ohio were examined in 60 samples from 10 sampling sites. Soils contain a large proportion of fines (~ 32% clay and ~37% silt). X-ray diffraction showed that quartz, chlorite, illite, and kaolinite are the major minerals present. Surface soils in the arable land are slightly acidic (pH ~ 6.5) while forest soils are near-neutral to slightly basic. All soils become more basic with depth because of carbonate bedrock. Soil Eh and electrical conductivity (EC) values are ranged from 300 to 450 mV and 100 to 375 ìS, respectively. Soil samples were digested according to EPA 3050B method and analyzed for heavy metals with ICP-AES. Arsenic in soil increases from 4.6 to 11 mg/kg from surface to 50 cm depth, while Cu and Pb contents decrease from 27 to 17 mg/kg and 16 to 10 mg/kg, respectively, from surface to 50 cm depth. Surface enrichment of Cu and Pb are a result of aerosol deposition, while the downward increase in As content is related to pedogenic variation. The average concentrations of Cr, Ni, and Zn in soils are 22, 25, and 64 mg/kg, respectively, with no discernible aerosol deposition enrichments or pedogenic variation. Land-use induced differences in heavy metal content in soil are insignificant except for As. As content in near surface arable soil is relatively higher (6 mg/kg) than that of the forest soil (4 mg/kg); however, deeper samples have similar As concentration (~8 mg/kg) in both land-uses. This relative enrichment of As in surface arable soil could indicate input from agricultural practices, or selective enhancement of As through soil geochemical processes. Surface soils in the forest have more ion exchangeable fraction of metals as indicated by higher EC; however, near neutral pH and absence of swelling clay would limit degree of mobility. Similarly, slightly acidic arable soil can have higher mobility of metals. Heavy metals and arsenic contents in these soils are very low compared to the limits set by the USEPA and thus pose no environmental risks.