Solid-Phase Chemical Fractionation of Selected Trace Metals in Some Northern Kentucky Soils

The fractionation and distribution with depth of Cd, Cr, Cu, Ni, Pb, and Zn in 26 soils of Northern Kentucky were determined through a sequential extraction procedure in response to environmental concerns about increasing anthropogenic inputs in a fast-paced, urbanizing area. The selected sites have not received any biosolid- or industrial-waste applications. Average total concentrations per metal in soil profiles derived from alluvial, glacial till, and residual materials ranged from 0.43 to 56.00 mg kg⁻¹ in the sequence Zn > Ni > Pb > Cr > Cu > Cd, suggesting relatively small anthropogenic inputs. The distribution of Cu, Cr, Ni, and Zn increased with soil depth, whereas Cd and Pb remained stable, indicating a strong geological or pedogenic influence. Residual forms were most important for the retention of Cu, Zn, and Ni. Cadmium and Pb exhibited a strong affinity for the Fe-Mn oxide fraction, while Cr showed the strongest association with the organic fraction. In terms of metal mobility and toxicity potential inferred from metal concentrations in labile fractions, Cd posed the greatest risk, followed by Cr ∼ Pb > Ni > Zn > Cu. Soil pH, OM, and clay content were the most important parameters explaining the partitioning of metals in labile and residual fractions, emphasizing the importance of metal fractionation in soil management decisions. Alluvial soils generally contained the highest total and labile metal concentrations, suggesting potential metal enrichment through anthropogenic additions and depositional processes. These environments exhibit the highest risk for metal mobilization due to drastic changes in redox conditions, which can destabilize existing metal retention pools.

Keywords:

• Sequential extraction
• metal distribution
• soil depth
• parent material.

Notes

^†Organic matter.

^‡Cation exchange capacity.

^†EXCH = Exchangeable; CARB = “Carbonate”; FMOX = Fe-Mn; ORG = Organic; RES = Residual.

^‡A = surface horizons; B = middle horizons; C = lowest horizons; ABC = all horizons.

^§TSP = Average cumulative total metal concentrations ± SD in all fractions of A, B, and C soil depths (values followed by a different letter are significantly different at α = 0.10).

^#BDL = Below Detection Limit.

^†EXCH = Exchangeable; CARB = “Carbonate”; FMOX = Fe-Mn; ORG = Organic; RES = Residual.

^‡A = surface horizons; B = middle horizons; C = lowest horizons; ABC = all horizons.

^#Fractions with metal concentrations below the detection limit were assumed to have 0 contribution.

***, **, * = P < 0.01, < 0.05, and < 0.10, respectively.