Copper Distribution Profiles in Soils From a Long-Term Polluted Field.

Copper (Cu) is strong bounder to soil organic matter and mineral colloids than other heavy metals reducing its mobility as free Cu²⁺. However, in association with soil colloids and dissolved organic matter, Cu can be transported into deeper horizons and to groundwater. Previous studies showed that soil structure plays a principal role in the movement of Cu associated with colloids and organic matter. Knowing the distribution of Cu along the soil profile, together with soil physical and chemical characteristics, is important to predict the transfer of Cu from the soil surface.

Hygum site in Jutland, Denmark, is a historical Cu polluted field cultivated for 80 years and fallow since 1993. Samples at four depths (from 0 to 100 cm) were collected at seven points following the Cu concentration gradient present in the field (from 25 to 3300 mg Cu kg^-1 soil). Samples were air dried, 2-mm sieved and analyzed for texture, organic matter, pH, electrical conductivity, total Cu and exchangeable Cu (in CaCl₂).

Preliminary results showed that total Cu concentration decreased with depth from 25 to 3 mg Cu kg^-1 soil in the lowest polluted point and from 3288 to 448 mg Cu kg^-1 soil in the hot spot. Concentration profiles showed high transfer of Cu from the surface to deeper horizons at the highly polluted locations. The ratio of Cu at each depth to the total amount in the soil profile was positively correlated with the organic matter content (R² = 0.78). Regarding these results, NIR/MIR analyses in the samples are being carried out to examine changes in soil organic matter quality and Cu binding with depth.