Abstract
Areas reclaimed for agricultural uses following coal mining often receive biosolids applications to increase organic matter and fertility. Transport of heavy metals within these soils may be enhanced by the additional presence of biosolids colloids. Intact monoliths from reclaimed and undisturbed soils in Virginia and Kentucky were leached to observe Cu and Zn mobility with and without biosolids application. Transport of Cu and Zn was observed in both solution and colloid associated phases in reclaimed and undisturbed forest soils, where the presence of unweathered spoil material and biosolids amendments contributed to higher metal release in solution fractions. Up to 81% of mobile Cu was associated with the colloid fraction, particularly when gibbsite was present, while only up to 18% of mobile Zn was associated with the colloid fraction. The colloid bound Cu was exchangeable by ammonium acetate, suggesting that it will release into groundwater resources.
Highlights
Water dispersible colloids may be a carrier vector for contaminants in the unsaturated soils zone, transporting metals to surface and groundwater [1,2,3,4]
The highest recovered concentration of Zn was observed in the biosolids materials (60.8 mg kg−1), while the highest Cu levels were extracted from the Kentucky spoil (23.0 mg kg−1) and biosolids (21.4 mg kg−1) materials, respectively
Within the Virginia sites, Cu was highest in the spoil material, while Zn was highest in the reclaimed soils
Summary
Water dispersible colloids may be a carrier vector for contaminants in the unsaturated soils zone, transporting metals to surface and groundwater [1,2,3,4]. Up to 95% of biosolids associated metals have been accounted for in the soil profile following biosolids application [7, 8], while under increasingly acidic conditions trace metals were observed to at least a 1 m depth in mine soils receiving biosolids [9]. Within this soil matrix, metal sorption is controlled by pH, clay mineralogy [10], or complexation with soil organic matter [11, 12]. Early models which partition metals between an immobile solid and mobile liquid phase only have to be revised to include colloid particulate material as a third mobile solid phase, and a potential vector of metal transport [17]
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