EFFECTS OF THE ST. LUCIE ESTUARY MUCK SEDIMENT APPLICATION ON METAL SOLUBILITY AND pH OF SANDY SOILS: A LABORATORY OBSERVATION 1

Abstract

Heavy metal contamination from the beneficial re-use of muck sediment in agriculture is a cause for concern. Information is needed about the leachability of metals from land-applied muck sediment and the effects of muck sediment application on soil properties. For this purpose, the water solubility of metals from muck sediments at various pH values and the effects of muck sediment application on metal leachability and pH values of sandy soils were determined by leaching soil samples amended with different rates of muck sediments. The leachates and soil solutions extracted from the muck-amended soils were analyzed for pH, electrical conductivity (EC), and concentrations of heavy metals (Cd, Cr, Cu, Co, Ni, Pb, and Zn). Rapid increases in solubility of heavy metals from the muck at pH levels below 6.0 suggest that muck sediments may be most suitable for application to slightly acid to slightly alkaline soils. Soil solution pH values from soils amended with muck sediments increased with increasing muck rates. Electrical conductivity of soil solution in the muck-amended soils was higher than in soils without muck amendment. The EC values increased with increasing muck rates. Application of muck sediment increased the concentrations of Cd, Co, Ni, and Pb, and decreased the concentrations of Cu and Zn in soil solution. However, the concentrations of Cd (<40 μg L−1), Co (<44 μg L−1), Cr (<30 μg L−1), Cu (<105 μg L−1), Ni (<84 μg L−1), Pb (<128 μg L−1), and Zn (<134 μg L−1) were generally low in the soil solution from muck-amended soils. The salts in muck sediments were easily removed from the amended soils by leaching, suggesting that the added salts from muck sediments may not have long-term effects on plant growth. Relatively high EC values in the first leachates from the muck-amended soils were observed, especially for soils amended with muck at a high rate. However, application of increasing amounts of muck sediments increased soil pH. The pH increased with increasing muck rates, and was correlated positively with Na/Ca, Na, K, Na/(Ca+Mg+K), and Na/(Ca+Mg+K+Na) in the leachates and water soluble Na/Ca, Na, Na/(Ca+Mg+K), and Na/(Ca+Mg+K+Na) in the muck sediments; it was negatively correlated with Ca in leachates and water soluble Ca in the muck sediments. These results suggest that application of muck sediments does not result in a marked change in soil pH at low rates.