Leaching of As and Cr in wood-ash-amended soil columns

High volume application of wood ash as a soil amendment in forested areas may introduce toxic elements to these ecosystems. Column studies were conducted under unsaturated conditions to determine As and Cr leachability in wood ashamended soil columns. Three treatments were used in columns 1.8 cm diameter and 20 cm long: (a) ash alone, (b) ash mixed with topsoil at 900 Mg ha(-1) application rate, and (c) ash mixed with topsoil overlying a spodic horizon, Water, humic, fulvic, and a mixture of humic and fulvic acids were also used to leach ash in separate columns. Leachate concentrations of organic carbon, Cl-, As, and Cr and pH were determined. There was higher As and Cr leaching in the water-leached ash and soil-ash columns than in the acid-leached ash columns. The lower Cr leaching in HA-leached columns was due to the high reaction between Cr and HA. There was also lower dissolved organic carbon (DOC) leached in the acid-leached ash columns due to possible flocculation. Mixing ash with soil led to a higher increase in Cr leaching than As, which flocculated with DOC in the columns. High ash pH dissolved OC but high ionic strength led to DOC-oxyanion flocculation in this study.