Copper mobility in a copper-contaminated sandy soil as affected by pH and solid and dissolved organic matter

The effects of solid, dissolved organic matter and of pH on copper mobility in a copper-contaminated sandy soil has been studied in the laboratory as well as in the field. The soil, with pH ranging from 3.8 to 5.7, had been polluted with copper in the range from 0.13 to 1.9 mmol/kg more than 1 decade ago. Copper bound by dissolved organic matter (purified humic acid) was determined by a Cu ion selective electrode (Cu-ISE) in a pH range from 4 to 8 and a free copper range from 10(-4) to 10(-12) mol/L. Column experiments were carried out to investigate the mobility of DOC itself and the effect of DOC on Cu mobility. Copper binding by dissolved organic matter (DOG) as well as copper binding by (soil) solid organic matter (SOC) could be described well with the non-ideal competitive adsorption (NICA) model and with the Two Species Freundlich (TSF) model. Both models could be used to predict the copper concentration at different depths in a field using the total Cu content pH, and solid and dissolved organic matter content. At pH 3.9 about 30% of the Cu in solution was copper bound by DOG, and at pH 6.6 CuDOC comprised more than 99%. DOC mobility was very sensitive to pH and calcium concentration.