EFFECT OF CA ON THE SOLUBILITY AND MOLECULAR-SIZE DISTRIBUTION OF DOCAND CU BINDING IN SOIL SOLUTION SAMPLES

Flocculation of soil-derived dissolved organic carbon (DOC) was used a s a tool to study the molecular size distribution of DOC and the nativ e amount of copper bound to different size fractions. DOC was extracte d from arable soils that had received varying amounts of animal manure , inorganic fertilizer, or CuSO4. Addition of calcium to the DOC extra cts resulted in flocculation of up to 50% of the DOC originally presen t in the samples. High performance size exclusion chromatography (HPSE C) analysis revealed that the DOC removed mainly consisted of high mol ecular weight (HMW) organic acids. Low molecular weight (LMW) substanc es remained soluble even at high calcium concentrations. Copper soluti on concentrations decreased almost linearly with decreasing DOC levels , suggesting that copper remained bound to the flocculated material de spite increasing calcium concentrations. The amounts of copper bound t o both LMW and HMW components depended on the copper content of the so il and were described by two Langmuir sorption equations. Maximum bind ing capacities varied between 250 mu mol of copper g(-1) of C for HMW components and 450 mu mol of copper g(-1) of C for LMW components, but binding affinities were higher for HMW components. The Langmuir equat ion described the measured copper solution concentrations from the bat ch experiments very well (R-2 = 0.994). The observation that up to 50% of the DOC in solution was not removed by calcium indicates that a si gnificant part of copper is potentially highly mobile in soils and can be prone to DOC-facilitated transport.