MUTUAL Cu, Fe AND Mn SOLUBILITY CONTROL UNDER DIFFERENTIATED SOIL MOISTURE STATUS

The effect of three different moisture statuses, i.e., 150, 200 and 300% FWC (Field Water Capacity) on copper (Cu), iron (Fe) and manganese (Mn) solubility and solution activity was investigated on soil samples characterised by different levels of copper contamination. Soils (200 g) were weighted into polyethylene containers (500 cm3) and amounts of bidistilled water were properly added to reach the targeted moisture status of 150, 200 and 300% of the FWC. The incubation was held under laboratory conditions at the temperature of 19-20oC for a period of 30 days. Supernatants (10 cm3) were collected at given intervals of time, filtered and analysed for pH (potentiometrically) as well as for Cu, Fe, and Mn (spectrophotometrically). It was found that the activity of Cu2+ ions decreased gradually with increasing pH of the solution, irrespective of the moisture status and that this process was more pronounced for 150 and 200% than for 300% FWC. The activity of Fe varied in a narrow range i.e. –5.0 and –6.0 molcdm -3 and was related to pH changes (in the range 4.0-7.5). The impact of increased moisture status on the solubility process was less pronounced. Further studies should be undertaken in order to elucidate such Fe behaviour. Manganese solution activity varied mostly between – 4.0 and –7.0 molcdm -3, and was found to be less sensitive to pH changes. But it must be pointed out that the effect of high pH on the increase of Mn activity was limited, which implied that Mn2+ activity was moisture-dependent, basically. Care should be taken to avoid any submersion of soils subjected to contamination or pollution by trace metals, since any excess of stagnant water (anoxic conditions) leads to increased solubility and simultaneous activity of trace metals in the solution. This process is greatly strengthened by significant amounts of soil-born Fe and organic matter.