Freshwater trace element complexes

Gamier, J.M., Pham, M.K., Ciffroy, P. and Martin, J.M. (1997) Kinetics of trace element complexation with suspended matter and with filterable ligands in freshwater. Environ. Sci. Technol, 31, 1597-1606. 

Table 6 Complexes of Selected Trace Elements in Freshwater and Seawater...

Literature data on the distribution of trace elements amongst the different size fractions in natural freshwaters are summarised in Table 8.1. There is a striking paucity of data for the environmentally important elements Cu, Pb and Cd. Elements which have a low affinity for complexing sites on NOM are present predominandy in the low molecular weight fraction, e.g. Cs, Sr, V while those which specifically coordinate to particular functional groups in NOM, e.g. Ag, Cd, tend to be present in the particulate and colloidal fractions. A major difficulty when trying to compare the literature data is that operational and variable size limits are used, and that filtration, which may lead to drastic artefacts, is still largely used for size fractionation. 

There is or was just some narrow pH interval which permitted nowadays essential elements to remain dissolved in water up to levels which made them all accessible in step 2. For example, (recent seawater provides plenty of Mg or Ca but only minute traces (pico- to lower nanomolar amounts Nozaki 1997) of Fe, Mn, Cu or Zn whereas modem freshwater contains adequate Fe and Mo but too little of the other metals, especially weakly complexing elements to have them bound to precipitates of insoluble salts of simple ligands. 

---