Variation on the adsorption efficiency of humic substances from estuarine waters using XAD resins

The XAD8 and XAD4 resins, used in series, show different behaviours in relation to the retention of dissolved organic matter (DOM) from estuarine water samples according to different salinities. For the XAD8 resin, the removal of DOM measured in terms of light absorbance at 250 nm varies from 69.4% ± 0.5 to 51.4% ± 3.5 and for the XAD4 resin it varies from 20.0% ± 1.0 to 25.2% ± 3.0 for salinities ranging from 0.6 to 33.4. The isolation, with XAD8, of DOM from samples increasing in salinity, measured in terms of emission fluorescence intensity at selected wavelengths (410, 440 and 460 nm) for an excitation of 340 nm, decreases. In the same experimental conditions, the increase of fluorescent organic matter (FOM) removed by the addition of XAD4 resin is always greater than 20%. However, addition of NaCl to the sample with the lowest salinity, shows that the retention in both resins is related more to the nature of DOM than to the ionic strength of the sample.