INFLUENCE OF PH AND HEAVY-METALS IN THE DETERMINATION OF YELLOW SUBSTANCE IN ESTUARINE AREAS

Absorption and fluorescence changes of yellow substance in the presence of pH and heavy metal excursions were examined for water samples collected in the deltaic area of the Po river (Sacca di Goro) and for solutions of natural humic and fulvic acids isolated from lake waters and podsol soils, respectively. An important effect on the light absorption and induced fluorescence was found for the pH variations that occur during the mixing of fresh and saline waters. For this reason, correction factors are required to normalize the absorption and fluorescence values for use in remote-sensing water quality of estuarine / coastal areas. If the factor is chosen to equal 1 at pH 7, the percentage error in the uncorrected estimate of the yellow substance absorption varies from 0% to 18% with a mean of 5% relative to a set of samples collected in Sacca di Goro. Among the heavy metals Cu2+, Pb2+, and Cd2+ present as pollutants in trace levels in estuarine environments, only Cu2+ and Pb2+ in high concentration (> 15-mu-g/L for Pb and > 10-mu-g/L for Cu) have been found to depress the induced fluorescence response of water samples containing yellow substance and humic acid solutions.