Effects of UV-A irradiation on dissolved organic matter in humic surface waters

Exposure of sterile filtered humic surface water to low intensity UV-A radiation for 89 h significantly affected the organic matter in these systems. A UV-induced degradation of organic matter was demonstrated by a decrease in UV absorbance, dissolved organic carbon (DOG) and fulvic acid content in irradiated replicates, compared to dark controls. Furthermore, qualitative changes in the DOC were observed. The absorbance ratio 254/365 nm increased in the irradiated replicates, indicating a decreased size of UV-absorbing organic matter. A UV-induced production of several low molecular weight (LMW) organic acids was also observed. A highly sensitive (mu g L(-1) level) capillary zone electrophoresis (CZE) method was used for identification and quantification of these organic acids. Oxalic, malonic, formic, and acetic acid were the major carboxylic acids produced, together accounting for about 0.18 mgCL(-1). This organic fraction could have a profound effect on the surface water environment, being highly available substrates for aerobic microorganisms as well as being potentially important for the function and distribution of trace metals.