Excitation-emission fluorescence spectra and trihalomethane formation potential in the Tama River, Japan

Three-dimensional fluorescence spectroscopy was applied to investigate the water quality in the Tama River, Japan, and the variation of the excitation-emission matrix (EEM) profiles of the river water was discussed with particular reference to trihalomethane formation potential (THMFP). The EEMs of the water downstream of a lake exhibited a small but strong peak at 225 nm (excitation)/295 nm (emission) and a weak one at 270 nm/295 nm, which seemed to be derived from algae. The EEMs of the water receiving treated sewage had a distinctive, large and broad peak at around 345 nm/430 nm and also a strong fluorescence at 240 nm/330-450 nm. From the comparison with EEMs of human urine, humic acid and a laundry detergent with fluorescent whitening agents, the peak at around 345 nm/430 nm on the EEM of treated sewage was also found on the EEM of the laundry detergent. The fluorescence intensity had a good correlation with T-THMFP for a wide range of excitation/emission wavelengths considered. The fluorescence intensity at 255-295 nm/345-385 nm correlated with T-THMFP better than E260, and the maximum value of the determination coefficient was R² = 0.90 at 260 nm/355 nm, where no distinctive peak was found on the EEMs of the river water samples. The highest correlation coefficient between the fluorescent intensity and DOC was R² = 0.77 at 280 nm/335 nm. Multiple regression analysis revealed that the fluorescence emission from a unit concentration of THM precursors was 1,000 times or more higher than that of the overall DOC, particularly in the wavelength range of 250-265 nm/325-480 nm, and that the THM precursors in the river water contributed to a much larger degree to the fluorescence than the other DOMs not forming THM.