Sources and sinks of hydroxyl radicals upon irradiation of natural water samples.
Hydroxyl radical formation rates, steady-state concentration, and overall scavenging rate constant were measured by irradiation of surface lake water samples from Piedmont (NW Italy) and nitrate-rich groundwater samples from Moldova (NE Romania). Dissolved organic matter (DOM) was the main source and sink of *OH upon lake water irradiation, with [*OH] being independent of DOM amount. Water oxidation by photoexcited DOM is a likely *OH source in the presence of very low levels of nitrate and dissolved iron. Under different circumstances it is not possible to exclude other processes, e.g., DOM-enhanced photo-Fenton reactions. Under the hypotheses of no interaction and absence of mutual screening of radiation, nitrate would prevail over DOM as *OH source for a NO3-/DOM ratio higher than 3.3 x 10(-5) (mol NO3-) (mg C)(-1), DOM prevailing for lower values. Substantial DOM photolability was observed upon irradiation of nitrate-rich groundwater, mainly due to the elevated *OH generation rate. For the first time to our knowledge, evidence was also obtained of the photoformation of potentially toxic and/or mutagenic nitroaromatic compounds upon irradiation of natural lake water and groundwater samples, proportionally to the nitrate levels.
Vione
Davide
D
Dipartimento di Chimica Analitica, Università di Torino, Via P. Giuria 5, 10125 Torino, Italy. davide.vione@unito.it
Falletti
Gianpaolo
G
Maurino
Valter
V
Minero
Claudio
C
Pelizzetti
Ezio
E
Malandrino
Mery
M
Ajassa
Roberto
R
Olariu
Romeo-Iulian
RI
Arsene
Cecilia
C
D005618:Fresh Water / Q000737:chemistry*; D017665:Hydroxyl Radical / Q000032:analysis*; D009930:Organic Chemicals / Q000737:chemistry / Q000528:radiation effects; D010084:Oxidation-Reduction; D011827:Radiation; D012995:Solubility; D013472:Sunlight
D009930:Organic Chemicals; D017665:Hydroxyl Radical