Photodegradation of nitrite in lake waters: role of dissolved organic matter
Davide Vione A C , Marco Minella A , Claudio Minero A , Valter Maurino A , Paolo Picco A , Aldo Marchetto B and Gabriele Tartari BA Dipartimento di Chimica Analitica, Università di Torino, 10125 Torino, Italy.
B CNR-ISE, Istituto per lo Studio degli Ecosistemi, 28922 Verbania – Pallanza (VB), Italy.
C Corresponding author. Email: davide.vione@unito.it
Environmental Chemistry 6(5) 407-415 https://doi.org/10.1071/EN09050
Submitted: 28 April 2009 Accepted: 12 August 2009 Published: 22 October 2009
Environmental context. Nitrite is an important nutrient in surface waters, a key intermediate in the interconversion of nitrate into ammonium, and a considerable photochemical source of reactive species such as the hydroxyl radical. We have found that scavengers of hydroxyl radicals such as dissolved organic matter, which are usually supposed to inhibit the photodegradation of dissolved compounds, are able on the contrary to enhance the phototransformation of nitrite. The three weeks’ lifetime of nitrite in the surface layer of lakes, derived from the results of the present work, would make photochemistry an important issue in determining the concentration of nitrite in lake water.
Abstract. Here we studied the degradation rate of nitrite (NO2–), added to lake water at sub-micromolar levels, upon ultraviolet (UV) irradiation. NO2– photodegradation was considerably faster in lake water compared with ultra-pure water. A key issue was the presence in lake water of hydroxyl radical (•OH) scavengers that inhibited the reaction between NO2– and •OH. Such a reaction, while causing additional NO2– transformation, produced nitrogen dioxide (NO2•) that was subsequently involved into the regeneration of NO2– by dimerisation or the reaction with nitric oxide (NO•). The scavenging of •OH by compounds different from NO2– (mainly dissolved organic matter, DOM) prevented the regeneration reactions from taking place, and enhanced the phototransformation of NO2–. Model calculations for the direct photolysis of NO2–, applied to the lake water samples, yielded a NO2– half-life time of around three weeks in the mixing layer of the lakes because of photodegradation. Therefore, we conclude that photodegradation is a potentially important process to control the concentration of NO2– in shallow lakes, or in deeper ones under stratification conditions.
Additional keywords: environmental photochemistry, hydroxyl radical scavenging, nitrite photodegradation, nitrogen geochemistry.
Acknowledgements
Financial support by Università di Torino – Ricerca Locale and the Italian Inter-University Consortium of Chemistry and the Environment (INCA) is gratefully acknowledged.
[1]
N. Rabalais ,
Nitrogen in aquatic ecosystems.
Ambio 2002
, 31, 102.
[Verified 6 October 2009]
[22]
C. Minero ,
V. Lauri ,
G. Falletti ,
V. Maurino ,
E. Pelizzetti ,
D. Vione ,
Spectrophotometric characterisation of surface lakewater samples: Implications for the quantification of nitrate and the properties of dissolved organic matter.
Ann. Chim. 2007
, 97, 1107.
| Crossref | GoogleScholarGoogle Scholar |
[23]
S. Canonica ,
Oxidation of aquatic organic contaminants induced by excited triplet states.
Chimia 2007
, 61, 641.
| Crossref | GoogleScholarGoogle Scholar |
[24]
C. Richard ,
G. Guyot ,
O. Trubetskaya ,
O. Trubetskoi ,
M. Grigatti ,
L. Cavani ,
Fluorescence analysis of humic-like substances extracted from composts: influence of composting time and fractionation.
Environ. Chem. Lett. 2009
, 7, 61.
| Crossref | GoogleScholarGoogle Scholar |
[25]
D. Vione ,
F. Merlo ,
V. Maurino ,
C. Minero ,
Effect of humic acid on the Fenton degradation of phenol.
Environ. Chem. Lett. 2004
, 2, 129.
| Crossref | GoogleScholarGoogle Scholar |
[26]
S. Canonica ,
H. U. Laubscher ,
Inhibitory effect of dissolved organic matter on triplet-induced oxidation of aquatic contaminants.
Photochem. Photobiol. Sci. 2008
, 7, 547.
| Crossref | GoogleScholarGoogle Scholar |
[27]
J. V. Goldstone ,
M. J. Pullin ,
S. Bertilsson ,
B. M. Voelker ,
Reaction of hydroxyl radicals with humic substances: bleaching, mineralization, and production of bioavailable carbon substrates.
Environ. Sci. Technol. 2002
, 36, 364.
| Crossref | GoogleScholarGoogle Scholar |
[28]
P. Warneck ,
C. Wurzinger ,
Product quantum yields for the 305-nm photodecomposition of NO3– in aqueous solution.
J. Phys. Chem. 1988
, 92, 6278.
| Crossref | GoogleScholarGoogle Scholar |
[29]
G. Mark ,
H.-G. Korth ,
H.-P. Schuchmann ,
C. von Sonntag ,
The photochemistry of aqueous nitrate ion revisited.
J. Photochem. Photobiol. Chem. 1996
, 101, 89.
| Crossref | GoogleScholarGoogle Scholar |
[30]
D. Vione ,
G. Falletti ,
V. Maurino ,
C. Minero ,
E. Pelizzetti ,
M. Malandrino ,
R. Ajassa ,
R. I. Olariu ,
C. Arsene ,
Sources and sinks of hydroxyl radicals upon irradiation of natural water samples.
Environ. Sci. Technol. 2006
, 40, 3775.
| Crossref | GoogleScholarGoogle Scholar |
[31]
S. E. Braslavsky ,
Glossary of terms used in photochemistry. 3rd edn.
Pure Appl. Chem. 2007
, 79, 293.
| Crossref | GoogleScholarGoogle Scholar |
[32]
[33]
D. Vione ,
V. Maurino ,
C. Minero ,
M. E. Carlotti ,
S. Chiron ,
S. Barbati ,
Modelling the occurrence and reactivity of the carbonate radical in surface freshwater.
C. R. Chim. 2009
, 12, 865.
| Crossref | GoogleScholarGoogle Scholar |
[34]
D. Vione ,
J. Feitosa-Felizzola ,
C. Minero ,
S. Chiron ,
Phototransformation of selected human-used macrolides in surface waters: kinetics, model predictions and degradation pathways.
Water Res. 2009
, 43, 1959.
| Crossref | GoogleScholarGoogle Scholar |
