The role of indirect photolysis in limiting the persistence of crop protection products in surface waters

The photodegradation of six crop protection products (CPPs) was studied in 16 natural waters collected from across the midwest of the United States under simulated sunlight to determine the significance of indirect photolysis. The rate of degradation of five of the CPPs was faster in irradiated natu...

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Bibliographic Details
Published in:Environmental toxicology and chemistry 2010-03, Vol.29 (3), p.575-581
Main Authors: Wallace, Derek F., Hand, Laurence H., Oliver, Robin G.
Format: Article
Language:English
Subjects:
Bicarbonates
Chemical compounds
Correlation analysis
Crop protection product
Crops
Crops, Agricultural
Degradation
Dissolved organic carbon
Hydroxyl Radical
Hydroxyl radicals
Insecticides
Light
Natural waters
Nitrate content
Nitrates
Organic Chemicals - analysis
Photodegradation
Photolysis
Photosensitizer
Plant protection
Regression analysis
Studies
Surface water
Water Pollutants, Chemical - analysis
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Summary:The photodegradation of six crop protection products (CPPs) was studied in 16 natural waters collected from across the midwest of the United States under simulated sunlight to determine the significance of indirect photolysis. The rate of degradation of five of the CPPs was faster in irradiated natural waters than in buffer systems, with the effect particularly significant with the relatively photostable compounds propiconazole and prometryn. Degradation rates were correlated with the concentration of one or more photosensitizers, or ratios thereof, by means of a Pearson's correlation and linear regression analysis. It was found that the photodegradation of chlorotoluron, pinoxaden, propiconazole and prometryn were linked to the concentration of nitrate, pointing to a significant role of hydroxyl radical (.OH) as a reactive intermediate. Increased concentrations of dissolved organic carbon (DOC) and bicarbonate relative to nitrate were found to decrease the rate of degradation of these compounds, consistent with a quenching role. Chlorothalonil appeared to be rapidly degraded by means of the carbonate radical (.CO 3−), whereas the photodegradation of emamectin was particularly complex. Overall, indirect photolysis significantly enhanced the rate of CPP degradation and fate models based on these experiments appear to offer more realism than those that only take into account direct photolysis. Environ. Toxicol. Chem. 2010;29:575–581. © 2009 SETAC
ISSN:0730-7268
1552-8618
1552-8618
DOI:10.1002/etc.65