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

Abstract

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.

The behavior of isopyrazam in aquatic ecosystems: Implementation of a tiered investigation

“…Natural water bodies, particularly those close to agricultural areas, often contain significant concentrations of photosensitizers, which can promote indirect photolysis. The most significant of these has been shown to be nitrate, which can be positively correlated with enhanced degradation through indirect photolysis [6][7][8].Furthermore, studies conducted in systems containing water and sediment are intended to provide data on the rate of dissipation from the water column and the overall rate of microbial degradation in the system. To this end, they are specifically designed to exclude the growth of algae and do not contain aquatic macrophytes.…”

Environmental Fate and Toxicology of Chlorothalonil

“…CO 3 -) dominated under situations, in which degradation via the hydroxyl radical ( . OH) was minimal (Wallace et al 2010). In summary, direct photolysis of chlorothalonil proceeds rapidly and is enhanced by the presence of photosensitizers.…”

“…Chlorothalonil, exposed directly to light (300-400nm) photolytically degraded more rapidly in natural waters (DT 50 = 0.21-0.76 d) than in a buffered aqueous system (pH 7; DT 50 = 1.1d; Wallace et al 2010). Monadjemi et al (2011) investigated the photodegradation of chlorothalonil on a simulated plant surface, specifically using paraffin wax (irradiated at wavelengths between 300-800nm).…”

Photodegradation of clothianidin under simulated California rice field conditions

“…27 This calculation relates the intensity of light in the photoreactor to a 12 h photoperiod of natural sunlight intensity and a time-of-day correction factor. 22,27 2.6 Sample analysis Samples were analyzed using an Agilent 1220 HPLC with an 1220 series autosampler coupled to a model 6420 triple quadrupole mass spectrometer (Santa Clara, CA) equipped with an atmospheric pressure chemical ionization source (APCI) and controlled by Mass Hunter (v.B.06.00). An Ultra PFP analytical column (5 μm particle size, 3.2 × 100 mm i.d.…”

“…20,21 Conversely, the contribution of indirect photolysis to the rate of transformation of a compound can be difficult to characterize -studies have reported both increases (due to reactions with photosensitizers) and decreases (due to higher light attenuation) in photolysis rates in natural waters. 22 Ultimately, the degree to which a pesticide will undergo photolysis in the environment is dependent upon the physicochemical properties of the compound and influenced by spatiotemporal variability in the composition of natural waters and the intensity of natural sunlight. 23 California rice fields are flooded (typically 4-6 cm depth) prior to planting.…”