The photodegradation of pesticides is reviewed, with particular reference to the studies that describe the mechanisms of the processes involved, the nature of reactive intermediates and final products. Potential use of photochemical processes in advanced oxidation methods for water treatment is also discussed. Processes considered include direct photolysis leading to homolysis or heterolysis of the pesticide, photosensitized photodegradation by singlet oxygen and a variety of metal complexes, photolysis in heterogeneous media and degradation by reaction with intermediates generated by photolytic or radiolytic means.

/pdf/reaction-pathways-and-mechanisms-of-photodegradation-of-2mfzeh69kf.pdf

Reaction pathways and mechanisms of photodegradation of pesticides.

The levels and relative proportions of 11 organophosphorus flame retardants and plasticizers (OPs), some of which are reportedly toxic to aquatic organisms, were investigated in human breast milk and samples of fish and mussels from Swedish lakes and coastal areas in order to assess spatial differences in environmental exposure and spatial and temporal differences in human exposure Some of the biota samples were collected at locations with known potential sources of OPs, but most were collected in background locations Tris-2-chloroisopropyl phosphate (TCPP) and triphenyl phosphate (TPP) dominated in the biota with levels ranging from 170 to 770 ng g−1 for TCPP in perch and between 21 and 180 ng g−1 for TPP In milk samples, TCPP (median 45 ng g−1) and tributyl phosphate (median 12 ng g−1) were the most frequently occurring OPs Among samples of fish from background locations, the concentrations and profiles of most OPs were quite similar, indicating that their sources were diffuse However, in fish from sample locations near known sources, there were marked differences in OP concentrations and profiles Fish from a stream receiving surface water from Arlanda airport displayed high levels of OPs (10 200 ng g−1) that are commonly used in aircraft hydraulic fluids Fish collected at points 1 or 2 km downstream of sewage treatment plants showed significantly higher levels of tris(2-butoxyethyl) phosphate (TBEP), one of the most typically abundant OP in effluents from such plants In the milk samples obtained from women in different towns no distinct differences were detected in OP concentrations or profiles However, the levels of TBEP tended to be higher in milk collected 10 years ago than in milk collected more recently However, human exposure to OPs through eating fish or to breastfeeding babies seems to be of minor importance in relation to other potential sources, such as indoor dust inhalation and ingestion

Organophosphorus flame retardants and plasticizers in marine and fresh water biota and in human milk

Biogeochemical indicators to evaluate pollutant removal efficiency in constructed wetlands

Sunlight photodegradation is one of the most destructive pathways for pesticides after their release into the environment. Plant surfaces, especially leaf surfaces, are the first reaction environment for a pesticide molecule after application, and spray drift would indirectly present a similar situation. Photolysis on soil surfaces becomes important when a pesticide is directly applied to soil or not significantly intercepted by plants, providing that the leaf cover does not shade the ground from sunlight. Because the foliar interception of pesticides depends on plant species and usually increases with their growth stage (Linders et al. 2000), the importance of soil photolysis is considered to be lessened when plants become mature. Spray drift after pesticide application or washoff from plants by rain is the indirect route by which a pesticide reaches the soil.

https://bilder.buecher.de/zusatz/14/14812/14812358_lese_1.pdf?origin=publication_detail

Photodegradation of Pesticides on Plant and Soil Surfaces

Photochemical degradation contributes to the environmental fate of many pesticides in surface waters. A better understanding of the role of direct and indirect photochemical degradation of pesticides is necessary in order to predict their environmental fate and persistence. This review includes all major pesticide classes and focuses on the importance of dissolved organic matter (DOM) as a sensitizer in indirect photodegradation within aquatic systems. Photochemical studies conducted under environmentally relevant conditions (i.e., aqueous solutions with irradiation wavelengths >290 nm) are included. Comparisons are made between observed photodegradation rates in pure or buffered water and in water containing DOM to assess the extent of pesticide susceptibility to DOM-sensitized indirect photolysis. When data is available, the role of specific reactive species in indirect photodegradation is described. While it is possible to assess the relative importance of direct and indirect photodegradation on a pesticide-by-pesticide basis in many cases, it is often difficult to make generalizations based on compound class. Knowledge gaps and inconstancies in the current body of literature are discussed and areas that require additional research are described.

/pdf/the-role-of-indirect-photochemical-degradation-in-the-qmvgtnue3f.pdf

The role of indirect photochemical degradation in the environmental fate of pesticides: a review.

Photodegradation of pesticides in the presence of humic substances.

The decline and mineralization to 14CO2 of [phenyl-1-14C]fenamiphos (f) together with the main metabolite fenamiphos sulfoxide (ox) was investigated over a period of 90 days, at two temperatures using 16 soils originating from different geographic areas (9 soils from a cool to temperate climate at 16–22°C and 7 soils from a subtropical to tropical climate at 22–28°C, resp.). The mineralization rates at 22°C, as determined by curve fitting, were in good correlation with the % Cmic/Corg-ratio (percentage of the microbial biomass in the total organic carbon content in the soil). The degradation rates for (f) plus (ox) could be described by first-order kinetics. The half-lives at 22°C ranged from 12 to 87 days. By means of a multiple computation, using regression analysis, between soil properties and decline rates it was possible to explain 70% of the total variance by differences in the pH (H2O)-values and in the % Cmic/Corg-ratio.

Influence of soil properties on the degradation of the nematocide fenamiphos

Fate of triphenyl phosphate in soil

Es wurde der Metabolismus von Ring-14C-Fenamiphos in vier Bodentypen verschiedener Herkunft bei einer Standardtemperatur von 22 °C und jeweils einer anderen Temperaturstufe (16 °C bzw. 28 °C) untersucht. Die Aufwandmenge betrug 7,7 mg/kg Boden. Das Nematizid Fenamiphos wurde in unterschiedlichen Konzentrationsverhaltnissen nach 90 Tagen Inkubation zu Fenamiphossulfoxid, Fenamiphossulfoxidphenol, Fenamiphossulfon, Fenamiphossulfonphenol, Fenamiphossulfonanisol und CO2 abgebaut. Die Halbwertszeiten der TTR (total toxic residues) betrugen 47, 31, 34, 127 Tage fur die Boden A-D. Zwischen 1% (Boden D) und 41 % (Boden B) der applizierten Radioaktivitat wurden innerhalb von 90 Tagen zu CO2 mineralisiert. Der nicht extrahierbare Anteil erreichte 26%–35% bei 22 °C. Da die Metaboliten in allen Boden nachgewiesen werden konnten, kann von einem qualitativ gleichen Abbaumuster ausgegangen werden.

Michael Spiteller

Papers

Photodegradation of pesticides in the presence of humic substances.

Influence of soil properties on the degradation of the nematocide fenamiphos

Fate of triphenyl phosphate in soil

Abbau von Fenamiphos in vier verschiedenen Bodentypen

Metabolism of pesticides in various soils - a literature study.