Variation in chlorotoluron photodegradation rates as a result of seasonal changes in the composition of natural waters

Synthesis of anti-photolysis lignin-based dispersant and its application in pesticide suspension concentrate

In the formulation of pesticide Suspension Concentrate (SC), some photosensitive pesticides are easily decomposed in the preparation. In this study, a hindered amine modified lignosulfonate (SL-Temp) with anti-photolysis function was synthesized using 4-amino-2,2,6,6-tetramethylpiperidine (Temp) and Sodium Lignosulfonate (SL) to solve this problem. The obtained SL-Temp was used as a dispersant to prepare 5% SC of avermectin, which shows good physical stability. The decomposition rate of the avermectin in SC after accelerating hot storage is 0%, which is much lower than 6.1% when SL was used as the dispersant. After being exposed to UV irradiation for 60 hours, the highest retention rate of avermectin is 87.1% when SL-Temp was used as the dispersant, which is much higher than 73.6% when SL was used as the dispersant, and also higher than 76.3% when a small molecule antioxidant (BHT) was added to the formulation. QCM-D studies revealed that the SL-Temp adsorption layer on avermectin particles can compete to absorb partial ultraviolet rays, hinder the penetration of ultraviolet light, and scavenge the free radicals produced by photooxidation, so as to protect avermectin from degradation.

Hindered amine grafted lignosulfonate was synthesized and used as functional dispersant in suspension concentrate of photosensitive pesticide avermectin.

Photodegradation of clothianidin under simulated California rice field conditions

BACKGROUND

Photodegradation can be a major route of dissipation for pesticides applied to shallow rice field water, leading to diminished persistence and reducing the risk of offsite transport. The objective of this study was to characterize the aqueous-phase photodegradation of clothianidin under simulated California rice field conditions.

RESULTS

Photodegradation of clothianidin was characterized in deionized, Sacramento River and rice field water samples. Pseudo-first-order rate constants and DT50 values in rice field water (mean k = 0.0158 min(-1) ; mean DT50 = 18.0 equivalent days) were significantly slower than in deionized water (k = 0.0167 min(-1) ; DT50 = 14.7 equivalent days) and river water (k = 0.0146 min(-1) ; DT50 = 16.6 equivalent days) samples. Quantum yield ϕc values demonstrate that approximately 1 and 0.5% of the light energy absorbed results in photochemical transformation in pure and field water respectively. Concentrations of the photodegradation product thiazolymethylurea in aqueous photolysis samples were determined using liquid chromatography-tandem mass spectrometry and accounted for ≤17% in deionized water and ≤8% in natural water.

CONCLUSION

Photodegradation rates of clothianidin in flooded rice fields will be controlled by turbidity and light attenuation. Aqueous-phase photodegradation may reduce the risk of offsite transport of clothianidin from flooded rice fields (via drainage) and mitigate exposure to non-target organisms. © 2015 Society of Chemical Industry.

An experimentally refined tool to assess the risks of the human dermal exposure to herbicide chlorotoluron

Dermal absorption of the herbicide chlorotoluron was measured using ex vivo pig skin in Franz diffusion cells in an automated system. The steady-state flux was calculated, as well as the permeability coefficient, which is 0.0038 cm h(-1). The permeability coefficient (Kp) is a key factor when predicting human health risks resulting from dermal exposition to a substance. The experimental determination of this parameter filled data gaps regarding the dermal absorption of chlorotoluron. The experimental permeability coefficient was subsequently used to calculate the dermal absorbed dose during some exposure scenarios. Reference doses were revised, and screening risk assessment process was done to calculate the risks resulting from exposure to chlorotoluron. This refined new approach proved to be a useful tool for human health risk assessment in the areas with these herbicide applications. Graphical Abstract An experimentally refined tool to assess the risks of the human dermal exposure to herbicide chlorotoluron.

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

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.