Photocatalytic degradation of the herbicide clopyralid: kinetics, degradation pathways and ecotoxicity evaluation

Abstract

BACKGROUND: Photocatalytic decomposition and mineralization of the herbicide clopyralid in aqueous solutions has been studied, aiming at an extended kinetic analysis, the elucidation of potential degradation pathways and the determination of ecotoxicity. RESULTS:The pseudo-first-order degradation kinetics was studied under different operational conditions, such as type of photocatalyst, catalyst loading, initial pH and hydrogen peroxide (H 2 O 2 ) concentration. The degradation rates proved to be strongly influenced by these parameters. Organic chlorine and nitrogen were easily converted into inorganic in the presence of TiO 2 P25, resulting in 90% conversion in both cases within 180 min of illumination, while conversion was enhanced in the presence of H 2 O 2 . Ten possible transformation products were identified by means of LC-DAD-ESI/MS analysis. Acute toxicity profiles using marine bacteria Vibrio fischeri showed an increasing trend during the first 60 min of illumination, which thereafter, progressively decreased. CONCLUSIONS: Intermediates were formed mainly through pyridine ring transformation, dechlorination and decarboxylation reactions. The increasing trend in ecotoxicity at the first stages of degradation could be attributed to the progressive formation of intermediates more toxic than the parent molecule, or due to synergistic effects among the transformation products.

Photocatalytic disinfection and purification of water employing reduced graphene oxide/TiO2 composites

“…Photocatalytic oxidation of clopyralid was performed in a bench-scale photocatalytic reactor, equipped with a central UV-A lamp, at a working volume of 250 mL, as described previously. 39 Chemical actinometry 48 determined the incident photon flow of the irradiation source, which was 115 × 10 −6 Einstein L −1 min −1 . Experiments were conducted at 5.0 ± 0.1 initial pH and constant temperature (25 ± 0.1 ∘ C).…”

“…More specifically, clopyralid (3,6‐dichloro‐2‐pyridine‐carboxylic acid), a systemic herbicide often detected in drinking water, has been employed as a model pollutant in the present study . It is highly soluble in water and particularly stable against hydrolysis and photolysis .…”

“…More specifically, clopyralid (3,6-dichloro-2-pyridine-carboxylic acid), a systemic herbicide often detected in drinking water, has been employed as a model pollutant in the present study. 39 It is highly soluble in water and particularly stable against hydrolysis and photolysis. 40 Its chemical stability, along with its mobility, enables this herbicide to penetrate through soil, causing a long-term contamination of ground and surface water supplies.…”

Mechanism and identify photolysis products of fluopyram under TiO2: Experiments, DFT and ab initio Molecular dynamics study

“…Heterogeneous photocatalysis has been proven to be effective for the degradation of a variety of toxic substances, including insecticides, fungicides and herbicides, under artificial or solar irradiation (Berberidou et al 2015;Stamatis et al 2015). However, many target compounds were not completely mineralized during the photocatalytic reaction time (Šojić et al 2009;Yang et al 2010).…”

Visible‐light‐driven photocatalytic degradation of fenpyroximate in rotating packed bed reactor using Fe3O4@PbS@Ni2P magnetic nanocomposite photocatalyst: Response surface modelling and optimization

“…The advanced oxidation processes based on the generation of hydroxyl radicals are efficient and more applicable protocols for treating complex compounds such as pesticides, acaricides and herbicides . Amongst them, photocatalytic degradation based on semiconductors with a significant capability for the generation of highly reactive and nonselective hydroxyl radicals is a low‐cost, highly efficient and sustainable treatment technique . In spite of the broad application of photocatalytic degradation as an efficient method for the degradation of various pollutants on a laboratory scale, few researches have been devoted to extending its usage in large‐scale reactors due to some limitations such as poor light distribution inside the reactor and low photocatalyst surface area per unit volume of reactor .…”