BACKGROUND: Quantification of spray deposition on a target crop is of vital importance to optimize pesticide application. In traditional determinations of spray deposition, a large amount of organic solvent is used to extract pesticides from the target crops. In this study, a water‐soluble food dye of Allura Red was developed as a tracer to determine pesticide spray deposition on a rice target crop. RESULTS: The addition of Allura Red does not obviously alter the physicochemical properties of pesticides (viscosity, density and surface tension) and droplet spectra. An ultra‐performance liquid chromatography (UPLC) analytical method was developed and validated to determine the deposition amount of Allura Red on rice plants. Method accuracy and precision for Allura Red were found to be satisfactory with recoveries of 96.07% to 107.48%. To validate the method, comparative deposition analyses were carried out using representative systematic and non‐systematic pesticides (nitenpyram and chlorothalonil) under the same spraying scenarios using a Potter spray tower. Allura Red and pesticides showed comparable deposition under the same application conditions with ratios from 0.98 to 1.21. A field trial using an unmanned aerial vehicle sprayer further indicated that the deposition rates for Allura Red and nitenpyram on rice seedling were 13.04% and 11.07%, with corresponding relative standard deviation values (n = 5) of 16.39% and 18.79%. CONCLUSION: A laboratory test and field trial confirmed that the developed method of using Allura Red as a tracer for spray deposition assessment is feasible and practicable. © 2019 Society of Chemical Industry

The degradation of 130 mL of mixtures of food azo dyes E122, E124 and E129 has been studied by electro-Fenton (EF) and UVA photoelectro-Fenton (PEF) using a stirred tank reactor with either a boron-doped diamond (BDD) or Pt anode and an air-diffusion cathode. The main oxidant was hydroxyl radical formed at the anode from water oxidation and in the bulk from Fenton's reaction between added Fe2+ and H2O2 generated at the cathode. In sulfate medium, fast decolorization was found for all systems, but the almost total mineralization was more rapidly achieved by PEF with BDD. The performance with a real water matrix was slightly worse, although the removal of total organic load was still as high as 95%. The solar PEF (i.e., SPEF) treatment of dye mixtures using a 2.5 L flow plant with a BDD/air-diffusion cell coupled to a planar solar photoreactor is also reported. Fast decolorization and almost total mineralization was found in the presence of either sulfate, perchlorate, nitrate or a mixture of sulfate + chloride ions. In chloride medium, however, the formation of recalcitrant chloroderivatives decelerated the degradation process. Greater current efficiency and lower specific energy consumption were attained in sulfate medium at lower current density and higher azo dye content. A plausible reaction sequence based on 18 aromatic intermediates identified by GC–MS and 6 short-linear carboxylic acids detected by ion-exclusion HPLC has been proposed. The SPEF process promoted the photodegradation of Fe(III)-oxalate complexes and other undetected products. Sulfate and nitrate ions were always released to the medium.