Adsorbing vs. Nonadsorbing Tracers for Assessing Pesticide Transport in Arable Soils

Abstract

Core Ideas Atrazine preferential flow shortly after application was governed by soil type. Injection of atrazine at depth enhanced preferential flow. Uranine realistically illustrated the rapid and significant atrazine breakthrough. In reserve, bromide mimicked early atrazine breakthrough only with moraine soil. Using dye tracers as pesticide surrogates might assist in making sustainable decisions. The suitability of two different tracers to mimic the behavior of pesticides in agricultural soils and to evidence the potential for preferential flow was evaluated in outdoor lysimeter experiments. The herbicide atrazine [6‐chloro‐N‐ethyl‐N′‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine] was used as a model compound. Two tracers were used: a nonadsorbing tracer (bromide) and a weakly adsorbing dye tracer (uranine). Two soils that are expected to show a different extent of macropore preferential flow were used: a well‐drained sandy‐loamy Cambisol (gravel soil) and a poorly drained loamy Cambisol (moraine soil). Conditions for preferential flow were promoted by applying heavy simulated rainfall shortly after pesticide application. In some of the experiments, preferential flow was also artificially simulated by injecting the solutes through a narrow tube below the root zone. With depth injection, preferential leaching of atrazine occurred shortly after application in both soil types, whereas with surface application, it occurred only in the moraine soil. Thereafter, atrazine transport was mainly through the porous soil matrix, although contributions of preferential flow were also observed. For all the application approaches and soil types, after 900 d, <3% of the applied amount of atrazine was recovered in the drainage water. Only uranine realistically illustrated the early atrazine breakthrough by transport through preferential flow. Uranine broke through during the first intense irrigation at the same time as atrazine. Bromide, however, appeared earlier than atrazine in some cases. The use of dye tracers as pesticide surrogates might assist in making sustainable decisions with respect to pesticide application timing relative to rainfall or soil potential for preferential flow.

Predicting the Fate of Preferentially Moving Herbicides

“…Indeed, the pan samplers that are constructed in field settings can best represent the local field conditions and, although expensive, have great utility investigating groundwater pollution risks (Boesten, 2007; Köhne et al, 2009b), at least at the general soil class level. Our observation that pesticides are breaking through at the same time as the non‐adsorbed tracers has been noticed by others (Kladivko et al, 1991; Flury, 1996; Kung et al, 2000b; Torrentó et al, 2018). Thus, the similarity of travel time independent of the sorption properties is largely due to the fast flow of water and, consequently, the short time that is available for adsorption to occur.…”

“…Atrazine 2,4-D at least at the general soil class level. Our observation that pesticides are breaking through at the same time as the non-adsorbed tracers has been noticed by others (Kladivko et al, 1991;Flury, 1996;Kung et al, 2000b;Torrentó et al, 2018). Thus, the similarity of travel time independent of the sorption properties is largely due to the fast flow of water and, consequently, the short time that is available for adsorption to occur.…”

Solid-phase extraction method for stable isotope analysis of pesticides from large volume environmental water samples

“…Finally, for the layered cartridges containing 8 g of SDB-1 and 8 g of Sepra ZT, matrix spikes were extracted to assess the influence of matrix components of real samples. To this end, known amounts of the target analytes (0.1 to 5 µg) were added to 10 L filtered (0.7-μm glass fibre filters) samples of agricultural drainage water 59 (Table 3). At 0.1 μg L -1 , similar recoveries were obtained for drainage water and tap water, except for DPC (24±30%) and DIA (35±14%).…”

“…Samples from the drainage water of lysimeters filled with arable soils were used. 59 Sorbent performance was evaluated in 10 L filtered (0.7-μm glass fibre filters) drainage water samples spiked with 0.1 to 50 µg L -1 of the target compounds. Finally, the integrity of the isotope values after large-volume SPE was assessed.…”

Hydrological tracers for assessing transport and dissipation processes of pesticides in a model constructed wetland system

“…For instance, Vallée et al (2015) found that the removal rates of boscalid in two pilot-scale wetlands ranged from 38 % to 67 %, whereas Gikas et al (2018) obtained removal rates for S-metolachlor (pesticide from the same group as metazachlor) that reached up to 92.6 % in a constructed wetland planted with Phragmites australis. Other authors have reported removal rates of between 45 % and 90 % for tebuconazole in wetland systems Tournebize et al, 2013). A possible explanation for the high removal rates obtained in our experiment could be the fact that contact of solutes with the medium was promoted due to a long period of stagnation (i.e., about 2 months in each run).…”