Coumarins represent an important family of allelochemicals with fungicidal, bactericidal, insecticidal, nematicidal, and herbicidal properties. Like for other allelochemicals, the short persistence of coumarins in soils can reduce their biological activity and hamper their application as environmentally friendly agrochemicals. We evaluated the sorption of the coumarin umbelliferone by eight soils and six sorbent materials, and then selected two nanoengineered sorbents, hexadecyltrimethylammonium-modified Arizona montmorillonite (SA-HDTMA) and olive-mill waste biochar (BC), to assess the effect of their addition to two distinct soils on umbelliferone sorption, persistence, and leaching. Umbelliferone was sorbed to a greater extent by the acid soils (A1-A2, K_d > 4.0 L kg⁻¹) than by the alkaline soils (B1-B6, K_d < 0.5 L kg⁻¹). The addition of BC and SA-HDTMA at a rate of 4% to alkaline soil (B2) increased the umbelliferone sorption K_d value from 0.3 to 1.6–2.0 L kg⁻¹, whereas their addition to acid soil (A1) increased the K_d value from 4.6 to 12.2–19.0 L kg⁻¹. Incubation experiments showed that BC had more impact than SA-HDTMA on the persistence of umbelliferone in the soils, increasing its half-life from 0.3-2.5 to 1.2–14.4 days, depending on the soil. Furthermore, the addition of BC to the top 0–5 cm of soil columns reduced leaching of umbelliferone and led to accumulation of umbelliferone residues in the top 0–5 cm soil layer. The addition of nanoengineered materials, such as organoclays and biochars, could thus be a suitable strategy to increase the persistence and reduce the mobility of coumarins in the rhizosphere with the aim of prolonging their biological activity.

9 páginas.-- 5 figuras.-- 2 tablas.-- 56 referencias.-- Supplementary data to this article can be found online at http://dx.doi.org/10.1016/j.geoderma.2017.01.024.Sorption, persistence, and leaching of the enantiomers of the herbicide imazaquin, S-imazaquin and R-imazaquin, in two soils under different application regimes were studied. Imazaquin dissipation was evaluated after a single application of the racemic herbicide and the pure enantiomers, and after a repeated application of the racemic herbicide. The effects of adding two olive-mill wastes (ALP and ALPc), biochar (BC), and organoclay (SA-HDTMA) on sorption, dissipation, and leaching of imazaquin enantiomers applied as racemic herbicide to the soils was also evaluated. For all treatments, sorption, dissipation, and leaching of imazaquin in the soils were either non-enantioselective or scarcely enantioselective. No interconversion of R-imazaquin to S-imazaquin or vice-versa was observed in the experiments with the pure isomers. Addition of ALP, ALPc, or BC did not enhance the negligible sorption of imazaquin enantiomers by the soils, but accelerated their dissipation. Addition of SA-HDTMA increased sorption of both enantiomers and delayed their dissipation and leaching. The results illustrate how agricultural practices can impact the behavior of imazaquin enantiomers in soils and support the suitability of replacing currently used racemic formulations of imazaquin with formulations based on the single biologically-active (R) enantiomer to reduce the environmental impact of this chiral pesticide.This work was supported by the Spanish Ministry of Economy and Competitiveness (MINECO grants AGL2011-23779 and AGL2014-51897-R) and Junta de Andalucía (JA Research Group AGR-264), co-financed with FEDER-FSE funds. The authors thank L. Cox for kindly supplying samples of ALP and ALPc. R. López-Cabeza also thanks MINECO for a pre-doctoral fellowship (grant BES-2012-059945).Peer Reviewe

Encapsulation efficiency of nanoformulated pesticides is often determined by centrifugal ultrafiltration.