Influence of adsorption-desorption phenomena on pesticide run-off from soil using simulated rainfall

• Published in: Pesticide Science 1999-02, Vol.55 (2), p.175-182
• Main Authors: Gouy, Véronique, Dur, Jeanne-Chantal, Calvet, Raoul, Belamie, René, Chaplain, Véronique
• Format: Article
• Language: English
• Subjects: adsorption; Agronomy. Soil science and plant productions; Biological and medical sciences; Fundamental and applied biological sciences. Psychology; pesticides; rainfall simulation; risk assessment; run-off; soil; Soil and water pollution; Soil science
• ISSN: 0031-613X; 1526-498X; 1096-9063
• DOI: 10.1002/(SICI)1096-9063(199902)55:2<175::AID-PS857>3.0.CO;2-0

The surface run‐off of a number of pesticides (diuron, isoproturon, atrazine, alachlor, aclonifen, trifluralin, lindane and simazine), chosen for their range of adsorption behaviours, was studied using simulated rainfall applied to small plots over a short time (one hour). Pesticides were applied together onto bare soil using two different sandy loam soils from Jaillière and Coet Dan sites. The surface run‐off samples were collected throughout the running of the event and concentrations of pesticides were measured in both liquid and solid phases. Sorption isotherms for isoproturon and diuron on Jaillière soil as well as eroded particles were measured under equilibrium conditions and compared to their partitioning during surface run‐off. At the rainfall intensity used, both soils generated a large load of eroded particles. The average run‐off flow rate increased with time for the Jalliére soil, while it remained relatively constant at a higher level for the Coet Dan soil. The concentrations of each pesticide in the run‐off samples decreased as the experiments proceeded. The pesticides were classified into two types by their partitioning between the solid and liquid phases. Atrazine, simazine, diuron, isoproturon and alachlor were mainly transported in surface run‐off water. By contrast, 90% of trifluralin and aclonifen was adsorbed onto eroded particles. Lindane was intermediate, with a 37% adsorption level. When the contribution of eroded particles was minor, the agrochemical concentrations were inversely proportional to the water flow rate. We have proposed a model that describes the mass of chemicals extracted from soil into surface water during a surface run‐off event of a given average duration and flow rate. This model takes into account the dilution of the soil solution and the desorption of chemicals through two parameters called, respectively, the dilution factor and the extraction retardation factor. The desorption kinetic was the limiting step in the surface run‐off of weakly sorbed chemicals, such as isoproturon. © 1999 Society of Chemical Industry