Abstract
Leaching, the movement of water and chemicals into deeper soil layers and groundwater is a subject of worldwide interest because a high percentage of drinking water is extracted from groundwater. The objective of this study was to evaluate the potential leaching and persistence of sixteen pesticides (one fungicide, three nematicides/insecticides, and twelve herbicides) for three Mediterranean agricultural soils with similar texture (clay loam) but different organic matter content (1.2-3.1%). Adsorption was studied in batch experiments and leaching was tested using disturbed soil columns (40 cm length × 4 cm i.d.). Degradation studies were carried out during 120 days under laboratory conditions. Mobility experiments showed that pesticides can be grouped according to their potential leaching. Thus, pesticides showing medium leachability were included in group 1 (referred as G1) while those with high leachability were termed as G2. The differences observed in the leachability can be attributed to the different organic carbon (OC) content in the soils (0.7-1.8%). Values of log KOC were higher in the order: soil C > soil B > soil A, which agrees with the OC content in each soil. The calculated half-lives ranged from 4.2 days for carbofuran in soil A to 330 days for prometon in soil C. As a general rule, when higher OC content in the soil the greater persistence of the pesticide was observed as a consequence of the increased adsorption. The first order kinetics model satisfactorily explains the disappearance of the studied pesticides in the soil.
Highlights
Pesticides are widely applied to control pests and produce good quality food at reasonable prices and costs
Experimental values of the octanol/water partition coefficient (KOW), soil/ organic partition coefficient (KOC), aqueous solubility (SW), and groundwater ubiquity score (GUS) index were taken from The Pesticide Properties DataBase (AERU, 2015) and KOCWINTM included in the EPI Suite v4.11 program provides by USEPA (2015)
The mean concentration of pesticides (MCP) recovered in total leachates obtained from soil A was used
Summary
Pesticides are widely applied to control pests and produce good quality food at reasonable prices and costs Their use is constantly increasing and the probability of causing any unwanted side effects in the natural environment. Sorption will determine whether the pesticide will persist or not, be transported and become a pollutant or not, especially to groundwater and, often, whether it will be efficacious or not (Wauchope et al, 2002) Under certain conditions, these substances may move through the soil to groundwater from normal field applications and pollute those resources of water (Arias-Estévez et al, 2008). The higher the OC content is, the greater the pesticides adsorption is and the lower the mobility, reducing leaching (Spark & Swift, 2002; Alister et al, 2011)
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